Absorption circuit for flyback switching power supply MOS (Metal Oxide Semiconductor) tube and multi-path parallel flyback switching power supply with absorption circuit

Abstract

The utility model relates to an absorption circuit for a flyback switching power supply MOS tube and a multipath parallel flyback switching power supply with the absorption circuit, which are used for controlling voltage between a drain electrode and a source electrode of the MOS tube, and comprise a first flyback circuit, a second flyback circuit and an MOS tube absorption circuit, the output end of the MOS tube absorption circuit is connected with the power supply circuit; and the high-frequency capacitors C101 and C103 respectively form a loop with the primary side leakage inductance Lm of the transformer in the first flyback circuit and the second flyback circuit, so that the voltage amplitude generated by resonance of the leakage inductance Lm and the parasitic capacitance Coss of the MOS tube is reduced. Meanwhile, fast recovery diodes D102 and D104 are conducted, so that a high-frequency capacitor C102 absorbs voltage energy, a transient voltage suppression diode D101 performs voltage clamping, and terminal voltage of an MOS tube in the flyback circuit is controlled. The circuit is verified by an actual multi-path parallel flyback switching power supply, the work is stable and reliable, the stress control effect of the MOS tube is good, and the cost is relatively low.

Description

Technical Field

[0001] This utility model relates to the field of switching power supply circuit technology, specifically to an absorption circuit for a flyback switching power supply MOSFET and a multi-channel parallel flyback switching power supply having the absorption circuit. Background Technology

[0002] When a flyback switching power supply is operating, the flyback MOSFET repeatedly switches between on and off states at high frequency. Due to the leakage inductance Lm of the flyback transformer and the parasitic capacitance of the MOSFET, the switching between on and off states of the flyback MOSFET generates a large VDS voltage (the sum of the bus voltage, secondary-side emitter voltage, and transformer leakage inductance spike voltage), which can easily exceed the maximum voltage that the flyback MOSFET can withstand, causing it to break down and be damaged. At the same time, the stress spikes caused by the high-frequency switching state transitions generate strong noise pollution, forming electromagnetic interference that affects the operation of the entire power supply.

[0003] Traditional flyback switching power supplies use separate snubber circuits for each branch MOSFET, all employing RCD snubbers. This RCD snubber design results in significant power consumption and impacts circuit efficiency. Furthermore, having a separate snubber circuit for each branch leads to larger PCB layouts and higher costs. Utility Model Content

[0004] In view of this, it is necessary to provide a snubber circuit for MOSFETs in flyback switching power supplies that has small PCB layout space, low cost, and low power consumption, and a multi-parallel flyback switching power supply with the snubber circuit.

[0005] An absorption circuit for a flyback switching power supply MOSFET, used to control the voltage between the drain and source of the MOSFET, includes a transient voltage suppressor diode D101, a first high-frequency capacitor C101, a second high-frequency capacitor C102, a first fast recovery diode D102, and a ferrite bead inductor L101. The two ends of the first high-frequency capacitor C101 are connected in parallel to the two ends of the primary winding T1-A of a first transformer T1. The connection point between the first high-frequency capacitor C101 and the second end of the primary winding T1-A of the first transformer T1, and the drain of the first MOSFET Q1, is connected to the anode of the first fast recovery diode D102. The cathode of the first fast recovery diode D102 is connected to the first end of the second high-frequency capacitor C102, and the second end of the second high-frequency capacitor C102 is grounded (GND). The anode of the transient voltage suppressor diode D101 is connected to the circuit input terminal VDC, and the cathode of the transient voltage suppressor diode D101 is connected through the ferrite bead inductor L101 to the connection point between the cathode of the first fast recovery diode D102 and the first end of the second high-frequency capacitor C102.

[0006] When the MOSFET in the flyback circuit is turned off, the drain voltage of the MOSFET charges the second high-frequency capacitor C102 through the first fast recovery diode D102. After absorbing energy, the second high-frequency capacitor C102 is fully charged. When the voltage continues to rise and reaches the clamping voltage of the transient voltage suppression diode D101, the transient voltage suppression diode D101 clamps the voltage between the drain and source of the MOSFET within a predetermined range.

[0007] Furthermore, a multi-parallel flyback switching power supply with an absorption circuit includes a first flyback circuit, a second flyback circuit, and a MOSFET absorption circuit. The MOSFET absorption circuit includes the absorption circuit described above, a high-frequency capacitor, and a fast recovery diode connected to the absorption circuit. The first flyback circuit and the second flyback circuit are connected in parallel and connected to the output terminal of the MOSFET absorption circuit. The first flyback circuit and the second flyback circuit each include a transformer and a MOSFET connected in series. The MOSFET absorption circuit includes a fast recovery diode, a high-frequency capacitor, and a transient voltage suppression diode. When the MOSFET in the first flyback circuit and the second flyback circuit is turned off, the drain voltage of the MOSFET charges the high-frequency capacitor through the fast recovery diode. The high-frequency capacitor absorbs energy, and when the voltage of the high-frequency capacitor is fully charged and continues to rise to the clamping voltage of the transient voltage suppression diode, the transient voltage suppression diode clamps the voltage between the drain and source of the MOSFET within a predetermined range.

[0008] Preferably, the first flyback circuit includes a first transformer T1, a first MOSFET Q1, a first Schottky diode D103, and a first electrolytic capacitor CE1; the first terminal of the primary side T1-A of the first transformer T1 is connected to the circuit input terminal VDC, the second terminal of the primary side T1-A of the first transformer T1 is connected to the drain of the first MOSFET Q1, and the source of the first MOSFET Q1 is grounded to GND; the first terminal of the secondary side T1-B of the first transformer T1 is connected to the anode of the first Schottky diode D103, the cathode of the first Schottky diode D103 is connected to the anode of the first electrolytic capacitor CE1, and the second terminal of the secondary side T1-B of the first transformer T1 is connected to the cathode of the first electrolytic capacitor CE1; the anode of the first electrolytic capacitor CE1 is connected to the output terminal OUT1 of the first flyback circuit, and the cathode of the first electrolytic capacitor CE1 is grounded to GND.

[0009] Preferably, the second flyback circuit includes a second transformer T2, a second MOSFET Q2, a second Schottky diode D105, and a second electrolytic capacitor CE2; the first terminal of the primary side T2-A of the second transformer T2 is connected to the circuit input terminal VDC, the second terminal of the primary side T2-A of the second transformer T2 is connected to the drain of the second MOSFET Q2, and the source of the second MOSFET Q2 is grounded to GND; the second terminal of the secondary side T2-B of the second transformer T2 is connected to the anode of the second Schottky diode D105, the cathode of the second Schottky diode D105 is connected to the anode of the second electrolytic capacitor CE2, and the second terminal of the secondary side T2-B of the second transformer T2 is connected to the cathode of the second electrolytic capacitor CE2; the anode of the second electrolytic capacitor CE2 is connected to the output terminal OUT2 of the second flyback circuit, and the cathode of the second electrolytic capacitor CE2 is grounded to GND.

[0010] Preferably, the MOS transistor absorption circuit includes a transient voltage suppression diode D101, a first high-frequency capacitor C101, a second high-frequency capacitor C102, a third high-frequency capacitor C103, a first fast recovery diode D102, a second fast recovery diode D104, and a ferrite bead inductor L101; the two ends of the first high-frequency capacitor C101 are connected in parallel to the two ends of the primary side T1-A of the first transformer T1, and the connection point between the first high-frequency capacitor C101 and the second end of the primary side T1-A of the first transformer T1, and the drain of the first MOS transistor Q1, is connected to the anode of the first fast recovery diode D102; the two ends of the third high-frequency capacitor C103 are connected in parallel to the two ends of the primary side T2-A of the second transformer T2, and the third high-frequency capacitor C103 and the... The connection point between the second terminal of the primary side T2-A of the second transformer T2 and the drain of the second MOS transistor Q2 is connected to the anode of the second fast recovery diode D104; the cathode of the first fast recovery diode D102 is connected to the cathode of the second fast recovery diode D104, and is also connected to the first terminal of the second high-frequency capacitor C102, the second terminal of the second high-frequency capacitor C102 is grounded to GND; the anode of the transient voltage suppression diode D101 is connected to the circuit input terminal VDC, and the cathode of the transient voltage suppression diode D101 is connected through the ferrite bead inductor L101 to the connection point between the cathode of the first fast recovery diode D102, the cathode of the second fast recovery diode D104 and the first terminal of the second high-frequency capacitor C102.

[0011] In the aforementioned absorption circuit for the MOSFET in a flyback switching power supply and in a multi-channel parallel flyback switching power supply with the same absorption circuit, high-frequency capacitors C101 and C103 form a loop with the primary leakage inductance Lm of the transformers in the first and second flyback circuits, respectively, reducing the voltage amplitude generated by the resonance between the leakage inductance Lm and the parasitic capacitance Coss of the MOSFET. Simultaneously, fast recovery diodes D102 and D104 conduct, allowing high-frequency capacitor C102 to absorb voltage energy, and transient voltage suppression diode D101 clamps the voltage, controlling the terminal voltage of the MOSFET in the flyback circuit. This technical solution effectively solves the MOSFET voltage stress problem in a multi-channel parallel flyback switching power supply using only a transient voltage suppression diode, a high-frequency capacitor, and a fast recovery diode. The circuit has been verified through actual multi-channel parallel flyback switching power supplies, demonstrating stable and reliable operation, good MOSFET stress control, and low cost. The circuit structure of this invention is simple, easy to implement, low-cost, and easy to promote. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the absorption circuit for a flyback switching power supply MOSFET according to an embodiment of the present invention.

[0013] Figure 2 This is a schematic diagram of the structure of a multi-channel parallel flyback switching power supply with an absorption circuit according to an embodiment of the present invention.

[0014] Figure 3 This is a schematic diagram of the current direction when the MOSFET of a multi-channel parallel flyback switching power supply with an absorption circuit is turned on, according to an embodiment of this utility model.

[0015] Figure 4 This is a schematic diagram of the current direction when the MOS transistor of a multi-parallel flyback switching power supply with an absorption circuit is turned off, according to an embodiment of this utility model. Detailed Implementation

[0016] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0017] Please see Figure 1This illustration shows an absorption circuit for a flyback switching power supply MOSFET provided by an embodiment of the present invention, used to control the voltage between the drain and source of the MOSFET. It includes a transient voltage suppression diode D101, a first high-frequency capacitor C101, a second high-frequency capacitor C102, a first fast recovery diode D102, and a ferrite bead inductor L101. The two ends of the first high-frequency capacitor C101 are connected in parallel to the two ends of the primary side T1-A of the first transformer T1. The first high-frequency capacitor C101 is connected to the second end of the primary side T1-A of the first transformer T1, and the first MOSFET Q1... The connection point between the drains of the first fast recovery diode D102 is connected to the anode of the first fast recovery diode D102; the cathode of the first fast recovery diode D102 is connected to the first terminal of the second high-frequency capacitor C102, and the second terminal of the second high-frequency capacitor C102 is grounded to GND; the anode of the transient voltage suppression diode D101 is connected to the circuit input terminal VDC, and the cathode of the transient voltage suppression diode D101 is connected to the connection point between the cathode of the first fast recovery diode D102 and the first terminal of the second high-frequency capacitor C102 through the magnetic bead inductor L101;

[0018] When the MOSFET in the flyback circuit is turned off, the drain voltage of the MOSFET charges the second high-frequency capacitor C102 through the first fast recovery diode D102. After absorbing energy, the second high-frequency capacitor C102 is fully charged. When the voltage continues to rise and reaches the clamping voltage of the transient voltage suppression diode D101, the transient voltage suppression diode D101 clamps the voltage between the drain and source of the MOSFET within a predetermined range.

[0019] Specifically, the transient voltage suppression diode D101 can respond quickly to transient voltages exceeding a preset value within nanoseconds, protect the MOSFET through voltage clamping, absorb surge energy, and suppress the formation of VDS spike voltage at the drain and source terminals of the MOSFET.

[0020] For a multi-parallel flyback switching circuit, a high-frequency capacitor is connected in parallel to the primary winding of the transformer in the added flyback circuit, and a fast recovery diode is connected in parallel to the absorption circuit to achieve the protection function of the MOSFET in the multi-parallel flyback switching power supply.

[0021] Please see Figure 2 , Figure 3 and Figure 4This invention illustrates a multi-parallel flyback switching power supply with an absorption circuit, comprising a first flyback circuit, a second flyback circuit, and a MOSFET absorption circuit. The MOSFET absorption circuit includes the absorption circuit described above, a high-frequency capacitor connected to the absorption circuit, and a fast recovery diode. The first flyback circuit and the second flyback circuit are connected in parallel and connected to the output terminal of the MOSFET absorption circuit. The first flyback circuit and the second flyback circuit each include a transformer and a MOSFET connected in series. The MOSFET absorption circuit includes a fast recovery diode, a high-frequency capacitor, and a transient voltage suppression diode. When the MOSFETs in the first flyback circuit and the second flyback circuit are turned off, the drain voltage of the MOSFET charges the high-frequency capacitor through the fast recovery diode. The high-frequency capacitor absorbs energy, and when the voltage of the high-frequency capacitor is fully charged, it continues to rise until it reaches the clamping voltage of the transient voltage suppression diode. The transient voltage suppression diode clamps the voltage between the drain and source of the MOSFET within a predetermined range.

[0022] Preferably, the first flyback circuit includes a first transformer T1, a first MOSFET Q1, a first Schottky diode D103, and a first electrolytic capacitor CE1; the first terminal of the primary side T1-A of the first transformer T1 is connected to the circuit input terminal VDC, the second terminal of the primary side T1-A of the first transformer T1 is connected to the drain of the first MOSFET Q1, and the source of the first MOSFET Q1 is grounded to GND; the first terminal of the secondary side T1-B of the first transformer T1 is connected to the anode of the first Schottky diode D103, the cathode of the first Schottky diode D103 is connected to the anode of the first electrolytic capacitor CE1, and the second terminal of the secondary side T1-B of the first transformer T1 is connected to the cathode of the first electrolytic capacitor CE1; the anode of the first electrolytic capacitor CE1 is connected to the output terminal OUT1 of the first flyback circuit, and the cathode of the first electrolytic capacitor CE1 is grounded to GND.

[0023] Preferably, the second flyback circuit includes a second transformer T2, a second MOSFET Q2, a second Schottky diode D105, and a second electrolytic capacitor CE2; the first terminal of the primary side T2-A of the second transformer T2 is connected to the circuit input terminal VDC, the second terminal of the primary side T2-A of the second transformer T2 is connected to the drain of the second MOSFET Q2, and the source of the second MOSFET Q2 is grounded to GND; the second terminal of the secondary side T2-B of the second transformer T2 is connected to the anode of the second Schottky diode D105, the cathode of the second Schottky diode D105 is connected to the anode of the second electrolytic capacitor CE2, and the second terminal of the secondary side T2-B of the second transformer T2 is connected to the cathode of the second electrolytic capacitor CE2; the anode of the second electrolytic capacitor CE2 is connected to the output terminal OUT2 of the second flyback circuit, and the cathode of the second electrolytic capacitor CE2 is grounded to GND.

[0024] Preferably, the MOS transistor absorption circuit includes a transient voltage suppression diode D101, a first high-frequency capacitor C101, a second high-frequency capacitor C102, a third high-frequency capacitor C103, a first fast recovery diode D102, a second fast recovery diode D104, and a ferrite bead inductor L101; the two ends of the first high-frequency capacitor C101 are connected in parallel to the two ends of the primary side T1-A of the first transformer T1, and the connection point between the first high-frequency capacitor C101 and the second end of the primary side T1-A of the first transformer T1, and the drain of the first MOS transistor Q1, is connected to the anode of the first fast recovery diode D102; the two ends of the third high-frequency capacitor C103 are connected in parallel to the two ends of the primary side T2-A of the second transformer T2, and the third high-frequency capacitor C103 and the... The connection point between the second terminal of the primary side T2-A of the second transformer T2 and the drain of the second MOS transistor Q2 is connected to the anode of the second fast recovery diode D104; the cathode of the first fast recovery diode D102 is connected to the cathode of the second fast recovery diode D104, and is also connected to the first terminal of the second high-frequency capacitor C102, the second terminal of the second high-frequency capacitor C102 is grounded to GND; the anode of the transient voltage suppression diode D101 is connected to the circuit input terminal VDC, and the cathode of the transient voltage suppression diode D101 is connected through the ferrite bead inductor L101 to the connection point between the cathode of the first fast recovery diode D102, the cathode of the second fast recovery diode D104 and the first terminal of the second high-frequency capacitor C102.

[0025] When the circuit is operating, with the first MOSFET Q1 and the second MOSFET Q2 turned on, the cathode voltage of the transient voltage suppression diode D101 is essentially the same as the bus voltage; the first fast recovery diode D102 and the second fast recovery diode D104 are turned off. At this time, the current direction in the circuit is as follows: Figure 3 As shown.

[0026] When the first MOSFET Q1 and the second MOSFET Q2 are turned off, since the VDS voltage of the MOSFET cannot change abruptly, the current will charge the parasitic capacitance Coss across the MOSFET. At this time, the parasitic capacitance Coss across the MOSFET resonates with the leakage inductance Lm of the transformer, causing a VDS spike voltage to form across the MOSFET.

[0027] At this time, under the action of the MOSFET absorption circuit, the first high-frequency capacitor C101 and the third high-frequency capacitor C103 form a circuit with the leakage inductance Lm of the primary side T1-A of the first transformer T1 and the primary side T2-A of the second transformer T2, respectively, reducing the energy of the leakage inductance Lm, thereby reducing the voltage amplitude generated by the resonance between the leakage inductance Lm and the parasitic capacitance Coss of the MOSFET. Simultaneously, the first fast recovery diode D102 and the second fast recovery diode D104 are turned on, allowing the second high-frequency capacitor C102 to absorb voltage energy. When the voltage reaches the operating voltage of the transient voltage suppression diode D101, the transient voltage suppression diode D101 operates, clamping the voltage to the sum of the bus voltage and the operating voltage of the transient voltage suppression diode D101, thereby controlling the voltage stress of the flyback MOSFET. At this time, the current direction in the circuit is as follows: Figure 4 As shown.

[0028] In the aforementioned absorption circuit for the MOSFET in a flyback switching power supply and in a multi-channel parallel flyback switching power supply with the same absorption circuit, high-frequency capacitors C101 and C103 form a loop with the primary leakage inductance Lm of the transformers in the first and second flyback circuits, respectively, reducing the voltage amplitude generated by the resonance between the leakage inductance Lm and the parasitic capacitance Coss of the MOSFET. Simultaneously, fast recovery diodes D102 and D104 conduct, allowing high-frequency capacitor C102 to absorb voltage energy, and transient voltage suppression diode D101 clamps the voltage, controlling the terminal voltage of the MOSFET in the flyback circuit. This technical solution effectively solves the MOSFET voltage stress problem in a multi-channel parallel flyback switching power supply using only a transient voltage suppression diode, a high-frequency capacitor, and a fast recovery diode. The circuit has been verified through actual multi-channel parallel flyback switching power supplies, demonstrating stable and reliable operation, good MOSFET stress control, and low cost. The circuit structure of this invention is simple, easy to implement, low-cost, and easy to promote.

[0029] It should be noted that this utility model is not limited to the above-described embodiments. Based on the inventive spirit of this utility model, those skilled in the art can make other changes, and these changes made based on the inventive spirit of this utility model should be included within the scope of protection claimed by this utility model.

Claims

1. A snubber circuit for a flyback switching power supply MOSFET, used to control the voltage between the drain and source of the MOSFET, characterized in that, The circuit includes a transient voltage suppression diode D101, a first high-frequency capacitor C101, a second high-frequency capacitor C102, a first fast recovery diode D102, and a ferrite bead inductor L101. The two ends of the first high-frequency capacitor C101 are connected in parallel to the two ends of the primary winding T1-A of the first transformer T1. The connection point between the first high-frequency capacitor C101 and the second end of the primary winding T1-A of the first transformer T1, and the drain of the first MOSFET Q1, is connected to the anode of the first fast recovery diode D102. The cathode of the first fast recovery diode D102 is connected to the first end of the second high-frequency capacitor C102, and the second end of the second high-frequency capacitor C102 is grounded (GND). The anode of the transient voltage suppression diode D101 is connected to the circuit input terminal VDC, and the cathode of the transient voltage suppression diode D101 is connected through the ferrite bead inductor L101 to the connection point between the cathode of the first fast recovery diode D102 and the first end of the second high-frequency capacitor C102. When the MOSFET in the flyback circuit is turned off, the drain voltage of the MOSFET charges the second high-frequency capacitor C102 through the first fast recovery diode D102. After absorbing energy, the second high-frequency capacitor C102 is fully charged. When the voltage continues to rise and reaches the clamping voltage of the transient voltage suppression diode D101, the transient voltage suppression diode D101 clamps the voltage between the drain and source of the MOSFET within a predetermined range.

2. A multi-channel parallel flyback switching power supply with an absorption circuit, characterized in that, The device includes a first flyback circuit, a second flyback circuit, and a MOSFET snubber circuit. The MOSFET snubber circuit includes the snubber circuit as described in claim 1, a high-frequency capacitor connected to the snubber circuit, and a fast recovery diode. The first flyback circuit and the second flyback circuit are connected in parallel and connected to the output terminal of the MOSFET snubber circuit. The first flyback circuit and the second flyback circuit each include a transformer and a MOSFET connected in series. The MOSFET snubber circuit includes a fast recovery diode, a high-frequency capacitor, and a transient voltage suppressor diode. When the MOSFET in the first flyback circuit and the second flyback circuit is turned off, the drain voltage of the MOSFET charges the high-frequency capacitor through the fast recovery diode. The high-frequency capacitor absorbs energy, and when the voltage of the high-frequency capacitor is fully charged, it continues to rise until it reaches the clamping voltage of the transient voltage suppressor diode. The transient voltage suppressor diode clamps the voltage between the drain and source of the MOSFET within a predetermined range.

3. The multi-channel parallel flyback switching power supply with absorption circuit as described in claim 2, characterized in that, The first flyback circuit includes a first transformer T1, a first MOSFET Q1, a first Schottky diode D103, and a first electrolytic capacitor CE1. The first terminal of the primary side T1-A of the first transformer T1 is connected to the circuit input terminal VDC, and the second terminal of the primary side T1-A of the first transformer T1 is connected to the drain of the first MOSFET Q1. The source of the first MOSFET Q1 is grounded to GND. The first terminal of the secondary side T1-B of the first transformer T1 is connected to the anode of the first Schottky diode D103, and the cathode of the first Schottky diode D103 is connected to the anode of the first electrolytic capacitor CE1. The second terminal of the secondary side T1-B of the first transformer T1 is connected to the cathode of the first electrolytic capacitor CE1. The anode of the first electrolytic capacitor CE1 is connected to the output terminal OUT1 of the first flyback circuit, and the cathode of the first electrolytic capacitor CE1 is grounded to GND.

4. The multi-channel parallel flyback switching power supply with absorption circuit as described in claim 3, characterized in that, The second flyback circuit includes a second transformer T2, a second MOSFET Q2, a second Schottky diode D105, and a second electrolytic capacitor CE2. The first terminal of the primary winding T2-A of the second transformer T2 is connected to the circuit input terminal VDC, and the second terminal of the primary winding T2-A of the second transformer T2 is connected to the drain of the second MOSFET Q2. The source of the second MOSFET Q2 is grounded to GND. The second terminal of the secondary winding T2-B of the second transformer T2 is connected to the anode of the second Schottky diode D105, and the cathode of the second Schottky diode D105 is connected to the anode of the second electrolytic capacitor CE2. The second terminal of the secondary winding T2-B of the second transformer T2 is connected to the cathode of the second electrolytic capacitor CE2. The anode of the second electrolytic capacitor CE2 is connected to the output terminal OUT2 of the second flyback circuit, and the cathode of the second electrolytic capacitor CE2 is grounded to GND.

5. The multi-channel parallel flyback switching power supply with absorption circuit as described in claim 4, characterized in that, The MOS transistor absorption circuit includes a transient voltage suppression diode D101, a first high-frequency capacitor C101, a second high-frequency capacitor C102, a third high-frequency capacitor C103, a first fast recovery diode D102, a second fast recovery diode D104, and a ferrite bead inductor L101. The two ends of the first high-frequency capacitor C101 are connected in parallel to the two ends of the primary winding T1-A of the first transformer T1. The connection point between the first high-frequency capacitor C101 and the second end of the primary winding T1-A of the first transformer T1, and the drain of the first MOS transistor Q1, is connected to the anode of the first fast recovery diode D102. The two ends of the third high-frequency capacitor C103 are connected in parallel to the two ends of the primary winding T2-A of the second transformer T2. The third high-frequency capacitor C103 and the second... The connection point between the second terminal of the primary side T2-A of transformer T2 and the drain of the second MOSFET Q2 is connected to the anode of the second fast recovery diode D104; the cathode of the first fast recovery diode D102 is connected to the cathode of the second fast recovery diode D104, and is also connected to the first terminal of the second high-frequency capacitor C102, the second terminal of the second high-frequency capacitor C102 is grounded to GND; the anode of the transient voltage suppression diode D101 is connected to the circuit input terminal VDC, and the cathode of the transient voltage suppression diode D101 is connected through the ferrite bead inductor L101 to the connection point between the cathode of the first fast recovery diode D102, the cathode of the second fast recovery diode D104 and the first terminal of the second high-frequency capacitor C102.

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