Soft switching control circuit and voltage converter

Abstract

The invention provides a soft switching control circuit and a voltage converter, the soft switching control circuit comprises an energy storage module, a switch module and a control module, the first end of the energy storage module is electrically connected with the first conduction end of a first switch tube, a DC voltage input end and the first end of an input capacitor; the second end of the energy storage module is electrically connected with the first end of the switch module, and the third end of the energy storage module is electrically connected with the second end of the switch module and the control module, and is also used for being electrically connected with the second conduction end of the first switch tube and the first conduction end of the second switch tube. The fourth end of the energy storage module is used for being electrically connected with the first end of the output capacitor and the direct-current voltage output end. The control module is electrically connected with the control end of the switch module. The control module is used for being electrically connected with the control end of the first switch tube, the control end of the second switch tube and the control circuit. The soft switching function of all the switching tubes can be realized, the switching loss is greatly reduced, and the conversion efficiency of the voltage converter is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of voltage converters, and particularly relates to a soft switching control circuit and a voltage converter. BACKGROUND

[0002] In a conventional voltage converter (such as a step-down power converter), a main switching transistor works in a hard switching state of high-voltage and large-current turn-off and turn-on, resulting in large switching loss and low conversion efficiency of the voltage converter. In the prior art, in order to reduce the switching loss generated by the hard switching of the switching transistor, a resistor-capacitor snubber circuit is usually added. Although this method can reduce the switching loss of the switching transistor, it converts the switching loss into power loss of the resistor, so that the conversion efficiency of the voltage converter is still low. SUMMARY

[0003] The embodiments of the present application provide a soft switching control circuit and a voltage converter, which can solve the problem that the conversion efficiency of the voltage converter is still low due to the addition of the resistor-capacitor snubber circuit.

[0004] In a first aspect, the embodiments of the present application provide a soft switching control circuit, comprising an energy storage module, a switching module and a control module, a first end of the energy storage module is electrically connected with a first conduction end of a first switching transistor, a direct current voltage input end and a first end of an input capacitor respectively, a second end of the energy storage module is electrically connected with a first end of the switching module, a third end of the energy storage module is electrically connected with a second end of the switching module and the control module respectively, the third end of the energy storage module is electrically connected with a second conduction end of the first switching transistor and a first conduction end of a second switching transistor, a fourth end of the energy storage module is electrically connected with a first end of an output capacitor and a direct current voltage output end respectively; the control module is electrically connected with a control end of the switching module, and the control module is electrically connected with a control end of the first switching transistor, a control end of the second switching transistor and a control circuit respectively;

[0005] The control module is configured to output a first control signal and a second control signal to the control end of the first switching transistor and the control end of the second switching transistor respectively, and output a third control signal to the control end of the switching module according to a control signal output by the control circuit, and the control circuit is configured to output the control signal to the control module;

[0006] The first switching transistor is configured to be turned on or turned off according to the first control signal, the second switching transistor is configured to be turned on or turned off according to the second control signal, and the switching module is configured to be turned on or turned off according to the third control signal.

[0007] In a second aspect, the embodiments of the present application provide a voltage converter, comprising a first switch tube, a second switch tube, a control circuit and the soft switch control circuit of any one of the first aspect, a control end of the first switch tube is electrically connected with a control module in the soft switch control circuit, for receiving a first control signal, a first conduction end of the first switch tube is electrically connected with a first end of an energy storage module in the soft switch control circuit, a second conduction end of the first switch tube is respectively electrically connected with a first conduction end of the second switch tube, a third end of the energy storage module and the control module, a control end of the second switch tube is electrically connected with the control module, for receiving a second control signal, a second conduction end of the second switch tube is grounded, and the control circuit is electrically connected with the control module.

[0008] Compared with the prior art, the embodiments of the present application have the beneficial effects that:

[0009] The soft switch control circuit provided by the embodiments of the present application comprises an energy storage module, a switch module and a control module. The control module can output a first control signal and a second control signal to drive the first switch tube and the second switch tube to turn on and off, respectively, and can output a third control signal to drive the switch module to turn on and off. The control circuit outputs control signals to control the signal timing of the switch module. In the process of soft switch control of the first switch tube, the second switch tube and the switch module, six working modes are divided and periodically cycled. The first working mode is to control the first switch tube to turn on, control the second switch tube to turn off and control the switch module to switch from the on state to the off state. Due to the sixth working mode of the last cycle, the current flowing through the switch module gradually decreases, so as to ensure that the current flowing through the switch module is less than a preset current (the preset current can be a current value close to zero) in this period, i.e. the current flowing through the switch module is approximately zero, so that the soft off function of close-to-zero current can be realized when the switch module switches from the on state to the off state. After the switch module is turned off, the current flowing through the switch module is close to zero, and the current flowing through the first switch tube is equal to the current flowing through the third end and the fourth end of the energy storage module.

[0010] The second working mode is: controlling the first switch tube to transit from the conducting state to the off state, controlling the second switch tube to be off, and controlling the switch module to be off. Since the current flowing through the third terminal and the fourth terminal of the energy storage module is equal to the current flowing through the first switch tube in the first working mode, and the current flowing through the third terminal and the fourth terminal of the energy storage module cannot be abruptly changed, when the current flowing through the first switch tube becomes zero, the current path of the current flowing through the third terminal and the fourth terminal of the energy storage module is changed to continue flowing through the junction capacitor of the first switch tube, and at this moment, the junction capacitor starts to be charged. Since the voltage across the junction capacitor is close to zero volt at the moment when the first switch tube transits from the conducting state to the off state, the zero-current and zero-voltage soft-off function of the first switch tube can be realized. When the voltage of the junction capacitor of the first switch tube rises to be close to the input DC voltage value (the junction capacitor is fully charged), the current flowing through the junction capacitor is zero, and at this moment, since the current flowing through the third terminal and the fourth terminal of the energy storage module cannot be abruptly changed, the current path of the current flowing through the third terminal and the fourth terminal of the energy storage module is changed to continue flowing through the body diode of the second switch tube. Since the energy in the energy storage module starts to be released, the change rate of the current flowing through the third terminal and the fourth terminal of the energy storage module becomes negative, and starts to gradually decrease. At this moment, the current flowing through the switch module is still close to zero.

[0011] The third working mode is: controlling the first switch tube to be off, controlling the second switch tube to transit from the off state to the conducting state, and controlling the switch module to be off. The current path flowing through the third terminal and the fourth terminal of the energy storage module is changed from the body diode of the second switch tube in the second working mode to the semiconductor channel of the second switch tube, so that the on-resistance of the second switch tube is greatly reduced, and the conduction loss of the second switch tube is also greatly reduced, that is, the zero-voltage soft-on function of the second switch tube is realized. At this moment, the current flowing through the switch module is still close to zero.

[0012] The fourth working mode is: controlling the first switch tube to be off, controlling the second switch tube to be on, and controlling the switch module to transit from the off state to the conducting state. The current flowing through the switch module increases, and since the current flowing through the switch module is close to zero in the third working mode, and the energy storage module has inductive effect, the current flowing through the switch module starts to gradually increase from the value close to zero. Therefore, when the switch module transits from the off state to the conducting state, the soft-on function of the switch module with the current close to zero can be realized. At this moment, the current flowing through the third terminal and the fourth terminal of the energy storage module is equal to the sum of the current flowing through the switch module and the current flowing through the second switch tube, and the current flowing through the first terminal and the second terminal of the energy storage module starts to gradually increase under the action of the voltage difference between the input DC voltage and the voltage between the second terminal of the energy storage module on the auxiliary winding of the energy storage module.

[0013] The fifth working mode is: controlling the first switch tube to be off, controlling the second switch tube to be switched from the on state to the off state, and controlling the switch module to be on. The current flowing through the third end and the fourth end of the energy storage module can be switched to the body diode of the second switch tube without delay, and the parasitic reverse body diode can clamp the voltage between the drain and the source of the second switch tube to be close to zero volts, thereby realizing the zero-voltage soft-off function of the second switch tube. Since in the fourth working mode, the current flowing through the third end and the fourth end of the energy storage module is equal to the sum of the current flowing through the switch module and the current flowing through the second switch tube, when the gradually increasing current flowing through the switch module is equal to the current flowing through the third end and the fourth end of the energy storage module, it can be known that the current flowing through the second switch tube will decrease to zero, thereby realizing the zero-current soft-off function of the second switch tube. When the current flowing through the switch module continues to increase and is greater than the current flowing through the third end and the fourth end of the energy storage module, at this time, a part of the current will flow back to the direct current voltage input end through the body diode of the first switch tube, that is, the current flowing through the body diode of the first switch tube is equal to the difference between the current flowing through the switch module and the current flowing through the third end and the fourth end of the energy storage module. At this time, the junction capacitance voltage of the second switch tube gradually rises, and when the voltage of the junction capacitance of the second switch tube is greater than the input direct current voltage, the voltage of the junction capacitance of the second switch tube is equal to the sum of the input direct current voltage and the voltage across the body diode of the first switch tube, thereby the voltage between the drain and the source of the first switch tube will be clamped to a constant value through the body diode of the first switch tube. Since the on voltage of the body diode of the first switch tube is very small, the voltage range between the drain and the source of the first switch tube is approximately zero.

[0014] The sixth working mode is: controlling the first switch tube to be switched from the off state to the on state, controlling the second switch tube to be off, and controlling the switch module to be on. Since in the fifth working mode, the voltage between the drain and the source of the first switch tube is approximately zero, and the current flowing through the switch module gradually increases to be greater than the current flowing through the third end and the fourth end of the energy storage module, thereby the zero-voltage and zero-current soft-on function of the first switch tube can be realized. When the first switch tube is on, the current flowing through the first switch tube is equal to the difference between the current flowing through the third end and the fourth end of the energy storage module and the current flowing through the switch module. Since the current flowing through the third end and the fourth end of the energy storage module and the current flowing through the first switch tube are both positive due to the effect of the difference between the input direct current voltage and the output direct current voltage on the energy storage module, the current flowing through the third end and the fourth end of the energy storage module and the current flowing through the first switch tube are both gradually increasing. Since the direction of the voltage induced by the auxiliary winding of the energy storage module is opposite to the direction of the current flowing through the switch module at this time, the change rate of the current flowing through the switch module changes to be negative, and thus the current flowing through the switch module gradually decreases. When the current flowing through the switch module decreases to be close to zero, it can be ensured that the switch module in the first working mode of the next cycle has a zero-current soft-off condition.

[0015] In conclusion, the soft switch control circuit provided by the embodiments of the present application can make the first switch tube realize the functions of zero-voltage and zero-current turn-on and zero-voltage and zero-current turn-off, make the second switch tube realize the functions of zero-voltage turn-on and zero-voltage and zero-current turn-off, and make the switch module realize the functions of zero-current turn-off and zero-current turn-on. Therefore, the soft switch control circuit of the present application can make all the switch tubes in the voltage converter realize the soft switch function, greatly reduce the switching loss, and further improve the conversion efficiency of the voltage converter. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0017] Figure 1 is a circuit connection schematic diagram of an existing step-down power converter circuit;

[0018] Figure 2 is a circuit connection schematic diagram of another existing step-down power converter circuit;

[0019] Figure 3 is a working waveform schematic diagram of an existing step-down power converter;

[0020] Figure 4 is a circuit connection schematic diagram of another existing step-down power converter circuit;

[0021] Figure 5 is a principle block diagram of a soft switch control circuit provided by an embodiment of the present application;

[0022] Figure 6 is a circuit connection schematic diagram of a soft switch control circuit provided by an embodiment of the present application;

[0023] Figure 7 is a principle block diagram of a soft switch control circuit provided by another embodiment of the present application;

[0024] Figure 8 is a waveform timing schematic diagram of each control signal provided by an embodiment of the present application;

[0025] Figure 9 is a principle block diagram of a control module provided by an embodiment of the present application;

[0026] Figure 10 is a circuit connection schematic diagram of a first delay comparison unit provided by an embodiment of the present application;

[0027] Figure 11 is a circuit connection diagram of the first delay comparison unit provided by another embodiment of the present application;

[0028] Figure 12 is a circuit connection diagram of the second delay comparison unit provided by an embodiment of the present application;

[0029] Figure 13 is a circuit connection diagram of the second delay comparison unit provided by another embodiment of the present application;

[0030] Figure 14 is a circuit connection diagram of the reference voltage unit provided by an embodiment of the present application;

[0031] Figure 15 is a circuit connection diagram of the reference voltage unit provided by another embodiment of the present application;

[0032] Figure 16 is a circuit connection diagram of the first drive unit provided by an embodiment of the present application;

[0033] Figure 17 is a circuit connection diagram of the first drive unit provided by another embodiment of the present application;

[0034] Figure 18 is a circuit connection diagram of the second drive unit provided by an embodiment of the present application;

[0035] Figure 19 is a circuit connection diagram of the second drive unit provided by another embodiment of the present application;

[0036] Figure 20 is a circuit connection diagram of the third delay comparison unit provided by an embodiment of the present application;

[0037] Figure 21 is a circuit connection diagram of the third delay comparison unit provided by another embodiment of the present application;

[0038] Figure 22 is a circuit connection diagram of the third drive unit provided by an embodiment of the present application;

[0039] Figure 23 is a circuit connection diagram of the third delay comparison unit provided by another embodiment of the present application;

[0040] Figure 24 is a diagram of voltage, current waveforms and working modes provided by an embodiment of the present application;

[0041] Figure 25 is Figure 24 a diagram of three working modes of the present application;

[0042] Figure 26 are Figure 24 magnified schematic diagrams of another three working modes of the soft switching power supply;

[0043] Figure 27 is a schematic diagram of voltage, current waveforms and working modes according to another embodiment of the present application.

[0044] In the figure: 10, soft switching control circuit; 101, energy storage module; 102, switching module; 103, control module; 1031, first delay comparison unit; 1032, second delay comparison unit; 1033, reference voltage unit; 1034, first driving unit; 1035, second driving unit; 1036, third delay comparison unit; 1037, third driving unit; 104, auxiliary energy storage module; 105, bypass module. DETAILED DESCRIPTION

[0045] In the following description, for the purpose of explanation and not limitation, specific details are set forth, such as particular system configurations, techniques, etc., in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.

[0046] It should be understood that the term "comprises" when used in this specification and the appended claims, indicates the presence of the described features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0047] As used in this specification and the appended claims, the term "if" can be interpreted as meaning "when" or "once" or "in response to a determination" or "in response to detecting," as appropriate, depending on the context. Similarly, the phrase "if it is determined" or "if [a described condition or event] is detected" can be interpreted as meaning "once it is determined" or "in response to the determination" or "once [the described condition or event] is detected" or "in response to detecting [the described condition or event]," as appropriate, depending on the context.

[0048] In addition, in the description of the present application and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0049] References to "one embodiment" or "some embodiments" in this specification mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in one or more embodiments of the present application. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0050] like Figure 1 and Figure 2 As shown, the traditional voltage converter (such as the step-down power converter) mainly consists of an input filter capacitor, a high-side switching transistor, a low-side switching transistor (or Figure 2 It consists of a freewheeling diode (shown), a filter inductor, an output filter capacitor, a control circuit, and other parts. Figure 3 The working waveform diagram of the step-down power converter is shown. It can be seen that the high-voltage side switching transistor in the step-down power converter operates in a hard switching state of high voltage and large current shutdown and opening, resulting in large switching losses and low conversion efficiency of the voltage converter.

[0051] It should be noted that Figure 1 and Figure 2 In the figure, VI is the positive input DC voltage, VI-GND is the negative input DC voltage, and VI's reference zero potential; VO is the positive output DC voltage, VO-GND is the negative output DC voltage, and VO's reference zero potential; VCC1 is the positive first auxiliary DC power supply, VCC1-GND is the negative first auxiliary DC power supply, and VCC1's reference zero potential; VCC2 is the positive second auxiliary DC power supply, VCC2-GND is the negative second auxiliary DC power supply, and VCC2's reference zero potential. Point P is the circuit node connected to the source of Q1, the drain of Q2 (or the negative terminal of D1), and the current input terminal of L1. Figure 3 In the figure, Ton is the on-time period of Q1 in a switching cycle of the step-down power converter. Toff is the off-time period of Q1 in a switching cycle of the step-down power converter. T is a complete switching cycle period of Q1. U(G,S)-Q1 is the voltage waveform between the gate (G pole) and the source (S pole) of Q1. U(G,S)-Q2 is the voltage waveform between the gate (G pole) and the source (S pole) of Q2. ... Figure 2The middle control circuit does not output a U(G, S)-Q2 voltage signal. I(D, S)-Q1 is a current waveform flowing between the drain (D) and source (S) of Q1. I(D, S)-Q2 is a current waveform flowing between the drain (D) and source (S) of Q2. I(L1) is a current waveform flowing through L1. U(P, VI-GND) is a voltage waveform between the circuit node P and the input DC voltage negative terminal (VI-GND). Figure 1 and Figure 2 A voltage waveform between the circuit node P and the input DC voltage negative terminal (VI-GND).

[0052] It should be noted that R1 is used to limit the charge and discharge current of the parasitic capacitance between the gate G and source S of Q1, and R3 is used to limit the charge and discharge current of the parasitic capacitance between the gate G and source S of Q2. When Q1 is turned off, R2 is used to discharge the residual charge of the parasitic capacitance between the gate G and source S of Q1. When Q2 is turned off, R4 is used to discharge the residual charge of the parasitic capacitance between the gate G and source S of Q2.

[0053] Based on the above problems, in order to reduce the switching loss generated by hard switching of the switching transistor, the existing improved scheme usually adds a resistance-capacitance absorption circuit between the drain and source of Q1 and between the drain and source of Q2, as shown in the following formula: Figure 4 In this way, the sudden current flowing through the semiconductor channel between the drain and source of Q1 during hard switching can be temporarily bypassed and shunted through the resistance-capacitance branch, so that the rate of change di / dt of the current flowing through Q1 is reduced to a certain extent, thereby reducing the switching loss of Q1 to a limited extent, and the voltage spike of the circuit node P and the electromagnetic interference EMI are limitedly reduced, which can improve the reliability. However, this design converts the switching loss of Q1 and Q2 into power loss of R5 and R6, so the efficiency of the step-down power converter is not improved, but rather reduced.

[0054] Based on the above problems, the soft switching control circuit provided by the embodiment of the present application comprises an energy storage module, a switching module and a control module. The control module can output a first control signal and a second control signal to drive the first switch tube and the second switch tube to turn on and turn off, respectively, and can also output a third control signal to drive the switching module to turn on and turn off. The control circuit outputs control signals to control the signal timing of the switching module. In the process of soft switching control of the first switch tube, the second switch tube and the switching module, six working modes are divided, and the six working modes are periodically cycled. The first working mode is to control the first switch tube to turn on, control the second switch tube to turn off, and control the switching module to change from the on state to the off state. Due to the sixth working mode of the last cycle, the current flowing through the switching module gradually decreases, so that the current flowing through the switching module is less than the preset current (the preset current can be a current value close to zero) at this time, i.e. the current flowing through the switching module is approximately zero, so that the soft-off function of near-zero current can be realized when the switching module changes from the on state to the off state. When the switching module is turned off, the current flowing through the switching module is close to zero, and the current flowing through the first switch tube is equal to the current flowing through the third terminal and the fourth terminal of the energy storage module.

[0055] The second working mode is to control the first switch tube to change from the on state to the off state, control the second switch tube to turn off, and control the switching module to turn off. Since the current flowing through the third terminal and the fourth terminal of the energy storage module is equal to the current flowing through the first switch tube in the first working mode, and the current flowing through the third terminal and the fourth terminal of the energy storage module cannot be suddenly changed, when the current flowing through the first switch tube changes to zero amperes, the current path flowing through the third terminal and the fourth terminal of the energy storage module changes to continue flowing through the junction capacitor of the first switch tube, and at this time the junction capacitor starts to charge. Since the voltage across the junction capacitor is close to zero volts at the moment when the first switch tube changes from the on state to the off state, the zero-current and zero-voltage soft-off function of the first switch tube can be realized. When the voltage of the junction capacitor of the first switch tube rises to close to the input DC voltage value (the junction capacitor is full), the current flowing through the junction capacitor is zero, and at this time, since the current flowing through the third terminal and the fourth terminal of the energy storage module cannot be suddenly changed, the current path flowing through the third terminal and the fourth terminal of the energy storage module changes to continue flowing through the body diode of the second switch tube. Since the energy in the energy storage module starts to release, the change rate of the current flowing through the third terminal and the fourth terminal of the energy storage module changes to a negative value, and starts to gradually decrease. At this time, the current flowing through the switching module is still close to zero.

[0056] The third working mode is: controlling the first switch tube to be off, controlling the second switch tube to be switched from off state to on state, and controlling the switch module to be off. The current path flowing through the third end and the fourth end of the energy storage module is switched from the body diode of the second switch tube in the second working mode to the semiconductor channel of the second switch tube, so that the on-voltage drop of the second switch tube is greatly reduced, and the on-loss of the second switch tube is also greatly reduced, that is, the zero-voltage soft opening function of the second switch tube is realized. At this time, the current flowing through the switch module is still close to zero.

[0057] The fourth working mode is: controlling the first switch tube to be off, controlling the second switch tube to be on, and controlling the switch module to be switched from off state to on state. The current flowing through the switch module increases. Since the current flowing through the switch module is close to zero in the third working mode, and the energy storage module has inductive effect, the current flowing through the switch module gradually increases from the value close to zero. Therefore, when the switch module is switched from off state to on state, the soft opening function of the switch module with close to zero current can be realized. At this time, the current flowing through the third end and the fourth end of the energy storage module is equal to the sum of the current flowing through the switch module and the current flowing through the second switch tube, and the current flowing through the first end and the second end of the energy storage module gradually increases under the action of the voltage difference between the input DC voltage and the voltage between the second end of the energy storage module.

[0058] The fifth operating mode is as follows: the first switch is controlled to turn off, the second switch is controlled to switch from the on state to the off state, and the switch module is controlled to turn on. The current flowing through the third and fourth terminals of the energy storage module can be switched to the body diode of the second switch without delay for freewheeling. This parasitic reverse body diode can clamp the drain and source voltages of the second switch to near zero volts, thereby achieving the zero-voltage soft shutdown function of the second switch. Because in the fourth operating mode, the current flowing through the third and fourth terminals of the energy storage module is equal to the sum of the current flowing through the switch module and the current flowing through the second switch, when the gradually increasing current flowing through the switch module equals the current flowing through the third and fourth terminals of the energy storage module, it can be seen that the current flowing through the second switch will drop to zero, thereby achieving the zero-current soft shutdown function of the second switch. When the current flowing through the switch module continues to increase and becomes greater than the current flowing through the third and fourth terminals of the energy storage module, a portion of the current will flow back to the DC voltage input terminal through the body diode of the first switch. That is, the current flowing through the body diode of the first switch is equal to the difference between the current flowing through the switch module and the current flowing through the third and fourth terminals of the energy storage module. During this period, the voltage across the junction capacitance of the second switch gradually rises. When the voltage across the junction capacitance of the second switch exceeds the input DC voltage, the voltage across the junction capacitance of the second switch equals the sum of the input DC voltage and the voltage across the body diode of the first switch. As a result, the voltage between the drain and source of the first switch is clamped to a constant value through the body diode of the first switch. Because the conduction voltage of the body diode of the first switch is extremely small, the voltage range between the drain and source of the first switch is approximately zero.

[0059] The sixth operating mode is: controlling the first switch tube to switch from the off state to the on state, controlling the second switch tube to turn off, and controlling the switch module to turn on. Since in the fifth operating mode, the voltage between the drain and source of the first switch tube is approximately zero, and the current flowing through the switch module gradually increases to be greater than the current flowing through the third and fourth terminals of the energy storage module, the zero-voltage and zero-current soft-turn-on function of the first switch tube can be achieved. When the first switch is turned on, the current flowing through the first switch is equal to the difference between the current flowing through the third and fourth terminals of the energy storage module and the current flowing through the switch module. Due to the effect of the difference between the input DC voltage and the output DC voltage on the energy storage module, the rate of change of the current flowing through the third and fourth terminals of the energy storage module and the rate of change of the current of the first switch both become positive. Therefore, the current flowing through the third and fourth terminals of the energy storage module and the current flowing through the first switch gradually increase. At this time, the direction of the voltage induced by the auxiliary winding of the energy storage module is opposite to the direction of the current of the switch module, causing the rate of change of the current flowing through the switch module to become negative. Therefore, the current flowing through the switch module gradually decreases. When the current flowing through the switch module decreases to near zero, it can be ensured that the switch module meets the zero-current soft shutdown condition in the first operating mode of the next cycle.

[0060] In conclusion, the soft switching control circuit provided by the embodiments of the present application can make the first switch tube realize the functions of zero-voltage and zero-current turn-on and zero-voltage and zero-current turn-off, make the second switch tube realize the functions of zero-voltage turn-on and zero-voltage and zero-current turn-off, and make the switch module realize the functions of zero-current turn-off and zero-current turn-on. Therefore, the soft switching control circuit of the present application can make all the switch tubes in the voltage converter realize the soft switching function, greatly reduce the switching loss, and further improve the conversion efficiency of the voltage converter.

[0061] It should be noted that when the circuit is controlled, the first working mode, the second working mode, the third working mode, the fourth working mode, the fifth working mode and the sixth working mode can be controlled in the order of "first working mode→second working mode→third working mode→fourth working mode→fifth working mode→sixth working mode", that is, the first working mode, the second working mode, the third working mode, the fourth working mode, the fifth working mode and the sixth working mode are controlled in a cycle, so that the six working modes form a cycle control process.

[0062] It should be noted that the soft switching control circuit proposed by the present application is compatible with Figure 1 and Figure 2 two topological structures. When applied to Figure 2 , since a diode D1 is used as a freewheeling element, the control circuit does not need to output a second control signal to D1. While Figure 1 topology contains double switch tubes (Q1 and Q2), the switching loss problem is more representative. In view of this, the present application takes Figure 1 as an example to elaborate in detail, so as to more comprehensively show the optimization mechanism of the soft switching technology for the switching loss in the multi-switch tube topology.

[0063] In order to illustrate the technical solutions described in the present application, specific embodiments will be described below.

[0064] Taking Figure 1 topology circuit as an example, Figure 5 a principle block diagram of the soft switching control circuit 10 provided by an embodiment of the present application is shown. Referring to Figure 5As shown, the soft switch control circuit 10 comprises an energy storage module 101, a switch module 102 and a control module 103. The first end of the energy storage module 101 is electrically connected with the first conduction end of the first switch tube Q1, the direct current voltage input end and the first end of the input capacitor C1 respectively. The second end of the energy storage module 101 is electrically connected with the first end of the switch module 102. The third end of the energy storage module 101 is electrically connected with the second end of the switch module 102 and the control module 103 respectively. The third end of the energy storage module 101 is electrically connected with the second conduction end of the first switch tube Q1 and the first conduction end of the second switch tube Q2. The fourth end of the energy storage module 101 is electrically connected with the first end of the output capacitor C2 and the direct current voltage output end respectively. The control module 103 is electrically connected with the control end of the switch module 102. The control module 103 is electrically connected with the control ends of the first switch tube Q1 and the second switch tube Q2 and the control circuit respectively.

[0065] Specifically, the control module 103 can output a first control signal Dr1 to drive the first switch tube Q1 to turn on and turn off. The control module 103 can also output a second control signal Dr1 to drive the second switch tube Q2 to turn on and turn off. The control module 103 can also output a third control signal Dr3 to drive the switch module 102 to turn on and turn off. The control circuit outputs control signals (the first control signal Dr1-1 and the second control signal Dr2-1) to control the signal timing of the switch module 102. In the process of soft switch control of the first switch tube Q1, the second switch tube Q2 and the switch module 102, six working modes are divided, which are periodically cycled. Among them, the first working mode is to control the first switch tube Q1 to turn on, control the second switch tube Q2 to turn off, and control the switch module 102 to change from the on state to the off state. Due to the sixth working mode of the last period, the current flowing through the switch module 102 gradually decreases, so as to ensure that the current flowing through the switch module 102 is less than the preset current (the preset current can be a current value close to zero) in this period, that is, the current flowing through the switch module 102 is approximately zero. Therefore, when the switch module 102 changes from the on state to the off state, the soft off function of the current close to zero can be realized. When the switch module 102 is off, the current flowing through the switch module 102 is close to zero, and the current flowing through the first switch tube Q1 is equal to the current flowing through the third end and the fourth end of the energy storage module 101.

[0066] The second working mode is: controlling the first switch tube Q1 to change from the conducting state to the off state, controlling the second switch tube Q2 to be off, and controlling the switch module 102 to be off. Since the current flowing through the third end and the fourth end of the energy storage module 101 is equal to the current flowing through the first switch tube Q1 in the first working mode, and the current flowing through the third end and the fourth end of the energy storage module 101 cannot be abruptly changed, when the current flowing through the first switch tube Q1 changes to zero ampere, the current path flowing through the third end and the fourth end of the energy storage module 101 changes to continue flowing through the junction capacitor of the first switch tube Q1, at this time, the junction capacitor starts to charge. Since the voltage across the junction capacitor is close to zero volts at the moment when the first switch tube Q1 changes from the conducting state to the off state, the zero-current and zero-voltage soft-off function of the first switch tube Q1 can be realized. When the voltage of the junction capacitor of the first switch tube Q1 rises to close to the input DC voltage value (the junction capacitor is fully charged), the current flowing through the junction capacitor is zero, at this time, since the current flowing through the third end and the fourth end of the energy storage module 101 cannot be abruptly changed, the current path of the main winding N1 of the first inductor L1 changes to continue flowing through the body diode of the second switch tube Q2. Since the energy in the energy storage module starts to be released, the change rate of the current flowing through the third end and the fourth end of the energy storage module changes to a negative value, and starts to gradually decrease. At this time, the current flowing through the switch module 102 is still close to zero.

[0067] The third working mode is: controlling the first switch tube Q1 to be off, controlling the second switch tube Q2 to change from the off state to the conducting state, and controlling the switch module 102 to be off. The current path flowing through the third end and the fourth end of the energy storage module 101 changes from continuing to flow through the body diode of the second switch tube Q2 in the second working mode to flowing through the semiconductor channel of the second switch tube Q2, so that the on-voltage drop of the second switch tube Q2 is greatly reduced, and the conduction loss of the second switch tube Q2 is also greatly reduced, that is, the zero-voltage soft-on function of the second switch tube Q2 is realized. At this time, the current flowing through the switch module 102 is still close to zero.

[0068] The fourth working mode is: controlling the first switch tube Q1 to be off, controlling the second switch tube Q2 to be on, and controlling the switch module 102 to be switched from the off state to the on state. The current flowing through the switch module 102 increases, and since the current flowing through the switch module 102 is close to zero in the third working mode, and the inductive effect of the energy storage module, the current flowing through the switch module 102 gradually increases from a value close to zero. Therefore, when the switch module 102 is switched from the off state to the on state, the soft opening function of the switch module 102 close to zero current can be realized. At this time, the current flowing through the third end and the fourth end of the energy storage module 101 is equal to the sum of the current flowing through the switch module 102 and the current flowing through the second switch tube Q2, and the current flowing through the first end and the second end of the energy storage module 101 gradually increases under the action of the voltage difference between the input DC voltage and the second end of the energy storage module on the auxiliary winding of the energy storage module. The current change rate of the first end and the second end of the energy storage module 101 changes to a positive value, and gradually increases.

[0069] The fifth working mode is: controlling the first switch tube Q1 to be off, controlling the second switch tube Q2 to be switched from the on state to the off state, and controlling the switch module 102 to be on. The current flowing through the third end and the fourth end of the energy storage module 101 can be switched to the body diode of the second switch tube Q2 without delay. The parasitic reverse body diode can clamp the voltage between the drain D and the source S of the second switch tube Q2 to be close to zero, thereby realizing the zero voltage soft off function of the second switch tube Q2. Since the current flowing through the third end and the fourth end of the energy storage module 101 is equal to the sum of the current flowing through the switch module 102 and the current flowing through the second switch tube Q2 in the fourth working mode, when the gradually increasing current flowing through the switch module 102 is equal to the current flowing through the third end and the fourth end of the energy storage module 101, it can be known that the current flowing through the second switch tube Q2 will decrease to zero, thereby realizing the zero current soft off function of the second switch tube Q2. When the current flowing through the switch module 102 continues to increase and is greater than the current flowing through the third end and the fourth end of the energy storage module 101, at this time, part of the current will flow back to the DC voltage input end through the body diode of the first switch tube Q1, that is, the current flowing through the body diode of the first switch tube Q1 is equal to the difference between the current flowing through the switch module 102 and the current flowing through the third end and the fourth end of the energy storage module 101. At this time, the junction capacitance voltage of the second switch tube Q2 gradually rises, and when the voltage of the junction capacitance of the second switch tube Q2 is greater than the input DC voltage VI, the voltage of the junction capacitance of the second switch tube Q2 is equal to the sum of the input DC voltage VI and the voltage across the body diode of the first switch tube Q1. Therefore, the voltage between the drain and the source of the first switch tube Q1 will be clamped to a constant value through the body diode of the first switch tube Q1. Since the on voltage of the body diode of the first switch tube Q1 is very small, the voltage range between the drain D and the source S of the first switch tube Q1 is approximately zero.

[0070] The sixth working mode is: controlling the first switch tube Q1 to switch from the off state to the on state, controlling the second switch tube Q2 to be off, and controlling the switch module 102 to be on. Because in the fifth working mode, the voltage between the drain D and the source S of the first switch tube Q1 is approximately zero, and the current flowing through the switch module 102 gradually increases to be greater than the current of the main winding N1 of the first inductor L1, thereby realizing the zero-voltage and zero-current soft opening function of the first switch tube Q1. When the first switch tube Q1 is on, the current flowing through the first switch tube Q1 is equal to the difference between the current flowing through the third terminal and the fourth terminal of the energy storage module 101 and the current flowing through the switch module 102. Because the current change rate of the main winding N1 of the first inductor L1 and the current change rate of the first switch tube Q1 are both changed to positive values under the action of the difference between the input DC voltage and the output DC voltage on the energy storage module, the current flowing through the third terminal and the fourth terminal of the energy storage module 101 and the current flowing through the first switch tube Q1 are both gradually increasing. Because the voltage induced in the auxiliary winding of the energy storage module at this time is in the opposite direction to the current direction of the switch module, the current change rate of the switch module 102 is changed to a negative value, so the current flowing through the switch module 102 gradually decreases. When the current flowing through the switch module decreases to near zero, it can be ensured that the switch module 102 in the first working mode of the next cycle has a zero-current soft-off condition.

[0071] In summary, the soft switching control circuit 10 provided by the embodiment of the present application can make the first switch tube Q1 realize the functions of zero-voltage and zero-current opening and zero-voltage and zero-current closing, make the second switch tube Q2 realize the functions of zero-voltage opening and zero-voltage and zero-current closing, and make the switch module 102 realize the functions of zero-current closing and zero-current opening. Therefore, the soft switching control circuit 10 of the present application can make all the switch tubes in the voltage converter realize soft switching functions, greatly reduce switching loss, and further improve the conversion efficiency of the voltage converter.

[0072] It should be noted that the gate G of the first switch tube Q1 is used as the control terminal of the first switch tube Q1, for receiving the first control signal Dr1 and turning on or off according to the first control signal Dr1. The drain D of the first switch tube Q1 is used as the first conduction terminal of the first switch tube Q1, and the source S of the first switch tube Q1 is used as the second conduction terminal of the first switch tube Q1. The gate G of the second switch tube Q2 is used as the control terminal of the second switch tube Q2, for receiving the second control signal Dr2 and turning on or off according to the second control signal Dr2. The drain D of the second switch tube Q2 is used as the first conduction terminal of the second switch tube Q2, and the source S of the second switch tube Q2 is used as the second conduction terminal of the second switch tube Q2, connected with VI-GND and VO-GND.

[0073] It should be noted that the control signal includes a first control sub-signal Dr1-1 and a second control sub-signal Dr2-1, wherein the reference zero potential of the second control sub-signal Dr2-1 and the second control signal Dr2 is VCC1-GND, the reference zero potential of the first control sub-signal Dr1-1, the first control signal Dr1 and the third control signal Dr3 is VCC2-GND, and the other symbol meanings are exactly the same as those provided in the prior art Figure 1 to Figure 4 and will not be described in detail here.

[0074] Exemplarily, Figure 1 and Figure 4 The two resistors R1 and R2 connected at the gate G of Q1 and the two resistors R3 and R4 connected at the gate G of Q2 shown can all be selected as limit values, for example, the resistance values of R1 and R3 can both be 0Ω, which is equivalent to short circuit, and a connecting line short circuit can be used instead. The resistance values of R2 and R4 can both be infinite, which is equivalent to open circuit, and can be removed. D2 connected between VCC2 and VCC1 of the control circuit can also be removed. When the above-mentioned devices are selected as limit values, the most simplified circuit can be obtained, as shown in Figure 5 In addition, the designer can also select the types of the first switch tube Q1 and the second switch tube Q2, for example, the first switch tube Q1 and the second switch tube Q2 can both be selected as NMOS tubes.

[0075] In an embodiment of the present application, as shown in Figure 6 The energy storage module includes a unidirectional conducting diode D3 and a first inductor L1, the anode of the unidirectional conducting diode D3 is used as the first end of the energy storage module 101, and is electrically connected with the first conducting end of the first switch tube Q1, the direct current voltage input end and the first end of the input capacitor C1 respectively, the first end of the auxiliary winding N2 of the first inductor L1 is electrically connected with the cathode of the unidirectional conducting diode D3, the second end of the auxiliary winding N2 of the first inductor L1 is used as the second end of the energy storage module 101, and is electrically connected with the first end of the switch module 102, the first end of the main winding N1 of the first inductor L1 is used as the third end of the energy storage module 101, and is electrically connected with the second end of the switch module 102 and the control module 103 respectively, the first end of the main winding N1 of the first inductor L1 is used for electrically connecting with the second conducting end of the first switch tube Q1 and the first conducting end of the second switch tube Q2, and the second end of the main winding N1 of the first inductor L1 is used as the fourth end of the energy storage module 101, and is electrically connected with the first end of the output capacitor C2 and the direct current voltage output end respectively.

[0076] Specifically, the main winding N1 and the auxiliary winding N2 of the first inductor L1 are used to store and release energy, and adjust the current flowing through the first switch Q1, the second switch Q2 and the switch module 102 by storing and releasing energy, so as to realize the soft switching function of the first switch Q1, the second switch Q2 and the switch module 102.

[0077] Specifically, the unidirectional conducting diode D3 mainly plays a role of unidirectional conduction, so as to ensure that the current flowing direction in the auxiliary loop meets the design requirements of the circuit. Specifically, the unidirectional conducting diode D3, the switch module 102 and the auxiliary winding N2 of the first inductor L1 form an auxiliary loop. In the auxiliary loop, the unidirectional conducting diode D3 can prevent the current from flowing reversely, ensure that the energy in the auxiliary loop can be transmitted along the predetermined path in a specific working mode, and bear the reverse voltage when the switch module 102 is turned off, so as to maintain the current in the auxiliary loop to be zero, help the switch module 102 to realize zero-current turn-off, and cooperate with the first inductor L1 to make the switch module 102 realize zero-current soft turn-on when the switch module 102 is turned on, thereby reducing the switching loss and improving the efficiency and reliability of the voltage converter.

[0078] In an embodiment of the present application, as shown in Figure 6 The switch module 102 includes a third switch Q3. The control end of the third switch Q3 is electrically connected with the control module 103, and is used to receive a third control signal Dr3. The first conduction end of the third switch Q3 is electrically connected with the second end of the auxiliary winding N2 of the first inductor L1. The second conduction end of the third switch Q3 is electrically connected with the control module 103. The second conduction end of the third switch Q3 is electrically connected with the second conduction end of the first switch Q1 and the first end of the main winding N1 of the first inductor L1, respectively.

[0079] Specifically, the gate G of the third switch Q3 serves as the control end of the third switch Q3, and is used to receive the third control signal Dr3 and turn on or turn off according to the third control signal Dr3. The drain D of the third switch Q3 serves as the first conduction end of the third switch Q3, and the source S of the third switch Q3 serves as the second conduction end of the third switch Q3. The third switch Q3 cooperates with the auxiliary winding N2 of the first inductor L1, the unidirectional conducting diode D3 and other elements to realize zero-current turn-off in the first working mode and realize zero-current turn-on in the fourth working mode. Specifically, at the beginning of the first working mode, the third switch Q3 is turned off from being turned on, and the current flowing through the third switch Q3 is close to zero, so as to realize zero-current turn-off and reduce the turn-off loss. In the fourth working mode, when the third switch Q3 is turned on, the current in the auxiliary loop starts from zero and gradually increases, so as to realize zero-current turn-on. Therefore, the third switch Q3 can realize zero-current turn-on and zero-current turn-off, so as to greatly reduce the overall switching loss and improve the efficiency of the voltage converter.

[0080] For example, the designer can select the type of the third switch Q3, for example, the third switch Q3 can select NMOS tube.

[0081] In an embodiment of the present application, as shown in Figure 6 The soft switching control circuit 10 further comprises an auxiliary energy storage module 104, the auxiliary energy storage module 104 is electrically connected with the cathode of the unidirectional conducting diode D3, and the auxiliary energy storage module 104 is electrically connected with the first end of the auxiliary winding N2 of the first inductor L1. The first end of the auxiliary energy storage module 104 is electrically connected with the cathode of the unidirectional conducting diode D3, and the second end of the auxiliary energy storage module 104 is electrically connected with the first end of the energy storage module 101.

[0082] Alternatively, the first end of the auxiliary energy storage module 104 is electrically connected with the DC voltage input end, and the second end of the auxiliary energy storage module 104 is electrically connected with the anode of the unidirectional conducting diode D3.

[0083] Specifically, the auxiliary energy storage module 104 mainly adjusts the current of the auxiliary loop by storing and releasing energy in the soft switching control circuit 10 to realize the soft switching function of each switch. Specifically, in the sixth working mode, the energy storage of the auxiliary energy storage module 104 is released to the output end and the input end of the main loop through the main winding N1 and the auxiliary winding N2 of the first inductor L1, and at the beginning of the first working mode, its energy storage is close to the end of the release, so that the current of the elements such as the unidirectional conducting diode D3, the third switch Q3 and the auxiliary winding N2 of the first inductor L1 in series in the auxiliary loop is close to zero, and the third switch Q3 realizes zero-current turn-off. In the fourth working mode, the auxiliary energy storage module 104 cooperates with the auxiliary winding N2 of the first inductor L1 to make the current of the auxiliary loop gradually increase from zero when the third switch Q3 is turned on, so as to realize the zero-current soft turn-on of the third switch Q3. In addition, the auxiliary energy storage module 104 can also make the first switch Q1 have soft turn-on conditions when the current of the auxiliary loop increases to a certain value in the fifth working mode.

[0084] It should be noted that since the auxiliary energy storage module 104 and the unidirectional conducting diode D3 are in series, the auxiliary energy storage module 104 can also be interchanged with the unidirectional conducting diode D3, and the effect is the same as the circuit shown in Figure 6 The same as the circuit shown in

[0085] In an embodiment of the present application, as shown in Figure 7As shown, the soft switch control circuit 10 further comprises a bypass module 105 connected between the first conduction end of the first switch tube Q1 and the second conduction end of the first switch tube Q1, for providing a current bypass for the main winding N1 of the first inductor L1 when the first switch tube Q1 is switched from conduction to non-conduction according to the first control signal Dr1, the second switch tube Q2 is non-conduction according to the second control signal Dr2, and the switch module 102 is non-conduction according to the third control signal Dr3.

[0086] Specifically, the bypass module 105 is connected between the drain D and the source S of the first switch tube Q1, and is used for providing a non-delay current bypass for the main winding N1 of the first inductor L1 when the first switch tube Q1 is switched from conduction to non-conduction according to the first control signal Dr1, the second switch tube Q2 is non-conduction according to the second control signal Dr2, and the third switch tube Q3 is non-conduction according to the third control signal Dr3. That is, in the second working mode, the current of the main winding N1 of the first inductor L1 is continued to flow through the bypass module 105 at the moment when the first switch tube Q1 is non-conduction. Since the voltage across the bypass module 105 is close to zero and the current can flow without delay, the first switch tube Q1 realizes zero-voltage and zero-current soft non-conduction, avoids high loss and electromagnetic interference caused by hard switching, and at the same time, the voltage between the drain D and the source S of the first switch tube Q1 gradually rises after the bypass module 105 is charged, further reduces the switching stress, and improves the efficiency and reliability of the voltage converter.

[0087] In an embodiment of the present application, as shown in Figure 6 The auxiliary energy storage module 104 comprises a second inductor L2, a first end of the second inductor L2 is electrically connected with the cathode of the unidirectional conducting diode D3, and a second end of the second inductor L2 is electrically connected with the first end of the energy storage module 101.

[0088] Alternatively, the first end of the second inductor L2 is electrically connected with the direct current voltage input end, and the second end of the second inductor L2 is electrically connected with the anode of the unidirectional conducting diode D3.

[0089] Specifically, the second inductor L2 as the core element of the auxiliary energy storage module 104 adjusts the auxiliary loop current through the energy storage and energy release process in the soft switching control circuit 10 to realize the soft switching function of each switch tube. Specifically, in the sixth working mode, the second inductor L2 releases energy to the output end and the input end of the main loop through the main winding N1 and the auxiliary winding N2 of the first inductor L1, and at the beginning of the first working mode, the energy storage thereof is close to the end of the release, so that the current of the elements such as the unidirectional conduction diode D3, the third switch tube Q3, and the auxiliary winding N2 of the first inductor L1 in the auxiliary loop is close to zero, and the third switch tube Q3 realizes zero-current turn-off. In the fourth working mode, the second inductor L2 cooperates with the auxiliary winding N2 of the first inductor L1 to gradually increase the current in the auxiliary loop from zero when the third switch tube Q3 is turned on, thereby realizing the zero-current soft turn-on of the third switch tube Q3. In addition, the second inductor L2 can also make the first switch tube Q1 have a soft turn-on condition after the current in the auxiliary loop increases to a certain value in the fifth working mode.

[0090] Since the second inductor L2 and the unidirectional conduction diode D3 are in series, the second inductor L2 can also be interchanged with the unidirectional conduction diode D3, and the effect thereof is completely the same as that of the circuit shown in Figure 6 , and thus will not be described again.

[0091] It should be noted that, Figure 5 , the auxiliary energy storage module 104 (for example, the inductance of the second inductor L2 is zero) is not arranged in the circuit shown in Figure 6 , and the auxiliary energy storage module 104 shown in is directly omitted. The leakage inductance of the auxiliary winding N2 of the first inductor L1 is used for energy storage and energy release, and the auxiliary winding N2 of the first inductor L1 cooperates with other elements (for example, the third switch tube Q3 and the unidirectional conduction diode D3) to realize the soft switching control function of the switch tube, thereby meeting the demand of the circuit for the auxiliary loop current adjustment and the soft switching state.

[0092] For example, the second inductor L2 in the auxiliary energy storage module 104 can be replaced by multiple inductors or other energy storage elements (for example, a capacitor, a transformer winding, etc.) according to the functional demand of the circuit, and the specific element type and connection mode are not limited, as long as the energy storage and energy release adjustment function of the auxiliary loop current is met to realize the soft switching control of the switch tube.

[0093] In an embodiment of the present application, as shown in Figure 6 , the bypass module 105 includes a bypass capacitor C3, a first end of the bypass capacitor C3 is configured to be electrically connected with the first conduction end of the first switch tube Q1, and a second end of the bypass capacitor C3 is configured to be electrically connected with the second conduction end of the first switch tube Q1.

[0094] Specifically, the bypass capacitor C3 is connected between the drain D and the source S of the first switch tube Q1, and the core function thereof is to provide a non-delay current bypass for the main winding N1 of the first inductor L1 when the first switch tube Q1 is turned off, so as to realize the zero-voltage and zero-current soft turn-off of the first switch tube Q1. Specifically, when the first switch tube Q1 is switched from the on state to the off state, the current of the main winding N1 of the first inductor L1 cannot be abruptly changed, and can continue to flow through the bypass capacitor C3, thereby avoiding the high voltage spike caused by the abrupt change of the current. At this time, the voltage across the bypass capacitor C3 is initially close to zero volts, allowing the current to bypass without delay, so that the voltage stress of the first switch tube Q1 at the moment of turn-off is greatly reduced, and the voltage rising rate is determined by the capacitance value of the bypass capacitor C3, thereby eliminating the hard switching loss. In addition, after the first switch tube Q1 is turned off, the bypass capacitor C3 is charged to close to the input DC voltage VI, thereby creating conditions for the subsequent zero-voltage soft turn-on of the first switch tube Q1, while reducing electromagnetic interference by suppressing the current change rate (di / dt), thereby improving the efficiency and reliability of the voltage converter.

[0095] It should be noted that, Figure 5 In the circuit shown, the bypass module 105 (such as the bypass capacitor C3) is not provided, but is directly omitted Figure 6 The bypass module 105 shown uses the junction capacitance between the drain D and the source S of the first switch tube Q1 to provide a current bypass, and uses the energy storage characteristic of the junction capacitance to realize the zero-voltage soft turn-off of the first switch tube Q1. In addition, the timing control of the control module 103 is used to reduce the voltage stress of the first switch tube Q1 during the turn-off process, thereby reducing the switching loss, and further meeting the demand of the circuit for soft switching control function, and realizing the control of the auxiliary loop current regulation and the soft switching state.

[0096] For example, the number of bypass capacitors C3 is not limited, and a single or multiple capacitors can be used according to actual needs, or other elements with energy storage characteristics can be used, as long as the circuit function of providing a current bypass for the first switch tube Q1 when turned off and adjusting the voltage change rate to realize soft switching control can be realized.

[0097] In an embodiment of the present application, as Figure 6 shown, the switch module 102 further includes a first resistor R121 and a second resistor R122, a first end of the first resistor R121 is electrically connected with the control module 103, a second end of the first resistor R121 is respectively electrically connected with a first end of the second resistor R122 and a control end of the third switch tube Q3, and a second end of the second resistor R122 is respectively electrically connected with a second conduction end of the third switch tube Q3 and the control module 103.

[0098] Specifically, the first resistor R121 is connected in series between the gate G of the third switch tube Q3 and the third control signal Dr3, and is used to limit the charge and discharge current of the parasitic capacitance between the gate G and the source S of the third switch tube Q3. This can prevent excessive current from damaging the third switch tube Q3, and at the same time ensure that the rise and fall rates of the gate G voltage are within a reasonable range, so that the third switch tube Q3 can be stably turned on and off. The second resistor R122 is connected in parallel between the gate G and the source S of the third switch tube Q3, and when the third switch tube Q3 is turned off, it is used to discharge the residual charge in the parasitic capacitance between the gate G and the source S of the third switch tube Q3. This ensures that after the third switch tube Q3 is turned off, the gate G voltage can quickly drop to a low level, avoiding the third switch tube Q3 from being turned on or turned off late due to residual charge, thereby improving the reliability and switching speed of the circuit.

[0099] It should be noted that the purpose of adding R1, R2, R3, R4 and the first resistor R121 and the second resistor R122 is to increase the reliability of the voltage converter and reduce electromagnetic interference.

[0100] For example, Figure 6 The first resistor R121 and the second resistor R122 shown connected to the gate G of the third switch Q3 can both be set to extreme values. For example, the resistance of the first resistor R121 can be 0Ω, equivalent to a short circuit, and can be replaced by a short-circuited connecting wire. The resistance of the second resistor R122 can be infinite, equivalent to an open circuit, and can be removed. When these resistors are set to extreme values, the simplified circuit can be achieved.

[0101] Figure 8 The control signals (first control signal Dr1 ( Figure 8 Drs1 in ), the second control signal Dr2 ( Figure 8 Drs2 in the ), the third control signal Dr3 ( Figure 8 Drs3 in ) and the first control sub-signal Dr1-1 ( Figure 8 Schematic diagram of the waveform timing of Drs1-1) in FIG. Among them, all control signals use a high level as the transistor-on period Ton and a low level as the transistor-off period Toff.

[0102] The following combination Figure 5 to Figure 8 The changes in current and voltage in six different working modes within a working cycle of this application are described in detail.

[0103] (1) First working mode (i.e. working mode 1):

[0104] The first control signal Dr1 outputted by the control module 103 is high relative to the reference zero potential point VCC2-GND, while the second control signal Dr2 outputted by the control module 103 is low relative to the reference zero potential point VCC1-GND, and the third control signal Dr3 outputted by the control module 103 is converted from high in the sixth working mode of the previous period to low relative to the reference zero potential point VCC2-GND.

[0105] At this time, the first switch tube Q1 is turned on, the second switch tube Q2 is turned off, the voltage between the drain D and the source S of the first switch tube Q1 and the voltage across the bypass capacitor C3 are close to zero volt, that is, U DS-Q1 = U C3 ≈ 0V, the voltage value of the circuit node P relative to the reference zero potential point VI-GND is close to the input voltage value, that is, U P,VI-GND ≈ VI, the main winding N1 of the first inductor L1 bears an applied forward voltage (defined as the end of the main winding N1 connected to the circuit node P as the positive voltage end, and the end of the main winding N1 connected to the voltage output end VO as the negative voltage end).

[0106] At this time, the auxiliary winding N2 of the first inductor L1 induces an output forward voltage (defined as the end of the auxiliary winding N2 connected to the second inductor L2 (auxiliary inductor) as the positive voltage end, and the end of the auxiliary winding N2 connected to the drain D of the third switch tube Q3 as the negative voltage end), the voltage and current in the auxiliary circuit are calculated as formula 1:

[0107] I DS-Q3 = I D3 = I N2-L1 = I L2

[0108] U L2 = -(U N2-L1 + U D3 + U DS-Q3 + U DS-Q1 )

[0109] ΔI DS-Q3 = ΔI L2 = U L2 * ΔT ON-Q1 / L2

[0110] Wherein, I DS-Q3 is the instantaneous value of the current flowing through the drain D and the source S of the third switch tube Q3, which is a bidirectional current, and the current flowing from the drain D to the source S is defined as the positive direction. I D3 is the instantaneous value of the current flowing through the unidirectional conducting diode D3, which is a unidirectional positive current. I N2-L1 is the instantaneous value of the current flowing through the auxiliary winding N2 of the first inductor L1. I L2The instantaneous value of the current flowing through the second inductor L2 is a unidirectional positive current. U L2 The instantaneous value of the voltage across the second inductor L2 is a unidirectional positive voltage. The positive end of the voltage is the end of the second inductor L2 connected to the cathode of the unidirectional diode D3, and the negative end of the voltage is the end of the second inductor L2 connected to the auxiliary winding N2. U N2-L1 The instantaneous value of the voltage across the auxiliary winding N2 of the first inductor L1 is a unidirectional positive voltage. The positive end of the voltage is the end of the auxiliary winding N2 connected to the second inductor L2, and the negative end of the voltage is the end of the auxiliary winding N2 connected to the drain D of the third switch Q3. U D3 The instantaneous value of the voltage across the unidirectional diode D3 is a unidirectional positive voltage. U DS-Q3 The instantaneous value of the voltage between the drain D and the source S of the third switch Q3 is a unidirectional positive voltage. U DS-Q1 The instantaneous value of the voltage between the drain D and the source S of the first switch Q1 is a unidirectional positive voltage. The rate of change of the current flowing through the drain D and the source S of the third switch Q3 is a unidirectional positive current. The rate of change of the current flowing through the second inductor L2 is a unidirectional positive current. T ON-Q1 The conduction period of the first switch Q1 in a switching cycle is a unidirectional positive current. L2 is the inductance of the second inductor L2.

[0111] Since in the sixth working mode period of the last cycle, in formula 1, the third switch Q3 is turned on, i.e. U DS-Q3 ≈0V, the forward conduction voltage drop of the unidirectional diode D3 is very low, i.e. U D3 ≈0.7V, the first switch Q1 is turned on, and the voltage between the drain D and the source S of the first switch Q1 is close to zero, i.e. U DS-Q1 ≈0V. Therefore, formula 1 can be simplified as: U L2 ≈-U N2-L1 , ΔI L2 ≈-U N2-L1 *ΔT ON-Q1 / L2. The second inductor L2 is in the energy storage release and current continuation state, and the self-induction voltage U L2 of the second inductor L2 is in the same direction as the current I L2 , i.e. defined as negative voltage direction, while the induction voltage U N2-L1 of the auxiliary winding N2 of the first inductor L1 is opposite to the direction of the current I L2 , i.e. defined as positive voltage direction, so in the sixth working mode period, the second inductor L2 releases the stored energy to the load and the input through the main winding N1 and the auxiliary winding N2 of the first inductor L1.

[0112] As shown in formula 1, in the sixth working mode period of the last cycle, U L2 is negative, ΔI L2 is negative, and I L2decreases gradually. By choosing proper component parameters, I L2 drops to near zero ampere I L2 ≈0A. Thus, at the beginning of the first working mode, the third switch tube Q3 can realize zero current and zero voltage turn-off, and the turn-off loss of the third switch tube Q3 is near zero watt.

[0113] At this period, after the third switch tube Q3 is turned off, the induced voltage U N2-L1 of the auxiliary winding N2 of the first inductor L1 is positive voltage, and the voltage direction between the drain D and the source S of the third switch tube Q3 is the same as the conduction direction of the inverse body diode of the third switch tube Q3. Therefore, after the third switch tube Q3 is turned off, the voltage between the drain D and the source S of the third switch tube Q3 is still near zero volt, that is, U DS-Q3 ≈0V. At this time, the voltage applied to the unidirectional conduction diode D3 is the reverse cut-off voltage, and thus the current in the auxiliary loop is kept as zero ampere, that is, I N2-L1 =I L2 =I DS-Q3 =I D3 =I N2-L1 =0A.

[0114] At this period, the current flowing through the main winding N1 of the first inductor L1 is calculated as formula 2:

[0115] ΔI N1-L1 =U N1-L1 *T ON-Q1 / L1= (VI-VO)*T ON-Q1 / L1

[0116] I N1-L1 =I DS-Q1 +I DS-Q3 =I DS-Q1

[0117] wherein ΔI N1-L1 is the current change rate flowing through the main winding N1 of the first inductor L1. U N1-L1 is the voltage instantaneous value between the main winding N1 of the first inductor L1, and the positive voltage end is the end of the main winding N1 connected to the circuit node P, and the negative voltage end is the end of the main winding N1 connected to the voltage output end VO. L1 is the inductance of the first inductor L1. I N1-L1 is the current instantaneous value flowing through the main winding N1 of the first inductor L1. I DS-Q1 is the current instantaneous value flowing through the drain D and the source S of the first switch tube Q1, and is bidirectional current, and the positive direction is defined as the current flowing from the drain D to the source S.

[0118] According to formula 2, at this period, I DS-Q3= 0A, therefore, the drain D and source S current of the first switch tube Q1 is equal to the current of the main winding N1 of the first inductor L1, that is, I DS-Q1 = I N1-L1 .

[0119] At this period, the current flows from the positive terminal VI of the DC voltage input, through the drain D and source S of the first switch tube Q1, into the positive terminal of the main winding N1 of the first inductor L1, and flows out from the negative terminal of the main winding N1 of the first inductor L1, and is then divided into two paths, one of which flows into the positive terminal of the output capacitor C2, and the other of which flows into the positive terminal of the load through the positive terminal VO of the DC output voltage, and the load current converges into the negative terminal VI-GND of the voltage input through the negative terminal VO-GND of the DC output voltage, while the charging current of the output capacitor C2 also converges into the negative terminal VI-GND of the input through the negative terminal of C2.

[0120] (2) The second working mode (i.e. working mode 2):

[0121] The first control signal Dr1 output by the control module 103 is converted from high level to low level relative to the reference zero potential point VCC2-GND in the first working mode, while the second control signal Dr2 output by the control module 103 is low relative to the reference zero potential point VCC1-GND, and the third control signal Dr3 output by the control module 103 is low relative to the reference zero potential point VCC2-GND.

[0122] At this period, the first switch tube Q1 is converted from the on state to the off state in the first working mode, therefore, the drain D and source S current of the first switch tube Q1 is also converted to zero ampere, that is, I DS-Q1 = 0A. Since the current of the main winding N1 of the first inductor L1 is equal to the drain D and source S current of the first switch tube Q1 I N1-L1 = I DS-Q1 in the first working mode, and the current flowing through the third and fourth terminals of the energy storage module 101 cannot be abruptly changed, therefore, when the drain D and source S current of the first switch tube Q1 is converted to zero ampere I DS-Q1 = 0A, the path of the current of the main winding N1 of the first inductor L1 is converted to all flowing through the bypass capacitor C3, that is, I N1-L1 = I C3 . Among them, I C3 is the instantaneous value of the current flowing through the bypass capacitor C3, which is a bidirectional current, and the positive direction is defined as the direction from the end connected to the drain D of the first switch tube Q1 to the end connected to the source S of the first switch tube Q1.

[0123] Since the voltage U C3 across the bypass capacitor C3 is close to zero volt at the moment when the first switch tube Q1 is converted from the on state to the off state, that is, U C3= U DS-Q1 ≈ 0V, while the current of the first inductor L1 can bypass through the bypass capacitor C3 without delay, so that the first switch Q1 realizes the function of zero-voltage and zero-current soft-off.

[0124] At this time, the bypass capacitor C3 begins to charge, and when the bypass capacitor C3 is fully charged, the voltage between the drain D and the source S of the first switch Q1 (the voltage across the bypass capacitor C3) is close to zero volts U DS-Q1 = U C3 ≈ 0V, which is converted to close to the input DC voltage VI, U DS-Q1 = U C3 ≈ VI. The voltage U of the circuit node P relative to the reference zero potential point VI-GND P，VI-GND is converted to close to zero volts U P,VI-GND ≈ VI P,VI-GND ≈ 0V, at which time the bypass capacitor C3 charges to zero amperes I C3 = 0A. Since the main winding N1 current of the first inductor L1 cannot be abrupt, the freewheeling path of the first inductor L1 is converted to the body diode freewheeling between the drain D and the source S of the second switch Q2, that is, I N1-L1 = I VD-Q2 , where I VD-Q2 is the current instantaneous value flowing through the body diode between the drain D and the source S of the second switch Q2.

[0125] At this time, the self-induction voltage across the main winding N1 of the first inductor L1 is negative, U N1-L1 ≈ -(VO+V VD-Q2 )(as defined, the end of the main winding N1 connecting the circuit node P is the positive voltage end, and the end of the main winding N1 connecting the voltage output end VO is the negative voltage end), and the auxiliary winding N2 of the first inductor L1 also induces a negative voltage (as defined, the end of the auxiliary winding N2 connecting the second inductor L2 is the positive voltage end, and the end of the auxiliary winding N2 connecting the drain D of the third switch Q3 is the negative voltage end). At this time, the third diode D3 bears a forward voltage, and since the third switch Q3 is in the off state, the current in the auxiliary circuit still remains zero amperes, that is, I L2 = I DS-Q3 = I D3 = I N2-L1 = 0A, the drain D and the source S of the third switch Q3 bear a forward (defined: drain D is positive, source S is negative) voltage, that is, U DS-Q3 ≈ -U N2-L1 .

[0126] At this period, due to the self-induction freewheeling effect of the first inductor L1, the current flows from the negative terminal VI-GND of the DC voltage input end, through the source S of the second switch tube Q2, the body diode of the second switch tube Q2, the drain D of the second switch tube Q2, into the voltage positive terminal of the main winding N1 of the first inductor L1, and flows out from the voltage negative terminal of the main winding N1 of the first inductor L1, and is then divided into two paths, one of which flows into the positive terminal of the output capacitor C2, and the other of which flows into the positive terminal of the load through the positive terminal VO of the DC output voltage, and the load current converges into the negative terminal VI-GND of the voltage input end through the negative terminal VO-GND of the DC output voltage, and at the same time, the charging current of the capacitor C2 also converges into the negative terminal VI-GND of the input end through the negative terminal of the C2.

[0127] At this period, the current flowing through the main winding N1 of the L1 satisfies the following formula 3:

[0128] ΔI N1-L1 =-U N1-L1 *T OFF-Q1 / L1

[0129] =-(VO+V VD-Q2 )*T OFF-Q1 / L1

[0130] ≈-VO*T OFF-Q1 / L1

[0131] Wherein, T OFF-Q1 is the off period of the first switch tube Q1 in one switching cycle.

[0132] It can be obtained from the formula 3 that the current change rate ΔI N1-L1 of the main winding N1 of the first inductor L1 is a negative constant, so the current I N1-L1 of the main winding N1 of the first inductor L1 linearly decreases in the second working mode.

[0133] (3) The third working mode (i.e. working mode 3):

[0134] The first control signal Dr1 output by the control module 103 is low relative to the reference zero potential point VCC2-GND, at the same time, the second control signal Dr2 output by the control module 103 is converted from low to high relative to the reference zero potential point VCC1-GND in the second working mode, and the third control signal Dr3 output by the control module 103 is low relative to the reference zero potential point VCC2-GND.

[0135] At this period, due to the conversion of the second switch tube Q2 from the off state in the second working mode to the on state, the current flowing through the drain D and the source S of the second switch tube Q2 is also converted from I N1-L1 =I VD-Q2, the semiconductor channel of the second switch Q2 is converted to flow through (defined as the positive direction of current from the drain D to the source S of the second switch Q2) I N1-L1 = -I DS-Q2 , wherein I DS-Q2 is the instantaneous value of the current flowing through the drain D and the source S of the second switch Q2, and is a bidirectional current, defined as the positive direction of current from the drain D to the source S. Thus, the on-state voltage drop is greatly reduced U DS-Q2 <U VD-Q2 , wherein U DS-Q2 is the instantaneous value of the voltage between the drain D and the source S of the second switch Q2. Thus, the on-state loss of the second switch Q2 is also greatly reduced.

[0136] At this time, in addition to the internal current path of the second switch Q2 being converted, the remaining current paths are exactly the same as described in the second working mode. The current flowing through the main winding N1 of the first inductor L1 still satisfies the above formula 3, and the current flowing through the auxiliary winding N2 of the first inductor L1 still maintains zero amperes, and will not be described in detail here.

[0137] (4) Fourth working mode (i.e. working mode 4):

[0138] The first control signal Dr1 output by the control module 103 is low relative to the reference zero potential point VCC2-GND, and the second control signal Dr2 output by the control module 103 is high relative to the reference zero potential point VCC1-GND, and the third control signal Dr3 output by the control module 103 is converted from low to high relative to the reference zero potential point VCC2-GND.

[0139] At this time, since the third switch Q3 is converted from the off state to the on state in the third working mode, the voltage between the drain D and the source S of the third switch Q3 is also converted from U DS-Q3 ≈ -U N2-L1 to near zero volts U DS-Q3 ≈ 0V. At this time, due to the presence of the second inductor L2, the current in the auxiliary circuit starts to gradually increase from the initial zero amperes I DS-Q3 ≈ 0A, so that the third switch Q3 realizes zero-current soft turn-on.

[0140] At this time, the drain D and the source S voltage of the main winding N1, the auxiliary winding N2, the second inductor L2, the one-way conduction diode D3, the first switch Q1, the second switch Q2, and the third switch Q3 of the first inductor L1 satisfy the following formula 4:

[0141] U L2 = VI - U P，VI-GND - U N2-L1 - UD3 -U DS-Q3

[0142] U P，VI-GND -U N1-L1 = VO

[0143] U DS-Q1 = U C3 = VI - U P，VI-GND = VI - U DS-Q2

[0144] At this period, the current flowing through the drain D and source S of the third switch tube Q3 and the current of the auxiliary winding N2 of the first inductor L1, the second inductor L2 and the unidirectional conducting diode D3 satisfy the following formula 5:

[0145] I DS-Q3 = I N2-L1 = I D3 = I L2

[0146] ΔI DS-Q3 = ΔI N2-L1 = ΔI D3 = ΔI L2 = U L2 * T4 / L2

[0147] Where, ΔI N2-L1 is the current change rate flowing through the auxiliary winding N2 of the first inductor L1. ΔI D3 is the current change rate flowing through the unidirectional conducting diode D3.

[0148] At this period, the current of the main winding N1 of the first inductor L1 satisfies the following formula 6:

[0149] I N1-L1 = I DS-Q3 + I DS-Q2 = I N2-L1 + I DS-Q2 = I O + I C3

[0150] As formula 4, the second working mode and the third working mode, the voltage of the circuit node P relative to the reference zero potential point VI-GND is close to zero volt U P,VI-GND ≈ 0V at the initial time of the fourth working mode, and the forward conducting voltage drop of the unidirectional conducting diode D3 is about 0.7 volt U D3 ≈ 0.7V, while U DS-Q3 ≈ 0V as above, formula 4 can be simplified as the following formula 7:

[0151] VI = U L2 + U N2-L1

[0152] According to equation 7, at this time, because a voltage VI is applied across the second inductor L2 and the auxiliary winding N2 of the first inductor LI, a voltage is induced across the second inductor L2 and the auxiliary winding N2 that is opposite in direction to the voltage induced across the main winding Nl of the first inductor LI (i.e., defined as a negative voltage). At this time, because the main winding Nl of the first inductor LI is still in the freewheeling state, the main winding Nl of the first inductor LI still induces a negative voltage. L2 According to equation 7, at this time, because a voltage VI is applied across the second inductor L2 and the auxiliary winding N2 of the first inductor LI, a voltage is induced across the second inductor L2 and the auxiliary winding N2 that is opposite in direction to the voltage induced across the main winding Nl of the first inductor LI (i.e., defined as a negative voltage). At this time, because the main winding Nl of the first inductor LI is still in the freewheeling state, the main winding Nl of the first inductor LI still induces a negative voltage.

[0153] As described above, because in the fourth working mode the phase of the voltage induced across the main winding Nl and the auxiliary winding N2 of the first inductor LI is different, a certain leakage inductance can be designed between the two windings of the first inductor LI. At this time, the positive voltage induced across the auxiliary winding N2 of the first inductor LI causes the leakage inductance to be in the energy storage state.

[0154] According to equation 5, the current I flowing through the drain D and the source S of the third switch Q3 is DS-Q3 will increase at a fixed slope. Generally, the inductance of the second inductor L2 is chosen to be very small, so the slope of the increase of the current I DS-Q3 is also relatively large. Because the inductance of the first inductor LI is relatively large, the change value of the current I L2 in this time period can be considered to be approximately a constant value, compared to the change value of the current I L1-N1 flowing through the second inductor L2 with very small inductance.

[0155] According to equation 5, the current I flowing through the drain D and the source S of the second switch Q2 is DS-Q2 in the direction from the source S to the drain D, because the body diode and the parasitic junction capacitor of the second switch Q2 have current bypassing and voltage clamping effects when the absolute value of the current I DS-Q2 is greater than zero amperes, i.e., |I DS-Q2 | > 0 A, the second switch Q2 has the condition for zero-voltage turn-off, thereby preparing for the zero-voltage turn-off of the second switch Q2 in the fifth working mode.

[0156] At this period, due to the self-induction freewheeling effect of the first inductor L1, the main path current flows from the negative terminal VI-GND of the DC voltage input end, through the source S of the second switch Q2, the body diode of the second switch Q2, the drain D of the second switch Q2, and then flows into the voltage positive terminal of the main winding N1 of the first inductor L1. At the same time, the auxiliary path current flows from the positive terminal VI of the DC input voltage, through the anode and cathode of the unidirectional diode D3, the second inductor L2, the voltage positive terminal of the auxiliary winding N2 of the first inductor L1, the voltage negative terminal of the auxiliary winding N2, and then through the drain D and source S of the third switch Q3, and then flows into the voltage positive terminal of the main winding N1 of the first inductor L1. The current after the two paths converge flows out from the voltage negative terminal of the main winding N1 of the first inductor L1, and then is divided into two paths, one of which flows into the positive terminal of the output capacitor C2, and the other of which flows into the positive terminal of the load through the positive terminal VO of the DC output voltage, and the load current flows into the negative terminal VI-GND of the DC input voltage through the negative terminal VO-GND of the DC output voltage, and at the same time, the charging current of the output capacitor C2 also flows into the negative terminal VI-GND of the DC input voltage through the negative terminal of C2.

[0157] (5) The fifth working mode (i.e., working mode 5):

[0158] The first control signal Dr1 output by the control module 103 is low relative to the reference zero potential point VCC2-GND, at the same time, the second control signal Dr2 output by the control module 103 is converted from high to low relative to the reference zero potential point VCC1-GND, and at the same time, the third control signal Dr3 output by the control module 103 is high relative to the reference zero potential point VCC2-GND.

[0159] At this period, due to the body diode between the drain D and the source S of the second switch Q2, when the second switch Q2 is converted from the on state to the off state, the freewheeling current of the voltage converter can be switched to flow through the body diode without delay, and the current direction remains unchanged. The body diode clamps the voltage of the drain D and the source S of the second switch Q2 to be close to zero volts U DS-Q2 ≈0V, so that the second switch Q2 realizes the zero-voltage soft-off function.

[0160] As formula 5, when I DS-Q3 increases to equal I N1-L1 , it can be known that the current I DS-Q2 flowing through the drain D and the source S of the second switch Q2 will decrease to zero ampere I DS-Q2 =0A. After that, when I DS-Q3 continues to increase, I DS-Q3 >I L1-N1When the current is 1, part of the current will flow back to the DC input voltage positive terminal VI through the body diode of the first switch tube Q1, and the drain D and source S current I DS-Q1 The current of the main winding N1 of the first inductor L1 is calculated as follows:

[0161] I VD-Q1 =I DS-Q3 -I L1-N1

[0162] Among them, I VD-Q1 is the instantaneous value of the current flowing through the body diode between the drain D and the source S of the first switch tube Q1.

[0163] At this time, the voltage of the circuit node P relative to the zero potential reference point VI-GND is close to zero volt U in the previous period in the fifth working mode. P,VI-GND ≈0V, which is converted to the voltage in the latter period of the fifth working mode close to the input DC voltage VI, that is, U P,VI-GND ≈VI.

[0164] As mentioned above, when the junction capacitance voltage between the drain D and the source S of the second switch tube Q2 gradually rises to a value greater than the input voltage U DS-Q2 When the DC voltage VI is input, the body diode between the drain D and source S of the first switch tube Q1 is clamped at a constant value. The voltage value is calculated as shown in Formula 9:

[0165] U DS-Q2 =U P,VI-GND =VI+U VD-Q1

[0166] U DS-Q1 =VI-U DS-Q2 ≥-U VD-Q1

[0167] 0V≥U DS-Q1 ≥-U VD-Q1

[0168] Among them, U VD-Q1 It is the instantaneous value of the conduction voltage drop of the body diode between the drain D and the source S of the first switch tube Q1, and is defined as a unidirectional positive voltage value.

[0169] According to formula 9, the forward voltage of the body diode is very low U VD-Q1 ≈0.7V, so at this time the voltage range between the drain D and source S of the first switch tube Q1 is approximately zero volt U DS-Q1 =U C3 ≈0V, preparing for the first switch tube Q1 to achieve zero voltage and zero current soft turn-on in the sixth working mode.

[0170] (6) Sixth working mode (i.e. working mode 6):

[0171] The first control signal Dr1 outputted by the control module 103 is converted from low level to high level relative to the reference zero potential point VCC2-GND in the fifth working mode, while the second control signal Dr2 outputted by the control module 103 is low relative to the reference zero potential point VCC1-GND, and the third control signal Dr3 outputted by the control module 103 is high relative to the reference zero potential point VCC2-GND.

[0172] At this time, since the first switch tube Q1 is converted from the off state to the on state in the fifth working mode, the voltage between the drain D and the source S of the first switch tube Q1 is also converted from the near zero voltage U DS-ON in the fifth working mode to a smaller value by selecting a suitable on resistance R DS-Q1 of the first switch tube Q1, so as to further reduce the on loss. The current I C3 between the drain D and the source S of the first switch tube Q1 gradually increases from the negative current value (from the source S to the drain D of the first switch tube Q1) in the fifth working mode to the positive current value (from the drain D to the source S of the first switch tube Q1). DS-Q1

[0173] At this time, the voltage value of the circuit node P relative to the reference zero potential point VI-GND is close to the input direct current voltage VI, that is, U P,VI-GND ≈VI, and the positive voltage U N1 ≈VI-VO is applied to the two ends of the main winding N1 of the first inductor L1 (as defined, the end of the main winding N1 connected to the circuit node P is the positive voltage end, and the end of the main winding N1 connected to the voltage output end VO is the negative voltage end).

[0174] At this time, the auxiliary winding N2 of the first inductor L1 also induces the positive voltage (as defined, the positive end of the auxiliary winding N2 is connected to one end of the second inductor L2, and the negative end of the auxiliary winding N2 is connected to one end of the drain D of the third switch tube Q3) with the same phase as the main winding N1, which makes the current I N2-L1 start to decrease from the maximum value, and the current value is calculated as shown in the above formula 1.

[0175] At this time, the current in the main winding N1 of the first inductor L1 starts to increase, and the current is calculated as shown in formula 10:

[0176] ΔI LI-N1 =U N1-L1 *T ON-Q1 / L1= (VI-VO)*T ON-Q1 / L1

[0177] ​As can be seen from formula 10, the current change rate ΔI L1-N1 of the main winding N1 of the first inductor L1 is a positive constant, and at this time period, the energy stored in the first inductor L1 increases linearly.

[0178] At this time period, the current flowing through the first switch Q1 gradually increases from a very small negative current value close to zero ampere, and the current calculation is shown in formula 11:

[0179] I DS-Q1 = I N1-LI -I DS-Q3

[0180] ΔI DS-Q1 = ΔI N1-LI - ΔI DS-Q3

[0181] = [(VI-VO)*T ON-Q1 / L1]+[U N2-L1 * ΔT ON-Q1 / L2]

[0182] At the sixth working mode period, since the current change rate ΔI N1-L1 of the main winding N1 of the first inductor L1 and the current change rate ΔI DS-Q1 of the drain D and the source S of the first switch Q1 are both positive constants, the current flowing through the main winding N1 of the first inductor L1 and the current flowing through the drain D and the source S of the first switch Q1 gradually increase. Since the current change rate ΔI DS-Q3 of the drain D and the source S of the third switch Q3 is a negative constant, the current flowing through the drain D and the source S of the third switch Q3 (the current of the auxiliary winding N2 of the first inductor L1) gradually decreases.

[0183] As can be seen from the above, the soft switching control circuit 10 provided by the embodiment of the present application can make the first switch Q1 realize the functions of zero-voltage and zero-current turn-on and zero-voltage and zero-current turn-off, make the second switch Q2 realize the functions of zero-voltage turn-on and zero-voltage and zero-current turn-off, and make the switch module 102 realize the functions of zero-current turn-off and zero-current turn-on. Therefore, the soft switching control circuit 10 of the present application can make all the switches in the voltage converter realize soft switching functions, greatly reduce switching loss, and further improve the conversion efficiency of the voltage converter.

[0184] It should be noted that in the prior art, the first switch tube Q1 is in a hard switching state, which not only produces a large electromagnetic interference and voltage stress, reduces the reliability of the power converter, but also the hard switching loss is proportional to the switching frequency, under the constraints of the temperature of the first switch tube Q1 and the efficiency of the converter, it is difficult to improve the working frequency of the step-down power converter, and thus the first inductor L1 is large in size due to the low working frequency. Unlike the prior art, the three switch tubes (Q1, Q2 and Q3) can all achieve soft switching under the same components, working frequency, input and output voltage specifications and output power, which significantly reduces the switching loss, improves the efficiency, and greatly reduces the electromagnetic interference and switch voltage stress, and improves the reliability of the voltage converter. Moreover, the application can reduce the size of the magnetic element by increasing the working frequency, and the switching loss will not increase significantly. In summary, the application effectively solves the problems of the prior art, can meet the requirements of energy saving, carbon reduction, small size, light weight and other social and economic requirements for the development trend of switching power converter industry, has good economic and social benefits, and has the prospect of mass application.

[0185] In one embodiment of the application, as shown in Figure 9 The control module 103 includes a first delay comparison unit 1031, a second delay comparison unit 1032, a reference voltage unit 1033, a first drive unit 1034, a second drive unit 1035, a third delay comparison unit 1036 and a third drive unit 1037. The first delay comparison unit 1031 is electrically connected with the reference voltage unit 1033, the second delay comparison unit 1032, the first drive unit 1034, the second drive unit 1035, the DC voltage input terminal and the switch module 102. The second delay comparison unit 1032 is electrically connected with the reference voltage unit 1033, the second drive unit 1035 and the switch module 102. The first drive unit 1034 is electrically connected with the control circuit. The third delay comparison unit 1036 is electrically connected with the control circuit, the first conduction end of the second switch tube Q2 and the third drive unit 1037.

[0186] Specifically, the reference voltage unit 1033 can provide a reference voltage signal VREF, and output the reference voltage signal VREF to the first delay comparison unit 1031 and the second delay comparison unit 1032, providing a reference standard for the subsequent comparison process. The first driving unit 1034 is electrically connected with the control circuit, and can output a third control signal Dr3 according to the first control sub-signal Dr1-1 output by the control circuit, to drive the first delay comparison unit 1031 and the second delay comparison unit 1032 to act, and at the same time drive the third switch tube Q3. The first delay comparison unit 1031 receives the third control signal Dr3, the direct current input voltage VI and the reference voltage signal VREF, and outputs a first comparison signal after delay comparison processing, which is used to reflect the difference and timing relationship between signals. The second delay comparison unit 1032 also receives the third control signal Dr3 and the reference voltage signal VREF, and outputs a second comparison signal after delay comparison, which acts together with the first comparison signal. The second driving unit 1035 superimposes the first comparison signal and the second comparison signal, and outputs a first control signal Dr1 based on the superimposed signal, to realize accurate control of the first switch tube Q1, thereby ensuring the normal operation of the entire soft switching control circuit 10. The third delay comparison unit 1036 receives the second control sub-signal Dr2-1 output by the control circuit and the first conduction end P voltage signal of the second switch tube, and outputs a third comparison signal after delay comparison processing, which is used to reflect the difference and timing relationship between signals. The third driving unit 1037 outputs a second control signal Dr2 based on the third comparison signal, to realize accurate control of the first switch tube Q2, thereby ensuring the normal operation of the entire soft switching control circuit 10.

[0187] The working principle of the six working modes will be described in detail below. Figure 9

[0188] ①The voltage difference waveform of the first control sub-signal Dr1-1 output by the control circuit relative to the reference zero potential VCC2-GND and the voltage difference waveform of the second control sub-signal Dr2-1 relative to the reference zero potential VCC1-GND are complementary waveforms of high and low levels outside the dead time period T D , and are T ON period when the first control sub-signal Dr1-1 is high, and T OFF period when the first control sub-signal Dr1-1 is low (as shown in Figure 3 , the first control sub-signal Dr1-1 and the second control sub-signal Dr2-1 are simultaneously low relative to the respective reference zero potentials within the short dead time period T D (for example: usually T D <500nS).

[0189] ​②When the first control sub-signal Dr1-1 outputted by the control circuit is converted from high level to low level relative to the reference zero potential VCC2-GND, the control circuit enters the T OFF period, at the same time, the third control signal Dr3 outputted by the control module 103 is converted from high level to low level relative to the reference zero potential VCC2-GND. At this time, the low level of the third control signal Dr3 will trigger the control module 103 to enter the delay T S1 timing state. At this time, the first control signal Dr1 outputted by the control module 103 remains unchanged at high level. At this time, the control circuit enters the dead time T OFF period in the T D period, its second control sub-signal Dr2-1 will remain at low level relative to the reference zero potential VCC1-GND. At this time, the second control signal Dr2 outputted by the control module 103 remains unchanged at low level relative to the reference zero potential VCC1-GND.

[0190] At this time, the voltage converter in the present application enters the first working mode.

[0191] ③After the above-mentioned ②, when the above-mentioned delay time of the control module 103 is greater than or equal to a set time value T S1 (For example, T S1 = 200nS), or the voltage difference between the input direct current voltage VI and the P point approaches zero volt, the first control signal Dr1 will be converted from high level to low level. At this time, the second control signal Dr2 outputted by the control module 103 remains unchanged at low level relative to the reference zero potential VCC1-GND. At this time, the third control signal Dr3 outputted by the control module 103 remains unchanged at low level relative to the reference zero potential VCC2-GND.

[0192] At this time, the voltage converter in the present application enters the second working mode.

[0193] ④After the above-mentioned ③, when the dead time period T D of the control circuit timing is completed, the second control sub-signal Dr2-1 is converted from low level to high level relative to the reference zero potential VCC1-GND. At this time, the high level of the second control sub-signal Dr2-1 will trigger the control module 103 to enter the delay T S2 timing state. When the above-mentioned delay time of the control module 103 is greater than or equal to a set time value T S2 (For example, T S2 = 300nS), or the voltage difference between the P point and the reference zero potential VCC1-GND approaches zero volt, the second control signal Dr2 will be converted from low level to high level. At this time, the first control signal Dr1 and the third control signal Dr3 outputted by the control module 103 remain unchanged at low level relative to the reference zero potential VCC2-GND.

[0194] At this time, the voltage converter in the present application enters the third working mode.

[0195] ⑤After the above ④, when the second control sub-signal Dr2-1 output by the control circuit is converted from high level to low level relative to the reference zero potential VCC1-GND. At this time, the low level of the second control sub-signal Dr2-1 will trigger the control module 103 to enter the delay T S3 counting state, set T S3 > D At this time, the control circuit operates in the T D period, the first control sub-signal Dr1-1 relative to the reference zero potential VCC1-GND remains low level. At this time, the first control signal Dr1 and the third control signal Dr3 output by the control module 103 relative to the reference zero potential VCC2-GND remain low level. When the T D period of the control circuit ends, the first control sub-signal Dr1-1 output by the control circuit is converted from low level to high level relative to the reference zero potential VCC2-GND, and the control circuit enters the T ON period, while making the third control signal Dr3 output by the control module 103 relative to the reference zero potential VCC2-GND converted from low level to high level. At the same time, the high level of the third control signal Dr3 will trigger the control module 103 to start the delay T S4 counting.

[0196] At this time, the voltage converter in the present application enters the fourth working mode.

[0197] ⑥After the above ⑤, after the control module 103 delays T S3 counting is completed, the second control signal Dr2 is converted from high level to low level relative to the reference zero potential VCC1-GND. At this time, the third control signal Dr3 output by the control module 103 relative to the reference zero potential VCC2-GND is still high level. At the same time, the control module 103 starts to detect the potential difference between the circuit node P and VI. The first control signal Dr1 output by the control module 103 relative to the reference zero potential VCC2-GND remains low level. At this time, the third control signal Dr3 output by the control module 103 relative to the reference zero potential VCC2-GND remains high level.

[0198] At this time, the voltage converter in the present application enters the fifth working mode.

[0199] ⑦After the above ⑥, when the control module 103 detects that the potential of the circuit node P gradually rises to the potential U P ≈U VI , that is, U DS-Q1 =U C3When the voltage at the circuit node P is equal to the voltage VI, the first control signal Dr1 outputted by the control module 103 is converted from low level to high level relative to the reference zero potential VCC2-GND. If the voltage at the circuit node P does not rise to the voltage VI and the first control signal Dr1 is converted from low level to high level when the maximum soft-on waiting timing of the first switch tube Q1 ends, the third control signal Dr3 outputted by the control module 103 remains high level relative to the reference zero potential VCC2-GND. At this time, the second control signal Dr2 outputted by the control module 103 remains low level relative to the reference zero potential VCC1-GND.

[0200] At this time, the voltage converter in the present application enters the sixth working mode.

[0201] In one embodiment of the present application, as shown in Figure 10 the first delay comparison unit 1031 includes a third resistor R212, a fourth resistor R213, a fifth resistor R210, a sixth resistor R211, a seventh resistor R214, a first diode D210, a fourth switch tube Q210 and a first operational amplifier IC210. The first end of the third resistor R212 is electrically connected with the reference voltage unit 1033 for receiving the reference voltage signal VREF. The second end of the third resistor R212 is electrically connected with the first end of the fourth resistor R213 and the first input end of the first operational amplifier IC210 respectively. The first end of the fifth resistor R210 is used for receiving the input direct current voltage VI. The second end of the fifth resistor R210 is electrically connected with the first end of the sixth resistor R211, the second end of the seventh resistor R214 and the second input end of the first operational amplifier IC210 respectively. The second end of the sixth resistor R211 and the second end of the fourth resistor R213 are grounded. The control end of the fourth switch tube Q210 is electrically connected with the first driving unit 1034 for receiving the third control signal Dr3. The first conduction end of the fourth switch tube Q210 is electrically connected with the power supply. The second conduction end of the fourth switch tube Q210 is electrically connected with the first end of the seventh resistor R214. The anode of the first diode D210 is electrically connected with the output end of the first operational amplifier IC210. The cathode of the first diode D210 is electrically connected with the second delay comparison unit 1032 and the second driving unit 1035 respectively.

[0202] Specifically, the third resistor R212 is used to receive the reference voltage signal VREF output by the reference voltage unit 1033 and transmit it to the first input end (the same-phase input end) of the first operational amplifier IC210, so as to provide a reference for the first operational amplifier IC210. The fourth resistor R213 is connected in series with the third resistor R212 and grounded, and is used to divide voltage to determine the reference voltage division value of the first input end of the first operational amplifier IC210. The fifth resistor R210 receives the input direct current voltage VI, is connected in series with the sixth resistor R211 and grounded, and transmits the voltage division signal of the input direct current voltage VI to the second input end (the opposite-phase input end) of the first operational amplifier IC210 through voltage division. The sixth resistor R211 divides voltage together with the fifth resistor R210 and simultaneously stabilizes the voltage division signal. The seventh resistor R214 participates in voltage division together with the fifth resistor R210 and the sixth resistor R211 when the fourth switch tube Q210 is turned on, and adjusts the voltage of the second input end of the first operational amplifier IC210. The control end of the fourth switch tube Q210 receives the third control signal Dr3 output by the first driving unit 1034, and controls whether the seventh resistor R214 is connected to the voltage division circuit through turning on or turning off, so as to adjust the voltage of the second input end of the first operational amplifier IC210. When the third control signal Dr3 is converted from high level to low level, the delay T S1 is started. The first operational amplifier IC210 compares the voltage signals of its two input ends, and outputs a corresponding level signal according to the comparison result. The first diode D210 is used to unidirectionally transmit the high-level signal output by the first operational amplifier IC210 to the second driving unit 1035, prevents external high-level signals from flowing back, and ensures normal work of the circuit.

[0203] In an embodiment of the present application, as shown in Figure 11 , the first delay comparison unit 1031 further comprises R215, R216, R217, C212, C210, C211 and D211. The connection relationship of these devices can be referred to Figure 11 , and corresponding description is not given here. R215 is a storage charge discharge resistor of the parasitic capacitance between the gate G and the source S of the fourth switch tube Q210. R216 is a current limiting resistor of the fourth switch tube Q210. R217 and D211 are a positive feedback loop circuit when the output trigger level of the first operational amplifier IC210 flips. C210, C211 and C212 have anti-interference and delay functions, and can enhance the reliability of the circuit when working at high speed. Adding the above elements can enhance the reliability of the circuit when working at high speed and improve the anti-interference ability.

[0204] Exemplarily, Figure 11The R215 and R216 connected to the gate G of the fourth switch tube Q210 shown can both use extreme values. For example, the resistance of R215 can be infinite, which is equivalent to an open circuit and can be removed. The resistance of R216 can be 0Ω, which is equivalent to a short circuit and can be replaced by a short-circuited connecting wire. Similarly, the resistance of R217 can be infinite, which is equivalent to an open circuit and can be removed. The capacitance of C210, C211 and C212 can all be 0uF and can be removed. D211 can also be removed. When the above-mentioned resistors, capacitors and diodes are all used at extreme values, the most simplified circuit can be obtained, as shown in FIG. Figure 10 shown.

[0205] The following combination Figure 10 and Figure 11 The working principle of the first delay comparison unit 1031 is described in detail.

[0206] When the third control signal Dr3 is at a high level relative to the reference zero potential VCC2-GND, the voltage difference between the gate G (Dr3) and the source S (VCC2) of the fourth switch tube Q210 is close to zero volt U GS-Q210 ≈0V, at this time, the source S (VCC2) and drain D of the fourth switch tube Q210 are in the off state, and the current flowing through it is close to zero ampere I DS-Q210 =I R213 ≈0A. At this time, the inverting input terminal U of the first operational amplifier IC210 (IC210-) The voltage difference relative to the reference zero potential VCC2-GND is calculated as shown in Formula 12:

[0207] U (IC210-) =U R211 =U VI *R211 / (R211+R210)

[0208] The non-inverting input terminal U of the first operational amplifier IC210 (IC210+) The voltage difference relative to the reference zero potential VCC2-GND is calculated as shown in Formula 13:

[0209] U (IC210+) =U R213 =U VREF *R213 / (R212+R213)

[0210] As shown in Formula 12 and Formula 13, the non-inverting input terminal of the first operational amplifier IC210 can be set to a very small reference voltage value (for example, less than 0.1V) relative to the reference zero potential VCC2-GND by selecting an appropriate resistor value. When the voltage at the inverting input terminal of the first operational amplifier IC210 is greater than the voltage at the non-inverting input terminal, that is, U (IC210-) >U (IC210+)When the output voltage is low, U OUT-IC210 ≈0V. As shown in equation 9 above, when the first switch Ql is in the off state, U DS-Q1 =U C3 =U VI -U P,VI-GND When the voltage difference between VI and the circuit node P (zero potential reference point VCC2-GND) is greater than the set value, it indicates that the voltage between the drain D and the source S of the first switch Ql does not yet meet the zero voltage soft-on condition, at this time the output voltage of the first operational amplifier IC210 is low, U OUT-IC210 ≈0V, which is one of the judgment conditions for whether the first switch Ql is on or not.

[0211] When the voltage of the inverting input terminal of the first operational amplifier IC210 is less than the voltage of the non-inverting input terminal, that is, U IC210- <U IC210+ , it indicates that the voltage between the drain D and the source S of the first switch Ql meets the zero voltage soft-on condition, at this time the output voltage of the first operational amplifier IC210 is high, U OUT-IC210 ≈U VCC2 , which is one of the judgment conditions for whether the first switch Ql is on or not.

[0212] When the third control signal Dr3 is low with respect to the reference zero potential VCC2-GND, the voltage difference between the gate G (close to the Dr3 voltage) and the source S (the same as the VCC2 voltage) of the first switch Ql is close to the negative amplitude of VCC2, U GS-Q210 ≈-U VCC2 , at this time the source S (VCC2) and the drain D of the fourth switch Q210 are in the on state, U DS-Q210 ≈0V. At this time, the current flowing through the seventh resistor R214 will raise the voltage of the inverting input terminal of the first operational amplifier IC210. At this time, the voltage difference of the inverting input terminal of the first operational amplifier IC210 with respect to the reference zero potential VCC2-GND is calculated as equation 14:

[0213] U (IC210-) =(R211*R210*U VCC2 +R214*R211*U VI )

[0214] / (R214*R210+R214*R211+R211*R210)

[0215] As shown in Formula 14, when the third control signal Dr3 is at a low level relative to the reference zero potential VCC2-GND, by selecting a suitable resistance value, the voltage value of the inverting input terminal of the first operational amplifier IC210 can be made much greater than the set voltage value U of the non-inverting input terminal. (IC210-) >U (IC210+) At this time, the output voltage of the first operational amplifier IC210 is low level U OUT-IC210 ≈0V, this determination serves as one of the conditions for determining whether the first switch tube Q1 is still in the off state.

[0216] In one embodiment of the present application, Figure 12 As shown, the second delay comparison unit 1032 includes an eighth resistor R220, a first capacitor C220, a second diode D220 and a second operational amplifier IC220. The first end of the eighth resistor R220 is electrically connected to the first driving unit 1034 for receiving the third control signal Dr3. The second end of the eighth resistor R220 is electrically connected to the first input end of the second operational amplifier IC220 and the first end of the first capacitor C220, respectively. The second end of the first capacitor C220 is grounded. The second input end of the second operational amplifier IC220 is electrically connected to the reference voltage unit 1033 for receiving the reference voltage signal VREF. The output end of the second operational amplifier IC220 is electrically connected to the anode of the second diode D220, and the cathode of the second diode D220 is electrically connected to the first delay comparison unit 1031 and the second driving unit 1035, respectively.

[0217] Specifically, the second input terminal (inverting input terminal) of the second operational amplifier IC220 is connected to the output terminal of the reference voltage unit 1033, and is used to receive the reference voltage signal VREF. The voltage value U VREF The positive terminal of the first capacitor C220 is connected to the first input terminal (non-inverting input terminal) of the second operational amplifier IC220, and the voltage value U C220 As the floating comparison voltage value set by the second delay comparison unit 1032. When the third control signal Dr3 output by the control module 103 changes from a low level to a high level relative to the reference zero potential VCC2-GND, the third control signal Dr3 charges the first capacitor C220 through the eighth resistor R220, so that the voltage value U across the first capacitor C220 becomes C220 Gradually rise, then start delay T S4 Timing.

[0218] When the floating comparison voltage value of the second delay comparison unit 1032 is still smaller than the fixed reference voltage value, that is, U C220 VREF When the output voltage of the second operational amplifier IC220 is low level U OUT-IC220 ​≈0V, this determination as the first switch tube Q1 still maintains the determination of one of the conditions of the off state.

[0219] When the second delay comparison unit 1032 U OUT-IC220 ≈0V and the first delay comparison unit 1031 U OUT-IC210 ≈0V occurs simultaneously, the first switch tube Q1 continues to maintain the off state.

[0220] When the second delay comparison unit 1032 floating comparison voltage value rises to greater than the fixed reference voltage value, that is, U C220 >U VREF , the output voltage value of the second operational amplifier IC220 is converted from low to high U OUT-IC220 ≈U VCC2 , this high level through the second diode D220 and the second drive unit 1035, so that the first control signal Dr1 output high level and large current, to drive the first switch tube Q1 gate G and source S between the junction capacitance, so that the first switch tube Q1 from the off state to the on state.

[0221] In an embodiment of the application, as Figure 13 shown, the second delay comparison unit 1032 also includes R221 and C221, wherein the connection relationship of the two devices can be seen in Figure 13 , here is not the corresponding description. R221 as a voltage dividing resistor, C221 has anti-interference and delay function, can enhance the reliability of the circuit in high speed work.

[0222] Exemplary, Figure 13 shown in the connection of the second operational amplifier IC220 in-phase input R221 can be selected for the limit value, for example, R221 resistance can be for infinity, equivalent to open circuit, can be removed. C221 can be for 0uF, can be removed. When the above resistance and capacitance are selected for the limit value, thus can get the most simplified circuit, as Figure 12 shown.

[0223] In an embodiment of the application, as Figure 20As shown, the third delay comparison unit 1036 comprises a fourteenth resistor R260, a fifteenth resistor R261, a sixteenth resistor R264, a second capacitor C260, a fifth switch tube Q260, and a third operational amplifier IC260. The first input end of the third operational amplifier IC260 is grounded. The first end of the fourteenth resistor R260 is configured to receive the voltage at the first conduction end P of the second switch tube Q2. The second end of the fourteenth resistor R260 is electrically connected with the first end of the fifteenth resistor R261, the second end of the sixteenth resistor R264, the first end of the second capacitor C260, and the second input end of the third operational amplifier IC260, respectively. The second end of the fifteenth resistor R261 and the second end of the second capacitor C260 are both grounded. The control end of the fifth switch tube Q260 is configured to be electrically connected with the control circuit and configured to receive the second control sub-signal Dr2-1. The first conduction end of the fifth switch tube Q260 is electrically connected with the power supply. The second conduction end of the fifth switch tube Q260 is electrically connected with the first end of the sixteenth resistor R264. The output end of the third operational amplifier IC260 is electrically connected with the third drive unit 1037.

[0224] Specifically, the first input end (the same-phase input end) of the first operational amplifier IC210 is connected with the reference zero potential VCC1-GND, so as to ensure that the first operational amplifier IC210 is a zero potential reference. The fourteenth resistor R260 receives the voltage at the first conduction end P of the second switch tube Q2, is connected with the fifteenth resistor R261 in series, and is grounded. The voltage at the first conduction end P of the second switch tube Q2 is divided by the voltage divider, and the divided voltage signal is transmitted to the second input end (the opposite-phase input end) of the third operational amplifier IC260. The fifteenth resistor R261 divides the voltage in cooperation with the fourteenth resistor R260, and simultaneously plays a role of stabilizing the divided voltage signal. The sixteenth resistor R264 participates in voltage division together with the fourteenth resistor R260 and the fifteenth resistor R261 when the fifth switch tube Q260 is turned on, and adjusts the voltage at the second input end of the third operational amplifier IC260. The control end of the fifth switch tube Q260 receives the second control sub-signal Dr2-1 output by the control circuit, controls whether the sixteenth resistor R264 is connected to the voltage divider by being turned on or turned off, so as to adjust the voltage at the second input end of the third operational amplifier IC260. When the second control sub-signal Dr2-1 is converted from high level to low level, the delay T S3 is started. The third operational amplifier IC260 compares the voltage signals at the two input ends, and outputs a corresponding level signal according to the comparison result, which is transmitted to the third drive unit 1037.

[0225] In an embodiment of the present application, as shown in Figure 21 , the third delay comparison unit 1036 further comprises R262, R265, R266, R267, C261, and D261. The connection relationship of these devices can be referred to Figure 21R262 is used to receive the reference zero potential VCC1-GND signal and transmit it to the first input end of the first operational amplifier IC210. R265 is a storage charge discharge resistance for the parasitic capacitance between the gate G and the source S of the fifth switch tube Q260. R266 is a current limiting resistance of the fifth switch tube Q260. R267 and D261 are positive feedback return difference circuits when the output trigger level of the third operational amplifier IC260 is flipped. C261 has an anti-interference function and can enhance the reliability of the circuit when working at high speed. Adding the above elements can enhance the reliability of the circuit when working at high speed and improve the anti-interference ability.

[0226] As shown in the example, Figure 21 The R265 and R266 connected at the gate G of the fifth switch tube Q260 can be selected as limit values. For example, the resistance of R265 can be infinite, equivalent to an open circuit, and can be removed. The resistance of R266 can be 0Ω, equivalent to a short circuit, and a connection line short circuit can be used instead. Similarly, the resistance of R267 can be infinite, equivalent to an open circuit, and can be removed. The resistance of R262 can be 0Ω, equivalent to a short circuit, and a connection line short circuit can be used instead. The capacitance of C261 can be 0uF, and can be removed. D261 can also be removed. When the above resistors, capacitors and diodes are selected as limit values, the simplest circuit can be obtained, as shown in Figure 20 .

[0227] The working principle of the third delay comparison unit 1036 will be described in detail below. Figure 20 and Figure 21 The working principle of the third delay comparison unit 1036 will be described in detail below.

[0228] The fifth switch tube Q260 is a PMOS field effect tube. When the second control sub-signal Dr2-1 is high relative to the reference zero potential VCC1-GND, the voltage difference between the gate G (Dr2-1) and the source S (VCC1) of the fifth switch tube Q260 is close to zero volts U GS-Q260 ≈0V, at this time the source S (VCC1) and the drain D of the fifth switch tube Q260 are in an off state, and the current flowing through it is close to zero amperes I DS-Q260 R264 ≈0A. At this time, the voltage difference of the inverting input end U (IC260-) of the third operational amplifier IC260 relative to the reference zero potential VCC1-GND is calculated as formula 15:

[0229] U (IC260-) = U R261 = U P *R261 / (R261+R260)

[0230] The voltage difference of the non-inverting input end U​(IC260+) The voltage of the non-inverting input of the third operational amplifier IC260 is close to the reference zero potential VCC1-GND.

[0231] As shown in equation 15, the voltage of the non-inverting input of the third operational amplifier IC260 is close to the reference zero potential VCC1-GND, i.e. 0V<U (IC260+) ≈0V. When the voltage of the non-inverting input of the third operational amplifier IC260 is lower than that of the inverting input, i.e. U (IC260-) <U (IC260+) , the voltage of the output of the third operational amplifier IC260 is high, i.e. U OUT-IC210 ≈VCC1. As in the second working mode described above, the voltage of the circuit node P relative to the reference zero potential point VI-GND is U P，VI-GND converted from the input DC voltage U P,VI-GND ≈VI to a negative voltage close to zero, i.e. 0V>U P,VI-GND ≈0V, as shown in equation 15, at this time, U (IC260-) <U (IC260+) , thus the output of the third operational amplifier IC260 is converted to high, i.e. U OUT-IC260 ≈VCC1, and the second control signal DR2 is converted from low to high through the current amplification of the third driving unit 1037, so that the second switch tube Q2 realizes zero-voltage soft turn-on.

[0232] When the signal Dr2-1 output by the control circuit is low relative to the reference zero potential VCC1-GND, the voltage difference between the gate G (close to the voltage of Dr2-1) and the source S (the same as the voltage of VCC1) of the fifth switch tube Q260 is close to the amplitude U GS-Q260 ≈-U VCC1 of negative VCC1, at this time, the source S (VCC1) and the drain D of the fifth switch tube Q260 are in a conductive state U DS-Q260 ≈0V. At this time, the current flowing through the eighteenth resistor R264 will raise the voltage of the inverting input of the first operational amplifier IC260. At this time, the voltage difference of the inverting input of the third operational amplifier IC260 relative to the reference zero potential VCC1-GND is calculated as shown in equation 16:

[0233] U (IC260-) =(R261*R260*U VCC1 +R264*R261*U P )

[0234] / (R264*R260+R264*R261+R261*R260)

[0235] As shown in equation 16, when the second control sub-signal Dr2-1 is low relative to the reference zero potential VCC1-GND, the voltage value at the inverting input terminal of the third operational amplifier IC260 can be much greater than the voltage value U close to the reference zero potential VCC1-GND at the non-inverting input terminal of the third operational amplifier IC260 by selecting a suitable resistance value (IC260-) >U (IC260+) At this time, the output voltage of the third operational amplifier IC260 is converted to low U OUT-IC260 ≈0V, and the second control signal Dr2 is converted from high to low by the current amplification of the third driving unit 1037. Since U P,VI-GND ≈0V in the above-mentioned fifth working mode, the second switch tube Q2 is realized to be soft-off at zero voltage.

[0236] In an embodiment of the present application, as shown in Figure 14 , the reference voltage unit 1033 comprises a ninth resistor R230 and a zener IC230, the first end of the ninth resistor R230 is used to be electrically connected with the power supply, the second end of the ninth resistor R230 is electrically connected with the cathode of the zener IC230, the reference pole of the zener IC230, the first delay comparison unit 1031 and the second delay comparison unit 1032 respectively, and the anode of the zener IC230 is grounded.

[0237] Specifically, the current flows from the positive pole VCC2 of the second auxiliary power supply, flows through the ninth resistor R230, flows into the cathode and the reference pole of the three-terminal zener IC230, and is then divided into two paths, one of which flows into the reference zero potential VCC2-GND of the auxiliary power supply, and the other of which flows out of the port to output the reference voltage signal VREF. The voltage waveform between the reference voltage signal VREF and the reference zero potential VCC2-GND is a constant direct current voltage.

[0238] It should be noted that, as shown in Figure 15 , the reference voltage unit 1033 further comprises C230, which is connected between the second end of the ninth resistor R230 and the reference zero potential VCC2-GND, and functions to filter high-frequency alternating current interference.

[0239] For example, the capacitance of C230 can be 0uF, which can be removed. When the above-mentioned capacitor is selected to be the limit value, the most simplified circuit can be obtained, as shown in Figure 14 .

[0240] In an embodiment of the present application, as shown in Figure 16As shown, the first driving unit 1034 comprises a tenth resistor R240, an eleventh resistor R241, a first triode Q240 and a second triode Q241. The first end of the tenth resistor R240 is electrically connected with the first end of the eleventh resistor R241 and the control circuit respectively, for receiving the first control sub-signal Dr1-1. The second end of the tenth resistor R240 is electrically connected with the base B of the first triode Q240 and the base B of the second triode Q241 respectively. The collector C of the first triode Q240 is electrically connected with the power supply. The emitter E of the first triode Q240 is electrically connected with the emitter E of the second triode Q241, the first delay comparison unit 1031 and the second delay comparison unit 1032 respectively. The collector C of the second triode Q241 and the second end of the eleventh resistor R241 are grounded.

[0241] Specifically, when the first control sub-signal Dr1-1 is high, the current flows from Dr1-1 and is divided into two paths. One path of the current flows through the eleventh resistor R241 and is merged into the second auxiliary power supply reference zero potential VCC2-GND. The other path of the current flows through the tenth resistor R240 and is merged into the emitter E of the first triode Q240 due to the current amplification of the first triode Q240. Meanwhile, another larger current flows from the positive electrode VCC2 of the second auxiliary power supply, flows through the collector C of the first triode Q240 and is also merged into the emitter E. Finally, the current flows out from the output port, i.e., outputs the third control signal Dr3. The third control signal Dr3 flows into the gate G of the third switch tube Q3 and is merged into the second auxiliary power supply reference zero potential VCC2-GND from the source S of the third switch tube Q3.

[0242] When the first control sub-signal Dr1-1 is low, the discharge current of the charges stored in the gate G and the source S parasitic capacitance of the third switch tube Q3 flows into Dr3 and then flows through the emitter E of the second triode Q241 and is divided into two paths. One path of the larger current flows through the collector C of the second triode Q241 and is merged into the second auxiliary power supply reference zero potential VCC2-GND. The other path of the smaller current flows through the base B of the second triode Q241 and the tenth resistor R240 and is divided into two paths. One path of the current flows through the eleventh resistor R241 and is merged into the second auxiliary power supply reference zero potential VCC2-GND. The other path of the current flows out from the port to the control circuit.

[0243] For example, the designer can select the types of the first triode Q240 and the second triode Q241 according to actual needs. For example, the first triode Q240 can be selected as NPN type. The second triode Q241 can be selected as PNP type.

[0244] It should be noted that, as Figure 17As shown, the first driving unit 1034 further comprises R242 as a current-limiting resistor and C240 connected between the positive pole VCC2 of the second auxiliary power supply and the reference zero potential VCC2-GND of the auxiliary power supply, which functions to filter high-frequency AC interference.

[0245] For example, the resistance of R242 can be 0Ω, which is equivalent to a short circuit, and a connecting wire short circuit can be used instead. The capacitance of C240 can be 0uF, which can be removed. When the above resistance and capacitance are selected to be limit values, the simplest circuit can be obtained, as shown in Figure 16 .

[0246] In an embodiment of the present application, as shown in Figure 18 , the second driving unit 1035 comprises a twelfth resistor R250, a thirteenth resistor R251, a third transistor Q250 and a fourth transistor Q251. The first end of the twelfth resistor R250 is electrically connected with the first end of the thirteenth resistor R251, the first delay comparison unit 1031 and the second delay comparison unit 1032 respectively. The second end of the twelfth resistor R250 is electrically connected with the base B of the third transistor Q250 and the base B of the fourth transistor Q251 respectively. The collector C of the third transistor Q250 is electrically connected with the power supply. The emitter E of the third transistor Q250 is electrically connected with the emitter E of the fourth transistor Q251, which is used to output the first control signal Dr1. The collector C of the fourth transistor Q251 and the second end of the thirteenth resistor R251 are grounded.

[0247] Specifically, when the signal obtained by superimposing the first comparison signal and the second comparison signal is high, the current is divided into two paths. One path of current flows into the second auxiliary power supply reference zero potential VCC2-GND through the thirteenth resistor R251. Another path of current flows into the base B of the third transistor Q250 through the twelfth resistor R250, and then flows into the emitter E due to the current amplification effect of the third transistor Q250. At the same time, another larger current flows from the second auxiliary power supply positive pole VCC2, and also flows into the emitter E through the collector C of the third transistor Q250. Finally, the current flows out from the output port, i.e. the first control signal Dr1 is output. The first control signal Dr1 flows into the gate G of the first switch tube Q1, and then flows into the second auxiliary power supply reference zero potential VCC2-GND from the source S of the first switch tube Q1.

[0248] When the signal after superimposing the first comparison signal and the second comparison signal is low, the discharge current of the charge stored in the parasitic capacitance between the gate G and the source S of the first switch tube Q1 flows into Dr1, and then is divided into two paths through the emitter E of the fourth PNP type transistor Q251. One path with larger current flows into the second auxiliary power supply reference zero potential VCC2-GND through the collector C of the fourth transistor Q251. The other path with smaller current flows out from the port through the base B of the fourth transistor Q251, the twelfth resistor R250, and then is divided into two paths. One path flows into the second auxiliary power supply reference zero potential VCC2-GND through the thirteenth resistor R251. The other path flows out from the port.

[0249] For example, the designer can select the types of the third transistor Q250 and the fourth transistor Q251 according to actual needs. For example, the third transistor Q250 can be selected as an NPN type, and the fourth transistor Q251 can be selected as a PNP type.

[0250] It should be noted that, as shown in Figure 19 , the second driving unit 1035 further includes R252 and C250. R252 is used as a current-limiting resistor, and C250 is connected between the positive electrode VCC2 of the second auxiliary power supply and the auxiliary power supply reference zero potential VCC2-GND. The role of C250 is to filter out high-frequency alternating current interference noise.

[0251] For example, the resistance value of R252 can be 0Ω, which is equivalent to short circuiting. The connection line short circuiting can be used instead. The capacitance value of C250 can be 0uF, which can be removed. When the above-mentioned resistor and capacitor are selected to the limit value, the most simplified circuit can be obtained, as shown in Figure 18 .

[0252] In an embodiment of the present application, as shown in Figure 22 , the third driving unit 1037 includes the seventeenth resistor R270, the eighteenth resistor R271, the fifth transistor Q270, and the sixth transistor Q271. The first end of the seventeenth resistor R270 is electrically connected with the first end of the eighteenth resistor R271 and the third delay comparison unit 1036, respectively. The second end of the seventeenth resistor R270 is electrically connected with the base B of the fifth transistor Q270 and the base B of the sixth transistor Q271, respectively. The collector C of the fifth transistor Q270 is used to be electrically connected with the power supply. The emitter E of the fifth transistor Q270 is electrically connected with the emitter E of the sixth transistor Q271, and is used to output the second control signal Dr2. The collector C of the sixth transistor Q271 and the second end of the eighteenth resistor R271 are both grounded.

[0253] Specifically, when the third comparison signal is high, the current flows into two paths, one of which flows through the eighteenth resistor R271 and then converges into the first auxiliary power reference zero potential VCC1-GND, and the other of which flows through the seventeenth resistor R270 and then converges into the base B of the NPN type fifth transistor Q270 and the emitter E. Meanwhile, another larger current flows from the first auxiliary power positive electrode VCC1, converges into the emitter E through the collector C of the fifth transistor Q270, and finally flows out from the output port, that is, the second control signal Dr2 is output. The second control signal Dr2 flows into the gate G of the second switch tube Q2 and converges into the first auxiliary power reference zero potential VCC1-GND from the source S of the second switch tube Q2.

[0254] When the third comparison signal is low, the discharge current of the charges stored in the parasitic capacitance between the gate G and the source S of the second switch tube Q2 flows into Dr2, and then converges into the first auxiliary power reference zero potential VCC1-GND through the emitter E of the PNP type sixth transistor Q271. The emitter E of the sixth transistor Q271 converges into the first auxiliary power reference zero potential VCC1-GND through the collector C of the sixth transistor Q271, and converges into the first auxiliary power reference zero potential VCC1-GND through the base B of the sixth transistor Q271 and the seventeenth resistor R270. The base B of the sixth transistor Q271 converges into the first auxiliary power reference zero potential VCC1-GND through the eighteenth resistor R271, and converges into the output port from the collector C of the sixth transistor Q271.

[0255] For example, the designer can select the types of the fifth transistor Q270 and the sixth transistor Q271 according to actual needs. For example, the fifth transistor Q270 can be selected as an NPN type, and the sixth transistor Q271 can be selected as a PNP type.

[0256] It should be noted that, as shown in Figure 23 , the third driving unit 1037 further includes R272 and C270. R272 is used as a current limiting resistor, and C270 is connected between the first auxiliary power positive electrode VCC1 and the auxiliary power reference zero potential VCC1-GND, and is used to filter high-frequency alternating current interference.

[0257] For example, the resistance value of R272 can be 0Ω, which is equivalent to a short circuit, and a connection line short circuit can be used instead. The capacitance value of C270 can be 0uF, and C270 can be removed. When the above-mentioned resistors and capacitors are selected to have limit values, the most simplified circuit can be obtained, as shown in Figure 22 .

[0258] The above circuit is functionally tested by setting the voltage parameters, the working frequency of the control signal, the inductance value and other key parameters, and based on the measured data of the driving voltage waveforms of each switch tube, the voltage between the drain D and the source S, the current waveforms, the inductance current waveforms and the node voltage waveforms obtained by the test, the soft switching working mode, the energy transmission process and the loss mechanism are systematically analyzed and the principle is verified.

[0259] For example, if the following parameters are set: U VI = 12V, U VO = 3.3V, U VCC1 = 12V (reference zero potential VCC1-GND), U VCC2 = 12V (reference zero potential VCC2-GND), U VREF = 2.5V (reference zero potential VCC2-GND), L L2 = 39nH, L N1-L1 = 20uH (inductance of the main winding N1 of the first inductor L1, the auxiliary winding N2 is open measured), Lk N1-L1 = 0.4uH (inductance of the main winding N1 of the first inductor L1, the auxiliary winding N2 is short measured), L N2-L1 = 50nH (leakage inductance of the auxiliary winding N2 of the first inductor L1, the main winding N1 is open measured), Lk N2-L1 = 2.5nH (inductance of the auxiliary winding N2 of the first inductor L1, the main winding N1 is short measured), N1 / N2 = 20 (turn ratio of the main winding N1 and the auxiliary winding N2 of the first inductor L1), the model of N-type field effect transistor Q1, Q2, Q3 can be SPU30N03S2-08(infineon), the working frequency of Dr1-1 and Dr2-1 is 500kHz.

[0260] The driving voltage VG-Q1, VG-Q2, VG-Q3 between the gate G and the source S of Q1, Q2, Q3, the current I-Q1, I-Q2, I-Q3 flowing through the drain D and the source S of Q1, Q2, Q3, the current I-C3 flowing through C3, the voltage VDS-Q1 between the drain D and the source S of Q1, the voltage V-P between the circuit node P and the zero potential reference point VI-GND, the current I-N1 of the main winding N1 of the first inductor L1, the above voltage and current waveforms and working mode are shown in Figure 24 、 Figure 25 and Figure 26 .

[0261] I-Q1, I-Q3, I-N1, I-OUT, VO, I-C3, VG-Q3, V-N2, V-N1, V-L2, and the like, are shown in the waveforms and operating mode chart of Fig. 1. Figure 27

[0262] It should be noted that Figure 24 to Figure 27 The meanings of the symbols in the above equations are as follows:

[0263] I-Q* : The instantaneous value of the current flowing through the drain D and the source S of the N-type field effect transistor Q*, which is a bidirectional current. The positive direction is defined as the current flowing from the drain D to the source S. The * indicates an arbitrary positive integer.

[0264] I-N1 : The instantaneous value of the current flowing through the main winding N1 of the first inductor L1, with the positive direction defined as the current flowing from the circuit node P to the voltage output terminal VO.

[0265] I-N2 : The instantaneous value of the current flowing through the auxiliary winding N2 of the first inductor L1, which is a unidirectional positive current.

[0266] VDS-Q* : The instantaneous value of the voltage between the drain D and the source S of the N-type field effect transistor Q*, which is a bidirectional voltage. The * indicates an arbitrary positive integer. VG-Q* : The instantaneous value of the voltage between the gate G and the source S of the N-type field effect transistor Q*, which is a bidirectional voltage. The * indicates an arbitrary positive integer.

[0267] V-N1 : The instantaneous value of the voltage across the main winding N1 of the first inductor L1, with the positive direction defined as the voltage between the N1 winding and the circuit node P, and the negative direction defined as the voltage between the N1 winding and the voltage output terminal VO.

[0268] V-N2 : The instantaneous value of the voltage across the auxiliary winding N2 of the first inductor L1, with the positive direction defined as the voltage between the N2 winding and the second inductor L2, and the negative direction defined as the voltage between the N2 winding and the drain D of Q3.

[0269] I-OUT : The current flowing from the DC voltage positive terminal VO to the load, and from the zero potential reference point VO-GND back to the DC voltage positive terminal VO, which is a unidirectional positive current.

[0270] V-L2 : The instantaneous value of the voltage across the second inductor L2, with the positive direction defined as the voltage between the L2 and the anode of the unidirectional diode D3, and the negative direction defined as the voltage between the L2 and the auxiliary winding N2 of the first inductor L1. ​

[0271] I-C3: Indicates the instantaneous value of the current flowing through the bypass capacitor C3. It is a bidirectional current. The positive direction is defined as the current flowing from the end connected to the drain D of Q1 to the end connected to the source S of Q1.

[0272] VP: represents the instantaneous value of the voltage between the circuit node P and the zero potential reference point VI-GND.

[0273] VI: The instantaneous value of the voltage between the positive terminal VI of the input DC voltage VI and the zero potential reference point VI-GND.

[0274] VO: The instantaneous value of the voltage between the output DC voltage positive terminal VO and the zero potential reference point VO-GND.

[0275] like Figure 24 to Figure 27 As shown, in the first working mode (i.e. Figure 24 、 Figure 25 and Figure 27 In the corresponding 1), when VG-Q3 changes from a high level to a low level, the current I-Q3 has already dropped to zero ampere 0A in advance, so the third switch tube Q3 realizes the zero-current soft turn-off function.

[0276] In the second working mode (i.e. Figure 24 、 Figure 25 and Figure 27 Corresponding to 2), when VG-Q1 changes from a high level to a low level, the current I-Q1 drops from its maximum value to 0A without delay, and at the same time, the current I-C3 rises from 0A to its maximum value without delay. Therefore, when Q1 is turned off, C3 acts as a current bypass without delay. At the same time, since the voltage across C3 (i.e., the DS voltage VDS-Q1 of Q1) cannot change suddenly, the bypass current causes the VDS-Q1 voltage to gradually increase, so that the first switch tube Q1 achieves zero current and zero voltage shutdown.

[0277] In the third working mode (i.e. Figure 24 、 Figure 25 and Figure 27 In the corresponding 3), since the freewheeling current of the first inductor L1 flows through the parasitic reverse body diode of Q2, when VG-Q2 is converted from a low level to a high level, the circuit node P voltage VP (i.e., the DS voltage VDS-Q2 of Q2) has already dropped to close to zero volts in advance, so the second switch tube Q2 realizes the zero-voltage soft turn-on function.

[0278] In the fourth working mode (i.e. Figure 24 、 Figure 26 and Figure 27 Corresponding to 4), when VG-Q3 changes from high level to low level, due to the leakage inductance L flowing through the second inductor L2 and the auxiliary winding N2 of the first inductor L1, N2-L1The current I-Q3 cannot be abruptly changed, so I-Q3 gradually increases from zero ampere, thus the third switch Q3 realizes the zero-current soft turn-on function.

[0279] In the fifth working mode (i.e. Figure 24 , Figure 26 and Figure 27 corresponding to 5), when VG-Q2 is converted from high level to low level, the current I-Q2 has been gradually decreased from the maximum value to near zero ampere in advance, thus the second switch Q2 realizes the zero-current soft turn-off function. And since a small negative current flows through the DS parasitic reverse body diode of Q2 when Q2 is turned off, the DS voltage of Q2 is also clamped to near zero volt, thus the second switch Q2 realizes the zero-voltage soft turn-off function. Since Q2 is turned off at near zero ampere, the time of current flowing through the body diode of Q2 is extremely short, thus the conduction loss of Q2 is minimized.

[0280] In the sixth working mode (i.e. Figure 24 , Figure 26 and Figure 27 corresponding to 6), when VG-Q1 is converted from low level to high level, since the voltage VDS-Q1 has been decreased to near zero volt in advance, the first switch Q1 realizes the zero-voltage soft turn-on function. And since the current I-Q1 gradually increases from near zero ampere to the maximum current value, the first switch Q1 also realizes the zero-current soft turn-on function.

[0281] Thus in the voltage converter of the present application, the first switch Q1 realizes the zero-voltage, zero-current soft turn-on and zero-current soft turn-off functions, the second switch Q2 realizes the zero-voltage soft turn-on and zero-voltage, zero-current soft turn-off functions, and the third switch Q3 realizes the zero-current soft turn-on and zero-current soft turn-off functions.

[0282] According to the theoretical approximate calculation formula of the switching loss of high-frequency switch transistor, the following formula 15:

[0283] P SW-Q* = V MAX-Q* *I MAX-Q* *(T rise +T fail )*f SW / 6

[0284] wherein P SW-Q* is the effective value of the switching loss of N-type field effect transistor Q*, * represents any positive integer. V MAX-Q* is the maximum voltage value between the drain D and the source S of N-type field effect transistor Q* when it is turned off, * represents any positive integer. I MAX-Q*The maximum current value flowing between the drain D and the source S of the N-type field effect transistor Q* when it is turned on, and * represents any positive integer. rise The time period during which the voltage value between the drain D and the source S of the N-type field effect transistor Q* rises from close to zero volt to a maximum value when the N-type field effect transistor Q* is converted from the on state to the off state. fail The time period during which the voltage value between the drain D and the source S of the N-type field effect transistor Q* drops from a maximum value to close to zero volt when the N-type field effect transistor Q* is converted from the off state to the on state. SW The frequency value of Dr1, Dr2, Dr3 output by the control circuit and the control module 103.

[0285] As can be seen from formula 15, when the transistor Q* is in the over-time period of turning on or off, if the voltage applied to the transistor Q* is zero volt, i.e., zero-voltage turn-on or turn-off, the switching loss is approximately zero watt. Similarly, when the transistor Q* is in the over-time period of turning on or off, if the current flowing through the transistor Q* is zero ampere, i.e., zero-current turn-on or turn-off, the switching loss is also approximately zero watt. As described above, the Q1, Q2, and Q3 of the voltage converter of the present application all achieve the zero-voltage or zero-current soft switching state, so the switching loss of each is close to zero watt. Therefore, under the comparable conditions of the same components, the same working frequency, the same input and output voltage specifications, and the same output power, the soft switching working state of the Q1, Q2, and Q3 of the present application significantly reduces the switching loss and significantly improves the efficiency.

[0286] The embodiment of the present application also discloses a voltage converter, which comprises a first switch tube Q1, a second switch tube Q2, a first inductor L1, a control circuit, and the above-mentioned soft switching control circuit 10. The control end of the first switch tube Q1 is electrically connected with the control module 103 in the soft switching control circuit 10 and is used for receiving a first control signal Dr1. The first conduction end of the first switch tube Q1 is electrically connected with the first end of the energy storage module 101 in the soft switching control circuit 10. The second conduction end of the first switch tube Q1 is electrically connected with the first conduction end of the second switch tube Q2, the third end of the energy storage module 101, and the control module 103, respectively. The control end of the second switch tube Q2 is electrically connected with the control module 103 and is used for receiving a second control signal Dr2. The second conduction end of the second switch tube Q2 is grounded. The control circuit is electrically connected with the control module 103.

[0287] Specifically, the voltage converter adopts the above-mentioned soft switching control circuit 10. By accurately controlling the driving time sequence and the voltage and current state of the first switch tube Q1 and the second switch tube Q2, the first switch tube Q1 and the second switch tube Q2 can respectively achieve the soft switching working mode of zero-voltage turn-on / turn-off or zero-current turn-on / turn-off, effectively reduce the energy loss in the switching process, and further significantly improve the overall operating efficiency of the voltage converter.

[0288] It should be noted that the voltage transformer can be applied to high-frequency switching combined power supply of any appearance and structural form, can be realized in any printed circuit board layout connection mode, and the components in the voltage transformer can be any packaged similar principle performance components and their series and parallel combination. In addition, the soft switching control circuit 10 provided by the application is first applied in the field of industrial power supply, solar power supply, desktop computer power supply, adapter, charger, medical power supply, precision instruments and meters, etc.

[0289] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A soft switching control circuit, characterized in that: The energy storage module comprises an energy storage module, a switch module and a control module, wherein the first end of the energy storage module is used to be electrically connected to the first conduction end of the first switch tube, the DC voltage input end and the first end of the input capacitor respectively; the second end of the energy storage module is electrically connected to the first end of the switch module; the third end of the energy storage module is electrically connected to the second end of the switch module and the control module respectively; the third end of the energy storage module is used to be electrically connected to the second conduction end of the first switch tube and the first conduction end of the second switch tube; the fourth end of the energy storage module is used to be electrically connected to the first end of the output capacitor and the DC voltage output end respectively; the control module is electrically connected to the control end of the switch module, and the control module is used to be electrically connected to the control end of the first switch tube, the control end of the second switch tube and the control circuit respectively; The control module is configured to output a first control signal and a second control signal to the control end of the first switch tube and the control end of the second switch tube respectively according to the control signal output by the control circuit, and output a third control signal to the control end of the switch module, and the control circuit is configured to output the control signal to the control module; The first switch tube is used to be turned on or off according to the first control signal, the second switch tube is used to be turned on or off according to the second control signal, and the switch module is used to be turned on or off according to the third control signal.

2. The soft switching control circuit according to claim 1, characterized in that: The energy storage module includes a unidirectional conducting diode and a first inductor. The anode of the unidirectional conducting diode serves as the first end of the energy storage module, and is respectively electrically connected to the first conducting end of the first switching tube, the DC voltage input end, and the first end of the input capacitor. The first end of the auxiliary winding of the first inductor is electrically connected to the cathode of the unidirectional conducting diode. The second end of the auxiliary winding of the first inductor serves as the second end of the energy storage module, and is electrically connected to the first end of the switching module. The first end of the main winding of the first inductor serves as the third end of the energy storage module, and is respectively electrically connected to the second end of the switching module and the control module. The first end of the main winding of the first inductor is used to be electrically connected to the second conducting end of the first switching tube and the first conducting end of the second switching tube. The second end of the main winding of the first inductor serves as the fourth end of the energy storage module, and is respectively electrically connected to the first end of the output capacitor and the DC voltage output end.

3. The soft switching control circuit according to claim 2, characterized in that: The switch module includes a third switch tube, wherein a control end of the third switch tube is electrically connected to the control module and is configured to receive the third control signal, a first conductive end of the third switch tube is electrically connected to the second end of the auxiliary winding of the first inductor, a second conductive end of the third switch tube is electrically connected to the control module, and a second conductive end of the third switch tube is electrically connected to the second conductive end of the first switch tube and the first end of the main winding of the first inductor, respectively; The switch module also includes a first resistor and a second resistor, the first end of the first resistor is electrically connected to the control module, the second end of the first resistor is electrically connected to the first end of the second resistor and the control end of the third switch tube, and the second end of the second resistor is electrically connected to the second conduction end of the third switch tube and the control module.

4. The soft switching control circuit according to claim 1, wherein: The control module includes a first delay comparison unit, a second delay comparison unit, a third delay comparison unit, a reference voltage unit, a first drive unit, a second drive unit and a third drive unit, the first delay comparison unit is electrically connected to the reference voltage unit, the second delay comparison unit, the first drive unit, the second drive unit, the DC voltage input terminal and the switch module respectively, the second delay comparison unit is electrically connected to the reference voltage unit, the second drive unit and the switch module respectively, the third delay comparison unit is electrically connected to the control circuit, the energy storage module, the third drive unit and the switch module respectively, and the first drive unit is used to be electrically connected to the control circuit; The control signal includes a first control sub-signal and a second control sub-signal, the reference voltage unit is used to output a reference voltage signal to the first delay comparison unit and the second delay comparison unit; the first driving unit is used to output the third control signal according to the first control sub-signal output by the control circuit; the first delay comparison unit is used to output a first comparison signal according to the third control signal, the DC input terminal voltage signal and the reference voltage signal; the second delay comparison unit is used to output a second comparison signal according to the third control signal and the reference voltage signal; the third delay comparison unit is used to output a third comparison signal according to the second control sub-signal output by the control circuit and the voltage signal of the first conduction terminal of the second switch tube; the second driving unit outputs the first control signal according to the signal obtained by superimposing the first comparison signal and the second comparison signal, and the third driving unit outputs the second control signal according to the third comparison signal.

5. The soft switching control circuit according to claim 4, characterized in that: The first delay comparison unit includes a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a first diode, a fourth switch tube, and a first operational amplifier. The first end of the third resistor is electrically connected to the reference voltage unit for receiving the reference voltage signal. The second end of the third resistor is electrically connected to the first end of the fourth resistor and the first input terminal of the first operational amplifier, respectively. The first end of the fifth resistor is electrically connected to the first end of the sixth resistor, the second end of the seventh resistor, and the second input terminal of the first operational amplifier, respectively. The second end of the sixth resistor and the second end of the fourth resistor are both grounded. The control end of the fourth switch tube is electrically connected to the first driving unit for receiving the third control signal. The first conductive end of the fourth switch tube is electrically connected to a power supply, and the second conductive end of the fourth switch tube is electrically connected to the first end of the seventh resistor. The anode of the first diode is electrically connected to the output terminal of the first operational amplifier, and the cathode of the first diode is electrically connected to the second delay comparison unit and the second driving unit, respectively.

6. The soft switching control circuit according to claim 4, characterized in that: The second delay comparison unit includes an eighth resistor, a first capacitor, a second diode and a second operational amplifier. The first end of the eighth resistor is electrically connected to the first driving unit for receiving the third control signal. The second end of the eighth resistor is electrically connected to the first input end of the second operational amplifier and the first end of the first capacitor, respectively. The second end of the first capacitor is grounded. The second input end of the second operational amplifier is electrically connected to the reference voltage unit for receiving the reference voltage signal. The output end of the second operational amplifier is electrically connected to the anode of the second diode, and the cathode of the second diode is electrically connected to the first delay comparison unit and the second driving unit, respectively.

7. The soft switching control circuit according to claim 4, characterized in that: The reference voltage unit includes a ninth resistor and a voltage regulator tube, wherein the first end of the ninth resistor is used to be electrically connected to the power supply, the second end of the ninth resistor is electrically connected to the cathode of the voltage regulator tube, the reference electrode of the voltage regulator tube, the first delay comparison unit and the second delay comparison unit respectively, and the anode of the voltage regulator tube is grounded.

8. The soft switching control circuit according to claim 4, characterized in that: The first driving unit includes a tenth resistor, an eleventh resistor, a first transistor, and a second transistor. The first end of the tenth resistor is electrically connected to the first end of the eleventh resistor and the control circuit, respectively, for receiving the control signal. The second end of the tenth resistor is electrically connected to the base of the first transistor and the base of the second transistor, respectively. The collector of the first transistor is electrically connected to a power supply. The emitter of the first transistor is electrically connected to the emitter of the second transistor, the first delay comparison unit, and the second delay comparison unit, respectively, for outputting the third control signal. The collector of the second transistor and the second end of the eleventh resistor are both grounded.

9. The soft switching control circuit according to claim 4, characterized in that: The second driving unit includes a twelfth resistor, a thirteenth resistor, a third transistor and a fourth transistor. The first end of the twelfth resistor is electrically connected to the first end of the thirteenth resistor, the first delay comparison unit and the second delay comparison unit respectively. The second end of the twelfth resistor is electrically connected to the base of the third transistor and the base of the fourth transistor respectively. The collector of the third transistor is used to be electrically connected to a power supply. The emitter of the third transistor is electrically connected to the emitter of the fourth transistor for outputting the first control signal. The collector of the fourth transistor and the second end of the thirteenth resistor are both grounded.

10. The soft switching control circuit according to claim 4, characterized in that: The third delay comparison unit includes a fourteenth resistor, a fifteenth resistor, a sixteenth resistor, a second capacitor, a fifth switch tube and a third operational amplifier, wherein the first input terminal of the third operational amplifier is grounded, the first end of the fourteenth resistor is used to receive the voltage of the first conduction end of the second switch tube, the second end of the fourteenth resistor is electrically connected to the first end of the fifteenth resistor, the second end of the sixteenth resistor, the first end of the second capacitor and the second input terminal of the third operational amplifier respectively, the second end of the fifteenth resistor and the second end of the second capacitor are both grounded, the control end of the fifth switch tube is used to be electrically connected to the control circuit, the first conduction end of the fifth switch tube is electrically connected to the power supply, the second conduction end of the fifth switch tube is electrically connected to the first end of the sixteenth resistor, and the output end of the third operational amplifier is electrically connected to the third driving unit; The third driving unit includes a seventeenth resistor, an eighteenth resistor, a fifth transistor and a sixth transistor. The first end of the seventeenth resistor is electrically connected to the first end of the eighteenth resistor and the third delay comparison unit, respectively. The second end of the seventeenth resistor is electrically connected to the base of the fifth transistor and the base of the sixth transistor, respectively. The collector of the fifth transistor is used to be electrically connected to a power supply. The emitter of the fifth transistor is electrically connected to the emitter of the sixth transistor for outputting the second control signal. The collector of the sixth transistor and the second end of the eighteenth resistor are both grounded.

11. The soft switching control circuit according to claim 2, characterized in that: The soft switching control circuit further includes an auxiliary energy storage module, wherein a first end of the auxiliary energy storage module is electrically connected to the cathode of the unidirectional conducting diode, and a second end of the auxiliary energy storage module is electrically connected to the first end of the energy storage module; Alternatively, the first end of the auxiliary energy storage module is electrically connected to the DC voltage input end, and the second end of the auxiliary energy storage module is electrically connected to the anode of the unidirectional conducting diode; The auxiliary energy storage module is used to store energy and release energy to regulate the current flowing through the switch module.

12. The soft switching control circuit according to claim 11, characterized in that: The auxiliary energy storage module includes a second inductor, a first end of the second inductor is electrically connected to the cathode of the unidirectional conducting diode, and a second end of the second inductor is electrically connected to the first end of the energy storage module; Alternatively, the first end of the second inductor is electrically connected to the DC voltage input end, and the second end of the second inductor is electrically connected to the anode of the unidirectional conducting diode.

13. The soft switching control circuit according to claim 11, wherein: The soft switching control circuit also includes a bypass module, which is connected between the first conduction end of the first switch tube and the second conduction end of the first switch tube, and is used to provide a current bypass for the energy storage module when the first switch tube is switched from on to off according to the first control signal, the second switch tube is turned off according to the second control signal, and the switch module is turned off according to the third control signal.

14. The soft switching control circuit according to claim 13, wherein: The bypass module includes a bypass capacitor, a first end of the bypass capacitor is used to be electrically connected to the first conduction end of the first switch tube, and a second end of the bypass capacitor is used to be electrically connected to the second conduction end of the first switch tube.

15. A voltage converter, characterized in that: The soft switch control circuit comprises a first switch tube, a second switch tube, a control circuit, and the soft switch control circuit according to any one of claims 1 to 14, wherein the control end of the first switch tube is electrically connected to the control module in the soft switch control circuit for receiving a first control signal, the first conduction end of the first switch tube is electrically connected to the first end of the energy storage module in the soft switch control circuit, the second conduction end of the first switch tube is electrically connected to the first conduction end of the second switch tube, the third end of the energy storage module, and the control module respectively, the control end of the second switch tube is electrically connected to the control module for receiving a second control signal, the second conduction end of the second switch tube is grounded, and the control circuit is electrically connected to the control module.

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