A switching power supply converter circuit

Abstract

The application discloses a switching power supply converter circuit, which comprises a flyback converter, a stress limiting circuit and a control circuit; the flyback converter comprises a main power transformer, an input capacitor, a main switch tube, a rectifier switch tube and an output capacitor; the stress limiting circuit is connected in parallel with a secondary winding; the stress limiting circuit comprises a first clamping switch tube and a first clamping capacitor, and the first clamping switch tube and the first clamping capacitor are connected in series; the control circuit is provided with a feedback signal input end, a Vd voltage input end, a main switch tube control signal output end and a first clamping switch tube control signal output end; the feedback signal input end collects a voltage signal of an output end of the flyback converter; and the Vd voltage input end collects a voltage signal of one end of the rectifier switch tube connected with the secondary winding. The application can prevent the first clamping switch tube and the rectifier switch tube from being commonly used, and ensure the reliability of the system on the basis of clamping the stress of the rectifier switch tube.

Description

TECHNICAL FIELD

[0001] The present application relates to a switching power supply, in particular to a switching power supply converter circuit. BACKGROUND

[0002] With the rapid development of power electronics technology, switching power supply is developing towards high miniaturization and high power density. In order to improve the power density of the switching power supply, increasing the working frequency is a feasible method. However, with the increase of the switching frequency of the switching power supply, the loss of the internal switching device will also increase greatly. At the same time, with the increase of the switching frequency, the influence of the parasitic parameters in the switching power supply system is becoming more and more great. At the moment of switching action, the energy charging and discharging of the reactance element will cause the switching tube to withstand a large voltage stress and current stress, and often form an overvoltage condition. In order to solve this problem, it is often necessary to select a switching device with higher voltage resistance, which increases the cost and the risk of system reliability. Therefore, in the switching power supply system, it is often necessary to set a stress absorption circuit at the switching tube to limit the stress of the switching tube and improve the reliability of the system.

[0003] In the field of power electronics engineering, there are usually the following methods to solve the stress of the secondary side rectifier switching tube: parallel RC circuit is connected at both ends of the secondary side rectifier switching tube, and the voltage stress is absorbed by the RC circuit, which is suitable for the case of small voltage stress; in the case of large stress, the RC absorption circuit has large loss and cannot meet the system application, and RCD absorption is usually used, which can meet the occasion of slightly larger stress, but this is also a lossy stress absorption method, which has a certain influence on the efficiency of the system.

[0004] In the case of higher stress, the conventional stress limiting method cannot meet the application of the system. Patent No. CN208424210U proposes a DC-DC converter, which adopts a stress limiting circuit, as shown in Figure 1 The circuit principle diagram of the above patent is shown in Figure 2The driving timing diagram of the circuit of the above patent is shown, the stress of the two ends of the secondary side rectifier tube is limited by adopting the stress clamping circuit composed of the parallel switch tube and the clamping capacitor on the secondary side winding, when the main switch tube is turned on, the secondary side rectifier switch tube is connected in parallel through the clamping tube body diode, thereby limiting the voltage across the secondary side rectifier switch tube. With the turn-on of the clamping switch tube, the voltage stored on the clamping capacitor is transmitted to the primary side of the transformer, and the input is discharged. In this way, the lossless absorption of the voltage stress of the secondary side rectifier switch tube is realized. However, the circuit proposed in this patent also has the problem that the clamping switch tube discharges the primary side when the main switch tube is turned on, which seriously affects the detection of the primary side inductor current, especially when the system works in a lighter load and is in DCM mode, the turn-on time of the clamping switch tube is comparable to that of the main switch tube, which has a greater impact on the sampling of the primary side inductor current. And because the turn-on delay between the clamping switch tube and the main switch tube is fixed, it may cause the secondary side clamping switch tube and the secondary side rectifier switch tube to be common, causing the switch tube to be damaged. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a switching power supply converter circuit which can prevent the first clamping switch tube and the rectifier switch tube from being common, and can reduce the influence of the turn-on of the first clamping switch tube on the peak current sampling of the primary side circuit, and ensure the reliability of the system on the basis of clamping the stress of the rectifier switch tube.

[0006] To solve the above technical problems, the technical solution adopted by the present application is as follows:

[0007] A switching power supply converter circuit, characterized in that it comprises a flyback converter, a stress limiting circuit and a control circuit; the flyback converter comprises a main power transformer, an input capacitor, a main switch tube, a rectifier switch tube and an output capacitor, the main switch tube is connected in series in the circuit of the primary winding of the main power transformer, the input capacitor is connected in parallel on the power input side of the flyback converter, the rectifier switch tube is connected in series in the circuit of the secondary winding of the main power transformer, and the output capacitor is connected in parallel on the power output side of the flyback converter;

[0008] The stress limiting circuit is connected in parallel with the secondary winding, and the stress limiting circuit comprises a first clamping switch tube and a first clamping capacitor, the first clamping switch tube and the first clamping capacitor are connected in series;

[0009] The control circuit is provided with a feedback signal input end, a Vd voltage input end, a main switch tube control signal output end and a first clamping switch tube control signal output end, the feedback signal input end collects the voltage signal of the output end of the flyback converter, the Vd voltage input end collects the voltage signal of one end of the rectifier switch tube connected with the secondary winding, and the main switch tube control signal output end and the first clamping switch tube control signal output end are connected with the control ends of the main switch tube and the first clamping switch tube respectively;

[0010] During operation, the control circuit controls the first clamping switch tube to be turned on only when the voltage inputted by the Vd voltage input terminal rises to a set threshold value.

[0011] Optionally, the switching power converter circuit further comprises a second clamping switch tube and a second clamping capacitor, the second clamping switch tube and the second clamping capacitor are connected in series, and the circuit after the series connection is connected in parallel with the primary winding of the main power transformer; the control circuit is further provided with a second clamping switch tube control signal output terminal, and the second clamping switch tube control signal output terminal is connected with the control terminal of the second clamping switch tube.

[0012] Optionally, the switching power converter circuit further comprises a third clamping switch tube and a third clamping capacitor, the main power transformer is provided with a third winding, the third clamping switch tube and the third clamping capacitor are connected in series on the circuit of the third winding, the control circuit is further provided with a VCC signal input terminal and a third clamping switch tube control signal output terminal, the VCC signal input terminal collects the voltage signal of the non-identical terminal of the third winding, and the third clamping switch tube control signal output terminal is connected with the control terminal of the third clamping switch tube.

[0013] Optionally, the non-identical terminal of the primary winding is connected with the positive electrode of the power input side, the input terminal of the main switch tube is connected with the non-identical terminal of the primary winding, and the output terminal of the main switch tube is grounded; the non-identical terminal of the secondary winding is connected with the positive electrode of the power output side, the input terminal of the rectifier switch tube is connected with the non-identical terminal of the secondary winding, and the output terminal of the rectifier switch tube is grounded; the first terminal of the first clamping capacitor is connected with the non-identical terminal of the secondary winding, the second terminal of the first clamping capacitor is connected with the first terminal of the first clamping switch tube, and the second terminal of the first clamping switch tube is connected with the non-identical terminal of the secondary winding.

[0014] Optionally, the flyback converter further comprises a sampling resistor, and the output terminal of the main switch tube is grounded through the sampling resistor.

[0015] Optionally, the rectifier switch tube is a MOS tube, and the control circuit is further provided with a rectifier switch tube control signal output terminal, and the rectifier switch tube control signal output terminal is connected with the control terminal of the rectifier switch tube.

[0016] Optionally, the rectifier switch tube is a diode.

[0017] Optionally, when the first clamping switch tube is turned on during the conduction time period of the main switch tube, the turn-off time of the first clamping switch tube should be earlier than the turn-off time of the main switch tube.

[0018] Optionally, when the switching power converter circuit works in the CCM mode, the first clamping switch tube is turned on within the conduction time period of the main switch tube.

[0019] Optionally, when the switching power converter circuit works in the DCM mode, the first clamping switch tube is turned on outside the conduction time period of the main switch tube.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] The present application can ensure that the rectifier switch tube has been closed, and the first clamping switch tube will not cause common when it is turned on, thereby preventing the first clamping switch tube and the rectifier switch tube from being common.

[0022] In the DCM mode, the conduction time of the main switch tube is short, and when the control circuit controls the first clamping switch tube to release the voltage on the first clamping capacitor to the primary circuit, the control circuit controls the main switch tube to be turned off, which will not affect the detection of the inductor current when the main switch tube is turned on. In the CCM mode, the conduction time of the main switch tube is long, and the conduction time of the first clamping switch tube is originally short in this mode and is turned on shortly after the main switch tube is turned on, so the influence on the detection of the inductor current in the conduction time of the main switch tube is small. The same is true when the CCM mode transitions to the DCM mode or the DCM mode transitions to the CCM mode.

[0023] It can be seen that the present application can prevent the first clamping switch tube and the rectifier switch tube from being common while reducing the influence of the first clamping switch tube on the detection of the inductor current when it is turned on, thereby ensuring the reliability of the system under the condition of clamping the stress of the rectifier switch tube. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The circuit schematic diagram of the patent with patent number CN208424210U in the background art;

[0025] Figure 2 The control timing diagram of the patent with patent number CN208424210U in the background art;

[0026] Figure 3 The circuit schematic diagram of the switching power supply converter circuit of embodiment one of the present application;

[0027] Figure 4 The control timing diagram of the switching power supply converter circuit of embodiment one of the present application;

[0028] Figure 5 The circuit schematic diagram of the switching power supply converter circuit of embodiment two of the present application;

[0029] Figure 6 The control timing diagram of the switching power supply converter circuit of embodiment two of the present application;

[0030] Figure 7 The circuit schematic diagram of the switching power supply converter circuit of embodiment three of the present application.

[0031] Meaning of reference signs in the drawings:

[0032] 11 - flyback converter; 22 - stress limiting circuit; 33 - control circuit. DETAILED DESCRIPTION

[0033] In the description of the present application, the meaning of one or more is one or more, the meaning of multiple is two or more, greater than, less than, more than, etc. are understood as not including the number, above, below, within, etc. are understood as including the number. If it is described as first, second, it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the sequence of indicated technical features.

[0034] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting, etc. should be broadly understood, and those skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0035] The present application will be further described below in conjunction with examples.

[0036] Example 1:

[0037] As Figure 3 shown is a switching power converter circuit of example 1, which includes a flyback converter 11, a stress limiting circuit 22 and a control circuit 33.

[0038] The flyback converter 11 includes a main power transformer T1, an input capacitor C1, a main switch tube Q1, a rectifier switch tube Q2 and an output capacitor C2, and the main power transformer T1 includes a primary winding and a secondary winding.

[0039] The main switch tube Q1 is connected in series on the circuit of the primary winding of the main power transformer T1, the input capacitor C1 is connected in parallel on the power input side of the flyback converter 11, the rectifier switch tube Q2 is connected in series on the circuit of the secondary winding of the main power transformer T1, and the output capacitor C2 is connected in parallel on the power output side of the flyback converter 11. The specific circuit is: the present embodiment also includes a sampling resistor RCS, wherein the rectifier switch tube Q2 is a MOS tube. The same name end 1 of the primary winding is connected to the positive electrode Vin+ of the power input side, the first end of the main switch tube Q1 is connected to the different name end 2 of the primary winding, the second end of the main switch tube Q1 is connected to the ground GND0 through the sampling resistor RCS; the different name end 4 of the secondary winding is connected to the positive electrode Vout+ of the power output side, the first end of the rectifier switch tube Q2 is connected to the same name end 3 of the secondary winding, and the second end of the rectifier switch tube Q2 is connected to the ground GND1.

[0040] The stress limiting circuit 22 of the embodiment is connected in parallel with the secondary winding, and the stress limiting circuit 22 comprises a first clamping switch tube Q3 and a first clamping capacitor C3 connected in series. Specifically, the first end of the first clamping capacitor C3 is connected with the non-identical end 4 of the secondary winding, the second end of the first clamping capacitor C3 is connected with the first end of the first clamping switch tube Q3, and the second end of the first clamping switch tube Q3 is connected with the identical end 3 of the secondary winding.

[0041] The control circuit of the embodiment is provided with a feedback signal input end, a Vd voltage input end, a main switch tube control signal output end G_Q1, a first clamping switch tube control signal output end G_Q3, and a rectifier switch tube control signal output end G_Q2. The feedback signal input end collects the voltage signal of the positive electrode Vout+ of the output end of the flyback converter, the Vd voltage input end collects the voltage signal of one end of the rectifier switch tube Q2 connected with the secondary winding, and the main switch tube control signal output end G_Q1, the first clamping switch tube control signal output end G_Q3, and the rectifier switch tube control signal output end G_Q2 are respectively connected with the control ends of the main switch tube Q1, the first clamping switch tube Q3, and the rectifier switch tube Q2, and are respectively used for controlling the main switch tube Q1, the first clamping switch tube Q3, and the rectifier switch tube Q2.

[0042] Among them, the first end of the main switch tube Q1, the first clamping switch tube Q3, and the rectifier switch tube Q2 of the embodiment is the drain thereof, and the second end thereof is the source thereof.

[0043] The switching power supply converter circuit in the running process, in the control circuit 33 detects the voltage input by the Vd voltage input end rises to the set threshold value V1 only control conduction first clamping switch tube; The threshold value V1 is set to be greater than zero positive value, because the Vd voltage is the drain voltage of the secondary synchronous rectifier switch tube, when it is greater than zero, then it can be guaranteed that the rectifier switch tube has been closed, at this time, the conduction of the first clamping switch tube will not lead to common; In the DCM mode, the conduction time of the main switch tube is short, when the control circuit controls the conduction of the first clamping switch tube, the voltage on the first clamping capacitor is released to the primary circuit, the control circuit controls the main switch tube to be turned off, which will not affect the detection of the inductor current when the main switch tube is turned on; In the CCM mode, the conduction time of the main switch tube is long, and the conduction time of the first clamping switch tube in this mode is originally short, and it is turned on soon after the main switch tube is turned on, so the detection of the inductor current in the conduction time of the main switch tube is less affected.

[0044] As Figure 4 The control timing diagram of the embodiment is shown in the figure, wherein:

[0045] At T0-t4, the circuit works in DCM mode, the main switch control signal output end G_Q1 of the control circuit 33 outputs a control signal to control the main switch Q1 to turn on, the conduction time of the main switch Q1 is determined by the feedback signal collected by the feedback signal input end, the main switch control signal output end G_Q1 of the control circuit 33 outputs a control signal to control the main switch Q1 to turn off at t1, the inductor current starts to demagnetize, after a Td1 dead time, the rectifier switch control signal output end G_Q2 of the control circuit 33 outputs a control signal to control the rectifier switch Q2 to turn on, after the completion of the demagnetization of the secondary side inductor current, the rectifier switch control signal output end G_Q2 of the control circuit 33 outputs a control signal to control the rectifier switch Q2 to turn off, the first end voltage Vd of the rectifier switch Q2 starts to rise, at t2, the first end voltage Vd of the rectifier switch Q2 rises to the threshold value V1, the first clamping switch control signal output end G_Q3 of the control circuit 33 outputs a control signal to control the first clamping switch Q3 to turn on, at this time, the first clamping capacitor C3 discharges through the primary winding circuit of the main power transformer T1, the reverse resonant current passes through the primary sampling resistor RCS to generate a negative voltage, but since the main switch Q1 has been closed at this time, the inductor current sampling is not affected. At t3, the first clamping switch Q3 turns off after turning on for T1 time.

[0046] At T4-t7, the circuit works in the process of transition from DCM to CCM mode, at t4, the main switch control signal output end G_Q1 of the control circuit 33 outputs a control signal to control the main switch Q1 to turn on, at t5, the main switch Q1 is controlled to turn off, after the demagnetization of the secondary circuit current to zero, at t6, the first end voltage Vd of the rectifier switch Q2 rises to the threshold value V1, the first clamping switch control signal output end G_Q3 of the control circuit 33 outputs a control signal to control the first clamping switch Q3 to turn on, at t7, the next period starts, the main switch Q1 is controlled to turn on.

[0047] At T7-t11, the circuit works in CCM mode, at t8, the first clamping switch Q3 turns off after turning on for T1 time, at t9, the first clamping switch Q3 is controlled to turn off, at t10, the rectifier switch Q2 is turned off, after a dead time Td4, at t11, the next period starts, the main switch Q1 is controlled to turn on.

[0048] At T11-t15, the circuit works in the process of transition from CCM mode to DCM mode, at t12, the first end voltage Vd of the rectifier switch tube Q2 rises to the threshold value V1, the first clamping switch tube control signal output end G_Q3 of the control circuit 33 outputs the control signal to control the first clamping switch tube Q3 to be turned on, at this time, the first clamping capacitor C3 discharges to the primary side circuit through the main power transformer, the discharge current reverses through the sampling resistor RCS to generate a negative voltage, but in this case, the main switch tube Q3 is turned on for a long time, so it will not affect the sampling of the peak inductance current; at t14, it is detected again that the first end voltage Vd of the rectifier switch tube Q2 rises to the threshold value V1, and the first clamping switch tube Q3 is turned on again.

[0049] At T15-t19, the circuit works in DCM mode, at t15, the main switch tube Q1 is turned on, at t16, the first clamping switch tube Q3 completes the conduction time T1 and is turned off; at t18, the first end voltage Vd of the rectifier switch tube Q2 rises to the threshold value V1, the first clamping switch tube control signal output end G_Q3 of the control circuit 33 outputs the control signal to control the first clamping switch tube Q3 to be turned on, and the turn-on time is T1. At T19, the next period starts, and the main switch tube Q1 is turned on.

[0050] From the above control timing analysis, it can be seen that in DCM mode, the first clamping switch tube Q3 is turned on outside the conduction time of the main switch tube Q1, at this time, the first clamping capacitor C3 discharges to the primary side circuit, and the negative voltage generated on the sampling resistor RCS of the primary side inductance current will not affect the system control, and in the transition from DCM mode to CCM mode or the transition from CCM mode to DCM mode and the system working in CCM mode, the time of the first clamping switch tube Q3 turned on in the conduction time of the main switch tube Q1 is much less than the conduction time of the main switch tube Q1, so the influence on the detection of the inductance current of the primary side circuit during the conduction of the main switch tube Q1 can be ignored, in addition, since the first clamping switch tube Q3 is turned on only when it is detected that the first end voltage Vd of the rectifier switch tube Q2 rises to the set threshold value V1, at this time, the first end voltage Vd of the rectifier switch tube Q2 rising to the set threshold value V1 indicates that the rectifier switch tube Q2 has been turned off, so it will not cause the first clamping switch tube Q3 to be common with the rectifier switch tube Q2, and the stability of the system is enhanced.

[0051] Among them, the rectifier switch tube of the embodiment can also be a diode.

[0052] Embodiment two:

[0053] As Figure 5The switching power converter circuit of the second embodiment is shown, and compared with the first embodiment, a second clamping switch Q4 and a second clamping capacitor C4 are added in the flyback converter 11 for clamping the voltage stress when the main switch Q1 is off. The circuit of the second clamping switch Q4 and the second clamping capacitor C4 in series is connected in parallel with the primary winding of the main power transformer, and the specific circuit is as follows: the first end of the second clamping capacitor C4 is connected with the same end of the primary winding, the second end of the second clamping capacitor C4 is connected with the first end of the second clamping switch Q4, and the second end of the second clamping switch Q4 is connected with the different end of the primary winding.

[0054] The control circuit 33 of the embodiment is additionally provided with a second clamping switch control signal output end G_Q4, which is connected with the control end of the second clamping switch Q4 for controlling the second clamping switch Q4.

[0055] The first end of the second clamping switch Q4 of the embodiment is the drain thereof, and the second end is the source thereof.

[0056] As Figure 6 The control timing diagram of the circuit of the second embodiment is shown:

[0057] In the embodiment, the flyback upper switch (i.e. the switch Q4) works in the trailing edge non-complementary mode, and the difference between the control timing and that of the first embodiment is that the control signal G_Q4 of the second clamping switch Q4 before the main switch Q1 is turned on is added, and the timing Tw is added, which is defined as the time between the time when the voltage Vd at the first end of the rectifier switch Q2 rises to the threshold V1 and the time when the second clamping switch Q4 is turned on. The dead time Td2 is the time between the time when the first clamping switch Q3 is turned on and the time when the second clamping switch Q4 is turned on, and the time Td3 is the dead time of the second clamping switch Q4 and the main switch Q1. In the DCM mode, the time T1 plus the time Td2 is less than the time Tw, so the first clamping switch Q3 can be turned on for the complete time T1 outside the conduction time of the main switch Q1. In the transition mode, the time T1 plus the time Td2 is greater than the time Tw, so the first clamping switch Q3 cannot be turned on for the complete time T1 outside the conduction time of the main switch Q1, and the first clamping switch Q3 needs to be turned on again inside the conduction time of the main switch Q1. In the CCM mode, the first clamping switch Q3 can only be turned on inside the conduction time of the main switch Q1. The other control timing is the same as that of the first embodiment, and will not be described here.

[0058] Embodiment three:

[0059] As Figure 7The third clamping switch tube Q5 and the third clamping capacitor C5 are connected in series on the circuit of the third winding, and the specific circuit is that: the first end of the third clamping switch tube Q5 is connected with the same end of the third winding, the second end of the third clamping switch tube Q5 is connected with the first end of the third clamping capacitor C5, and the second end of the third clamping capacitor C5 is connected with the different end of the third winding.

[0060] The control circuit of the embodiment is also provided with a VCC signal input end and a third clamping switch tube control signal output end G_Q5, the VCC signal input end collects the voltage signal of the different end of the third winding, the third clamping switch tube control signal output end is connected with the control end of the third clamping switch tube Q5, and is used for controlling the third clamping switch tube Q5.

[0061] The third clamping switch tube Q5 works in the post non-complementary mode, and the ZVS opening of the main switch tube Q1 can be realized, and the control timing thereof is the same as that of the control timing of the second embodiment.

[0062] The first end of the third clamping switch tube Q5 of the embodiment is the drain thereof, and the second end is the source thereof.

[0063] The above embodiments of the application are not the limitation of the protection scope of the application, and the embodiments of the application are not limited to the above, and any other forms of modification, replacement or change of the above structure of the application according to the above content of the application, the ordinary technical knowledge and the usual means in the art, without departing from the above basic technical idea of the application, should fall within the protection scope of the application.

Claims

1. A switching power supply converter circuit, characterized in that: It includes a flyback converter, a stress limiting circuit, and a control circuit; the flyback converter includes a main power transformer, an input capacitor, a main switch transistor, a rectifier switch transistor, and an output capacitor. The main switch transistor is connected in series in the primary winding of the main power transformer, the input capacitor is connected in parallel on the power input side of the flyback converter, the rectifier switch transistor is connected in series in the secondary winding of the main power transformer, and the output capacitor is connected in parallel on the power output side of the flyback converter. The stress limiting circuit is connected in parallel with the secondary winding. The stress limiting circuit includes a first clamping switch and a first clamping capacitor, which are connected in series. The control circuit is provided with a feedback signal input terminal, a Vd voltage input terminal, a main switch control signal output terminal, and a first clamp switch control signal output terminal. The feedback signal input terminal collects the voltage signal of the output terminal of the flyback converter, the Vd voltage input terminal collects the voltage signal of the end of the rectifier switch connected to the secondary winding, and the main switch control signal output terminal and the first clamp switch control signal output terminal are respectively connected to the control terminals of the main switch and the first clamp switch. During operation, the first clamping switch is turned on only when the control circuit detects that the voltage input at the Vd voltage input terminal has risen to a set threshold. When the first clamping switch is turned on during the on-time of the main switch, the off-time of the first clamping switch should be earlier than the off-time of the main switch.

2. The switching power supply converter circuit according to claim 1, characterized in that: The switching power converter circuit also includes a second clamping switch and a second clamping capacitor. The circuit after the second clamping switch and the second clamping capacitor are connected in series is connected in parallel with the primary winding of the main power transformer. The control circuit also has a control signal output terminal for the second clamping switch, which is connected to the control terminal of the second clamping switch.

3. The switching power supply converter circuit according to claim 1, characterized in that: The switching power converter circuit also includes a third clamping switch and a third clamping capacitor. The main power transformer has a third winding. The third clamping switch and the third clamping capacitor are connected in series in the circuit of the third winding. The control circuit also has a VCC signal input terminal and a control signal output terminal for the third clamping switch. The VCC signal input terminal collects the voltage signal of the opposite terminal of the third winding. The control signal output terminal for the third clamping switch is connected to the control terminal of the third clamping switch.

4. The switching power supply converter circuit according to any one of claims 1 to 3, characterized in that: The primary winding's corresponding terminal is connected to the positive terminal of the power input side; the input terminal of the main switch is connected to the opposite terminal of the primary winding; and the output terminal of the main switch is grounded. The secondary winding's opposite terminal is connected to the positive terminal of the power output side; the input terminal of the rectifier switch is connected to the corresponding terminal of the secondary winding; and the output terminal of the rectifier switch is grounded. The first terminal of the first clamping capacitor is connected to the opposite terminal of the secondary winding; the second terminal of the first clamping capacitor is connected to the first terminal of the first clamping switch; and the second terminal of the first clamping switch is connected to the corresponding terminal of the secondary winding.

5. The switching power supply converter circuit according to claim 4, characterized in that: The flyback converter also includes a sampling resistor, and the output terminal of the main switch is grounded through the sampling resistor.

6. The switching power supply converter circuit according to claim 1, characterized in that: The rectifier switch is a MOSFET, and the control circuit also has a rectifier switch control signal output terminal, which is connected to the control terminal of the rectifier switch.

7. The switching power supply converter circuit according to claim 1, characterized in that: The rectifier switch is a diode.

8. The switching power supply converter circuit according to claim 1, characterized in that: When the switching power converter circuit operates in CCM mode, the first clamping switch is turned on during the main switch's on-time period.

9. The switching power supply converter circuit according to claim 1, characterized in that: When the switching power converter circuit operates in DCM mode, the first clamping switch is turned on outside the conduction period of the main switch.

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