Zero-voltage conduction flyback switching power supply and control chip and control method thereof

Abstract

The application provides a zero-voltage conduction flyback switching power supply, a control chip and a control method thereof. The zero-voltage conduction flyback switching power supply comprises a zero-voltage conduction auxiliary tube, a power tube and a transformer. The control chip is used for determining a working mode of the switching power supply based on an input characteristic signal representing an input voltage of the switching power supply, a demagnetization sensing signal representing a demagnetization condition of a primary winding of the transformer and an output feedback signal representing an output load of the switching power supply; generating a first control signal for controlling the turn-on and turn-off of the zero-voltage conduction auxiliary tube based on the working mode; and generating a second control signal for controlling the turn-on and turn-off of the power tube based on the working mode, the output feedback signal and a current sensing signal representing a current flowing through the power tube.

Description

Technical Field

[0001] The present invention belongs to the field of integrated circuits, and in particular relates to a zero-voltage turn-on flyback switching power supply, a control chip thereof, and a control method thereof. Background Art

[0002] With the increasing demand for switching power supplies with small size, high frequency and high power density, flyback switching power supplies with zero voltage switch (ZVS) of power tubes are becoming more and more widely used.

[0003] In a traditional ZVS flyback switching power supply, the PWM controller turns on the ZVS auxiliary transistor in each switching cycle. In this case, the system reliability and operating efficiency are reduced. Summary of the Invention

[0004] An embodiment of the present invention provides a zero-voltage-turn-on flyback switching power supply, a control chip thereof, and a control method thereof. The invention can identify the operating mode of the zero-voltage-turn-on flyback switching power supply and control the on and off of a zero-voltage-turn-on auxiliary tube and a power tube (for example, a metal oxide semiconductor field-effect transistor (MOSFET), a bipolar junction NPN transistor (BJT-NPN), an insulated gate bipolar transistor (IGBT), and a gallium nitride (GaN) transistor, etc.) based on the operating mode. When no-load and light-load operating modes are detected, the zero-voltage-turn-on auxiliary tube is turned off, which can reduce the standby power consumption and light-load power consumption of the system, and can prevent the synchronous rectifier tube from being turned off prematurely due to the shutdown action after the ZVS auxiliary tube is turned on when the zero-voltage-turn-on flyback switching power supply operates in a continuous operating mode, thereby reducing the drain-source voltage VDS of the synchronous rectifier tube and reducing the temperature rise of the power tube.

[0005] In a first aspect, an embodiment of the present invention provides a control chip for a zero-voltage-turn-on flyback switching power supply, wherein the zero-voltage-turn-on flyback switching power supply includes a zero-voltage-turn-on auxiliary tube, a power tube, and a transformer. The control chip is configured to: determine an operating mode of the zero-voltage-turn-on flyback switching power supply based on an input characterization signal characterizing the input voltage of the zero-voltage-turn-on flyback switching power supply, a demagnetization sensing signal characterizing the demagnetization condition of the primary winding of the transformer, and an output feedback signal characterizing the output load of the zero-voltage-turn-on flyback switching power supply; generate a first control signal for controlling the conduction and shutdown of the zero-voltage-turn-on auxiliary tube based on the operating mode of the zero-voltage-turn-on flyback switching power supply; and generate a second control signal for controlling the conduction and shutdown of the power tube based on the operating mode of the zero-voltage-turn-on flyback switching power supply, the output feedback signal, and a current sensing signal characterizing the current flowing through the power tube.

[0006] In a second aspect, an embodiment of the present invention provides a control method for a zero-voltage-turn-on flyback switching power supply, wherein the zero-voltage-turn-on flyback switching power supply includes a zero-voltage-turn-on auxiliary tube, a power tube, and a transformer. The control method includes: determining an operating mode of the zero-voltage-turn-on flyback switching power supply based on an input characterization signal characterizing the input voltage of the zero-voltage-turn-on flyback switching power supply, a demagnetization sensing signal characterizing the demagnetization condition of the primary winding of the transformer, and an output feedback signal characterizing the output load of the zero-voltage-turn-on flyback switching power supply; generating a first control signal for controlling the conduction and shutdown of the zero-voltage-turn-on auxiliary tube based on the operating mode of the zero-voltage-turn-on flyback switching power supply; and generating a second control signal for controlling the conduction and shutdown of the power tube based on the operating mode of the zero-voltage-turn-on flyback switching power supply, the output feedback signal, and a current sensing signal characterizing the current flowing through the power tube.

[0007] In a third aspect, an embodiment of the present invention provides a zero-voltage turn-on flyback switching power supply, comprising the control chip as described in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0009] Figure 1 The schematic diagram of the structure of a traditional ZVS flyback switching power supply is shown;

[0010] Figure 2 A schematic diagram showing the waveform of signals of a conventional ZVS flyback switching power supply is shown;

[0011] Figure 3 A schematic structural diagram of a zero-voltage turn-on flyback switching power supply provided by an embodiment of the present invention is shown;

[0012] Figure 4 The embodiment of the present invention provides Figure 3 The structural diagram of the DCM / CCM and LLM detection unit 4103 is shown;

[0013] Figure 5 A flowchart showing the operating mode identification and logic control of a ZVS flyback switching power supply provided by an embodiment of the present invention is shown;

[0014] Figure 6 A schematic diagram showing waveforms of signals when the ZVS flyback switching power supply provided by an embodiment of the present invention operates in DCM and LLM operating modes;

[0015] Figure 7 A schematic diagram showing waveforms of signals when a ZVS flyback switching power supply according to an embodiment of the present invention operates in a DCM and a non-LLM operating mode is shown;

[0016] Figure 8 A schematic diagram showing waveforms of signals when the ZVS flyback switching power supply provided by an embodiment of the present invention operates in CCM and AC high voltage operating modes;

[0017] Figure 9 A schematic diagram showing waveforms of signals when the ZVS flyback switching power supply provided by an embodiment of the present invention operates in CCM and AC low-voltage operating modes; and

[0018] Figure 10 A flow chart of a control method for a zero-voltage turn-on flyback switching power supply provided by an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0019] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In order to make the objects, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present invention by illustrating examples of the present invention.

[0020] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, the elements defined by the phrase "comprising..." do not exclude the presence of other identical elements in the process, method, article, or device comprising the elements.

[0021] In order to better understand the zero voltage turn-on flyback switching power supply and its control chip and control method provided by the embodiment of the present invention, the following first introduces the traditional ZVS flyback switching power supply provided by the prior art. Figure 1 , Figure 1 FIG. 4 shows a schematic structural diagram of a traditional ZVS flyback switching power supply.

[0022] like Figure 1 As shown, a conventional ZVS flyback switching power supply mainly includes a control chip 100, a synchronous rectification (SR) controller 200, an error amplification and isolation module 300, etc. Among them, the control chip 100 mainly includes a frequency oscillator (OSC) 110, a pulse width modulation (PWM) comparator 120, an RS trigger 130, a first gate driver 140, a ZVS on-time control circuit 150, a dead time control module 160, and a second gate driver 170. The control chip 100 includes a load feedback pin FB, a current feedback pin CS, a first drive pin Gate1, and a second drive pin Gate0.

[0023] Specifically, the SR controller 200 can be used to synchronously turn on and off the rectifier tube S2, the control chip 100 can output a first control signal (Gate0) for controlling the conduction and shutdown of the ZVS auxiliary tube S0, and the first end of the error amplification and isolation module 300 is connected to the output end of the ZVS flyback switching power supply, and the second end is connected to the load feedback pin FB of the control chip 100, and the output feedback signal representing the output load of the ZVS flyback switching power supply is sent to the control chip 100. The control chip 100 can also receive a current sensing signal representing the current flowing through the power tube S1, and output a second control signal (Gate1) for controlling the conduction and shutdown of the power tube S1 based on the output feedback signal and the current sensing signal.

[0024] Combine Figure 1 and Figure 2 The working principle of the traditional ZVS flyback switching power supply provided by the existing technology is introduced in detail. Figure 2 FIG. 1 is a schematic diagram showing the waveforms of signals of a conventional ZVS flyback switching power supply.

[0025] As shown in the figure, during the period t0-t1, the second control signal Gate1 is at a high level, so that the power tube S1 is in the on state. During the period t4-t5, the first control signal Gate0 is at a high level, so that the ZVS auxiliary tube S0 is in the on state. The time period t5-t6 represents the dead time between the second control signal Gate1 and the first control signal Gate0. Specifically, the dead time length is started when the falling edge of the first control signal Gate0 is detected, and after the dead time length has passed, the second control signal Gate1 is changed from a low level to a high level to control the power tube S1 from the off state to the on state.

[0026] Specifically, at time t1, for example, after the primary power tube S1 changes from the on state to the off state, the main inductor Lp of the transformer begins to demagnetize, and the SR controller 200 on the secondary side of the transformer controls the synchronous rectifier tube S2 (for example, MOS tube) to be turned on, and the body diode of the ZVS auxiliary tube S0 is turned on to charge the ZVS capacitor Cz.

[0027] At time t2, the voltage on the ZVS capacitor Cz is charged to Vo*Ns3 / Ns1, and the body diode of the ZVS auxiliary transistor S0 is turned off. At time t3, after the secondary side demagnetization is completed, when the main inductor Lp is demagnetized, the main inductor Lp and the parasitic capacitance Cp of the primary power transistor S1 enter a free resonance state.

[0028] At time t4, the ZVS auxiliary transistor S0 is turned on, and the ZVS capacitor Cz discharges the ZVS auxiliary winding (Nas3), causing the current in the ZVS auxiliary winding to reverse and gradually increase. At this point, the voltage Vds on the parasitic capacitor Cp of the primary power transistor S1 is clamped to Vbulk + Ns1 / Np * Vout. After a period of constant conduction, the ZVS auxiliary transistor S0 transitions from the on state to the off state at time t5. The reverse current in the ZVS auxiliary winding is transferred to the primary winding, participating in LC resonance. This causes the voltage Vds on the parasitic capacitor Cp of the primary power transistor S1 to quickly resonate to its minimum voltage within the dead time, achieving near-zero voltage turn-on of the primary power transistor S1 at time t6. Therefore, the conduction time of the ZVS auxiliary transistor S0 and the charged voltage of the ZVS capacitor Cz determine the negative demagnetization energy of the ZVS auxiliary winding. For example, the higher the negative demagnetization energy of the ZVS auxiliary winding, the lower the voltage Vds resonance on the parasitic capacitance Cp of the primary power tube S1. Therefore, ZVS can achieve the goal of optimizing the switching loss and high-frequency EMI of the primary power tube S1.

[0029] However, the control chip of the traditional ZVS flyback switching power supply does not recognize the operating mode of the system and turns on the ZVS auxiliary tube S0 in each switching cycle. In this case, when the system is in no-load or light-load operating mode, the system operating current will be very large, resulting in high standby power consumption or light-load power consumption.

[0030] In addition, when a system output short circuit occurs or no-load and full-load switching occurs, the system will operate in continuous duty mode (CCM). At this time, the shutdown action after the ZVS auxiliary tube S0 is turned on will cause the SR controller 200 to mistakenly detect the rising edge of the VD voltage, causing the synchronous rectifier tube S2 to be turned off prematurely. The falling edge of the premature shutdown of the synchronous rectifier tube S2 will cause a large spike voltage in the drain-source voltage VDS of the synchronous rectifier tube S2, and will also cause the temperature of the primary power tube S1 to rise, which reduces the working efficiency of the system. The above problems are particularly prominent in high-frequency systems. The zero-voltage turn-on flyback switching power supply, its control chip, and control method provided in the embodiments of the present invention can well solve one or more of the above problems.

[0031] In order to solve the problems of the prior art, the present invention provides a zero voltage turn-on flyback switching power supply and its control chip and control method. The zero voltage turn-on flyback switching power supply and its control chip provided by the present invention are first introduced in detail below.

[0032] Figure 3 FIG. 1 shows a schematic diagram of the structure of a zero voltage turn-on flyback switching power supply provided by an embodiment of the present invention. Figure 3 As shown, the zero-voltage turn-on flyback switching power supply provided by the embodiment of the present invention mainly includes a control chip 400, an SR controller 200, and an error amplification and isolation module 300. Among them, the control chip 400 mainly includes a frequency oscillator (OSC) 110, a PWM comparator 120, an RS trigger 130, a first gate driver 140, an operating mode recognition and logic control module 410, a ZVS on-time control circuit 150, a dead time control module 160, and a second gate driver 170.

[0033] As an example, the dead time control module 160 may be configured to detect the falling edge of the first control signal Gate0 (eg Figure 7 The dead time length (corresponding to the t5 moment shown) is counted. Figure 7 After the dead time has elapsed, the second control signal Gate1 changes from a low level to a high level, so as to control the power tube S1 from an off state to an on state.

[0034] It can be seen that compared with Figure 1 , Figure 3 The switching power supply shown is Figure 1 The main difference between the switching power supplies shown is the control chip 400. Specifically, a working mode recognition and logic control module 410 is newly added to the control chip 400. Figure 3As shown, the working mode recognition and logic control module 410 may include an AC voltage detection unit 4101, a demagnetization signal detection unit 4102, a DCM / CCM and LLM detection unit 4103, etc. As an example, the control chip 400 may include a load feedback pin FB, a current feedback pin CS, a demagnetization detection pin DEM, a first drive pin Gate1, and a second drive pin Gate0, etc.

[0035] exist Figure 3 In the switching power supply shown in the figure, the control of the on and off of the power tube S1 and the ZVS auxiliary tube S0 is related to the recognition of the working mode, which is related to the Figure 1 The conventional switching power supply shown is different in Figure 1 In the process, no working mode identification is performed.

[0036] Specifically, the operating mode of the zero-voltage-turn-on flyback switching power supply can be determined based on an input characterization signal characterizing the input voltage of the zero-voltage-turn-on flyback switching power supply, a demagnetization sensing signal characterizing the demagnetization condition of the primary winding of the transformer (for example, a signal received via the demagnetization detection pin DEM), and an output feedback signal characterizing the output load of the zero-voltage-turn-on flyback switching power supply (for example, a signal received via the load feedback pin FB); based on the operating mode of the zero-voltage-turn-on flyback switching power supply, a first control signal Gate0 for controlling the on and off of the ZVS auxiliary tube S0 is generated; and based on the operating mode of the ZVS flyback switching power supply, the output feedback signal, and a current sensing signal characterizing the current flowing through the power tube S1 (for example, a signal received via the current feedback pin CS), a second control signal Gate1 for controlling the on and off of the power tube S1 is generated.

[0037] like Figure 3As shown, the output terminal of the switching power supply is connected to the load feedback pin FB of the control chip 400 via the error amplification and isolation module 300. The load feedback pin FB is connected to the first terminal of the OSC 110 and the first terminal (e.g., the non-inverting input terminal) of the PWM comparator 120 and the DCM / CCM and LLM detection unit 4103 via the diode D1 and the voltage divider network including the resistors R1 and R2, respectively, so as to provide a divided output feedback signal (e.g., FB_in) to the OSC 110, the PWM comparator 120 and the DCM / CCM and LLM detection unit 4103. The second terminal of the OSC 110 can receive the dead time (labeled as Tdead). The second terminal (e.g., the negative input terminal) of the PWM comparator 120 can be connected to the current feedback pin CS to receive the current sensing signal (VCS) representing the current flowing through the power transistor S1 via the current feedback pin CS. The PWM comparator 120 can compare the divided output feedback signal and the current sensing signal. 110 can also generate an upper clamping signal (labeled as clk_zvs) based on the output feedback signal. The third terminals of the OSC 110 and the PWM comparator 120 can be connected to the first terminal (e.g., the set terminal) and the second terminal (e.g., the reset terminal) of the RS trigger 130, respectively. The third terminal (e.g., the output terminal) of the RS trigger 130 can be connected to the first terminal (e.g., the input terminal) of the first gate driver 140. The second terminal (e.g., the output terminal) of the first gate driver 140 can be connected to the gate of the power tube S1 via the first drive pin Gate1 to output a second control signal for controlling the on and off of the power tube S1.

[0038] Figure 3 and Figure 1 The working principle of the ZVS flyback switching power supply shown in the figure is basically the same, so I will not go into details here. Figure 1 and Figure 3 Specifically, the ZVS flyback switching power supply provided by the embodiment of the present invention performs working mode recognition by utilizing the working mode recognition and logic control module 410, and controls the conduction and shutdown of the ZVS auxiliary tube S0 and the power tube S1 based on the recognition result.

[0039] As an example, the AC voltage detection unit 4101 can be configured to determine whether the ZVS flyback switching power supply is in a high-voltage operating mode or a low-voltage operating mode by directly detecting the input voltage (e.g., AC voltage) of the switching power supply or indirectly detecting the AC voltage, and can output a logic signal AC_in to the DCM / CCM and LLM detection unit 4103.

[0040] Specifically, the AC voltage detection unit 4101 can be configured to compare the AC voltage with a first preset threshold value, and when the AC voltage is greater than the first preset threshold value, determine that the ZVS flyback switching power supply is in the high-voltage operating mode; and compare the AC voltage with a second preset threshold value, and when the AC voltage is less than the second preset threshold value, determine that the ZVS flyback switching power supply is in the low-voltage operating mode, wherein the first preset threshold value is greater than the second preset threshold value.

[0041] As an example, the AC voltage may be indirectly detected by detecting the voltage from the demagnetization detection pin DEM during a period when the primary power transistor S1 is turned on.

[0042] In order to better understand the embodiments of the present invention Figure 3 The DCM / CCM and LLM detection unit 4103 shown in FIG. 4 is described in detail below by way of specific examples. For example, Figure 4 , Figure 4 The embodiment of the present invention provides Figure 3 The structural diagram of the DCM / CCM and LLM detection unit 4103 is shown.

[0043] As an example, the DCM / CCM and LLM detection unit 4103 can be configured to detect and identify the DCM / CCM and LLM operating modes based on the upper clamping signal Clk_zvs from the OSC 110, the signal AC_in from the AC voltage detection unit 4101, the output feedback signal FB_in, and the demagnetization pulse signal Demag from the demagnetization signal detection unit 4102, respectively, and then perform mode synthesis and logic control processing to output the logic signal ZVS_CTR, and generate the first control signal Gate0 for controlling the conduction and shutdown of the ZVS auxiliary tube S0 based on the logic signal ZVS_CTR.

[0044] like Figure 4 As shown, the DCM / CCM and LLM detection unit 4103 may include a DCM / CCM detection unit 510, an LLM detection unit 520, and a mode synthesis and logic control unit 530, etc. It can be understood that Figure 4 The examples shown are for illustration only and should not be construed as limiting. Figure 4 In the illustrated embodiment, it is possible to detect whether the switching power supply is in the LLM or non-LLM operating mode, and to detect whether the switching power supply is in the DCM or CCM operating mode. However, it should be noted that in other embodiments, it is possible to detect whether the switching power supply is in the LLM or non-LLM operating mode, or to detect whether the switching power supply is in the DCM or CCM operating mode, which are not shown in the figure.

[0045] exist Figure 4 In the embodiment, a first end of the DCM / CCM detection unit 510 can receive the upper clamping signal Clk_zvs from the OSC 110, a second end can receive the demagnetization pulse signal Demag from the demagnetization signal detection unit 4102, and a third end can be connected to a first end of the mode synthesis and logic control unit 530. A first end of the LLM detection unit 520 can receive the output feedback signal FB_in, a second end can be connected to a second end of the mode synthesis and logic control unit 530, a third end of the mode synthesis and logic control unit 530 can receive the logic signal AC_in, and a fourth end of the mode synthesis and logic control unit 530 can output the logic signal ZVS_CTR.

[0046] As an example, see Figure 3 and Figure 4 The voltage on the auxiliary winding Ns2 of the transformer is divided by the voltage divider network composed of resistors R3 and R4, and the voltage is transmitted to the demagnetization signal detection unit 4102 via the demagnetization detection pin DEM of the control chip 400. This voltage can represent the demagnetization condition of the primary winding of the transformer.

[0047] As an example, the demagnetization signal detection unit 4102 can be configured to detect a demagnetization sensing signal representing the demagnetization condition of the primary winding of the transformer, detect whether the demagnetization is completed according to the demagnetization sensing signal during the shutdown period of the primary power tube S1, and generate a demagnetization pulse signal Demag to the DCM / CCM detection unit 510 to determine whether the ZVS conduction flyback switching power supply is in CCM or DCM operating mode.

[0048] As an example, the control chip 400 may include an OSC 110 , which may be configured to output an upper frequency clamping signal Clk_zvs and a lower frequency clamping signal Fmin based on an output feedback signal.

[0049] As an example, the DCM / CCM detection unit 510 may be configured to determine whether the current operating mode is DCM or CCM according to the upper clamping signal Clk_zvs from the OSC 110 and the demagnetization pulse signal Demag from the demagnetization signal detection unit 4102 .

[0050] Specifically, the control chip 400 can be further configured to: when the upper clamping signal Clk_zvs is at a rising edge and it is detected that the secondary side demagnetization has ended (for example, the demagnetization pulse signal Demag is less than a fifth preset threshold), determine that the ZVS flyback switching power supply is in the DCM operating mode; when the upper clamping signal Clk_zvs is at a rising edge and it is detected that the secondary side demagnetization has not ended (for example, the demagnetization pulse signal Demag is greater than a sixth preset threshold), determine that the ZVS flyback switching power supply is in the CCM operating mode, wherein the fifth preset threshold is less than or equal to the sixth preset threshold.

[0051] As an example, the LLM detection unit 520 may be configured to determine whether the ZVS flyback switching power supply is in the LLM or non-LLM operation mode based on the output feedback signal FB_in representing the output load of the ZVS flyback switching power supply.

[0052] Specifically, the output feedback signal FB_in can be compared with a third preset threshold value VFB_LL. For example, when the output feedback signal FB_in is less than the third preset threshold value VFB_LL, it is determined that the ZVS flyback switching power supply is in the LLM operating mode; and the output feedback signal FB_in can be compared with a fourth preset threshold value VFB_HL. For example, when the output feedback signal FB_in is greater than the fourth preset threshold value VFB_HL, it is determined that the ZVS flyback switching power supply is in the non-LLM operating mode, wherein the third preset threshold value is less than the fourth preset threshold value.

[0053] As an example, the mode synthesis and logic control unit 530 can be configured to perform mode synthesis and logic control processing based on the current operating mode detection results from the DCM / CCM detection unit 510 and the LLM detection unit 520 and the signal AC_in from the AC voltage detection unit 4101, and generate a logic signal ZVS_CTR, and the logic signal ZVS_CTR can be processed by the second gate driver 170 to generate a first control signal Gate0 for controlling the conduction and shutdown of the ZVS auxiliary tube S0.

[0054] refer to Figure 5 , Figure 5 A flow chart of operating mode identification and logic control of a ZVS flyback switching power supply provided by an embodiment of the present invention is shown.

[0055] As an example, demagnetization sensing signal detection, AC voltage detection, and output feedback signal detection can be performed first, and then the operating mode can be identified based on the AC voltage, output feedback signal, demagnetization sensing signal, and frequency from the OSC (for example, upper clamping frequency or lower clamping frequency signal).

[0056] Among them, when the DCM / CCM and LLM detection unit 4103 (reference Figure 3 and Figure 4 ) When it is detected that the ZVS flyback switching power supply is in the DCM and LLM operating modes, the mode synthesis and logic control unit 530 can output the logic signal ZVS_CTR to control the ZVS auxiliary tube S0 to be in the off state, and control the power tube S1 from the off state to the on state based on the upper clamping signal Clk_zvs.

[0057] like Figure 6 As shown, Figure 6 A schematic diagram of signal waveforms of a ZVS flyback switching power supply provided by an embodiment of the present invention operating in DCM and LLM operating modes is shown. For example, after a period of time, if it is detected that the output feedback signal FB_in is less than the third preset threshold VFB_LL, it is determined that the switching power supply operates in the LLM operating mode, and if it is detected that the secondary side demagnetization has ended at the rising edge of the upper clamping signal CLK_zvs, it is determined that the switching power supply operates in the DCM operating mode. After detecting that the switching power supply operates in the DCM and LLM operating modes, the mode synthesis and logic control unit 530 can output the logic signal ZVS_CTR to keep the first control signal Gate0 at a low level to control the ZVS auxiliary transistor S0 to be in the off state, and the upper clamping signal Clk_zvs changes from a low level to a high level at time t2 and remains at a high level during the time period t2-t3. Based on the upper clamping signal Clk_zvs, the second control signal Gate1 is controlled to change from a low level to a high level at time t3 and remain at a high level during the time period t3-t4, so as to control the power transistor S1 to be in the on state during the time period t3-t4.

[0058] When the DCM / CCM and LLM detection unit 4103 (reference Figure 3 and Figure 4 ) When it is detected that the ZVS flyback switching power supply is in DCM and non-LLM operating mode, the mode synthesis and logic control unit 530 can output a logic signal ZVS_CTR to control the ZVS auxiliary tube S0 to change from the off state to the on state based on the upper clamping signal Clk_zvs, and then control the power tube S1 to change from the off state to the on state.

[0059] like Figure 7 As shown, Figure 7The waveform diagram of the signal of the ZVS flyback switching power supply provided by the embodiment of the present invention operating in the DCM and non-LLM operating modes is shown. For example, after a period of time, if the output feedback signal FB_in is detected to be greater than the fourth preset threshold value VFB_HL, it is determined that the switching power supply is operating in the non-LLM operating mode, and when the secondary side demagnetization is detected to have ended at the rising edge of the upper clamping signal CLK_zvs, it is determined that the switching power supply is operating in the DCM operating mode. After the switching power supply is detected to be operating in the DCM and non-LLM operating modes, the upper clamping signal Clk_zvs changes from a low level to a high level at time t3, and then the first control signal Gate0 also changes from a low level to a high level at time t3. The second control signal Gate1 changes from a low level to a high level and remains at a high level until time t4, so that the ZVS auxiliary tube S0 is in the on state during the time period t3-t4, and starts timing the dead time when the falling edge of Gate0 is detected. The time period t4-t5 corresponds to the dead time. After the dead time, that is, at time t5, the second control signal Gate1 changes from a low level to a high level and remains at a high level until time t6, so that the power tube S1 changes from the off state to the on state at time t5, and remains in the on state during the time period t5-t6.

[0060] When the DCM / CCM and LLM detection unit 4103 (reference Figure 3 and Figure 4 ) When it is detected that the ZVS flyback switching power supply is in the CCM and AC high voltage working mode, the mode synthesis and logic control unit 530 can output the logic signal ZVS_CTR to control the ZVS auxiliary tube S0 to be in the off state, and control the power tube S1 from the off state to the on state based on the lower clamping signal Fmin from the OSC 110.

[0061] like Figure 8 As shown, Figure 8A schematic diagram illustrates signal waveforms for a ZVS flyback switching power supply operating in CCM and AC high-voltage operating modes, provided by an embodiment of the present invention. For example, when an input characterizing signal is detected to be greater than a first preset threshold, the ZVS flyback switching power supply is determined to be in high-voltage operating mode. Furthermore, when secondary-side demagnetization is detected to be incomplete at the rising edge of the upper clamp signal CLK_zvs, the switching power supply is determined to be in CCM operating mode. After detecting that the switching power supply is operating in CCM and AC high-voltage operating modes, the first control signal Gate0 is maintained at a low level to control the ZVS auxiliary transistor S0 to be in an off state. The lower clamp signal Fmin changes from a low level to a high level at time t0, and the second control signal Gate1 changes from a low level to a high level at time t0 and remains at a high level during the time period t0-t1, causing the power transistor S1 to change from an off state to an on state at time t0 and remain in an on state during the time period t0-t1.

[0062] When the DCM / CCM and LLM detection unit 4103 (reference Figure 3 and Figure 4 ) When it is detected that the ZVS flyback switching power supply is in CCM and AC low-voltage working mode, the mode synthesis and logic control unit 530 can output the logic signal ZVS_CTR to control the ZVS auxiliary tube S0 to be in the off state, and control the power tube S1 from the off state to the on state based on the upper clamping signal Clk_zvs.

[0063] like Figure 9 As shown, Figure 9 A schematic diagram illustrates signal waveforms for a ZVS flyback switching power supply operating in CCM and AC low-voltage operating modes, provided by an embodiment of the present invention. For example, when the input characterizing signal is detected to be less than a second preset threshold, the ZVS flyback switching power supply is determined to be in low-voltage operating mode. Furthermore, when the secondary-side demagnetization is detected to be not yet complete at the rising edge of the upper clamping signal CLK_zvs, the switching power supply is determined to be in CCM operating mode. After detecting that the switching power supply is operating in CCM and AC low-voltage operating modes, the first control signal Gate0 is maintained at a low level to control the ZVS auxiliary transistor S0 to be in an off state. Based on the upper clamping signal Clk_zvs, the second control signal Gate1 is controlled to change from a level to a high level at time t2 and remain at a high level during a time period t2-t3, thereby controlling the power transistor S1 to change from an off state to an on state at time t2 and remain in an on state during a time period t2-t3.

[0064] As described above, unlike the prior art practice of turning on the ZVS auxiliary transistor S0 regardless of the switching power supply's operating mode, the switching power supply provided in the embodiments of the present invention turns on the ZVS auxiliary transistor S0 only when the switching power supply detects that it is in the DCM and non-LLM operating modes. In the other three modes, namely, operating in the DCM and LLM operating modes, the CCM and AC high-voltage operating mode, and the CCM and AC low-voltage operating mode, the ZVS auxiliary transistor S0 is not turned on. This reduces the standby power consumption and light-load power consumption of the switching power supply. It also prevents the synchronous rectifier S2 from being prematurely turned off due to the ZVS auxiliary transistor S0 turning off after turning on when the switching power supply operates in the CCM mode, thereby reducing the drain-source voltage VDS of the synchronous rectifier S2 and reducing the temperature increase of the primary power transistor S1.

[0065] In summary, the ZVS flyback switching power supply provided in the embodiment of the present invention performs operating mode recognition through the operating mode recognition and logic control module 410, and controls the conduction and shutdown of the ZVS auxiliary transistor S0 and the power transistor S1 based on the mode recognition results. On the one hand, the light-load operating mode recognition can be used to shut down the ZVS auxiliary transistor S0 when a no-load or light-load operating mode is detected, thereby reducing the standby power consumption and light-load power consumption of the switching power supply. On the other hand, the DCM / CCM operating mode recognition can be used to prevent the synchronous rectifier transistor S2 from being prematurely shut down due to the shutdown action after the ZVS auxiliary transistor S0 is turned on when the switching power supply operates in CCM mode, thereby achieving the purpose of reducing the drain-source voltage VDS of the synchronous rectifier transistor S2 and reducing the temperature increase of the primary power transistor S1.

[0066] In addition, the embodiment of the present invention also provides a control method for a zero voltage turn-on flyback switching power supply, referring to Figure 10 , Figure 10 A flow chart of a control method for a zero-voltage-conduction flyback switching power supply provided by an embodiment of the present invention is shown, wherein the zero-voltage-conduction flyback switching power supply includes a zero-voltage-conduction auxiliary tube, a power tube, and a transformer.

[0067] like Figure 10As shown, method 1000 may include the following steps: S1010, determining the operating mode of the zero-voltage-turn-on flyback switching power supply based on an input characterization signal characterizing the input voltage of the zero-voltage-turn-on flyback switching power supply, a demagnetization sensing signal characterizing the demagnetization condition of the primary winding of the transformer, and an output feedback signal characterizing the output load of the zero-voltage-turn-on flyback switching power supply; S1020, generating a first control signal for controlling the on and off of the zero-voltage-turn-on auxiliary transistor based on the operating mode of the zero-voltage-turn-on flyback switching power supply; and S1030, generating a second control signal for controlling the on and off of the power transistor based on the operating mode of the zero-voltage-turn-on flyback switching power supply, the output feedback signal, and a current sensing signal characterizing the current flowing through the power transistor.

[0068] It is understandable that the control method for the zero voltage turn-on flyback switching power supply provided in the embodiment of the present invention is combined with the above Figures 1 to 9 The described control chip for the zero-voltage turn-on flyback switching power supply has the same working principle. Therefore, for ease of description, the specific details of the method will not be repeated below.

[0069] It should be understood that the present invention is not limited to the specific configurations and processes described above and illustrated in the figures. For the sake of brevity, a detailed description of known methods is omitted. In the above embodiments, several specific steps are described and illustrated as examples. However, the method of the present invention is not limited to the specific steps described and illustrated. Those skilled in the art may make various changes, modifications, and additions, or change the order of the steps after understanding the spirit of the present invention.

[0070] The functional blocks shown in the above-described block diagram can be implemented as hardware, software, firmware or a combination thereof. When implemented in hardware, it can be, for example, an electronic circuit, an application specific integrated circuit (ASIC), appropriate firmware, a plug-in unit, a function card or the like. When implemented in software, the elements of the present invention are programs or code segments that are used to perform the required tasks. The program or code segment can be stored in a machine-readable medium, or transmitted on a transmission medium or a communication link by a data signal carried in a carrier wave. "Machine-readable medium" can include any medium capable of storing or transmitting information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROMs, flash memories, erasable ROMs (EROMs), floppy disks, CD-ROMs, optical disks, hard disks, optical fiber media, radio frequency (RF) links, etc. The code segment can be downloaded via a computer network such as the Internet, an intranet, etc.

[0071] It should also be noted that the exemplary embodiments described herein describe methods or systems based on a series of steps or devices. However, the present invention is not limited to the order of the steps described above. In other words, the steps may be performed in the order described in the embodiments, or in a different order, or several steps may be performed simultaneously.

[0072] The above description is only a specific embodiment of the present invention. Those skilled in the art will clearly understand that for the convenience and brevity of description, the specific working processes of the systems, modules and units described above can refer to the corresponding processes in the aforementioned method embodiments, and will not be repeated here. It should be understood that the protection scope of the present invention is not limited to this. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention.

Claims

1. A control chip for a zero voltage turn-on flyback switching power supply, characterized in that: The zero-voltage-conduction flyback switching power supply includes a zero-voltage-conduction auxiliary tube, a power tube, and a transformer. The control chip is configured as follows: determining an operating mode of the zero-voltage-conduction flyback switching power supply based on an input characterizing signal characterizing an input voltage of the zero-voltage-conduction flyback switching power supply, a demagnetization sensing signal characterizing a demagnetization condition of a primary winding of the transformer, and an output feedback signal characterizing an output load of the zero-voltage-conduction flyback switching power supply; Based on the operating mode of the zero-voltage-turn-on flyback switching power supply, generating a first control signal for controlling the on and off of the zero-voltage-turn-on auxiliary transistor; as well as Based on the working mode of the zero voltage turn-on flyback switching power supply, the output feedback signal, and the current sensing signal representing the current flowing through the power tube, a second control signal for controlling the on and off of the power tube is generated.

2. The control chip according to claim 1, characterized in that: The control chip is further configured as follows: Based on the input characterization signal, determining whether the zero-voltage turn-on flyback switching power supply is in a high-voltage operating mode or a low-voltage operating mode; Based on the demagnetization sensing signal, determining whether the zero voltage turn-on flyback switching power supply is in a continuous operation mode or a discontinuous operation mode; as well as Based on the output feedback signal, it is determined whether the zero voltage turn-on flyback switching power supply is in a light load operation mode or a non-light load operation mode.

3. The control chip according to claim 2, characterized in that: The control chip is further configured as follows: When the input characterization signal is greater than a first preset threshold, determining that the zero voltage turn-on flyback switching power supply is in the high voltage operation mode; as well as When the input characterization signal is less than a second preset threshold, it is determined that the zero voltage turn-on flyback switching power supply is in a low voltage operation mode, wherein the first preset threshold is greater than the second preset threshold.

4. The control chip according to claim 2, characterized in that: The control chip is further configured as follows: When the output feedback signal is less than a third preset threshold, determining that the zero voltage turn-on flyback switching power supply is in the light load operation mode; and When the output feedback signal is greater than a fourth preset threshold, it is determined that the zero voltage turn-on flyback switching power supply is in the non-light load operation mode, wherein the third preset threshold is less than the fourth preset threshold.

5. The control chip according to claim 2, characterized in that: The control chip includes a frequency oscillator, and the frequency oscillator is configured to generate an upper frequency clamping signal based on the output feedback signal. The control chip is further configured to: When the upper clamping signal is at a rising edge and the demagnetization sensing signal is less than a fifth preset threshold, determining that the zero voltage turn-on flyback switching power supply is in a discontinuous working mode; as well as When the upper clamping signal is at a rising edge and the demagnetization sensing signal is greater than a sixth preset threshold, it is determined that the zero voltage turn-on flyback switching power supply is in a continuous operation mode, wherein the fifth preset threshold is less than or equal to the sixth preset threshold.

6. The control chip according to claim 5, characterized in that: The control chip is further configured as follows: When it is determined that the zero voltage turn-on flyback switching power supply is in the discontinuous working mode and the light load working mode, the zero voltage turn-on auxiliary transistor is controlled to be in the off state, and the power transistor is controlled to change from the off state to the on state based on the upper clamping signal; as well as When it is determined that the zero voltage turn-on flyback switching power supply is in the discontinuous working mode and the non-light load working mode, the zero voltage turn-on auxiliary tube and the power tube are controlled to change from the off state to the on state based on the upper clamping signal.

7. The control chip according to claim 5, characterized in that: The frequency oscillator is further configured to generate a lower frequency clamping signal based on the output feedback signal, and the control chip is further configured to: When it is determined that the zero voltage turn-on flyback switching power supply is in the continuous operation mode and the high voltage operation mode, the zero voltage turn-on auxiliary transistor is controlled to be in the off state, and the power transistor is controlled to change from the off state to the on state based on the lower clamping signal; as well as When it is determined that the zero voltage turn-on flyback switching power supply is in the continuous working mode and the low voltage working mode, the zero voltage turn-on auxiliary tube is controlled to be in the off state, and the power tube is controlled to change from the off state to the on state based on the upper clamping signal.

8. The control chip according to claim 1, characterized in that: The control chip further includes a dead time control module, wherein the dead time control module is configured to start timing the dead time length when a falling edge of the first control signal is detected, and control the power tube to change from an off state to an on state after the dead time length has passed.

9. A control method for a zero voltage turn-on flyback switching power supply, characterized in that: The zero-voltage-conduction flyback switching power supply includes a zero-voltage-conduction auxiliary tube, a power tube, and a transformer. The control method includes: determining an operating mode of the zero-voltage-conduction flyback switching power supply based on an input characterizing signal characterizing an input voltage of the zero-voltage-conduction flyback switching power supply, a demagnetization sensing signal characterizing a demagnetization condition of a primary winding of the transformer, and an output feedback signal characterizing an output load of the zero-voltage-conduction flyback switching power supply; Based on the operating mode of the zero voltage turn-on flyback switching power supply, generating a first control signal for controlling the on and off of the zero voltage turn-on auxiliary transistor; and Based on the working mode of the zero voltage turn-on flyback switching power supply, the output feedback signal, and the current sensing signal representing the current flowing through the power tube, a second control signal for controlling the on and off of the power tube is generated.

10. The control method according to claim 9, characterized in that: The step of determining the working mode includes: Based on the input characterization signal, determining whether the zero-voltage turn-on flyback switching power supply is in a high-voltage operating mode or a low-voltage operating mode; Based on the demagnetization sensing signal, determining whether the zero voltage turn-on flyback switching power supply is in a continuous operation mode or a discontinuous operation mode; and Based on the output feedback signal, it is determined whether the zero voltage turn-on flyback switching power supply is in a light load operation mode or a non-light load operation mode.

11. The control method according to claim 10, characterized in that: The step of determining the working mode further comprises: When the input characterization signal is greater than a first preset threshold, determining that the zero voltage turn-on flyback switching power supply is in the high voltage operation mode; and When the input characterization signal is less than a second preset threshold, it is determined that the zero voltage turn-on flyback switching power supply is in a low voltage operation mode, wherein the first preset threshold is greater than the second preset threshold.

12. The control method according to claim 10, characterized in that: The step of determining the working mode further comprises: When the output feedback signal is less than a third preset threshold, determining that the zero voltage turn-on flyback switching power supply is in the light load operation mode; and When the output feedback signal is greater than a fourth preset threshold, it is determined that the zero voltage turn-on flyback switching power supply is in the non-light load operation mode, wherein the third preset threshold is less than the fourth preset threshold.

13. The control method according to claim 10, characterized in that: The zero-voltage turn-on flyback switching power supply includes a control chip, the control chip includes a frequency oscillator, and the frequency oscillator is configured to generate an upper clamping signal based on the output feedback signal. The control method further includes: When the upper clamping signal is at a rising edge and the demagnetization sensing signal is less than a fifth preset threshold, determining that the zero voltage turn-on flyback switching power supply is in a discontinuous operation mode; and When the upper clamping signal is at a rising edge and the demagnetization sensing signal is greater than a sixth preset threshold, it is determined that the zero voltage turn-on flyback switching power supply is in a continuous operation mode, wherein the fifth preset threshold is less than or equal to the sixth preset threshold.

14. The control method according to claim 13, characterized in that: The control method further comprises: When it is determined that the zero voltage turn-on flyback switching power supply is in the discontinuous working mode and the light load working mode, controlling the zero voltage turn-on auxiliary transistor to be in the off state, and controlling the power transistor to change from the off state to the on state based on the upper clamping signal; and When it is determined that the zero voltage turn-on flyback switching power supply is in the discontinuous working mode and the non-light load working mode, the zero voltage turn-on auxiliary tube and the power tube are controlled to change from the off state to the on state based on the upper clamping signal.

15. The control method according to claim 13, characterized in that: The frequency oscillator is further configured to generate a lower-clamp frequency signal based on the output feedback signal, and the control method further includes: When it is determined that the zero voltage turn-on flyback switching power supply is in the continuous operation mode and the high voltage operation mode, controlling the zero voltage turn-on auxiliary transistor to be in the off state, and controlling the power transistor to change from the off state to the on state based on the lower clamping signal; and When it is determined that the zero voltage turn-on flyback switching power supply is in the continuous working mode and the low voltage working mode, the zero voltage turn-on auxiliary tube is controlled to be in the off state, and the power tube is controlled to change from the off state to the on state based on the upper clamping signal.

16. The control method according to claim 9, characterized in that: The control method further includes: starting to measure the length of a dead time when a falling edge of the first control signal is detected, and controlling the power transistor to change from an off state to an on state after the dead time has elapsed.

17. A zero voltage turn-on flyback switching power supply, characterized in that: The device comprises the control chip according to any one of claims 1 to 8.

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