Power conversion circuit, control method and controller

Abstract

The embodiment of the invention provides a power conversion circuit, a control method and a controller. The power conversion circuit comprises a switching circuit unit, a resonance unit and a control unit, the switching circuit unit at least comprises a main inductor, a main diode and a main switching tube; the main switch tube is provided with a first inverted diode; the resonant unit comprises a resonant inductor, a resonant capacitor and an auxiliary switch tube; the auxiliary switch tube is provided with a second inverted diode; the resonant capacitor and the auxiliary switch tube are connected in series, and a series branch where the resonant capacitor and the auxiliary switch tube are located is connected in parallel with the resonant inductor; the resonance unit is connected in series in a follow current loop of the main inductor; one signal output end of the control unit is electrically connected with the control end of the main switch tube, and the other signal output end of the control unit is electrically connected with the control end of the auxiliary switch tube. The power conversion circuit is low in electric energy loss.

Description

Technical Field

[0001] The present application relates to the technical field of switch circuits, and in particular to a power conversion circuit, a control method and a controller with a soft switching function. Background Art

[0002] In various control electronic devices, not only common power sources such as AC power, batteries and other high-voltage input power sources are required, but also low-voltage working power sources, such as 3.3V, 5V, 12V, 15V, 24V and other voltages, are required to meet the needs of MCU, relays, power electronic switch devices, etc. This requires a power conversion circuit. Common power conversion circuits include BUCK (step-down) circuits, Flyback (flyback) conversion circuits, etc. However, the power conversion circuit itself will produce losses, and how to reduce the power loss of the power conversion circuit is a technical problem that needs to be solved. Summary of the invention

[0003] In view of this, an embodiment of the present invention provides a power conversion circuit, a control method and a controller with a soft switching function. The power conversion circuit has low power loss.

[0004] In a first aspect, an embodiment of the present invention provides a power conversion circuit, including a switch circuit unit, a resonance unit and a control unit; the switch circuit unit at least includes a main inductor, a main diode and a main switch tube;

[0005] The first end of the main switch tube is electrically connected to the first end of the main inductor, and the first end of the main switch tube is electrically connected to the cathode of the main diode; the main switch tube is provided with a first reverse diode; the resonance unit includes a resonant inductor, a resonant capacitor and an auxiliary switch tube; the auxiliary switch tube is provided with a second reverse diode; the resonant capacitor and the auxiliary switch tube are connected in series, and the series branch where the resonant capacitor and the auxiliary switch tube are located is connected in parallel with the resonant inductor; the resonance unit is connected in series with the freewheeling circuit of the main inductor, and the freewheeling circuit of the main inductor includes a common end; one signal output end of the control unit is electrically connected to the control end of the main switch tube, and the other signal output end of the control unit is electrically connected to the control end of the auxiliary switch tube.

[0006] The power conversion circuit includes a resonance unit, which can at least enable the main switch tube of the switch circuit unit to achieve zero voltage switching, which is beneficial to reducing the power loss of the power conversion circuit.

[0007] In a second aspect, an embodiment of the present invention provides a controller, comprising a first power line, a second power line and the above-mentioned power conversion circuit, wherein the first power line is electrically connected to the second end of the main switch tube of the power conversion circuit, and the second power line is electrically connected to the common end of the power conversion circuit.

[0008] The controller includes the power conversion circuit with zero voltage switching function, which is beneficial to reducing the power loss of the controller.

[0009] In a third aspect, an embodiment of the present invention provides a control method, the power conversion circuit mentioned above, the control method at least comprises the following steps:

[0010] The control unit controls the main switch tube to be disconnected;

[0011] The control unit at least controls the auxiliary switch to be turned on, so that the charge of the resonant capacitor is discharged to the resonant inductor;

[0012] The control unit at least controls the auxiliary switch to be disconnected, so that the current of the resonant inductor flows to the main diode and the first reverse diode;

[0013] The control unit at least controls the main switch to be turned on, so as to achieve zero voltage turn-on of the main switch tube.

[0014] The control method controls the auxiliary switch tube to be turned on after the main switch tube is turned off, so that the charge of the resonant capacitor is discharged to the resonant inductor, and the resonant inductor stores energy; then controls the auxiliary switch tube to be turned off, and the energy stored in the resonant inductor flows to the main diode and the first reverse diode in the form of current, thereby making the voltage across the main switch tube close to zero volts, and then controls the main switch tube to be turned on to achieve zero voltage turn-on of the main switch tube, so that the power conversion circuit has a soft switching function, which is beneficial to reducing the power loss of the power conversion circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 This is a schematic diagram of the power loss of the main switch tube in a common hard-switching power conversion circuit;

[0017] Figure 2 A schematic diagram of a power conversion circuit provided by an embodiment of the present invention;

[0018] Figure 3 A schematic diagram of another power conversion circuit provided by an embodiment of the present invention;

[0019] Figure 4 A schematic diagram of another power conversion circuit provided by an embodiment of the present invention;

[0020] Figure 5 A schematic diagram of a power conversion circuit with multiple outputs provided by an embodiment of the present invention;

[0021] Figure 6 A schematic block diagram of a circuit of a controller having the above power conversion circuit provided by an embodiment of the present invention;

[0022] Figure 7 The present invention provides a flow chart of a control method for the power conversion circuit. DETAILED DESCRIPTION

[0023] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0024] It should be clear that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the previous and next associated objects are in an "or" relationship. Electrical connection includes direct electrical connection and indirect electrical connection. The electrical connection relationship between components is based on the realization of circuit principles and does not narrowly limit the scope of protection of the present invention.

[0026] Among the commonly used power conversion circuits, the simple and single-channel output ones include the BUCK circuit (step-down circuit); the most commonly used one that requires multiple-channel outputs is the single-tube flyback switching power supply, i.e., the Flyback conversion circuit; but usually the BUCK circuit or Flyback conversion circuit is implemented through PWM hard switching. The switching loss of PWM hard switching devices is large, the switch tube is easy to heat up, and the power supply efficiency is low. After the third end of the main switch tube of the BUCK circuit or Flyback conversion circuit receives the start signal output by the control unit, a conduction current is generated between the first and second ends of the main switch tube, and the voltage at the first end begins to drop. Due to the Miller effect of the switching device, the main switch tube cannot be immediately turned from off to on, but has a turn-on transition time of about hundreds of nanoseconds. During this transition time, on the one hand, the voltage between the first and second ends of the main switch tube drops from high to low until it is close to 0V, and on the other hand, the current flowing from the first end to the second end rises sharply until it reaches the maximum, such as Figure 1As shown, it can be seen that within the hundreds of nanoseconds, there is a power loss of dP = v(t) * i(t) * dt at every moment. Each time it is turned on, there is a power loss of hundreds of nanoseconds. The main switch tube in the common switching power conversion circuit is usually turned on tens of thousands of times per second. In this way, the total turn-on power loss of the main switch tube is large, affecting the power efficiency. In addition, the leakage inductance energy of the hard-switched flyback switching power supply transformer cannot be transferred to the load and relies more on the RCD absorption circuit, resulting in low power efficiency; the main switch tube of the flyback conversion circuit needs to have a higher withstand voltage and a non-common specification. For example, when the typical single-phase AC220-240V input is used, the typical withstand voltage of 600-650V devices cannot be used, but non-typical withstand voltage devices of more than 700V must be used. For MOSFET devices, the higher the withstand voltage, the greater the on-resistance and the higher the cost.

[0027] In view of this, the embodiment of the present application provides a power conversion circuit, which is applicable to various controllers or electrical devices that need to reduce voltage. The power conversion circuit includes a buck circuit, which can reduce the input voltage to the required output voltage, and the main switch tube of the power conversion circuit operates at zero voltage switching (ZVS), with low switching loss, which is conducive to improving the overall circuit efficiency. Specifically, Figure 2 As shown, the power conversion circuit includes a switch circuit unit 2, a resonance unit 1 and a control unit 3; the switch circuit unit 2 at least includes a main inductor L1, a main diode D1 and a main switch tube Q1;

[0028] The first end of the main switch tube Q1 is electrically connected to the first end of the main inductor L1, the first end of the main switch tube Q1 is electrically connected to the cathode of the main diode D1, and the second end of the main switch tube Q1 is electrically connected to the input voltage Vi+; the main switch tube Q1 is provided with a first reverse diode D11; the resonance unit 1 includes a resonant inductor L2, a resonant capacitor C2 and an auxiliary switch tube Q2; the auxiliary switch tube is provided with a second reverse diode QD2; the resonant capacitor C2 and the auxiliary switch tube Q2 are connected in series, and the series branch where the resonant capacitor C2 and the auxiliary switch tube Q2 are located is connected in parallel with the resonant inductor L2; the resonance unit 1 is connected in series in the freewheeling circuit of the main inductor L1, and the freewheeling circuit is electrically connected to the common terminal COM; a signal output end of the control unit 3 is electrically connected to the control end of the main switch tube Q1, and another signal output end of the control unit 3 is electrically connected to the control end of the auxiliary switch tube Q2. Figure 2-5As shown, the switch circuit unit 2 is a BUCK circuit, and the control unit 3 controls the main switch tube Q1 according to at least the second sampling signal representing the output voltage Vo+ of the power conversion circuit and the first sampling signal representing the input voltage Vi+ of the power conversion circuit to meet the output load demand; and the control unit can also control the auxiliary switch tube Q2 so that the main switch tube Q1 can achieve zero voltage switching. It should be noted that the first / second reverse diode can be built-in to the main switch tube / auxiliary switch tube, respectively, or can be external.

[0029] The working principle of the above circuit is as follows:

[0030] by Figure 2 For example, a resonant unit 1 is connected in series to the main diode D1 loop. Before the main switch tube Q1 is turned on, the control unit first turns on the auxiliary switch tube Q2. The charge on the resonant capacitor C2 is discharged to the resonant inductor L2 through Q2, so that the current of the resonant inductor L2 increases rapidly on the basis of the original freewheeling current. The freewheeling current of the resonant inductor L2 and the discharge current of C2 to L2 are both from left to right. When the current of the resonant inductor L2 reaches or approaches the peak value, the auxiliary switch tube Q2 is turned off to cut off the current to the resonant inductor L2. The current of the resonant capacitor C2 forces the current of the resonant inductor L2 to flow to the main diode D1, and the first reverse diode QD1 is turned on, so that the voltage between the second end and the first end of the main switch tube drops to zero volt or below zero volt (the specific value refers to the PN junction voltage of the first reverse diode), and at this time, the main switch tube Q1 is turned on, and the zero voltage switching (ZVS) of the main switch tube is realized. The input voltage Vi+ is applied to the main inductor L1 through the main switch tube Q1, and the current of the main inductor L1 increases and is transmitted to the load. The control unit determines the conduction pulse width of the main switch tube Q1 according to the second sampling signal to ensure that the output voltage remains at the set value.

[0031] When the main switch tube Q1 is turned off, the negative current loop on the left side of the main inductor L1 comes from the main diode D1, the resonant capacitor C2, the second reverse diode QD2, the load and the main inductor L1 to form a current loop; at this moment, the resonant capacitor C2 is charged and the left side is negative and the right side is positive. Although the resonant inductor L2 also starts to generate current, it lags slightly behind the resonant capacitor C2. The resonant inductor L2 gradually shunts the charging current of the resonant capacitor until the resonant capacitor C2 is no longer charged. The charge of the resonant capacitor C2 is stored until the auxiliary switch tube Q2 is turned on in the next cycle.

[0032] Figure 2 In the figure, the freewheeling circuit of the main inductor L1 is the right side of the main inductor L1 → LOAD → resonant unit 1 → main diode D1 → left side of the main inductor L1. The power conversion circuit is suitable for being used as a current source to provide working current for the load.

[0033] In one embodiment, Figure 3As shown, the power conversion circuit also includes a first capacitor C1. One end of the first capacitor C1 is electrically connected to the second end of the main inductor L1, and the other end is electrically connected to the common terminal COM. The first capacitor C1 is used as an output filter capacitor, and the power conversion circuit is preferably used as a voltage source to provide a working voltage for the load. In this embodiment, the freewheeling circuit of the main inductor L1 includes the main inductor L1, the first capacitor C1, the resonant unit 1 and the main diode D1.

[0034] In one embodiment, Figure 3 As shown, the power conversion circuit further includes a third capacitor C3; a first end of the third capacitor C3 is electrically connected to the second end of the main switch tube Q1, and a second end of the third capacitor C3 is electrically connected to the common terminal COM. The third capacitor C3 is an input capacitor.

[0035] like Figure 4 As shown, in order to obtain the second sampling signal representing the output voltage Vo+, in one embodiment, the power conversion circuit is set to further include a first resistor R1 and a second resistor R2; the first end of the first resistor R1 is electrically connected to the second end of the main inductor L1, the second end of the first resistor R1 is electrically connected to the first end of the second resistor R2, and the second end of the second resistor R2 is electrically connected to the common terminal COM; the second end of the first resistor R1 is electrically connected to the control unit 3. The control unit 3 includes a control chip IC. The resistors R1 / R2 sample the output voltage Vo+ to generate a second sampling signal (also called a feedback signal FB) and output it to the control unit, and the control unit controls the main switch tube Q1 according to the second sampling signal to achieve the stability of the output voltage Vo+.

[0036] In one embodiment, in order to reduce the turn-off loss and electromagnetic interference (EMI) of the main switch tube Q1, as Figure 4 As shown, the power conversion circuit is further provided with a fourth capacitor C4, a first end of the fourth capacitor C4 is electrically connected to the first end of the main switch tube Q1, and a second end of the fourth capacitor C4 is electrically connected to the second end of the main switch tube Q1; and the capacitance of the fourth capacitor C4 is relatively small. After C4 is added, before the main switch tube is turned on, the charge of C4 is first discharged by the current of the resonant inductor L2 and reversely charged to the first reverse diode QD1 to be turned on; the function of the fourth capacitor C4 is that at the moment when the main switch tube Q1 is turned off, because the voltage across the capacitor needs to be charged before it rises, the current bypass at the moment when the main switch tube is turned off is realized and the main switch tube Q1 is turned off with zero current, thereby avoiding the turn-off loss of the main switch tube Q1.

[0037] In the above embodiment, the main switch tube Q1 and the auxiliary switch tube Q2 can be any controllable switch tubes, such as IGBT, MOS, triode and the like. Figure 4 Q1 and Q2 in the figure take N-MOS as an example.

[0038] Combine the following Figure 4 Further explanation Figure 4The working principle of the illustrated embodiment is as follows:

[0039] The purpose of inserting the resonant unit 1 is to enable the main switch tube to achieve zero voltage switching (ZVS). Under the premise that the main switch tube Q1 achieves ZVS, the fourth capacitor C4 is connected in parallel between the drain and source of the main switch tube Q1. The fourth capacitor C4 is used as a buffer capacitor to achieve current bypass at the moment when the main switch tube Q1 is turned off and to enable the main switch tube Q1 to achieve zero current shutdown, thereby avoiding the shutdown loss of the main switch tube. In addition, because the voltage of the fourth capacitor C4 cannot change suddenly and the dv / dt rising from zero voltage is small, the voltage rising rate of the main switch tube Q1 during the shutdown process is greatly reduced, thereby greatly reducing the shutdown loss of the main switch tube and the electromagnetic interference (EMI) of dv / dt. The working process is as follows:

[0040] Before the main switch tube Q1 is turned on, the control chip IC first turns on the auxiliary switch tube Q2, and the charge on the resonant capacitor C2 is discharged to the resonant inductor L2 through Q2, so that the current of L2 increases rapidly on the basis of the original freewheeling current. The freewheeling current of L2 and the discharge current of C2 to L2 are both from left to right. When the current of L2 reaches or approaches the peak moment, the auxiliary switch tube Q2 is turned off and the current to C2 is cut off, forcing the current of the resonant inductor L2 to flow to the main diode D1. Except for the original freewheeling current that continues to flow to the main inductor L1, the newly added resonant current can only flow to QD1 / / C4 at both ends of the main switch tube and the third capacitor C3 through the COM terminal to flow back to the resonant inductor L2 to form a closed current loop and return the magnetic energy of the resonant inductor L2 to the third capacitor C3 because the current of the main inductor cannot change suddenly. The current loop consumes the charge on the fourth capacitor C4. After the charge on C4 is discharged, the freewheeling current of L2 is redirected to QD1, and the voltage between the drain and source of Q1 is reduced to "zero" volts, or a negative voltage (generally not exceeding -1V). At this moment, the main switch tube Q1 is turned on, and the zero voltage switching (ZVS) of the main switch tube is realized. The input voltage Vi+ is applied to the main inductor L1 through the main switch tube Q1, and the current of L1 is increased and transmitted to the main filter capacitor C1 and the load. The control chip IC determines the conduction pulse width of the main switch tube Q1 according to the second sampling signal FB to ensure that the output voltage Vo+ is stable at the set value.

[0041] When the main switch tube Q1 is turned off, the negative current loop on the left side of the main inductor L1 comes from the main diode D1, the resonant capacitor C2, the second reverse diode QD2, the first capacitor C1 and the main inductor L1 to form a current loop; at this moment, the resonant capacitor C2 is charged and the left side is negative and the right side is positive. Although the resonant inductor L2 also starts to generate current, it lags slightly behind the resonant capacitor C2. The resonant inductor L2 gradually shunts the charging current of the resonant capacitor C2 until C2 is no longer charged, and the charge of C2 is stored until Q2 is turned on in the next cycle. At the same time, the fourth capacitor C4 starts to rise from zero voltage, absorbs the surge peak voltage caused by the connection distribution inductance, and allows the main switch tube Q1 to turn off before the capacitor is turned off, thereby greatly reducing the turn-off loss of the main switch tube and the electromagnetic interference (EMI) caused by dv / dt.

[0042] The power conversion circuit repeats the auxiliary switch tube Q2 being turned on and off, the main switch tube Q1 being turned on, and so on, to achieve soft switching of the main switch tube Q1 and output the required output voltage at the same time.

[0043] In addition, in some embodiments, the required power supply voltage may have two or more different voltage values. In this case, one buck circuit cannot meet the needs of multiple power supply voltages. In electronic products such as frequency conversion controllers, sometimes multiple working power supplies with different voltages or some power supplies that require isolation are required. In this case, a flyback high-frequency transformer TR1 can be used instead. Figure 1 The main inductor L1 is composed as follows Figure 2 The circuit shown is as follows Figure 5 As shown, the power conversion circuit also includes a transformer TR1, a second diode D2 and a fifth capacitor C5; the main inductor L1 is the primary winding of the transformer TR1, the first end of the secondary winding of the transformer TR1 is electrically connected to the anode of the second diode D2, the cathode of the second diode D2 is electrically connected to the first end of the fifth capacitor C5, and the second end of the fifth capacitor C5 is electrically connected to the second end of the secondary winding of the transformer TR1. The fifth capacitor is a filter capacitor, the transformer TR1 is a high-frequency transformer, and the second diode D2 is a high-frequency rectifier diode. The circuit has two output terminals, a first output terminal Vo1+ and a second output terminal Vo2+, and the two output terminals provide power supply voltage to the load terminal;

[0044] In this embodiment, the secondary winding of the transformer TR1 is connected with a second diode D2, a filter capacitor, etc. One of the characteristics of the circuit is that the first output terminal of the secondary winding connected to the anode of the second diode D2 and the second terminal of the primary winding connected to the first capacitor C1 / first output terminal VO1+ are the same terminals, such as Figure 5The second feature is that the ratio of the number of turns of the secondary winding of the second output or the nth output to the number of turns of the primary winding is (VO2+VDF2) / (VO1+VDF1), where VDFn is the forward voltage drop of the high-frequency rectifier diode of the nth output, including an ultra-fast recovery diode or a Schottky diode; the anode of the high-frequency rectifier diode Dn is connected to the secondary of the high-frequency transformer (the same-name end is as mentioned above), the cathode is connected to the filter capacitor and the second output terminal Vo2+, and the other end of the secondary filter capacitor is connected to the other end of the secondary winding of the transformer TR1 and the negative output.

[0045] Its working principle: when the main switch tube Q1 is turned on, the voltage across the primary winding of the transformer TR1 is left + right -, the secondary winding is left - right +, and the second diode D2 is turned off; when Q1 is turned off, the primary inductor current of the transformer TR1 must continue and the direction remains unchanged, that is, the current direction continues to flow from left to right, the voltage at the right end is +, connected to the first end of the first capacitor C1 and the first output terminal VO1+; the negative end passes through the main diode D1 and the resonance unit 1 to the second end of the first capacitor C1 / and the first output negative terminal VO1- (common terminal COM); while the right end of the primary is the positive output continuous current, the secondary winding is at the same end, the potential is left + right -, the second diode D2 is turned on, the secondary winding potential is output to the fifth capacitor C5 through D2, and the second power supply voltage (the difference between VO2+ and VO2-) is output. From the primary and secondary turns ratio, it can be seen that the nth secondary output potential is proportional to the number of primary turns. As long as VO1+ is controlled for closed-loop voltage regulation, the secondary output voltage is also basically stable. In this embodiment, a plurality of different supply voltages can be obtained by providing a plurality of secondary windings with different numbers of turns, and the secondary output of the transformer TR1 is an isolation voltage.

[0046] Based on the above power conversion circuit, such as Figure 6 As shown, the embodiment of the present application also provides a controller, including a first power line LH, a second power line LL and any one of the power conversion circuits disclosed in the above embodiments, the first power line LH is electrically connected to the second end of the main switch tube Q1 of the power conversion circuit, the second power line LL is electrically connected to the common end COM of the power conversion circuit, and when working, the voltage Vin between the first power line and the second power line is greater than the output voltage Vout of the power conversion circuit. The first power line can be a busbar of the controller, and the second power line can be a ground line of the controller. The first power line and the second power line can also be a high potential power line and a low potential power line on the output side of the rectifier bridge DB of the controller, respectively.

[0047] In one embodiment, the controller requires at least two different DC voltage sources or at least one isolated DC voltage source; Figure 5 The transformer and secondary side circuit design can meet the needs of two or more DC voltage sources and can provide at least one isolated DC voltage source.

[0048] Based on the above power conversion circuit, the embodiment of the present application also provides a control method, such as Figure 7 As shown, the control method at least includes the following steps:

[0049] Step S11: Control the main switch tube to be turned off: the control unit 3 controls the main switch tube Q1 to be turned off; specifically, the main switch is controlled at least according to the second sampling signal FB representing the output voltage.

[0050] Step S12: Control the auxiliary switch tube to be turned on: the control unit 3 at least controls the auxiliary switch tube Q2 to be turned on, so that the charge of the resonant capacitor C2 is discharged to the resonant inductor L2;

[0051] Step S13: Control the auxiliary switch tube to be turned off: the control unit 3 at least controls the auxiliary switch tube Q2 to be turned off, so that the current of the resonant inductor L2 flows to the main diode D1 and the first reverse diode QD1;

[0052] Step S14: Control the main switch tube to be turned on: when the current of the resonant inductor L2 flows to the main diode D1 and the first reverse diode QD1, the control unit controls the main switch to be turned on to achieve zero voltage turn-on of the main switch tube Q1.

[0053] According to the control method, after the main switch tube is disconnected, the current of the main inductor continues to flow forward, and the freewheeling circuit is turned on at this time, and the freewheeling current charges the resonant capacitor through the second reverse diode; before the main switch tube is turned on, the auxiliary switch tube is controlled to be turned on first, so that the charge of the resonant capacitor is discharged to the resonant inductor, and the resonant capacitor discharge current is in the same direction as the original freewheeling current of the resonant inductor, and the current gradually increases after superposition, and the current reaches the maximum after a certain period of time; then the auxiliary switch tube is controlled to be disconnected, and the energy stored in the resonant inductor flows to the main diode and the first reverse diode in the form of current, thereby making the voltage across the main switch tube close to zero volts, and then the main switch tube is controlled to be turned on to realize the zero-voltage turning-on of the main switch tube, so that the power conversion circuit has a soft switching function, which is beneficial to reducing the power loss of the power conversion circuit.

[0054] The control method of the main switch tube can be specifically obtained by: sampling to obtain a first sampling signal and a second sampling signal, wherein the first sampling signal represents the input voltage of the power conversion circuit, and the second sampling signal represents the output voltage of the power conversion circuit; the control unit controls the on / off and duty cycle of the main switch tube Q1 at least according to the first sampling signal and the second sampling signal to meet the output voltage requirement. At the same time, through the resonance effect of the resonance unit, the on / off of the auxiliary switch tube Q2 is controlled before the main switch tube Q1 is turned on, so as to promote the resonant current to flow to the fourth capacitor C4 and turn on the first reverse diode, thereby further realizing the soft switching function of the main switch tube and reducing energy consumption.

[0055] The working principle of the above control method can refer to the introduction of the working principle and working process in the previous article, and this application will not repeat it here.

[0056] Any of the above embodiments includes at least one of the following advantages:

[0057] 1. As shown in the figure, the simple BUCK step-down switching power supply can reduce the loss of the BUCK circuit because the main switch tube Q1 realizes ZVS opening;

[0058] 2. Under the action of buffer capacitor C4, the main switch tube Q1 is turned off at zero current and the dv / dt at the turn-off moment is slowed down, thereby greatly reducing the switching loss of the main switch tube, improving power efficiency and reducing electromagnetic interference (EMI);

[0059] 3. If Figure 5 The soft-switching BUCK+Flyback multi-channel output switching power supply shown has a freewheeling circuit, which solves the problem of lossless recovery of energy from the primary leakage inductance of the high-frequency transformer and eliminates the RCD absorption circuit and loss of the traditional flyback switching power supply.

[0060] 4. Figure 5 The main switch tube of the soft-switching BUCK+Flyback multi-output switching power supply shown can be a device with a lower voltage resistance than the main switch tube of the traditional flyback switching power supply.

[0061] The above description is only a preferred embodiment of this specification and is not intended to limit this specification. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of this specification should be included in the scope of protection of this specification.

Claims

1. A power conversion circuit, characterized in that: It includes a switch circuit unit, a resonance unit and a control unit; the switch circuit unit at least includes a main inductor, a main diode and a main switch tube; The first end of the main switch tube is electrically connected to the first end of the main inductor, and the first end of the main switch tube is electrically connected to the cathode of the main diode; the main switch tube is provided with a first reverse diode; the resonance unit includes a resonant inductor, a resonant capacitor and an auxiliary switch tube; the auxiliary switch tube is provided with a second reverse diode; the resonant capacitor and the auxiliary switch tube are connected in series, and the series branch where the resonant capacitor and the auxiliary switch tube are located is connected in parallel with the resonant inductor; the resonance unit is connected in series with the freewheeling circuit of the main inductor, and the freewheeling circuit of the main inductor includes a common end; one signal output end of the control unit is electrically connected to the control end of the main switch tube, and the other signal output end of the control unit is electrically connected to the control end of the auxiliary switch tube.

2. The power conversion circuit according to claim 1, characterized in that: It also includes a first capacitor; one end of the first capacitor is electrically connected to the second end of the main inductor, and the other end of the first capacitor is electrically connected to the common end; The freewheeling circuit of the main inductor includes the main inductor, the first capacitor, the resonance unit and the main diode.

3. The power conversion circuit according to claim 1, characterized in that: It also includes a third capacitor; the first end of the third capacitor is electrically connected to the second end of the main switch tube, and the second end of the third capacitor is electrically connected to the common end.

4. The power conversion circuit according to any one of claims 1 to 3, characterized in that: It also includes a first resistor and a second resistor; the first end of the first resistor is electrically connected to the second end of the main inductor, the second end of the first resistor is electrically connected to the first end of the second resistor, and the second end of the second resistor is electrically connected to the common end; the second end of the first resistor is electrically connected to the control unit.

5. The power conversion circuit according to any one of claims 1 to 3, characterized in that: It also includes a fourth capacitor, a first end of the fourth capacitor is electrically connected to the first end of the main switch tube, and a second end of the fourth capacitor is electrically connected to the second end of the main switch tube.

6. The power conversion circuit according to any one of claims 1 to 3, characterized in that: Also includes a transformer, a second diode and a fifth capacitor; The main inductor is the primary winding of the transformer, the first end of the secondary winding of the transformer is electrically connected to the anode of the second diode, the cathode of the second diode is electrically connected to the first end of the fifth capacitor, and the second end of the fifth capacitor is electrically connected to the second end of the secondary winding.

7. A controller, characterized in that: It includes a first power line, a second power line and a power conversion circuit as described in any one of claims 1 to 6, wherein the first power line is electrically connected to the second end of the main switch tube of the power conversion circuit, and the second power line is electrically connected to the common end of the power conversion circuit.

8. The controller according to claim 7, characterized in that: The controller requires at least two different DC voltage sources; or the controller requires at least one isolated DC voltage source.

9. A control method, characterized in that: Applicable to the power conversion circuit according to any one of claims 1 to 6, the control method at least comprises the following steps: The control unit controls the main switch tube to be disconnected; The control unit at least controls the auxiliary switch to be turned on, so that the charge of the resonant capacitor is discharged to the resonant inductor; The control unit at least controls the auxiliary switch to be disconnected, so that the current of the resonant inductor flows to the main diode and the first reverse diode; The control unit at least controls the main switch to be turned on, so as to achieve zero voltage turn-on of the main switch tube.

10. The control method according to claim 9, characterized in that: The following steps are involved: Sampling to obtain a first sampling signal and a second sampling signal, wherein the first sampling signal represents an input voltage of the power conversion circuit, and the second sampling signal represents an output voltage of the power conversion circuit; The control unit controls the on / off state and the duty cycle of the main switch tube at least according to the first sampling signal and the second sampling signal.

Images