Switching power supply circuit and electronic device

Abstract

The application relates to a switching power supply circuit and electronic equipment. An absorption capacitor in the switching power supply circuit can quickly absorb the turn-off voltage energy of a power switch through a direct connection path when the power switch is turned off. Since the resistance value of the direct connection path is smaller than that of a current limiting resistor, the charging speed of the absorption capacitor can be improved, so as to accelerate the turn-off efficiency of the power switch. The absorption capacitor can quickly release the stored energy through a switching path when the power switch is turned on. Since the resistance value of the switching path is also smaller than that of the current limiting resistor, the discharging speed of the absorption capacitor can be improved, so as to accelerate the turn-on efficiency of the power switch. The switching circuit is switched to different paths under different on-off states of the power switch, so as to accelerate the switching efficiency of the power switch, thereby reducing the switching loss, and improving the energy conversion efficiency of the switching power supply circuit.

Description

Technical Field

[0001] This application relates to the field of switching power supply circuit technology, and in particular to a switching power supply circuit and electronic device. Background Technology

[0002] Third-generation wide-bandgap power semiconductor materials have advantages such as high thermal conductivity, high breakdown field strength and high saturated electron drift velocity. Under the same voltage or current conditions, their on-resistance is only one-thousandth that of silicon devices, which can significantly reduce conduction losses; the switching frequency is more than ten times that of silicon devices, which can reduce the size of circuit design.

[0003] SiC MOS (Silicon Carbide Metal-Oxide-Semiconductor Field-Effect Transistor), as a third-generation wide-bandgap semiconductor power device, is often used as a power switch in switching power supply circuits. Due to the parasitic inductance and capacitance in the switching power supply circuit, a voltage surge occurs across the SiC MOS when it is turned off. This high-voltage surge increases the voltage stress requirement of the switching transistor. To reduce such high-voltage surges, a conventional solution in switching power supply circuits is to use an RCD structure snubber circuit on the primary winding side of the converter. While the RCD structure snubber circuit is simple to design, the current-limiting resistor in the RCD structure snubber circuit causes the absorption capacitor to charge and discharge slowly, which reduces the energy conversion efficiency of the switching power supply circuit. Utility Model Content

[0004] This application provides a switching power supply circuit and electronic device to solve the problem of low energy conversion efficiency in existing switching power supply circuits.

[0005] In a first aspect, this application provides a switching power supply circuit, characterized in that the switching power supply circuit includes a power switch, an absorption circuit, a converter, and a secondary rectifier circuit, wherein the source of the power switch is connected to the negative terminal of the power supply, the drain of the power switch is connected to the absorption circuit and the primary side of the converter respectively, the gate of the power switch is connected to a switching power supply chip, the absorption circuit is connected between the positive terminal of the power supply and the primary side of the converter, and the secondary side of the converter is connected to the secondary rectifier circuit;

[0006] The absorption circuit includes an absorption capacitor and a switching circuit. The first end of the absorption capacitor is connected to the positive terminal of the power supply and the first end of the primary side of the converter, respectively. The second end of the absorption capacitor is connected between the switching circuit and the second end of the primary side of the converter. The switching circuit is also connected to the drain of the power switch.

[0007] When the power switch is turned off, the switching circuit switches to the direct-connect circuit, and the absorption capacitor absorbs the off-voltage energy of the power switch through the direct-connect circuit; when the power switch is turned on, the switching circuit switches to the switching circuit, and the absorption capacitor releases the stored energy through the switching circuit. The resistance of the direct-connect circuit and the resistance of the switching circuit are both less than the resistance of the current-limiting resistor.

[0008] Optionally, a first body diode is connected between the source and drain of the power switch.

[0009] Optionally, a parasitic capacitance is also connected between the source and drain of the power switch.

[0010] Optionally, the switching circuit includes a switching switch and an electromagnetic induction device. The first terminal of the switching switch is connected to the second terminal of the absorption capacitor, the second terminal of the switching switch is connected to the first terminal of the electromagnetic induction device, and the third terminal of the switching switch is connected to the second terminal of the primary side of the converter, the second terminal of the electromagnetic induction device, and the drain of the power switch. A second body diode is connected between the third terminal of the switching switch and the drain.

[0011] When the power switch is turned on, the electromagnetic induction device is energized and turns on the switching switch to switch the switching circuit to the switching path; when the power switch is turned off, the electromagnetic induction device is de-energized and turns off the switching switch and turns on the second body diode to switch the switching circuit to the direct path.

[0012] Optionally, the electromagnetic induction device includes an auxiliary winding and / or an inductor.

[0013] Optionally, the switching switch is a field-effect transistor.

[0014] Optionally, the secondary rectifier circuit includes a rectifier diode and a rectifier capacitor. The positive terminal of the rectifier diode is connected to the first terminal of the secondary side of the converter, and the negative terminal of the rectifier diode is connected back to the second terminal of the secondary side of the converter through the rectifier capacitor.

[0015] Optionally, the converter is a DC-to-DC transformer.

[0016] Optionally, when the power switch is turned off, the absorption capacitor absorbs the turn-off voltage energy of the power switch and the leakage inductance voltage energy reflected from the secondary side of the DC-to-DC transformer to the primary side through the direct connection.

[0017] Secondly, this application provides an electronic device including the switching power supply circuit described in any of the above claims.

[0018] Fourthly, this application also provides a computer storage medium storing computer-executable instructions for executing the aforementioned switching power supply circuit.

[0019] Compared with the prior art, the technical solution provided in this application embodiment has the following advantages: The switching power supply circuit provided in this application embodiment includes a power switch, an absorption circuit, a converter, and a secondary rectifier circuit. The source of the power switch is connected to the negative terminal of the power supply, the drain of the power switch is connected to the absorption circuit and the primary side of the converter, the gate of the power switch is connected to the switching power supply chip, the absorption circuit is connected between the positive terminal of the power supply and the primary side of the converter, and the secondary side of the converter is connected to the secondary rectifier circuit. The absorption circuit includes an absorption capacitor and a switching circuit. The first... The first terminal of the power supply is connected to the positive terminal of the power supply and the first terminal of the primary side of the converter, respectively. The second terminal of the absorption capacitor is connected between the switching circuit and the second terminal of the primary side of the converter. The switching circuit is also connected to the drain of the power switch. When the power switch is turned off, the switching circuit switches to the direct-connect circuit, and the absorption capacitor absorbs the turn-off voltage energy of the power switch through the direct-connect circuit. When the power switch is turned on, the switching circuit switches to the switching path, and the absorption capacitor releases the stored energy through the switching path. The resistance of the direct-connect circuit and the resistance of the switching path are both less than the resistance of the current-limiting resistor.

[0020] In the aforementioned switching power supply circuit, the absorption capacitor can quickly absorb the turn-off voltage energy of the power switch through a direct-connection circuit when the power switch is off. Because the resistance of the direct-connection circuit is less than that of the current-limiting resistor, the charging speed of the absorption capacitor can be increased, thereby accelerating the turn-off efficiency of the power switch. When the power switch is on, the absorption capacitor quickly releases the stored energy through the switching path. Because the resistance of the switching path is also less than that of the current-limiting resistor, the discharging speed of the absorption capacitor can be increased, thereby accelerating the turn-on efficiency of the power switch. By switching the power switch to different paths under different on / off states through a switching circuit, the switching efficiency of the power switch can be accelerated, thereby reducing switching losses and improving the energy conversion efficiency of the switching power supply circuit. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the present invention and, together with the description, serve to explain the principles of the present invention.

[0022] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0024] Figure 1 This is a schematic diagram of a switching power supply circuit provided in an embodiment of this application;

[0025] Figure 2 This is a schematic diagram of a switching power supply circuit provided in an embodiment of this application;

[0026] Figure 3 This is a schematic diagram of a switching power supply circuit provided in an embodiment of this application;

[0027] Figure 4 This is a schematic diagram of a switching power supply circuit provided in an embodiment of this application. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] The following disclosure provides numerous different embodiments or examples for implementing various structures of the present invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the scope of the invention. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed.

[0030] Figure 1 This is a schematic diagram of a switching power supply circuit in one embodiment. This switching power supply circuit is applied to electronic devices, which can specifically be power supply devices, industrial equipment, smart home devices, terminal devices, or any other device requiring power conversion.

[0031] Reference Figure 1 The switching power supply circuit specifically includes a power switch Q1, an absorption circuit 110, a converter 120, and a secondary rectifier circuit 130. The source of the power switch Q1 is connected to the negative terminal of the power supply, the drain of the power switch Q1 is connected to the absorption circuit 110 and the primary side of the converter 120, the gate of the power switch Q1 is connected to the switching power supply chip 140, the absorption circuit 110 is connected between the positive terminal of the power supply and the primary side of the converter 120, and the secondary side of the converter 120 is connected to the secondary rectifier circuit 130.

[0032] The absorption circuit 110 includes an absorption capacitor C1 and a switching circuit 111. The first end of the absorption capacitor C1 is connected to the positive terminal of the power supply and the first end of the primary side of the converter 120, respectively. The second end of the absorption capacitor C1 is connected between the switching circuit 111 and the second end of the primary side of the converter 120. The switching circuit 111 is also connected to the drain of the power switch Q1.

[0033] When the power switch Q1 is turned off, the switching circuit 111 switches to the direct connection circuit, and the absorption capacitor C1 absorbs the turn-off voltage energy of the power switch Q1 through the direct connection circuit; when the power switch Q1 is turned on, the switching circuit 111 switches to the switching path, and the absorption capacitor C1 releases the stored energy through the switching path. The resistance values ​​of the direct connection circuit and the switching path are both less than the resistance value of the current limiting resistor.

[0034] Specifically, the power switch Q1 is a SiC MOS, and the absorption circuit 110 includes an absorption capacitor C1 and a switching circuit 111. The switching circuit 111 switches to different paths connected to the absorption capacitor C1 when the power switch Q1 is in different on / off states. When the power switch Q1 is off, the switching circuit 111 switches to the direct connection path. The resistance of the direct connection path is much smaller than the resistance of the current limiting resistor. Therefore, the absorption capacitor C1 can quickly absorb the turn-off voltage energy of the power switch Q1 to speed up the turn-off efficiency of the power switch Q1.

[0035] When the power switch Q1 is turned on, the switching circuit 111 switches to the switching path. The resistance of the switching path is also less than the resistance of the current limiting resistor. Therefore, the absorption capacitor C1 can quickly release the stored energy to accelerate the conduction efficiency of the power switch Q1.

[0036] By switching the power switch Q1 to different paths under different on / off states through the switching circuit 111, the switching efficiency of the power switch Q1 is accelerated, thereby reducing switching losses and improving the energy conversion efficiency of the switching power supply circuit.

[0037] In one embodiment, refer to Figure 2A first body diode is connected between the source and drain of the power switch Q1.

[0038] Specifically, when the power switch Q1 is turned on, its gate voltage causes the channel to form, and the current can flow from the drain to the source through the channel. At this time, the drain voltage is higher than the source voltage. Because the cathode of the first body diode is connected to the drain and the anode is connected to the source, the first body diode is in a reverse bias state, that is, the first body diode is in a cut-off state.

[0039] When power switch Q1 is turned off, the first body diode will conduct in the forward direction, and the current will flow from the source of power switch Q1 through the first body diode to the drain, thereby avoiding excessive drain voltage caused by the back electromotive force of switching circuit 111 and protecting power switch Q1.

[0040] In one embodiment, refer to Figure 2 A parasitic capacitance is also connected between the source and drain of the power switch Q1.

[0041] Specifically, when power switch Q1 is turned off, the drain voltage begins to rise. At this time, the power supply charges the parasitic capacitance of power switch Q1 through converter 120 and switching circuit 111. Since there is an absorption capacitor C1 in the current path, according to Lenz's law, the current cannot change abruptly. Therefore, the charging process of the parasitic capacitance is a relatively slow process, and the magnitude of the charging current is limited by other resistive components.

[0042] When power switch Q1 is turned on, the gate-to-source voltage rises above the threshold voltage. At this time, the parasitic capacitance discharges through the internal resistance of the gate drive circuit and related loops, and the discharge current flows from the drain to the source. Because the on-resistance of power switch Q1 is low, the discharge speed of the parasitic capacitance is relatively fast.

[0043] In one embodiment, the switching circuit 111 includes a switching switch Q2 and an electromagnetic induction device. The first terminal of the switching switch Q2 is connected to the second terminal of the absorption capacitor C1, the second terminal of the switching switch Q2 is connected to the first terminal of the electromagnetic induction device, and the third terminal of the switching switch Q2 is connected to the second terminal of the primary side of the converter 120, the second terminal of the electromagnetic induction device, and the drain of the power switch Q1. A second body diode is connected between the third terminal of the switching switch Q2 and the drain.

[0044] When the power switch Q1 is turned on, the electromagnetic induction device is energized and turns on the switching switch Q2 to switch the switching circuit 111 to the switching path; when the power switch Q1 is turned off, the electromagnetic induction device is de-energized and turns off the switching switch Q2, turns on the second body diode, and switches the switching circuit 111 to the direct connection path.

[0045] Specifically, when power switch Q1 is turned on, the electromagnetic induction device is energized, which in turn energizes the second terminal of switch Q2, thereby turning on switch Q2. The turn-on of switch Q2 causes switching circuit 111 to switch path, which includes switch Q2. The absorption capacitor C1 is then rapidly discharged through switch Q2 and power switch Q1, that is, the stored energy is rapidly released.

[0046] When power switch Q1 is turned off, the electromagnetic induction device is not energized, so the second terminal of switch Q2 cannot be energized, i.e. switch Q2 is turned off. When switch Q2 is turned off, switching circuit 111 switches to direct connection. Direct connection includes the second body diode of switch Q2, i.e., absorption capacitor C1 quickly absorbs the turn-off voltage energy of power switch Q1 through the second body diode.

[0047] By switching switch Q2 to different on / off states when power switch Q1 is in different on / off states, switching circuit 111 can be switched to different paths. Whether in a direct-connection path or a switching path, the switching efficiency of power switch Q1 can be accelerated, thereby reducing switching losses and improving the energy conversion efficiency of the switching power supply circuit.

[0048] In one embodiment, the electromagnetic induction device includes an auxiliary winding L1 and / or an inductor.

[0049] Specifically, the electromagnetic induction device includes inductive components such as auxiliary winding L1 and / or inductors, as described in the reference. Figure 2 In this embodiment, the electromagnetic induction device is implemented using an auxiliary winding L1.

[0050] When power switch Q1 is turned on, refer to Figure 3 The arrows in the diagram indicate the direction of current flow. The potential at point c of the auxiliary winding L1 is positive, and the potential at point d is negative. At this time, point c of the auxiliary winding L1 is energized, which causes the second terminal of the switching switch Q2 to be energized and turned on. The switching switch Q2 turns on, which causes the switching circuit 111 to switch to the switching path. The switching path includes the switching switch Q2. The absorption capacitor C1 is then quickly discharged through the switching switch Q2 and the power switch Q1, that is, the stored energy is quickly released.

[0051] When power switch Q1 is turned off, refer to Figure 4 The arrows in the diagram indicate the direction of current flow. The potential at point c of the auxiliary winding L1 is negative, and the potential at point d is positive, making the voltage at the second terminal of the switching switch Q2 zero, i.e., turning off the switching switch Q2. The turning off of the switching switch Q2 causes the switching circuit 111 to switch to the direct connection circuit. The direct connection circuit includes the second body diode of the switching switch Q2, i.e., the absorption capacitor C1 quickly absorbs the turn-off voltage energy of the power switch Q1 through the second body diode.

[0052] In one embodiment, refer to Figure 2 The switching switch Q2 is a field-effect transistor.

[0053] Specifically, if a field-effect transistor is used to implement the switching switch Q2, then the gate of the field-effect transistor is connected to the first end (point c) of the auxiliary winding L1, the drain of the field-effect transistor is connected to the absorption capacitor C1, and the source of the field-effect transistor is connected to the second end of the primary side of the converter 120 and the second end (point d) of the auxiliary winding L1, respectively.

[0054] Reference Figure 3 When the power switch Q1 is turned on, the potential at point c of the auxiliary winding L1 is positive and the potential at point d is negative. At this time, the potential at point c of the auxiliary winding L1 is energized, which causes the gate of the field-effect transistor to be energized and turned on. The turn-on of the field-effect transistor causes the switching circuit 111 to switch to the switching path. The switching path includes the field-effect transistor. The absorption capacitor C1 is then quickly discharged through the field-effect transistor and the power switch Q1, that is, the stored energy is quickly released.

[0055] Reference Figure 4 When the power switch Q1 is turned off, the potential at point c of the auxiliary winding L1 is negative and the potential at point d is positive, which makes the gate voltage of the field-effect transistor 0, that is, the field-effect transistor is turned off. The turn-off of the field-effect transistor causes the switching circuit 111 to switch to the direct connection circuit. The direct connection circuit includes the second body diode of the field-effect transistor, that is, the absorption capacitor C1 quickly absorbs the turn-off voltage energy of the power switch Q1 through the second body diode.

[0056] In one embodiment, refer to Figure 2 The secondary rectifier circuit 130 includes a rectifier diode D2 and a rectifier capacitor C2. The positive terminal of the rectifier diode D2 is connected to the first terminal of the secondary side of the converter 120, and the negative terminal of the rectifier diode D2 is connected back to the second terminal of the secondary side of the converter 120 through the rectifier capacitor C2.

[0057] Specifically, the secondary rectifier circuit 130 is used to convert the voltage output from the secondary side of the converter 120 into a DC voltage that meets the load's DC power requirements.

[0058] Reference Figure 3When power switch Q1 is turned on, the current on the primary side of converter 120 increases, and transformer TR1 stores energy. Due to the same-terminal characteristics of transformer TR1 and the principle of electromagnetic induction, the polarity of the voltage induced in the secondary winding causes rectifier diode D2 to experience a reverse voltage. That is, the magnetic field generated by the primary current in transformer TR1 is enhanced. According to Lenz's law, the polarity of the induced electromotive force in the secondary winding will cause the cathode potential of rectifier diode D2 to be higher than the anode potential, so rectifier diode D2 cannot conduct, preventing the current from flowing in reverse. At this time, rectifier capacitor C2 supplies power to the subsequent load, releasing the previously stored energy.

[0059] Reference Figure 4 When power switch Q1 is turned off, the primary side current of converter 120 drops rapidly, and the energy stored in converter 120 begins to be released. The polarity of the voltage induced in the secondary winding changes, causing rectifier diode D2 to experience a forward voltage. When this forward voltage exceeds the diode's forward voltage drop, rectifier diode D2 conducts. At this time, the current in the secondary winding of converter 120 charges rectifier capacitor C2 through rectifier diode D2 and supplies power to the load. During the charging process, rectifier capacitor C2 stores the energy released by converter 120 and simultaneously provides a stable DC voltage to the subsequent load. When the voltage across rectifier capacitor C2 reaches a certain value, the charging current gradually decreases, eventually reaching a dynamic equilibrium state to maintain a stable output voltage.

[0060] In one embodiment, the converter 120 is a DC-to-DC transformer TR1.

[0061] Specifically, a DC-DC transformer TR1 is used to implement converter 120, which converts one DC voltage into one or more DC voltages of different amplitudes. It can step down a higher input DC voltage to a lower DC voltage suitable for the load, or step up a lower DC voltage to a higher DC voltage. Its output voltage typically exhibits high stability, maintaining the output voltage within a specified accuracy range under certain load conditions and input voltage fluctuations.

[0062] Reference Figure 3 When power switch Q1 is turned on, according to Lenz's law, the potential at point a is positive and the potential at point b is negative; the potential at point e of the secondary winding is negative and the potential at point f is positive, and the secondary rectifier diode D2 is in the off state; the potential at point c of the auxiliary winding L1 is positive, which energizes the gate of the field-effect transistor Q2, causing Q2 to conduct, and the voltage surge stored in capacitor C1 is discharged through the field-effect transistor Q2 and power switch Q1.

[0063] Reference Figure 4When power switch Q1 is turned off, according to Lenz's law, the potential at point a is negative and the potential at point b is positive; the potential at point e of the secondary winding is positive and the potential at point f is negative, and the secondary rectifier diode D2 is in the conducting state; the potential at point c of the auxiliary winding L1 is negative, that is, the gate voltage of the field-effect transistor Q2 is 0, Q2 is turned off, and the voltage surge reflected from the secondary winding to the primary winding charges C1 through the body diode of Q2, absorbing the voltage surge.

[0064] In one embodiment, when the power switch Q1 is turned off, the absorption capacitor C1 absorbs the turn-off voltage energy of the power switch Q1 through the direct connection, as well as the leakage inductance voltage energy reflected from the secondary side of the DC-to-DC transformer TR1 to the primary side.

[0065] Specifically, when the power switch Q1 is turned off, the secondary side of the DC-to-DC transformer TR1 will reflect voltage energy back to the primary side. At this time, the absorption capacitor C1 will absorb not only the turn-off voltage energy of the power switch Q1 through the direct connection, but also the leakage inductance voltage energy reflected from the secondary side of the DC-to-DC transformer TR1 to the primary side, in order to prevent the reverse electromotive force generated by the leakage inductance voltage from superimposing with the turn-off voltage and exceeding the withstand voltage limit of the power switch Q1. At this time, the voltage of the absorption capacitor C1 rises rapidly to suppress the drain-source voltage of the power switch Q1 within a safe range.

[0066] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a general-purpose hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the related technology, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., including several instructions to cause an electronic device (which may be a personal computer, server, or network device, etc.) to execute the switching power supply circuit described in various embodiments or some parts of the embodiments.

[0067] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein may also mean including the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The switching power supply circuit steps, processes, and operations described herein are not construed as requiring them to be performed in the specific order described or illustrated unless the order of performance is explicitly indicated. It should also be understood that alternatives or substitutions may be used.

[0068] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A switching power supply circuit, characterized in that, The switching power supply circuit includes a power switch, a snubber circuit, a converter, and a secondary rectifier circuit. The source of the power switch is connected to the negative terminal of the power supply. The drain of the power switch is connected to the snubber circuit and the primary side of the converter. The gate of the power switch is connected to the switching power supply chip. The snubber circuit is connected between the positive terminal of the power supply and the primary side of the converter. The secondary side of the converter is connected to the secondary rectifier circuit. The absorption circuit includes an absorption capacitor and a switching circuit. The first end of the absorption capacitor is connected to the positive terminal of the power supply and the first end of the primary side of the converter, respectively. The second end of the absorption capacitor is connected between the switching circuit and the second end of the primary side of the converter. The switching circuit is also connected to the drain of the power switch. The switching circuit switches to the direct connection when the power switch is turned off, and the absorption capacitor absorbs the off-voltage energy of the power switch through the direct connection. The switching circuit switches to the switching path when the power switch is turned on, and the absorption capacitor releases the stored energy through the switching path. The resistance of the direct-connection path and the resistance of the switching path are both less than the resistance of the current-limiting resistor.

2. The switching power supply circuit according to claim 1, characterized in that, A first body diode is connected between the source and drain of the power switch.

3. The switching power supply circuit according to claim 2, characterized in that, A parasitic capacitance is also connected between the source and drain of the power switch.

4. The switching power supply circuit according to claim 1, characterized in that, The switching circuit includes a switching switch and an electromagnetic induction device. The first end of the switching switch is connected to the second end of the absorption capacitor. The second end of the switching switch is connected to the first end of the electromagnetic induction device. The third end of the switching switch is connected to the second end of the primary side of the converter, the second end of the electromagnetic induction device, and the drain of the power switch. A second body diode is connected between the third end of the switching switch and the drain. When the power switch is turned on, the electromagnetic induction device is energized and turns on the switching switch to switch the switching circuit to the switching path; when the power switch is turned off, the electromagnetic induction device is de-energized and turns off the switching switch and turns on the second body diode to switch the switching circuit to the direct path.

5. The switching power supply circuit according to claim 4, characterized in that, The electromagnetic induction device includes an auxiliary winding and / or an inductor.

6. The switching power supply circuit according to claim 4, characterized in that, The switching device is a field-effect transistor.

7. The switching power supply circuit according to claim 1, characterized in that, The secondary rectifier circuit includes a rectifier diode and a rectifier capacitor. The positive terminal of the rectifier diode is connected to the first terminal of the secondary side of the converter, and the negative terminal of the rectifier diode is connected back to the second terminal of the secondary side of the converter through the rectifier capacitor.

8. The switching power supply circuit according to claim 1, characterized in that, The converter is a DC-to-DC transformer.

9. The switching power supply circuit according to claim 8, characterized in that, When the power switch is turned off, the absorption capacitor absorbs the turn-off voltage energy of the power switch through the direct connection, as well as the leakage inductance voltage energy reflected from the secondary side of the DC-to-DC transformer to the primary side.

10. An electronic device, characterized in that, The electronic device includes a switching power supply circuit as described in any one of claims 1 to 9.

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