Switch control circuit, switch control method thereof and switch power supply

Abstract

The invention provides a switching control circuit, a switching control method thereof and a switching power supply. The switch control circuit comprises a sampling circuit, a comparison circuit and a driving circuit. The sampling circuit is used for being coupled with a secondary side switch tube and is used for obtaining a sampling signal representing drain-source voltage of the secondary side switch tube. The comparison circuit is coupled to the sampling circuit and is used for generating a comparison signal according to the sampling signal and a reference signal. The input end of the driving circuit is coupled with the comparison circuit, and the driving circuit is used for generating a secondary side driving signal to drive the secondary side switching tube. The secondary side driving signal comprises a first driving pulse and a second driving pulse, and the second driving pulse is a driving pulse set after secondary side follow current is finished. And the driving circuit adjusts the pulse width of the second driving pulse according to a comparison signal under a preset condition after the second driving pulse is ended. According to the switch control circuit, the switch control method thereof and the switch power supply provided by the invention, better zero-voltage switching-on can be adaptively realized for different systems.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics, relates to a switching power supply technology, and in particular to a switching control circuit and a switching control method thereof, and a switching power supply. Background Art

[0002] Synchronous rectification technology is a technology that uses metal oxide semiconductor field effect transistors (MOSFETs) to replace rectifier diodes to reduce rectification losses. It has been widely used in industrial power supplies, consumer electronics and other fields. As the frequency of flyback switching power supplies increases and the size decreases, synchronous rectifiers SR that simply reduce secondary side rectification losses are increasingly unable to meet system application requirements. Realizing zero voltage switching (ZVS) on the primary side has become a key technical area of ​​concern. In order to achieve such Figure 1 There are three common methods for ZVS opening of the primary control circuit shown in the figure, namely, adding an additional control algorithm to the primary control circuit, adding an additional control algorithm to the secondary control circuit, or adding an additional auxiliary circuit to realize ZVS opening of the primary control circuit. Among them, the method of realizing ZVS opening of the primary control circuit by adding an additional control algorithm to the secondary control circuit has attracted much attention due to its simplicity and low cost. However, the existing circuit implementation method still cannot achieve a good ZVS opening effect.

[0003] In view of this, it is necessary to provide a new structure or control method to solve at least part of the above problems. Summary of the invention

[0004] In view of one or more problems in the prior art, the present invention provides a switch control circuit and a switch control method thereof and a switch power supply.

[0005] According to one aspect of the present invention, a switch control circuit is disclosed, the switch control circuit comprising:

[0006] A sampling circuit, whose input end is coupled to the secondary-side switch tube, and is used to obtain a sampling signal representing the drain-source voltage of the secondary-side switch tube;

[0007] A comparison circuit, a first input terminal of which is coupled to the sampling circuit, for generating a comparison signal according to the sampling signal and the reference signal; and

[0008] A driving circuit, whose input end is coupled to the output end of the comparison circuit, is used to generate a secondary side driving signal to drive the secondary side switch tube, the secondary side driving signal includes a first driving pulse and a second driving pulse, the second driving pulse is a driving pulse set after the secondary side freewheeling ends; the driving circuit adjusts the pulse width of the second driving pulse according to the comparison signal at the preset condition after the second driving pulse ends, when the sampling signal is less than the reference signal, the pulse width of the second driving pulse in the next switching cycle is increased, and when the sampling signal is greater than the reference signal, the pulse width of the second driving pulse in the next switching cycle is reduced.

[0009] In one embodiment, the driving circuit is used to adjust the pulse width of the second driving pulse according to a comparison signal obtained at a preset time after the second driving pulse ends.

[0010] In one embodiment, the driving circuit is used to adjust the pulse width of the second driving pulse according to a comparison signal obtained when the rising edge of the sampling signal arrives after the second driving pulse ends.

[0011] In one embodiment, the switch control circuit includes a reference signal generating circuit, wherein the reference signal generating circuit is used to generate a reference signal according to a bus voltage and an output voltage, or the reference signal generating circuit is used to generate a reference signal according to a high voltage input voltage and a preset voltage.

[0012] In one embodiment, the driving circuit comprises:

[0013] A timing circuit, whose input terminal receives the second driving pulse, is used to start timing at the falling edge of the second driving pulse and output a first level after a set time period;

[0014] A trigger circuit, a set terminal of which receives a first driving pulse, and a reset terminal of which is coupled to an output terminal of the comparison circuit;

[0015] A first NOT gate, an input terminal of which is coupled to an output terminal of the timing circuit;

[0016] A D flip-flop, a data input terminal of which is coupled to the second output terminal of the trigger circuit, and a clock signal input terminal of which is coupled to the output terminal of the first NOT gate; and

[0017] The pulse width control circuit has an input terminal coupled to the D flip-flop and is used to adjust the pulse width of the second driving pulse according to a negation signal of an output signal of the D flip-flop.

[0018] In one embodiment, the driving circuit comprises:

[0019] A rising edge detection circuit, whose input terminal receives the second driving pulse, is used to output a first level after the falling edge moment of the second driving pulse and when the rising edge moment of the sampling signal arrives;

[0020] A trigger circuit, a set terminal of which receives a first driving pulse, and a reset terminal of which is coupled to an output terminal of the comparison circuit;

[0021] A first NOT gate, an input end of which is coupled to the output end of the rising edge detection circuit;

[0022] A D flip-flop, a data input terminal of which is coupled to the second output terminal of the trigger circuit, and a clock signal input terminal of which is coupled to the output terminal of the first NOT gate; and

[0023] The pulse width control circuit has an input terminal coupled to the D flip-flop and is used to adjust the pulse width of the second driving pulse according to a negation signal of an output signal of the D flip-flop.

[0024] In one embodiment, the driving circuit includes a slope detection circuit, and the slope detection circuit is used to obtain the rising edge time of the sampling signal according to the change rate of the sampling signal.

[0025] According to another aspect of the present invention, a switching power supply is disclosed. The switching power supply includes a primary circuit, a secondary circuit and a transformer. The secondary circuit includes the switch control circuit as described in any one of the above items.

[0026] According to another aspect of the present invention, a switch control method is disclosed. The switch control method is used to control a switch control circuit. The switch control method includes:

[0027] Obtaining a sampling signal representing the drain-source voltage of the secondary-side switch tube;

[0028] generating a comparison signal according to the sampled signal and the reference signal; and

[0029] A secondary drive signal is generated according to the comparison signal to drive the secondary side switch tube, the secondary drive signal includes a first drive pulse and a second drive pulse, the second drive pulse is a drive pulse set after the secondary side freewheeling ends; the pulse width of the second drive pulse is adjusted according to the comparison signal at the preset condition after the second drive pulse ends, when the sampling signal is less than the reference signal, the pulse width of the second drive pulse in the next switching cycle is increased, and when the sampling signal is greater than the reference signal, the pulse width of the second drive pulse in the next switching cycle is reduced.

[0030] In one embodiment, the step of adjusting the pulse width of the second driving pulse according to the comparison signal at the preset condition after the second driving pulse ends includes: adjusting the pulse width of the second driving pulse according to the comparison signal obtained at a preset time after the second driving pulse ends.

[0031] In one embodiment, the step of adjusting the pulse width of the second drive pulse according to the comparison signal at the preset condition after the second drive pulse ends includes: adjusting the pulse width of the second drive pulse according to the comparison signal obtained when the rising edge moment of the sampling signal arrives after the second drive pulse ends.

[0032] In one embodiment, the switch control method further includes: generating a reference signal according to the bus voltage and the output voltage, or generating a reference signal according to the high voltage input voltage and a preset voltage.

[0033] The present invention proposes a switch control circuit and a switch control method thereof and a switch power supply, wherein the switch control circuit includes a sampling circuit, a comparison circuit and a drive circuit. The input end of the sampling circuit is used to couple the secondary switch tube, and the sampling circuit is used to obtain a sampling signal representing the drain-source voltage of the secondary switch tube. The first input end of the comparison circuit is coupled to the sampling circuit, and the comparison circuit is used to generate a comparison signal according to the sampling signal and the reference signal. The input end of the drive circuit is coupled to the output end of the comparison circuit, and the drive circuit is used to generate a secondary drive signal to drive the secondary switch tube. The secondary drive signal includes a first drive pulse and a second drive pulse, and the second drive pulse is a drive pulse set after the secondary freewheeling ends. The drive circuit adjusts the pulse width of the second drive pulse according to the comparison signal at a preset condition after the second drive pulse ends. When the sampling signal is less than the reference signal, the drive circuit increases the pulse width of the second drive pulse in the next switching cycle. When the sampling signal is greater than the reference signal, the drive circuit reduces the pulse width of the second drive pulse in the next switching cycle. The switch control circuit and the switch control method thereof and the switch power supply proposed by the present invention can adaptively achieve better zero voltage turn-on effect for different power supply systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings are used to provide a further understanding of the present invention and are used together with the description to explain the embodiments of the present invention, but do not constitute a limitation of the present invention. In the accompanying drawings:

[0035] Figure 1 A schematic diagram of the circuit structure of a flyback switching power supply in the prior art is shown;

[0036] Figure 2 A schematic diagram of the circuit structure of a switch control circuit according to an embodiment of the present invention is shown;

[0037] Figure 3 A schematic diagram of the circuit structure of a switch control circuit according to another embodiment of the present invention is shown;

[0038] Figure 4 A schematic diagram of signal waveforms of a switch control circuit according to another embodiment of the present invention is shown;

[0039] Figure 5 A schematic diagram of the circuit structure of a switch control circuit according to another embodiment of the present invention is shown;

[0040] Figure 6A signal waveform diagram of a switch control circuit according to yet another embodiment of the present invention is shown. DETAILED DESCRIPTION

[0041] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0042] The description in this section is only for several typical embodiments, and the present invention is not limited to the scope of the embodiments. The combination of different embodiments, the mutual replacement of some technical features in different embodiments, and the mutual replacement of the same or similar prior art means with some technical features in the embodiments are also within the scope of the description and protection of the present invention.

[0043] "Coupled" or "connected" in the specification includes both direct connection and indirect connection. Indirect connection is a connection through an intermediate medium, such as a connection through an electrically conductive medium such as a conductor, wherein the electrically conductive medium may contain parasitic inductance or parasitic capacitance, or a connection through an intermediate circuit or component described in the embodiments in the specification; an indirect connection may also include a connection through other active or passive devices on the basis of achieving the same or similar functions, such as a connection through circuits or components such as switches, signal amplification circuits, and follower circuits. "Multiple" or "many" means two or more. In addition, in the present invention, words such as first and second are mainly used to distinguish one technical feature from another technical feature, and do not necessarily require or imply that there is a certain actual relationship or order between these technical features.

[0044] like Figure 2 As shown, one embodiment of the present invention discloses a switch control circuit, which includes a sampling circuit 10, a comparison circuit 20 and a drive circuit 30. The input end of the sampling circuit 10 is used to couple the secondary side switch tube, and the sampling circuit 10 is used to obtain a sampling signal representing the drain-source voltage of the secondary side switch tube. The sampling signal is equal to the drain-source voltage of the secondary side switch tube, or the sampling signal is obtained by calculating the drain-source voltage of the secondary side switch tube. The secondary side switch tube can be built-in or external to the secondary side control circuit. The first input end of the comparison circuit 20 is coupled to the output end of the sampling circuit 10, and the comparison circuit 20 is used to compare the sampling signal and the reference signal to generate a comparison signal. The input end of the drive circuit 30 is coupled to the output end of the comparison circuit 20, and the drive circuit 30 is used to generate a secondary side drive signal to drive the secondary side switch tube, thereby controlling the switching state of the secondary side switch tube. The secondary side drive signal includes a first drive pulse and a second drive pulse. Combined Figure 4It can be seen from the t1-t2 time period that in the same switching cycle, the first drive pulse PWM_Pulse is in front and the second drive pulse ZVS_pulse is in the back. As a prior art, the first drive pulse is used to control the secondary side freewheeling process. The second drive pulse is a drive pulse set after the secondary side freewheeling ends. The drive circuit 30 adjusts the pulse width of the second drive pulse according to the comparison signal after the second drive pulse ends and meets the preset conditions. Specifically, when the sampling signal is less than the reference signal, the drive circuit 30 controls to increase the pulse width of the second drive pulse in the next switching cycle. When the sampling signal is greater than the reference signal, the drive circuit 30 controls to reduce the pulse width of the second drive pulse in the next switching cycle.

[0045] like Figure 3As shown, an embodiment of the present invention discloses a switch control circuit, which includes a sampling circuit, a comparison circuit 21 and a drive circuit 31. The comparison circuit 21 includes a comparator, the non-inverting input terminal of the comparator receives a sampling signal, and the inverting input terminal of the comparator receives a reference signal. The sampling signal is the drain-source voltage Vds_s of the secondary switch tube. The reference signal is k*HV, k is an arbitrary value selected from 0 to 1, and HV is the high voltage input voltage. Among them, HV=Vbus / n+Vout, Vbus is the bus voltage, n is the turns ratio of the primary and secondary coils of the transformer, and Vout is the output voltage of the switching power supply. The drive circuit 31 includes a timing circuit, a trigger circuit, a first NOT gate, a D trigger, a second NOT gate and a pulse width control circuit. The input terminal of the timing circuit receives the second drive pulse, and the timing circuit is used to start timing at the falling edge of the second drive pulse, and output the first level after the set time Tref. The trigger circuit includes an RS trigger, the set terminal of the RS trigger receives the first drive pulse PWM_Pulse, and the reset terminal of the RS trigger is coupled to the output terminal of the comparison circuit. The input end of the first NOT gate is coupled to the output end of the timing circuit. The data input end D of the D flip-flop is coupled to the second output end QN of the trigger circuit, and the clock signal input end C of the D flip-flop is coupled to the output end of the first NOT gate. The input end of the second NOT gate is coupled to the first output end Q of the D flip-flop. The input end of the pulse width control circuit is coupled to the output end of the second NOT gate, and the pulse width control circuit is used to adjust the pulse width of the second drive pulse according to the negation signal UP of the output signal of the D flip-flop. The negation signal UP is at a first level (for example, UP is a high level), indicating that the current switching cycle has not achieved the expected ZVS effect, so the ZVS_Pulse pulse width of the next switching cycle needs to be further increased, that is, the ZVS_Pulse pulse width needs to be increased. The negation signal UP is at a second level (for example, UP is a low level), indicating that the current switching cycle has exceeded the expected ZVS effect, and the pulse width of ZVS_Pulse is reduced in the next switching cycle. The above judgment logic continues after the falling edge of ZVS_Pulse in the next switching cycle. After multiple switching cycles, the expected ZVS effect can be achieved, that is, at the time Tref delayed after the falling edge of ZVS_Pulse, Vds_s is approximately equal to k*HV. Figure 3 The ZVS_Pulse_min shown in is a preset minimum pulse width value for the second driving pulse ZVS_Pulse. In another embodiment, the driving circuit 31 further includes a time length configuration circuit, which is used to configure and generate a set time length Tref.

[0046] The secondary side control circuit includes a switch control circuit, combined with Figure 3 and Figure 4, the switch control circuit inserts a second drive pulse ZVS_pulse at an appropriate position after the secondary side freewheeling ends. The second drive pulse ZVS_pulse causes the output voltage Vout of the switching power supply to reversely excite the transformer, increasing the resonance strength of the power supply system. Therefore, at the moment of valley opening of the primary circuit, due to the enhanced resonance, the drain-source voltage Vds_p of the primary switch tube can be at a lower value, even close to 0V, so the zero voltage opening of the primary circuit can be achieved. Figure 4 The t0-t1 period is shown as a control waveform. In this period, there is no second drive pulse ZVS_pulse, and the resonance of the power supply system is not additionally strengthened. When the primary side is turned on at the bottom of the valley, the drain-source voltage Vds_p of the primary switch tube is still at a high value, and the switching loss at high frequency is still large. Figure 4 As shown in the t1-t2 time period of FIG, a second driving pulse ZVS_pulse is provided in this time period, and the resonance of the power supply system is additionally strengthened, and the drain-source voltage Vds_p of the primary switch tube is reduced when the primary side valley is turned on. However, since the pulse width of the second driving pulse ZVS_pulse is relatively narrow, the degree of strengthening of the resonance is not enough, so the true zero voltage turn-on is not achieved when the primary side valley is turned on. Figure 4 As shown in the t2-t3 time period, the pulse width of the second drive pulse ZVS_pulse increases, the resonance of the power supply system is further strengthened, and the drain-source voltage Vds_p of the primary switch tube is further reduced when the primary side is turned on at the bottom of the valley and is close to 0V. The primary circuit can achieve better zero-voltage turn-on. Figure 4 In the figure, Isd is the current flowing through the secondary switch tube, and Ilm is the current flowing through the primary inductor.

[0047] According to the characteristics of circuit resonance, the pulse width of the second drive pulse ZVS_Pulse determines the magnitude of the reverse excitation current injected into the transformer by the power supply output end, and the magnitude of the reverse excitation current determines the resonance strength of the power supply system. For the primary control circuit that is turned on at the bottom of the valley, the greater the resonance strength of the power supply system, the lower the Vds_p voltage at the time of the primary turn-on, that is, the ZVS effect can be achieved. Under the control of the second drive pulse ZVS_Pulse with a suitable pulse width, the Vds_p voltage is lower when the primary is turned on. However, the pulse width of the second drive pulse ZVS_Pulse corresponding to different power supply system parameters is also different, and setting a fixed second drive pulse ZVS_Pulse pulse width cannot achieve a good ZVS effect. The present invention can adaptively adjust the pulse width of the second drive pulse ZVS_Pulse for different power supply systems, and can achieve a better zero voltage turn-on effect.

[0048] like Figure 5As shown, an embodiment of the present invention discloses a switch control circuit, which includes a sampling circuit, a comparison circuit 22 and a drive circuit 32. The comparison circuit 22 includes an adder and a comparator 221, wherein the first input terminal of the adder receives a sampling signal, the second input terminal of the adder receives a configuration voltage Vref, and the output terminal of the adder outputs an addition signal. The non-inverting input terminal of the comparator is coupled to the output terminal of the adder, and the inverting input terminal of the comparator receives a high-voltage input signal HV. The sampling signal is the drain-source voltage Vds_s of the secondary switch tube. The input terminal of the rising edge detection circuit receives the second drive pulse ZVS_pulse, and the rising edge detection circuit is used to output a first level after the falling edge moment of the second drive pulse ZVS_pulse and when the rising edge moment of the sampling signal arrives. The trigger circuit includes an RS trigger, the set terminal of the RS trigger receives the first drive pulse PWM_Pulse, and the reset terminal of the RS trigger is coupled to the output terminal of the comparison circuit. The input terminal of the first NOT gate is coupled to the output terminal of the rising edge detection circuit. The data input terminal D of the D flip-flop is coupled to the second output terminal QN of the trigger circuit, and the clock signal input terminal C of the D flip-flop is coupled to the output terminal of the first NOT gate. The input terminal of the second NOT gate is coupled to the first output terminal Q of the D flip-flop. The input terminal of the pulse width control circuit is coupled to the output terminal of the second NOT gate, and the pulse width control circuit is used to adjust the pulse width of the second driving pulse according to the NOT signal UP of the output signal of the D flip-flop.

[0049] Combination Figure 5-6 It can be seen that the actual reference signal corresponding to the sampling signal is HV-Vref, where HV=Vbus / n+Vout, HV is the high voltage input voltage, Vbus is the bus voltage, n is the turns ratio of the primary and secondary coils of the transformer, and Vout is the output voltage of the switching power supply. Figure 6 As shown in the t1-t2 time period of FIG. 1 , a second drive pulse ZVS_pulse is provided in the t1-t2 time period, and the resonance of the power supply system is further enhanced. When the primary side valley is turned on, the drain-source voltage Vds_p of the primary side switch tube is reduced. However, since the pulse width of the second drive pulse ZVS_pulse is relatively narrow, the degree of resonance enhancement is not enough, so the true zero voltage turn-on is not achieved when the primary side valley is turned on. Figure 6As shown in the t2-t3 time period, the pulse width of the second drive pulse ZVS_pulse increases, the resonance of the power supply system is further strengthened, and the drain-source voltage Vds_p of the primary switch tube is close to 0V when the primary side is turned on at the bottom of the valley, and the primary circuit can achieve better zero voltage turn-on. Specifically, in the t1-t2 time period, at the starting moment of the rising edge of the sampling signal Vds_s, the sampling signal Vds_s is less than HV-Vref, and the UP terminal remains at the first level (e.g., a high level). Then the pulse width of the ZVS_Pulse in the next switching cycle continues to increase until the ZVS effect of the t2-t3 time period is achieved after several switching cycles, that is, at the rising edge of the sampling signal Vds_s, the sampling signal Vds_s is approximately equal to HV-Vref.

[0050] In one embodiment, the switch control circuit includes a reference signal generating circuit, and the reference signal generating circuit is used to generate a reference signal according to the bus voltage and the output voltage. In another embodiment, the reference signal generating circuit is used to generate a reference signal according to the high voltage input voltage and the preset voltage. The above reference signals are preferred embodiments of the present invention, and those skilled in the art may select other suitable reference signals according to the specific switching power supply requirements. In another embodiment, the drive circuit includes a slope detection circuit, and the slope detection circuit is used to obtain the rising edge moment of the sampling signal according to the rate of change of the sampling signal.

[0051] Another embodiment of the present invention further discloses a switching power supply, which includes a primary circuit, a secondary circuit and a transformer. The secondary circuit includes a switching control circuit as described in any of the above items. The switching control circuit is used to control the switching state of the secondary switch tube to enable the primary circuit to achieve zero voltage switching.

[0052] Another embodiment of the present invention further discloses a switch control method, which is used to control a switch control circuit. The switch control method includes:

[0053] Step S01: obtaining a sampling signal representing the drain-source voltage of the secondary-side switch tube;

[0054] Step S02: generating a comparison signal according to the sampling signal and the reference signal; and

[0055] Step S03: Generate a secondary drive signal according to the comparison signal to drive the secondary switch tube, the secondary drive signal includes a first drive pulse and a second drive pulse, the second drive pulse is a drive pulse set after the secondary freewheeling ends; adjust the pulse width of the second drive pulse according to the comparison signal at the preset condition after the second drive pulse ends, when the sampling signal is less than the reference signal, increase the pulse width of the second drive pulse in the next switching cycle, and when the sampling signal is greater than the reference signal, reduce the pulse width of the second drive pulse in the next switching cycle.

[0056] In a specific embodiment, the switch control circuit includes a sampling circuit, a comparison circuit and a drive circuit. The sampling circuit obtains a sampling signal representing the drain-source voltage of the secondary switch tube. The comparison circuit generates a comparison signal according to the sampling signal and a reference signal. The drive circuit generates a secondary drive signal according to the comparison signal to drive the secondary switch tube, and the secondary drive signal includes a first drive pulse and a second drive pulse, and the second drive pulse is a drive pulse set after the secondary freewheeling ends. The drive circuit adjusts the pulse width of the second drive pulse according to the comparison signal at a preset condition after the second drive pulse ends. When the sampling signal is less than the reference signal, the drive circuit controls to increase the pulse width of the second drive pulse in the next switching cycle. When the sampling signal is greater than the reference signal, the drive circuit controls to reduce the pulse width of the second drive pulse in the next switching cycle.

[0057] In one embodiment, the step of adjusting the pulse width of the second driving pulse according to the comparison signal at a preset condition after the second driving pulse ends specifically includes: the driving circuit adjusts the pulse width of the second driving pulse according to the comparison signal obtained at a preset time after the second driving pulse ends.

[0058] In another embodiment, the step of adjusting the pulse width of the second drive pulse according to the comparison signal at the preset condition after the second drive pulse ends includes: the drive circuit adjusts the pulse width of the second drive pulse according to the comparison signal obtained when the rising edge of the sampling signal arrives after the second drive pulse ends.

[0059] In one embodiment, the switch control method further includes: generating a reference signal according to the bus voltage and the output voltage, or generating a reference signal according to the high voltage input voltage and a preset voltage.

[0060] Those skilled in the art should know that the logic controls such as "high level" and "low level", "set" and "reset", "AND gate" and "OR gate", "non-inverting input terminal" and "inverting input terminal" in the logic controls involved in the specification or drawings can be interchanged or changed with each other, and the same function or purpose as the above embodiment can be achieved by adjusting the subsequent logic controls.

[0061] The description and application of the present invention here are illustrative, and it is not intended to limit the scope of the present invention to the above-mentioned embodiments. The effects or advantages involved in the specification may not be reflected in the actual experimental examples due to the uncertainty of specific condition parameters or other factors, and the effects or advantages are not used to limit the scope of the invention. The deformation and change of the embodiments disclosed here are possible, and the replacement of the embodiments and the various equivalent parts are well known to those of ordinary skill in the art. It should be clear to those skilled in the art that the present invention can be implemented in other forms, structures, arrangements, proportions, and with other components, materials and parts without departing from the spirit or essential features of the present invention. Other deformations and changes can be made to the embodiments disclosed here without departing from the scope and spirit of the present invention.

Claims

1. A switch control circuit, characterized in that: The switch control circuit comprises: A sampling circuit, whose input end is coupled to the secondary-side switch tube, and is used to obtain a sampling signal representing the drain-source voltage of the secondary-side switch tube; A comparison circuit, a first input terminal of which is coupled to the sampling circuit, for generating a comparison signal according to the sampling signal and the reference signal; and A driving circuit, whose input end is coupled to the output end of the comparison circuit, is used to generate a secondary side driving signal to drive the secondary side switch tube, the secondary side driving signal includes a first driving pulse and a second driving pulse, the second driving pulse is a driving pulse set after the secondary side freewheeling ends; the driving circuit adjusts the pulse width of the second driving pulse according to the comparison signal at the preset condition after the second driving pulse ends, when the sampling signal is less than the reference signal, the pulse width of the second driving pulse in the next switching cycle is increased, and when the sampling signal is greater than the reference signal, the pulse width of the second driving pulse in the next switching cycle is reduced.

2. The switch control circuit according to claim 1, characterized in that: The driving circuit is used for adjusting the pulse width of the second driving pulse according to a comparison signal obtained at a preset time after the second driving pulse ends.

3. The switch control circuit according to claim 1, characterized in that: The driving circuit is used for adjusting the pulse width of the second driving pulse according to the comparison signal obtained when the rising edge of the sampling signal arrives after the second driving pulse ends.

4. The switch control circuit according to claim 1, characterized in that: The switch control circuit includes a reference signal generating circuit, wherein the reference signal generating circuit is used to generate a reference signal according to a bus voltage and an output voltage, or the reference signal generating circuit is used to generate a reference signal according to a high voltage input voltage and a preset voltage.

5. The switch control circuit according to claim 1, characterized in that: The drive circuit includes: A timing circuit, whose input terminal receives the second driving pulse, is used to start timing at the falling edge of the second driving pulse and output a first level after a set time period; A trigger circuit, a set terminal of which receives a first driving pulse, and a reset terminal of which is coupled to an output terminal of the comparison circuit; A first NOT gate, an input terminal of which is coupled to an output terminal of the timing circuit; A D flip-flop, a data input terminal of which is coupled to the second output terminal of the trigger circuit, and a clock signal input terminal of which is coupled to the output terminal of the first NOT gate; and The pulse width control circuit has an input terminal coupled to the D flip-flop and is used to adjust the pulse width of the second driving pulse according to a negation signal of an output signal of the D flip-flop.

6. The switch control circuit according to claim 1, characterized in that: The drive circuit includes: A rising edge detection circuit, whose input terminal receives the second driving pulse, is used to output a first level after the falling edge moment of the second driving pulse and when the rising edge moment of the sampling signal arrives; A trigger circuit, a set terminal of which receives a first driving pulse, and a reset terminal of which is coupled to an output terminal of the comparison circuit; A first NOT gate, an input end of which is coupled to the output end of the rising edge detection circuit; A D flip-flop, a data input terminal of which is coupled to the second output terminal of the trigger circuit, and a clock signal input terminal of which is coupled to the output terminal of the first NOT gate; and The pulse width control circuit has an input terminal coupled to the D flip-flop and is used to adjust the pulse width of the second driving pulse according to a negation signal of an output signal of the D flip-flop.

7. The switch control circuit according to claim 3, characterized in that: The driving circuit includes a slope detection circuit, and the slope detection circuit is used to obtain the rising edge time of the sampling signal according to the change rate of the sampling signal.

8. A switching power supply, characterized in that: The switching power supply comprises a primary circuit, a secondary circuit and a transformer, and the secondary circuit comprises the switching control circuit according to any one of claims 1 to 7.

9. A switch control method for controlling a switch control circuit, characterized in that: The switch control method comprises: Obtaining a sampling signal representing the drain-source voltage of the secondary-side switch tube; generating a comparison signal according to the sampled signal and the reference signal; and A secondary drive signal is generated according to the comparison signal to drive the secondary side switch tube, the secondary drive signal includes a first drive pulse and a second drive pulse, the second drive pulse is a drive pulse set after the secondary side freewheeling ends; the pulse width of the second drive pulse is adjusted according to the comparison signal under the preset condition after the second drive pulse ends, when the sampling signal is less than the reference signal, the pulse width of the second drive pulse in the next switching cycle is increased, and when the sampling signal is greater than the reference signal, the pulse width of the second drive pulse in the next switching cycle is reduced.

10. The switch control method according to claim 9, characterized in that: The step of adjusting the pulse width of the second driving pulse according to the comparison signal at the preset condition after the second driving pulse ends includes: adjusting the pulse width of the second driving pulse according to the comparison signal obtained at a preset time after the second driving pulse ends.

11. The switch control method according to claim 9, characterized in that: The step of adjusting the pulse width of the second driving pulse according to the comparison signal at the preset condition after the second driving pulse ends includes: adjusting the pulse width of the second driving pulse according to the comparison signal obtained when the rising edge moment of the sampling signal arrives after the second driving pulse ends.

12. The switch control method according to claim 9, characterized in that: The switch control method further includes: generating a reference signal according to the bus voltage and the output voltage, or generating a reference signal according to the high voltage input voltage and a preset voltage.

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