A wide range soft-switching phase-shifted full-bridge circuit

Abstract

This invention discloses a wide-range soft-switching phase-shifted full-bridge circuit. An auxiliary circuit is added to a traditional phase-shifted full-bridge circuit. A leading branch is formed by a first MOS switch M1 and a third MOS switch M3, while a lagging branch is formed by a second MOS switch M2 and a fourth MOS switch M4. The circuit's first auxiliary switch M1 is adjusted... i1 Second auxiliary switch M i2 The conduction time and the first resonant capacitance C r1 First resonant inductor L r1 Second resonant capacitor C r2 Second resonant inductor L r2 To regulate the current flowing into the lagging branch, an auxiliary current is directly added to the lagging branch, while simultaneously adjusting the parasitic capacitance C of the second MOS switch M2 and the fourth MOS switch M4 in the lagging branch. lag During charging or discharging, the parasitic capacitance C is reduced before the second MOS switch M2 or the fourth MOS switch M4 is turned on. lag Discharge to zero to solve the soft switching problem of lagging branches.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more particularly to a wide-range soft-switching phase-shifted full-bridge circuit. Background Technology

[0002] With the development of power electronics technology, DC-DC converters, as power conversion devices, are increasingly widely used. Isolated full-bridge converters, due to their high power and input-output electrical isolation advantages, have a wide range of applications. Phase-shift control enables full-bridge converters to achieve ZVS soft-switching operation, further reducing converter conduction losses and improving transmission efficiency. Phase-shifted full-bridge (PSFB) converters, due to their zero-voltage switching, constant-frequency modulation, and simple structure, are mostly used in industrial fields, such as aerospace and power systems where power quality requirements are stringent. With the development of new energy technologies, full-bridge circuits, due to their inherent high power and input-output electrical isolation advantages, have been widely used in high-power power conversion devices. Furthermore, the use of phase-shift control in full-bridge circuits, with four switching transistors conducting alternately, reduces the conduction losses of the PSFB converter.

[0003] However, traditional PSFB converters suffer from several well-known drawbacks, such as narrow ZVS range, primary circulating current, severe secondary voltage oscillations, and duty cycle loss. In many applications, the input is relatively constant, but the output voltage varies significantly. A typical application is battery charging, which uses a front-end power factor correction circuit followed by an isolated DC-DC converter. In such applications, the DC-DC converter has a fairly stable input voltage, but its output voltage needs to vary considerably, almost by a ratio of 1:2. For these applications, the PSFB converter is the preferred topology due to its natural ZVS and simple structure. However, when this converter is used in variable output applications, the drawbacks of the PSFB converter become even more pronounced.

[0004] PSFB converters also have the drawback of not being able to simultaneously achieve a wide soft-switching range and a small secondary-side duty cycle loss. This drawback hinders the converter's high frequency and high efficiency.

[0005] There are several existing solutions, but each has its own drawbacks. For example, increasing the series inductance of the primary transformer can increase circuit losses and duty cycle losses on the load side, leading to a drop in output voltage and making it uneconomical. Alternatively, changing the switching frequency of the switching transistor can achieve soft switching, but this method can only achieve zero-voltage switching (ZVS) on the primary side when operating at low load power, which has significant limitations. Intelligent control methods can also be used to achieve soft switching, but these are quite complex. Summary of the Invention

[0006] Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention discloses a wide-range soft-switching phase-shifted full-bridge circuit to solve the problems mentioned in the background section.

[0008] Technical solution

[0009] This invention is a method for achieving soft switching of a lagging branch by controlling the conduction time and resonant current of the auxiliary branch. This method regulates the current flowing into the lagging branch by adjusting the conduction time of the auxiliary circuit's switching transistors and the resonant inductor and capacitor. By directly applying auxiliary current to the lagging branch and simultaneously charging (discharging) or discharging (charging) the parasitic capacitances of the two MOSFETs in the lagging branch, the parasitic capacitances are discharged to zero before the MOSFETs turn on, thus solving the soft switching problem of the lagging branch. This novel phase-shifted full-bridge control circuit PSFB topology with auxiliary circuitry is suitable for a wide load range. Compared with other solutions, it reduces conduction losses, improves circuit conduction performance, increases operating efficiency, and can be used under a wide range of loads.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A wide-range soft-switching phase-shifted full-bridge circuit includes a phase-shifted full-bridge circuit and auxiliary circuits. The phase-shifted full-bridge circuit consists of an input DC power supply Vin, a first MOS switch M1, a second MOS switch M2, a third MOS switch M3, a fourth MOS switch M4, a first rectifier diode D1, a second rectifier diode D2, a third rectifier diode D3, a fourth rectifier diode D4, an output capacitor C0, an output inductor L0, an output resistor R0, and a transformer T. The first MOS switch M1 and the third MOS switch M3 are connected in series and then in parallel with the input DC power supply Vin. The second MOS switch M2 and the fourth MOS switch M4 are connected in series and then in parallel with the input DC power supply Vin. The connection point between the first MOS switch M1 and the third MOS switch M3 is point A, and the connection point between the second MOS switch M2 and the fourth MOS switch M4 is point B. Both the first MOS switch M1 and the third MOS switch M3 have parasitic capacitance C. lead Both the second MOS switch M2 and the fourth MOS switch M4 have parasitic capacitance C. lag Points A and B are connected to the primary side of transformer T, and there is a leakage inductance L between point A and transformer T. k The first rectifier diode D1 and the third rectifier diode D3 are connected to point P, and the second rectifier diode D2 and the fourth rectifier diode D4 are connected to point Q. Points P and Q are respectively connected to the load side of transformer T. The output capacitor C0 and the output resistor R0 are connected in parallel and then connected in series with the output inductor L0 between the second rectifier diode D2 and the fourth rectifier diode D4. The auxiliary circuit consists of the first auxiliary switch M.i1 Second auxiliary switch M i2 First resonant capacitor C r1 First resonant inductor L r1 Second auxiliary switch M i2 Second resonant capacitor C r2 Second resonant inductor L r2 Composition, first auxiliary switch M i1 With the first resonant capacitor C r1 First resonant inductor L r1 The second auxiliary switch M is connected in series between Vin+ and point B. i2 With the second resonant capacitor C r2 Second resonant inductor L r2 It is connected in series between Vin- and point B.

[0012] The primary voltage of the transformer T in this invention is V1, the load voltage of the transformer T is V2, and the first auxiliary switch M... i1 The voltage across the terminals is VM i1 Second auxiliary switch M i2 The voltage across the terminals is VM i2 .

[0013] In this invention, the first MOS switch M1 and the third MOS switch M3 form a lead path, and there is a time dead time between the first MOS switch M1 and the third MOS switch M3. The second MOS switch M2 and the fourth MOS switch M4 form a lag branch, and there is also a time dead time between the second MOS switch M2 and the fourth MOS switch M4. The first auxiliary switch M... i1 Second auxiliary switch M i2 The drive time is determined by the switching time of the lagging branch, and the first auxiliary switch M i1 Responsible for implementing the soft switching of the fourth MOS switch M4, and the second auxiliary switch M i2 Responsible for implementing the soft switching of the third MOS switch M3, and the first auxiliary switch M i1 Second auxiliary switch M i2 When not in operation, the first resonant capacitor C r1 First resonant inductor L r1 Second resonant capacitor C r2 Second resonant inductor L r2 Charging is performed via transformer T, and the first auxiliary switch M... i1 Second auxiliary switch M i2 It also withstands a stable voltage at this time.

[0014] This invention adjusts the first auxiliary switch M of the auxiliary circuit. i1 Second auxiliary switch Mi2 The conduction time and the first resonant capacitance C r1 First resonant inductor L r1 Second resonant capacitor C r2 Second resonant inductor L r2 To regulate the current flowing into the lagging branch, an auxiliary current is directly added to the lagging branch, while simultaneously adjusting the parasitic capacitance C of the second MOS switch M2 and the fourth MOS switch M4 in the lagging branch. lag During charging or discharging, the parasitic capacitance C is reduced before the second MOS switch M2 or the fourth MOS switch M4 is turned on. lag Discharging to zero solves the soft switching problem of lagging branches.

[0015] Before the second MOS switch M2 of the present invention is turned on, the second auxiliary switch M i2 The second resonant capacitor C is already open. r2 Second resonant inductor L r2 Resonance begins to occur, and the energy stored in the second resonant capacitor C r2 Second resonant inductor L r2 The energy inside is transmitted through transformer T, the second MOS switch M2, and the second auxiliary switch M. i2 A circuit is formed, and the current flows into the second resonant capacitor C. r2 Current I i2 The direction is opposite to the voltage direction across the second MOS switch M2, which affects the parasitic capacitance C of the second MOS switch M2. lag Discharge the voltage of the second MOS switch M2 to zero before it is turned on, thereby achieving zero-voltage switch (ZVS) soft-switching turn-on.

[0016] Before the fourth MOS switch M4 of the present invention is turned on, the first auxiliary switch M i1 It's already open, the first resonant capacitor C r1 First resonant inductor L r1 Resonance begins to occur, and the energy stored in the first resonant capacitor C r1 First resonant inductor L r1 The energy inside is transmitted through transformer T, the fourth MOS switch M4, and the first auxiliary switch M. i1 A circuit is formed, and the current flows into the first resonant capacitor C. r1 Current I i1 The direction is opposite to the voltage direction across the fourth MOS switch M4, which affects the parasitic capacitance C of the fourth MOS switch M4. lag Discharge, and discharge its voltage to zero before the fourth MOS switch M4 is turned on, thereby realizing the zero voltage switch ZVS turn-on.

[0017] The first auxiliary switch M of the present invention i1Or the second auxiliary switch M i2 After being shut down, the auxiliary circuit continues to charge through transformer T, and the process ends.

[0018] The energy stored in the second MOS switch M2 and the fourth MOS switch M4 of this invention is V in This represents the output voltage of the input DC power supply Vin.

[0019] In order to achieve zero-voltage switching (ZVS) operation of the MOS switches on each arm of the phase-shifted full-bridge control circuit PSFB, the parasitic capacitance of the MOS switch to be turned on must be discharged, and at the same time, the parasitic capacitance of the other MOS switch in the same arm must be charged. Therefore, the energy relationship between them must satisfy the following:

[0020] (1)

[0021] in, , where I p Indicates leakage sensation L k The current, E aux The energy stored for auxiliary circuits.

[0022] Compared with the prior art, the present invention has the following technical effects:

[0023] (1) The circuit structure is more stable and reliable, suitable for high-power switching power supplies, low cost and simple structure, which can improve the shortcomings of the traditional phase-shifted full-bridge control circuit PSFB.

[0024] (2) It can reduce the energy loss of the MOSFET during turn-on and turn-off.

[0025] (3) It can achieve zero-voltage switching of lagging branches and duty cycle loss within a wide load range.

[0026] (4) Heat dissipation has also been improved, and soft switching can be achieved over a wide range. Attached Figure Description

[0027] Figure 1 This is a diagram showing the overall topology of a wide-range soft-switching phase-shifted full-bridge circuit according to the present invention.

[0028] Figure 2 This is a topology diagram of a phase-shifted full-bridge circuit with wide-range soft switching according to the present invention.

[0029] Figure 3The DC power supply Vin current of the wide-range soft-switching phase-shifted full-bridge circuit of the present invention is injected into the first MOS switch M1, the second MOS switch M2, the third MOS switch M3, the fourth MOS switch M4, and the first auxiliary switch M1 in the phase-shifted full-bridge circuit. i1 Second auxiliary switch M i2 Drive key waveforms. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0031] Please see Figures 1 to 3 The diagram shows a wide-range soft-switching phase-shifted full-bridge circuit according to the present invention.

[0032] A wide-range soft-switching phase-shifted full-bridge circuit includes a phase-shifted full-bridge circuit and an auxiliary circuit.

[0033] like Figure 1 , Figure 2 As shown, the phase-shifted full-bridge circuit consists of an input DC power supply Vin, a first MOS switch M1, a second MOS switch M2, a third MOS switch M3, a fourth MOS switch M4, a first rectifier diode D1, a second rectifier diode D2, a third rectifier diode D3, a fourth rectifier diode D4, an output capacitor C0, an output inductor L0, an output resistor R0, and a transformer T. The first MOS switch M1 and the third MOS switch M3 are connected in series and then in parallel with the input DC power supply Vin. The second MOS switch M2 and the fourth MOS switch M4 are connected in series and then in parallel with the input DC power supply Vin. The connection point between the first MOS switch M1 and the third MOS switch M3 is point A, and the connection point between the second MOS switch M2 and the fourth MOS switch M4 is point B. Both the first MOS switch M1 and the third MOS switch M3 have parasitic capacitance C. lead Both the second MOS switch M2 and the fourth MOS switch M4 have parasitic capacitance C. lag Points A and B are connected to the primary side of transformer T, and there is a leakage inductance L between point A and transformer T. k The first rectifier diode D1 and the third rectifier diode D3 are connected to point P, and the second rectifier diode D2 and the fourth rectifier diode D4 are connected to point Q. Points P and Q are respectively connected to the load side of transformer T. The output capacitor C0 and the output resistor R0 are connected in parallel and then connected in series with the output inductor L0 between the second rectifier diode D2 and the fourth rectifier diode D4. The auxiliary circuit consists of the first auxiliary switch M. i1 Second auxiliary switch M i2 First resonant capacitor C r1 First resonant inductor L r1 Second auxiliary switch Mi2 Second resonant capacitor C r2 Second resonant inductor L r2 Composition, first auxiliary switch M i1 With the first resonant capacitor C r1 First resonant inductor L r1 The second auxiliary switch M is connected in series between Vin+ and point B. i2 With the second resonant capacitor C r2 Second resonant inductor L r2 It is connected in series between Vin- and point B.

[0034] The primary voltage of the transformer T is V1, the load voltage of the transformer T is V2, and the first auxiliary switch M... i1 The voltage across the terminals is VM i1 Second auxiliary switch M i2 The voltage across the terminals is VM i2 .

[0035] like Figure 1 As shown, the first MOS switch M1 and the third MOS switch M3 form a leading path, with a time dead zone between them. The second MOS switch M2 and the fourth MOS switch M4 form a lagging branch, also with a time dead zone. The first auxiliary switch M... i1 Second auxiliary switch M i2 The drive time is determined by the switching time of the lagging branch, and the first auxiliary switch M i1 Responsible for implementing the soft switching of the fourth MOS switch M4, and the second auxiliary switch M i2 Responsible for implementing the soft switching of the third MOS switch M3, and the first auxiliary switch M i1 Second auxiliary switch M i2 When not in operation, the first resonant capacitor C r1 First resonant inductor L r1 Second resonant capacitor C r2 Second resonant inductor L r2 Charging is performed via transformer T, and the first auxiliary switch M... i1 Second auxiliary switch M i2 It also withstands a stable voltage at this time.

[0036] This invention adjusts the first auxiliary switch M of the auxiliary circuit. i1 Second auxiliary switch M i2 The conduction time and the first resonant capacitance C r1 First resonant inductor L r1 Second resonant capacitor Cr2 Second resonant inductor L r2 To regulate the current flowing into the lagging branch, an auxiliary current is directly added to the lagging branch, while simultaneously adjusting the parasitic capacitance C of the second MOS switch M2 and the fourth MOS switch M4 in the lagging branch. lag During charging or discharging, the parasitic capacitance C is reduced before the second MOS switch M2 or the fourth MOS switch M4 is turned on. lag Discharging to zero solves the soft-switching problem of the lagging branch. A novel phase-shifted full-bridge control circuit with auxiliary circuitry (PSFB) topology is suitable for a wide load range.

[0037] like Figure 3 As shown, before the second MOS switch M2 is turned on, the second auxiliary switch M... i2 The second resonant capacitor C is already open. r2 Second resonant inductor L r2 Resonance begins to occur, and the energy stored in the second resonant capacitor C r2 Second resonant inductor L r2 The energy inside is transmitted through transformer T, the second MOS switch M2, and the second auxiliary switch M. i2 A circuit is formed, and the current flows into the second resonant capacitor C. r2 Current I i2 The direction is opposite to the voltage direction across the second MOS switch M2, which affects the parasitic capacitance C of the second MOS switch M2. lag Discharge the voltage of the second MOS switch M2 to zero before it is turned on, thereby achieving zero-voltage switch (ZVS) soft-switching turn-on.

[0038] like Figure 3 As shown, before the fourth MOS switch M4 is turned on, the first auxiliary switch M... i1 It's already open, the first resonant capacitor C r1 First resonant inductor L r1 Resonance begins to occur, and the energy stored in the first resonant capacitor C r1 First resonant inductor L r1 The energy inside is transmitted through transformer T, the fourth MOS switch M4, and the first auxiliary switch M. i1 A circuit is formed, and the current flows into the first resonant capacitor C. r1 Current I i1 The direction is opposite to the voltage direction across the fourth MOS switch M4, which affects the parasitic capacitance C of the fourth MOS switch M4. lag Discharge, and discharge its voltage to zero before the fourth MOS switch M4 is turned on, thereby realizing the zero voltage switch ZVS turn-on.

[0039] The first auxiliary switch M i1 Or the second auxiliary switch Mi2 After being shut down, the auxiliary circuit continues to charge through transformer T, and the process ends.

[0040] The energy stored in the second MOS switch M2 and the fourth MOS switch M4 is V in This represents the output voltage of the input DC power supply Vin. The energy stored in the leakage inductance of the traditional phase-shifted full-bridge control circuit PSFB is... , where I p Indicates leakage sensation L k The current, the leakage inductance L itself k If it's small, the energy stored inside isn't enough to completely supply C. lag Discharge.

[0041] In order to achieve zero-voltage switching (ZVS) operation of the MOS switches on each arm of the phase-shifted full-bridge control circuit PSFB, the parasitic capacitance of the MOS switch to be turned on must be discharged, and at the same time, the parasitic capacitance of the other MOS switch in the same arm must be charged. Therefore, the energy relationship between them must satisfy the following:

[0042] (1)

[0043] in, , where I p Indicates leakage sensation L k The current, E aux The energy stored for auxiliary circuits.

[0044] The energy injected into the auxiliary branch and the leakage inductance L k The energy inherent in the circuit is greater than the energy in the lagging branch, which is sufficient to charge and discharge the lagging branch, thus enabling the zero-voltage switch (ZVS) of the lagging branch to be turned on.

[0045] The working principle and process of this invention are as follows:

[0046] This invention adds an auxiliary circuit to a traditional phase-shifted full-bridge circuit. The first MOS switch M1 and the third MOS switch M3 form a leading branch, and the second MOS switch M2 and the fourth MOS switch M4 form a lagging branch. The first auxiliary switch M... i1 Responsible for implementing the soft switching of the fourth MOS switch M4, and the second auxiliary switch M i2 Responsible for implementing the soft switching of the third MOS switch M3, and the first auxiliary switch M i1 Second auxiliary switch M i2 When not in operation, the first resonant capacitor C r1 First resonant inductor L r1 Second resonant capacitor Cr2 Second resonant inductor L r2 Charging is performed via transformer T, and the first auxiliary switch M... i1 Second auxiliary switch M i2 It also withstands a stable voltage at this time. This is achieved by adjusting the first auxiliary switch M in the auxiliary circuit. i1 Second auxiliary switch M i2 The conduction time and the first resonant capacitance C r1 First resonant inductor L r1 Second resonant capacitor C r2 Second resonant inductor L r2 To regulate the current flowing into the lagging branch, an auxiliary current is directly added to the lagging branch, while simultaneously adjusting the parasitic capacitance C of the second MOS switch M2 and the fourth MOS switch M4 in the lagging branch. lag During charging or discharging, the parasitic capacitance C is reduced before the second MOS switch M2 or the fourth MOS switch M4 is turned on. lag Discharge to zero to solve the soft switching problem of lagging branches.

Claims

1. A wide range soft-switching phase-shifted full-bridge circuit, characterized by: The circuit includes a phase-shifted full-bridge circuit and auxiliary circuits. The phase-shifted full-bridge circuit consists of an input DC power supply Vin, a first MOS switch M1, a second MOS switch M2, a third MOS switch M3, a fourth MOS switch M4, a first rectifier diode D1, a second rectifier diode D2, a third rectifier diode D3, a fourth rectifier diode D4, an output capacitor C0, an output inductor L0, an output resistor R0, and a transformer T. The first MOS switch M1 and the third MOS switch M3 are connected in series and then in parallel with the input DC power supply Vin. The second MOS switch M2 and the fourth MOS switch M4 are connected in series and then in parallel with the input DC power supply Vin. The connection point between the first MOS switch M1 and the third MOS switch M3 is point A, and the connection point between the second MOS switch M2 and the fourth MOS switch M4 is point B. Both the first MOS switch M1 and the third MOS switch M3 have parasitic capacitance C. lead Both the second MOS switch M2 and the fourth MOS switch M4 have parasitic capacitance C. lag Points A and B are connected to the primary side of transformer T, and there is a leakage inductance L between point A and transformer T. k The first rectifier diode D1 and the third rectifier diode D3 are connected to point P, and the second rectifier diode D2 and the fourth rectifier diode D4 are connected to point Q. Points P and Q are respectively connected to the load side of transformer T. The output capacitor C0 and the output resistor R0 are connected in parallel and then connected in series with the output inductor L0 between the second rectifier diode D2 and the fourth rectifier diode D4. The auxiliary circuit consists of the first auxiliary switch M. i1 Second auxiliary switch M i2 First resonant capacitor C r1 First resonant inductor L r1 Second auxiliary switch M i2 Second resonant capacitor C r2 Second resonant inductor L r2 Composition, first auxiliary switch M i1 With the first resonant capacitor C r1 First resonant inductor L r1 The second auxiliary switch M is connected in series between Vin+ and point B. i2 With the second resonant capacitor C r2 Second resonant inductor L r2 It is connected in series between Vin- and point B.

2. The wide range soft-switching phase-shifted full-bridge circuit of claim 1, wherein, The The first MOS switch tube M1 and the third MOS switch tube M3 constitute a leading branch, and there is a time dead zone between the first MOS switch tube M1 and the third MOS switch tube M3. The second MOS switch tube M2 and the fourth MOS switch tube M4 constitute a lagging branch, and there is also a time dead zone between the second MOS switch tube M2 and the fourth MOS switch tube M4. The first auxiliary switch tube M i1 and the second auxiliary switch tube M i2 are driven by the switching time of the lagging branch. The first auxiliary switch tube M i1 is responsible for the realization of the soft switching of the fourth MOS switch tube M4. The second auxiliary switch tube M i2 is responsible for the realization of the soft switching of the third MOS switch tube M3. When the first auxiliary switch tube M i1 and the second auxiliary switch tube M i2 are not turned on, the first resonant capacitor C r1 , the first resonant inductor L r1 , the second resonant capacitor C r2 , the second resonant inductor L r2 are charged through the transformer T, and the first auxiliary switch tube M i1 and the second auxiliary switch tube M i2 also bear stable voltages at this time.

3. The wide range soft-switching phase-shifted full-bridge circuit of claim 2, wherein, By adjusting the first auxiliary switch M of the auxiliary circuit i1 Second auxiliary switch M i2 The conduction time and the first resonant capacitance C r1 First resonant inductor L r1 Second resonant capacitor C r2 Second resonant inductor L r2 To regulate the current flowing into the lagging branch, an auxiliary current is directly added to the lagging branch, while simultaneously adjusting the parasitic capacitance C of the second MOS switch M2 and the fourth MOS switch M4 in the lagging branch. lag During charging or discharging, the parasitic capacitance C is reduced before the second MOS switch M2 or the fourth MOS switch M4 is turned on. lag Discharging to zero solves the soft switching problem of lagging branches.

4. The wide range soft-switching phase-shifted full-bridge circuit of claim 1, wherein, The second auxiliary switch tube M i2 has been opened, the second resonant capacitor C r2 , the second resonant inductor L r2 starts to produce resonance, the energy stored in the second resonant capacitor C r2 , the second resonant inductor L r2 forms a loop through the transformer T, the second MOS switch tube M2, the second auxiliary switch tube M i2 , and the current I r2 of the second resonant capacitor C i2 flows in. The direction of the voltage across the second MOS switch tube M2 is opposite to the direction of the voltage across the second MOS switch tube M2, and the parasitic capacitor C lag of the second MOS switch tube M2 is discharged, and the voltage of the second MOS switch tube M2 is discharged to zero before the second MOS switch tube M2 is turned on, thereby realizing zero voltage switching ZVS soft switching turn-on.

5. The wide range soft-switching phase-shifted full-bridge circuit of claim 1, wherein, Before the fourth MOS switch M4 is turned on, the first auxiliary switch M i1 It's already open, the first resonant capacitor C r1 First resonant inductor L r1 Resonance begins to occur, and the energy stored in the first resonant capacitor C r1 First resonant inductor L r1 The energy inside is transmitted through transformer T, the fourth MOS switch M4, and the first auxiliary switch M. i1 A circuit is formed, and the current flows into the first resonant capacitor C. r1 Current I i1 The direction is opposite to the voltage direction across the fourth MOS switch M4, which affects the parasitic capacitance C of the fourth MOS switch M4. lag Discharge, and discharge its voltage to zero before the fourth MOS switch M4 is turned on, thereby realizing the zero voltage switch ZVS turn-on.

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