A zero voltage switching control circuit and method for switching power supply

Abstract

The present invention discloses a control current and method for a zero-voltage switch, which utilizes a secondary-side feedback switching power supply auxiliary winding in combination with a PMOS tube to achieve the zero-voltage start-up function of the switching power supply. Compared with the existing technology, the circuit is relatively simple and has fewer circuit components, which is conducive to reducing the size of the charger and adapter.

Description

Technical Field

[0001] The present disclosure relates to a switching power supply, and in particular to a zero-voltage switching control circuit and method applicable to the switching power supply. Background Art

[0002] The market places higher demands on the power density and volume of chargers and adapters that can transform, regulate and stabilize voltage. That is, the power density should be higher with a smaller volume. An effective way to solve the above problems is to reduce the conduction loss and switching loss of the power tube.

[0003] In the prior art, a zero-voltage switching control circuit is formed by adding a MOSFET power tube, a capacitor, and a transformer winding to the charger or adapter, thereby reducing the conduction or switching loss of the transformer power tube in the charger and adapter and improving the output power density.

[0004] The above method effectively solves the output power density problem. However, the additional MOSFET power tubes, capacitors, and transformer windings are not conducive to reducing the size of the charger and adapter, and the circuit design is relatively complex. Summary of the Invention

[0005] To address the issue of reducing the size of chargers and adapters while increasing power density, the present disclosure proposes a novel zero-voltage switching control circuit and method with a simple structure and high output power. The method comprises:

[0006] Transformer, starting circuit, forced resonant circuit, among which

[0007] The transformer includes a primary winding, a secondary winding, and an auxiliary winding;

[0008] The starting circuit includes a starting capacitor;

[0009] The auxiliary winding, the first power switch of the PMOS structure and the starting capacitor form a forced resonant circuit, and the other end of the auxiliary winding is grounded;

[0010] The first power switch is respectively connected to one end of the auxiliary winding, the starting capacitor and the first pin of the switching power management chip;

[0011] Used to generate forced resonant voltage when the switching power supply is in discontinuous mode after flyback is completed;

[0012] Specifically, the power management chip includes a mode judgment circuit, a zero voltage drive circuit, and a valley conduction circuit;

[0013] The mode judgment circuit is connected to the auxiliary winding via the second pin of the power management chip, and is configured to generate a mode judgment signal when the second power switch outputs a low level;

[0014] The output terminal of the zero voltage driving circuit is connected to the first pin, and is configured to generate a ZVS driving signal including a switching frequency to drive the first power switch when the switching power supply is in the discontinuous mode;

[0015] a valley conduction circuit connected to the zero voltage driving circuit and the mode determination circuit, configured to generate a driving signal to the second power switch;

[0016] Specifically, it also includes a bus voltage compensation circuit, wherein:

[0017] The bus voltage compensation circuit includes a bus voltage compensation circuit, which is configured to generate a compensation voltage signal and / or a compensation current signal representing the input bus voltage, obtain the input bus voltage divided signal through the second pin of the power management chip, and obtain the compensation voltage signal and / or a compensation current signal representing the input bus voltage through the bus voltage compensation module.

[0018] Specifically, it also includes a bus voltage compensation circuit, wherein:

[0019] The bus voltage compensation circuit includes a bus voltage compensation circuit, which is configured to generate a compensation voltage signal and / or a compensation current signal representing the input bus voltage, obtain the input bus voltage divider signal through the sixth pin of the power management chip, and obtain the compensation voltage signal and / or a compensation current signal representing the input bus voltage through the bus voltage compensation module.

[0020] Specifically, the drain of the first power switch is connected to the auxiliary winding 1, and the source thereof is connected to the starting capacitor of the switching power supply;

[0021] The first power switch gate is connected to the first pin of the switching power management chip.

[0022] Specifically, the mode judgment circuit includes a zero-crossing module, a mode judgment module, a main drive module, and a mode judgment circuit of a logic control module;

[0023] The zero-crossing detection module, the mode judgment module, the logic control module and the main driving module are connected in sequence, and the input end of the zero-crossing detection module is connected to the second pin of the power management chip, and the main driving module is connected to the sixth pin of the power management chip.

[0024] Specifically, the zero voltage drive circuit includes a ZVS module and a ZVS drive module, wherein:

[0025] The ZVS module and the ZVS driving module are connected in sequence, and the input end of the ZVS module is connected to the other output end of the zero-crossing detection module, and the output end of the ZVS driving module is connected to the first pin of the power management chip.

[0026] Specifically, the ZVS module includes a capacitor and a preset voltage value and / or a preset current value;

[0027] The switching frequency modulation mode of the first power switch includes any one of the following modes or any combination thereof:

[0028] When the bus voltage compensation circuit receives the input bus voltage divided voltage signal and outputs the bus voltage compensation voltage signal, the ZVS module uses the compensation voltage signal as the reference voltage signal and charges the capacitor with a preset current to reach the reference voltage;

[0029] When the bus voltage compensation circuit receives the input bus voltage divided voltage signal and outputs the bus voltage compensation current signal, the ZVS module uses the compensation current signal as the capacitor charging current to charge the capacitor to reach a preset voltage value.

[0030] Specifically, the valley conduction circuit includes a clock module and a valley conduction module, wherein the clock module is respectively connected to the ZVS module, the valley conduction module and the logic control module, and the valley conduction module is respectively connected to the zero-crossing detection module, the mode judgment module, the logic judgment module and the ZVS module.

[0031] Specifically, when the switching power supply completes flyback and is in the discontinuous mode, the zero-crossing signal of the auxiliary winding falling edge sensed by the zero-crossing detection module is the first zero-crossing signal;

[0032] When the switching power supply completes the flyback and is in the discontinuous mode, the zero-crossing signal of the auxiliary winding rising edge sensed by the zero-crossing detection module is the second zero-crossing signal.

[0033] Specifically, after the switching power supply completes flyback and the first power switch is turned off in the discontinuous mode, the valley conduction module obtains the first zero-crossing signal as the valley conduction signal after receiving the clock signal generated by the clock module.

[0034] Accordingly, the present invention also proposes a zero voltage switching control method for a switching power supply, which is applied to a switching power supply including a main switch power tube and a transformer, comprising:

[0035] Receive the first zero-crossing signal and output the switching power supply to be in DCM (discontinuous mode) working mode;

[0036] The ZVS signal generated by the first second zero-crossing signal after the clock signal is obtained and outputted to make the switching power supply transformer enter the energy storage stage;

[0037] The first zero-crossing signal after the ZVS signal is obtained is output to enable the main switch power tube of the switching power supply to achieve zero voltage and or zero current start.

[0038] Specifically, when the first zero-crossing signal is not received, the output causes the switching power supply to operate in a CCM (continuous cycle mode);

[0039] Get the clock signal and output it to turn on the main switch power tube of the switching power supply.

[0040] Specifically, the steps of obtaining the ZVS signal of the first second zero-crossing signal after the clock signal and outputting the signal to cause the switching power supply transformer to enter the energy storage stage include:

[0041] receiving a clock signal;

[0042] receiving a first second zero-crossing signal;

[0043] Obtaining a compensation voltage signal and / or a compensation current signal representing an input bus voltage;

[0044] Output the ZVS signal after pulse width adjustment, so that the switching power supply transformer enters the energy storage stage;

[0045] Specifically, the first zero-crossing signal after the ZVS signal is output to enable the main switch power tube of the switching power supply to achieve zero voltage turn-on. The specific steps include:

[0046] Receive the ZVS signal after pulse width adjustment;

[0047] receiving the first zero-crossing signal after the pulse width-adjusted ZVS signal;

[0048] Output valley conduction signal to enable the main switch power tube of the switching power supply to achieve zero voltage turn-on.

[0049] Specifically, after obtaining the compensation voltage signal or the compensation current signal representing the input bus voltage, the method further includes:

[0050] Receive the supplementary voltage signal, and use the compensation voltage signal as a reference voltage to obtain the preset current charging time, and adjust the ZVS signal pulse width according to the charging time;

[0051] Receive the supplementary current signal, use the compensation current signal as the charging current, obtain the charging time, and adjust the ZVS signal pulse width according to the charging time.

[0052] The present invention provides a zero-voltage switch control current and method, which utilizes a secondary-side feedback switching power supply auxiliary winding in combination with a PMOS transistor to achieve the zero-voltage start-up function of the switching power supply. Compared with the prior art, the circuit is relatively simple, with fewer circuit components, which is conducive to reducing the size of the charger and adapter.

[0053] It can be seen that by applying the technical solution of the present application, the zero-voltage start-up function of the switching power supply is realized by combining the auxiliary winding of the secondary-side feedback switching power supply with the PMOS tube. Compared with the existing technology, the circuit is relatively simple and has fewer circuit components, which is conducive to reducing the size of the charger and adapter. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0055] Figure 1 FIG. 1 is a schematic diagram of a zero voltage switching control circuit provided by the present invention;

[0056] Figure 2 Shown is a circuit diagram of a mode judgment module in a specific embodiment of the present invention;

[0057] Figure 3 The figure shows a working waveform diagram of a control circuit for enabling the quasi-resonance function of a switching power supply provided by a specific embodiment of the present invention. DETAILED DESCRIPTION

[0058] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0059] refer to Figure 1 The embodiment described above is a zero voltage switching control circuit for a switching power supply, characterized by comprising:

[0060] It includes a transformer, a starting circuit, and a forced resonant circuit 1, wherein

[0061] A transformer including a primary winding Lp, a secondary winding Ls, an auxiliary winding Laux, a second power switch M0 and a check resistor Rcs;

[0062] A starting circuit including a starting capacitor Cvcc;

[0063] The auxiliary winding Laux and the first power switch M1 of the PMOS structure and

[0064] The starting capacitor Cvcc forms a forced resonant circuit 1, and the other end of the auxiliary winding Laux is grounded;

[0065] The first power switch M1 is respectively connected to one end of the auxiliary winding Laux, the startup capacitor Cvcc and the first pin driver of the switching power management chip;

[0066] Used to generate a forced resonant voltage Vds when the switching power supply completes the flyback and is in discontinuous mode;

[0067] The circuit described in the above embodiment differs from the prior art, which achieves zero-voltage turn-on of the second power switch M0 when the switching power supply is in the resonant phase by adding additional windings, capacitors, and power switches to the transformer. The present invention's forced resonant circuit 1 includes windings, power switches, and capacitors. However, through a rational design, it fully utilizes existing components in the circuit to form a circuit with the same functionality as the prior art. The winding is the transformer auxiliary winding Laux, and the capacitor is the startup capacitor Cvcc in the startup circuit. This simplifies the circuit and effectively reduces the size of the switching power supply.

[0068] It should be noted that the forced resonant circuit 1 can also be used to provide a self-powered voltage to the switching power management chip.

[0069] It should be noted that the present disclosure generates a forced resonant voltage by forcing the resonant circuit 1 to turn on or off when the switching power supply is reversed, thereby reducing the drain voltage of the second power switch to near zero, thereby achieving zero voltage or zero current conduction or cutoff of the second power switch. That is to say, for other power supplies that need to reduce the conduction loss or cutoff loss of the power switch, this can also be achieved through the circuit disclosed in the present disclosure.

[0070] refer to Figure 2 In another embodiment, the forced resonant circuit 1 is turned on or off and the second power switch M0 is turned on or off at zero voltage. This is performed in conjunction with a power management chip.

[0071] The power management chip includes a mode judgment circuit 2, a zero voltage drive circuit 3, and a valley conduction circuit 4;

[0072] The mode judgment circuit 2 is connected to the auxiliary winding Laux via the second pin zcd of the power management chip, and is configured to generate the mode judgment signal when the second power switch M0 outputs a low level;

[0073] The output end of the zero voltage driving circuit 3 is connected to the first pin driver, and is configured to generate a ZVS driving signal with a switching frequency to drive the first power switch when the switching power supply is in the discontinuous mode;

[0074] A valley conduction circuit 4 connected to the zero voltage drive circuit 3 and the mode determination circuit 1 is configured to generate a drive signal gate to the second power switch Mo;

[0075] In the above embodiment, when the second power switch M0 outputs a low level, the mode judgment circuit 2 outputs a DCM (discontinuous mode) signal to the logic judgment module when sensing the first zero-crossing signal Valley of the falling edge of the auxiliary winding Laux voltage, thereby causing the switching power supply to operate in DCM (discontinuous mode); and when the first zero-crossing signal Valley of the auxiliary winding Laux is not sensed, the mode judgment circuit 2 outputs a CCM (continuous mode) signal to the logic judgment module, thereby causing the switching power supply to operate in CCM (continuous mode).

[0076] It should be noted that the method of judging the working mode by sensing the zero-crossing signal can also be used to realize the DCM mode and CCM mode of the switching power supply by sensing the output / input voltage or current changes, or the DCM mode and CCM mode can be judged by realizing the switching power supply voltage or current changes through an external circuit.

[0077] When the switching power supply operates in DCM (discontinuous mode), the zero-voltage drive circuit 3 described in the above embodiment receives the second zero-crossing signal crest, which is a rising edge zero-crossing signal of the voltage of the auxiliary winding Laux, performs pulse width modulation on the second zero-crossing signal crest, and outputs the signal to drive the first power switch M1 to turn on. The transformer stores energy according to the pulse width of the second zero-crossing signal crest for a certain period of time and then turns off, thereby reducing the drain voltage or current of the second power switch M0 to near zero, thereby providing conditions for the second switch tube M0 to achieve zero voltage / zero current conduction in the next cycle.

[0078] The valley conduction circuit 4 of the above embodiment is respectively connected to the zero voltage drive circuit 2 and the mode judgment circuit 3. When the switching power supply operates in DCM (discontinuous mode), the valley conduction circuit 4 receives the clock signal CLK after receiving the second zero-crossing signal crest. After receiving the clock signal CLK, the valley conduction circuit 4 obtains the first zero-crossing signal valley as the valley conduction signal QR and outputs it to the logic control module to drive the second switch M0 to conduct with zero voltage or zero current.

[0079] It should be noted that the valley conduction circuit 4 receives the ZVS signal and then the clock signal CLK, obtaining the first zero-crossing signal Valley as the valley conduction signal QR. This is because the clock signal CLK is the start-up information for the main switch power tube of the switching power supply to enter the next cycle. In other words, after receiving CLK, the second power switch needs to be turned on. Therefore, the first zero-crossing signal Valley obtained after receiving the clock signal CLK is the valley conduction signal QR, achieving zero-voltage or zero-current turn-on of the second power switch. It should be noted that the ZVS signal should be received before outputting the valley conduction signal QR. This is because the ZVS signal is the drive signal that turns on the first power switch M1. A prerequisite for achieving zero-voltage or zero-current turn-on of the second power switch M0 is to reduce the drain voltage or current of the second power switch M0 to near zero. The conduction function of the first power switch M1 is to reduce the drain voltage or current of the second power switch M0 to near zero.

[0080] The above embodiment introduces the working mode and process of a zero voltage control circuit from the perspective of principle. The following embodiment describes the connection mode of a zero voltage control circuit from the perspective of circuit connection.

[0081] In another embodiment, the drain of the first power switch M1 is connected to the auxiliary winding Laux1, and the source thereof is connected to the switching power supply startup capacitor Cvcc;

[0082] The gate of the first power switch M1 is connected to the first pin driver of the switching power management chip.

[0083] refer to Figure 3 In another embodiment, the mode judgment circuit 2 includes a zero-crossing detection module 21, a mode judgment module 22, a main driving module 23 and a logic control module 24;

[0084] The zero-crossing detection module 21, the mode judgment module 22, the logic control module 24 and the main driving module 21 are connected in sequence, and the input end of the zero-crossing detection module 21 is connected to the second pin zcd of the power management chip, and the main driving module 23 is connected to the sixth pin gate of the power management chip.

[0085] It should be noted that the zero-crossing detection module 21 is connected to the second pin zcd through the input end, and is connected in series with the mode judgment module 22, the logic control module 24 and the main driving module 23 through the output end, wherein the output end of the main driving module 23 is connected to the sixth pin gate.

[0086] refer to Figure 2In another embodiment, the zero voltage drive circuit 3 includes a ZVS module 31 and a ZVS drive module 32, wherein the ZVS module 31 and the ZVS drive module 32 are connected in sequence, and the input end of the ZVS module 31 is connected to the other output end of the zero-crossing detection module 22, and the output end of the ZVS drive module 32 is connected to the first pin driver of the power management chip.

[0087] In another embodiment, the bus voltage compensation circuit 5 includes a bus voltage supplement module, wherein the bus voltage compensation circuit 5 is configured to generate a compensation voltage signal V and / or a compensation current signal I representing the input bus voltage Vin, obtain the input bus voltage zcd through the second pin zcd of the power management chip, and obtain the compensation voltage signal V and / or the compensation current signal I representing the input bus voltage through the bus voltage compensation module.

[0088] It should be noted that the bus voltage compensation circuit 5 in the above embodiment can also obtain the input bus voltage Vin in the following manner, that is, the bus voltage compensation module obtains the input bus voltage Vin through the seventh pin comp of the power management chip, and obtains the voltage V and / or current I of the feedback input bus voltage through the bus voltage compensation module.

[0089] It should be further explained that the bus voltage compensation circuit 5 can also obtain the compensation voltage signal V and / or the compensation current signal I representing the input bus voltage by sensing the input bus voltage Iin.

[0090] As can be seen from the two aforementioned embodiments, the bus voltage compensation circuit 5 and the zero voltage drive circuit 3 can implement pulse width modulation of the ZVS signal output by the ZVS module 31. Modulating the ZVS pulse width can change the on-time of the first power switch M1, thereby changing the energy storage of the switching power supply transformer during the resonant phase. In other words, the present disclosure can achieve zero voltage or zero current startup of the second power switch M0 for different input bus voltages.

[0091] The following embodiment shows how to perform pulse width modulation of the ZVS signal according to different input bus voltages.

[0092] In another embodiment, the ZVS module 31 includes a capacitor C and a preset voltage value Vth and / or a preset current value Ith;

[0093] The frequency modulation mode of the switch M1 of the first power switch includes any one of the following modes or any combination thereof:

[0094] When the bus voltage compensation circuit 5 receives the input bus voltage divided signal and outputs the bus voltage compensation voltage signal V, the ZVS module uses the compensation voltage signal V as the reference voltage signal Vref and charges the capacitor C with the preset current Ith to reach the reference voltage Vref;

[0095] When the bus voltage compensation circuit receives an input bus voltage divided voltage signal and outputs a bus voltage compensation current signal I, the ZVS module uses the compensation current signal I as the charging current of the capacitor C to charge the capacitor C to reach a preset voltage value Vth.

[0096] It should be noted that the supplementary voltage V is obtained through the bus voltage supplementary module, and the supplementary voltage V is used as the reference voltage Vref. When the preset current Ith is constant, the time it takes to charge the capacitor C so that its voltage reaches the reference voltage Vref is related to the value of the input bus voltage Vin. When the input bus voltage value is relatively high, the higher the supplementary voltage V obtained, the higher the reference voltage Vref, then the time it takes for the capacitor C to reach the reference voltage Vref when the preset current Ith remains unchanged is relatively long, thereby making the ZVS signal pulse width wider. On the contrary, when the input bus voltage Vin is relatively small, the adjusted ZVS signal pulse width is narrower.

[0097] It is understood that when the bus voltage supplement module obtains a compensation current signal I and uses the compensation current signal I as the charging current to charge capacitor C to a preset voltage value Vth, the magnitude of the charging current is related to the input bus voltage Vin. When the input bus voltage Vin is relatively high, the obtained compensation current signal I is relatively small, that is, the charging current is relatively small. It is also understood that when the preset voltage Vth of capacitor C is constant, the smaller the charging current, the longer it takes to reach the preset voltage Vth, thereby making the ZVS signal pulse width wider. Conversely, when the input bus voltage Vin is relatively low, the adjusted ZVS signal pulse width is narrower.

[0098] refer to Figure 2 In another embodiment, the valley conduction circuit 4 includes a clock module 41 and a valley conduction module 42, wherein the clock module 41 is respectively connected to the ZVS module 31, the valley conduction module 42 and the logic control module 24, and the valley conduction module 42 is respectively connected to the zero-crossing detection module 21, the mode judgment module 22, the logic judgment module 24 and the ZVS module 31.

[0099] In another embodiment, when the switching power supply completes flyback and is in the discontinuous mode, the falling edge zero-crossing signal of the auxiliary winding Laux sensed by the zero-crossing detection module 21 is the first zero-crossing signal Valley.

[0100] When the switching power supply completes flyback and is in the discontinuous mode, the rising edge zero-crossing signal of the auxiliary winding Laux sensed by the zero-crossing detection module 21 is the second zero-crossing signal crest.

[0101] In another embodiment, after the switching power supply completes flyback and is in discontinuous mode and the first power switch M1 is turned off, the first zero-crossing signal Valley obtained by the valley conduction module 42 after receiving the clock signal CLK generated by the clock module 41 is the valley conduction signal QR. The process and conditions for the circuit to obtain the valley conduction signal QR have been described in the previous embodiment and will not be repeated here.

[0102] Another embodiment provides a zero voltage switching control method for a switching power supply, which is applied to a switching power supply including a main switching power tube and a transformer, and is characterized in that:

[0103] receiving a first zero-crossing signal valley, and outputting a signal to put the switching power supply into a DCM (discontinuous mode) operating mode;

[0104] Obtaining a ZVS signal of the first second zero-crossing signal crest after the clock signal CLK, and outputting the signal to enable the switching power supply transformer to enter an energy storage stage;

[0105] The first zero-crossing signal valley after the ZVS signal is obtained and outputted so that the main switch power tube M0 of the switching power supply can be turned on with zero voltage and or zero current.

[0106] In the above embodiment, after the switching power supply completes flyback and receives the first zero-crossing signal Valley, the switching power supply enters the DCM discontinuous operation mode, which means that the main switch power tube M0 of the switching power supply can enable the zero voltage or zero current function.

[0107] It should be noted that when the switching power supply enters the DCM discontinuous working mode, when the switching power supply obtains the clock signal CLK, it indicates that the main switching power tube of the switching power supply is about to enter the next cycle. At this time, the ZVS signal is obtained through the second zero-crossing signal crest, and the ZVS signal is output to control the energy storage of the switching power supply transformer, providing conditions for the next step to achieve zero voltage or zero current startup of the main switching power tube of the switching power supply.

[0108] It should be noted that the ZVS signal controls the switching power supply to conduct after energy storage, reducing the voltage or current of the switching power supply's main switching power tube to zero, thereby achieving zero-voltage or zero-current startup. It is understood that the first zero-crossing signal "valley" sensed after the ZVS signal indicates that the voltage or current of the switching power supply's main switching power tube has dropped to zero. Therefore, this disclosure defines the first zero-crossing signal "valley" after the ZVS signal as the valley conduction signal QR indicating the turning-on of the switching power supply's main switching power tube.

[0109] In another embodiment, when the first zero-crossing signal Valley is not received, the output is used to put the switching power supply into a CCM (continuous mode) working mode; the clock signal CLK is obtained and the output is used to turn on the main switching power tube M0 of the switching power supply.

[0110] It should be noted that when the switching power supply does not receive the first zero-crossing signal Valley during the flyback completion resonance stage, the switching power supply does not have a zero crossing point and is in CCM (continuous mode) operation mode, and no harmonic valley conduction signal QR is output. Therefore, the clock signal CLK is output to start the main switching power tube M0 of the switching power supply and enter the next cycle.

[0111] In another embodiment, the specific steps of obtaining a ZVS signal of the first second zero-crossing signal crest after the clock signal CLK and outputting the signal to cause the switching power supply transformer to enter the energy storage stage include:

[0112] receiving the clock signal CLK;

[0113] Receiving the first second zero-crossing signal crest;

[0114] Obtaining a compensation voltage signal V or a compensation current signal I representing an input bus voltage Vin;

[0115] Outputting a pulse width-adjusted ZVS signal to cause the transformer switching power supply to enter an energy storage stage;

[0116] It should be noted that after the switching power supply receives the second zero-crossing signal crest, it will generate a ZVS signal with adjustable pulse width, and the pulse width adjustment of the ZVS signal is based on the compensation voltage signal V or compensation current signal I representing the input bus voltage Vin. Therefore, it is necessary to obtain the compensation voltage signal V or compensation current signal I representing the input bus voltage Vin.

[0117] It should be further explained that the purpose of pulse width modulation of the ZVS signal is to achieve zero voltage or zero current for different input bus voltages Vin. It is understood that the pulse width of the ZVS signal determines the energy storage of the transformer during the switching power supply's resonant phase, thereby determining whether the switching power supply's main switch, power transistor M0, can achieve zero voltage or zero current startup. Therefore, the present disclosure designs pulse width modulation of the ZVS signal.

[0118] It should be noted that the ZVS signal pulse width adjustment method is to receive the second zero-crossing signal crest to enable the ZVS signal adjustment function. Specifically, the compensation voltage signal V is received, and the compensation voltage signal V is used as the reference voltage Vref to obtain the charging duration of the preset current Ith, and the ZVS signal pulse width is adjusted based on the charging duration. Another method is to receive the compensation current signal I and use the compensation current signal I as the charging current to obtain the charging duration, and adjust the ZVS signal pulse width based on the charging duration.

[0119] In another embodiment, the specific steps of obtaining the first zero-crossing signal after the ZVS signal and outputting the signal to enable the secondary-side feedback switching power supply to achieve zero voltage start-up include:

[0120] Receiving the pulse width adjusted ZVS signal;

[0121] Obtaining the first zero-crossing signal valley after the pulse width adjusted ZVS signal;

[0122] The valley conduction signal QR is outputted to enable the main switch power tube of the switching power supply to achieve zero voltage turn-on.

[0123] It should be noted that the principle of this process has been explained in the above embodiment and will not be repeated here.

[0124] It can be seen that by applying the technical solution of the present application, the zero-voltage start-up function of the switching power supply is realized by combining the auxiliary winding of the secondary-side feedback switching power supply with the PMOS tube. Compared with the existing technology, the circuit is relatively simple and has fewer circuit components, which is conducive to reducing the size of the charger and adapter.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A zero voltage switching control circuit for a switching power supply, characterized in that: include: Transformer, starting circuit, forced resonant circuit, among which The transformer includes a primary winding, a secondary winding, and an auxiliary winding; The starting circuit includes a starting capacitor; The auxiliary winding, the first power switch of the PMOS structure and the starting capacitor form the forced resonant circuit, and the other end of the auxiliary winding is grounded; The first power switch is respectively connected to one end of the auxiliary winding, the starting capacitor and the first pin of the switching power management chip; The forced resonant circuit is used to generate a forced resonant voltage when the switching power supply completes flyback and is in discontinuous mode; The drain of the first power switch is connected to the auxiliary winding 1, and the source thereof is connected to the starting capacitor of the switching power supply; The first power switch gate is connected to the first pin of the switching power management chip.

2. A zero voltage switching control circuit for a switching power supply according to claim 1, characterized in that: The power management chip includes a mode judgment circuit, a zero voltage driving circuit, and a valley conduction circuit; The mode judgment circuit is connected to the auxiliary winding via the second pin of the power management chip, and is configured to generate the mode judgment signal when the second power switch outputs a low level; The output terminal of the zero voltage driving circuit is connected to the first pin, and is configured to generate a ZVS driving signal including a switching frequency to drive the first power switch when the switching power supply is in the discontinuous mode; A valley conduction circuit connected to the zero voltage drive circuit and the mode determination circuit is configured to generate a drive signal to the second power switch.

3. The zero voltage switching control circuit for a switching power supply according to claim 2, wherein: It also includes a bus voltage compensation circuit, wherein: The bus voltage compensation circuit is configured to generate a compensation voltage signal and / or a compensation current signal representing the input bus voltage, obtain the input bus voltage divided signal through the second pin of the power management chip, and obtain the compensation voltage signal and / or a compensation current signal representing the input bus voltage through the bus voltage compensation module.

4. A zero voltage switching control circuit for a switching power supply according to claim 2, characterized in that: It also includes a bus voltage compensation circuit, wherein: The bus voltage compensation circuit is configured to generate a compensation voltage signal and / or a compensation current signal representing the input bus voltage, obtain the input bus voltage divided signal through the sixth pin of the power management chip, and obtain the compensation voltage signal and / or a compensation current signal representing the input bus voltage through the bus voltage compensation module.

5. The zero voltage switching control circuit for a switching power supply according to claim 4, characterized in that: The mode judgment circuit includes a zero-crossing detection module, a mode judgment module, a main driving module and a logic control module; The zero-crossing detection module, the mode judgment module, the logic control module and the main driving module are connected in sequence, and the input end of the zero-crossing detection module is connected to the second pin of the power management chip, and the main driving module is connected to the sixth pin of the power management chip.

6. The zero voltage switching control circuit for a switching power supply according to claim 5, characterized in that: The zero voltage drive circuit includes a ZVS module and a ZVS drive module, wherein: The ZVS module and the ZVS driving module are connected in sequence, and the input end of the ZVS module is connected to the other output end of the zero-crossing detection module, and the output end of the ZVS driving module is connected to the first pin of the power management chip.

7. A zero voltage switching control circuit for a switching power supply according to claim 3, 4 or 5, characterized in that: The ZVS module includes a capacitor and a preset voltage value and / or a preset current value; The switching frequency modulation mode of the first power switch includes any one of the following modes or any combination thereof: When the bus voltage compensation circuit receives an input bus voltage divided voltage signal and outputs a compensation voltage signal of the bus voltage, the ZVS module uses the compensation voltage signal as a reference voltage signal and charges the capacitor with the preset current to reach the reference voltage; When the bus voltage compensation circuit receives an input bus voltage divided voltage signal and outputs a bus voltage compensation current signal, the ZVS module uses the compensation current signal as the capacitor charging current to charge the capacitor to reach a preset voltage value.

8. A zero voltage switching control circuit for a switching power supply according to claim 7, characterized in that The valley conduction circuit includes a clock module and a valley conduction module, wherein the clock module is respectively connected to the ZVS module, the valley conduction module and the logic control module, and the valley conduction module is respectively connected to the zero-crossing detection module, the mode judgment module, the logic judgment module and the ZVS module.

9. The zero voltage switching control circuit for a switching power supply according to claim 8, characterized in that: When the switching power supply completes flyback and is in discontinuous mode, the falling edge zero-crossing signal of the auxiliary winding sensed by the zero-crossing detection module is a first zero-crossing signal; When the switching power supply completes flyback and is in the discontinuous mode, the rising edge zero-crossing signal of the auxiliary winding sensed by the zero-crossing detection module is a second zero-crossing signal.

10. The zero voltage switching control circuit for a switching power supply according to claim 8, characterized in that: After the switching power supply completes flyback and the first power switch is turned off in the discontinuous mode, the first zero-crossing signal obtained by the valley conduction module after receiving the clock signal generated by the clock module is the valley conduction signal.

11. A zero voltage switching control method for a switching power supply, used in the zero voltage switching control circuit according to any one of claims 1 to 10, wherein the switching power supply comprises a main switching power tube and a transformer, characterized in that: The method comprises: receiving a first zero-crossing signal and outputting a signal to put the switching power supply into a DCM operating mode; Obtaining a ZVS signal generated by the first second zero-crossing signal after the clock signal, and outputting the signal to cause the switching power supply transformer to enter an energy storage stage; The first zero-crossing signal after the ZVS signal is obtained and outputted so that the main switch power tube of the switching power supply can be turned on with zero voltage and or zero current.

12. The zero voltage switching control method for a switching power supply according to claim 11, characterized in that: When the first zero-crossing signal is not received, outputting a signal to put the switching power supply into a CCM operating mode; The clock signal is obtained and output to turn on the main switch power tube of the switching power supply.

13. The zero voltage switching control method for a switching power supply according to claim 11, wherein: The specific steps of obtaining the ZVS signal of the first second zero-crossing signal after the clock signal and outputting it to make the switching power supply transformer enter the energy storage stage include: receiving the clock signal; receiving the first second zero-crossing signal; Obtaining a compensation voltage signal and / or a compensation current signal representing an input bus voltage; The ZVS signal after pulse width adjustment is outputted to make the switching power supply transformer enter the energy storage stage.

14. The zero voltage switching control method for a switching power supply according to claim 11, wherein: The specific steps of outputting the first zero-crossing signal after the ZVS signal so that the main switch power tube of the switching power supply can achieve zero voltage turn-on include: Receive the ZVS signal after pulse width adjustment; receiving a first zero-crossing signal after receiving the pulse-width-adjusted ZVS signal; Output valley conduction signal to enable the main switch power tube of the switching power supply to achieve zero voltage turn-on.

15. The zero voltage switching control method for a switching power supply according to claim 13, wherein: After obtaining the compensation voltage signal or compensation current signal representing the input bus voltage, the method further includes: Receive the supplementary voltage signal, and use the compensation voltage signal as a reference voltage to obtain a preset current charging time, and adjust the ZVS signal pulse width according to the charging time; The compensation current signal is received, and the charging current is used as the compensation current signal to obtain the charging time, and the ZVS signal pulse width is adjusted according to the charging time.

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