Soft switching isolation driving circuit

Abstract

The invention relates to a soft switching isolation driving circuit which comprises a driving transformer, a push-pull MOS tube, a power MOS tube, a driving resistor and an input capacitor. A primary winding of the driving transformer is connected in series between the push-pull MOS tube and the input capacitor; one end of the driving resistor is electrically connected to a secondary winding of the driving transformer, and the other end of the driving resistor is electrically connected to the power MOS tube. The soft switching isolation driving circuit provided by the invention is suitable for a topology with a fixed duty ratio close to 50%, realizes soft switching of the push-pull MOS tube and reduces the voltage stress of the push-pull MOS tube by adjusting the excitation inductance value of the driving transformer and the dead time of the push-pull MOS tube, effectively reduces the driving loss, reduces the heat, and improves the working efficiency of a switching power supply.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a soft switch isolation drive circuit. Background Art

[0002] With the development of power electronics technology, miniaturization, high frequency, high power density and high efficiency are the current development trends of switching power supplies. The increase in the operating frequency of switching power supplies greatly reduces the size of magnetic devices, the number and volume of capacitors, but it also increases the core loss of magnetic devices and the switching loss of power devices (such as MOS tubes), thereby reducing the efficiency of switching power supplies. Generally, there are two solutions to the increase in magnetic device losses: (1) Select magnetic materials with low magnetic loss; (2) Control the excitation range of the core in the design. There are also many solutions to the switching loss of power devices. For example, adding LC resonant circuits or clamping tubes to the switching converter, controlling the working timing of the switching tube, etc. to achieve soft switching, thereby reducing the switching loss of power devices.

[0003] In addition, the switching power supply will also face the problem of greatly increased drive circuit losses at high switching frequencies, which will lead to reduced power system efficiency and severe heating of drive circuit components. At present, research on how to reduce the losses of the drive circuit in high switching frequency applications is still insufficient and needs to be improved urgently. Summary of the invention

[0004] Based on this, it is necessary to provide a soft switch isolation drive circuit that can effectively reduce drive loss, reduce heat, and improve the working efficiency of the switching power supply.

[0005] The present application provides a soft switch isolation drive circuit, comprising: a drive transformer, a push-pull MOS tube, a power MOS tube, a drive resistor and an input capacitor; the primary winding of the drive transformer is connected in series between the push-pull MOS tube and the input capacitor; one end of the drive resistor is electrically connected to the secondary winding of the drive transformer, and the other end of the drive resistor is electrically connected to the power MOS tube.

[0006] Preferably, the primary winding includes: a first primary winding and a second primary winding; the push-pull MOS tube includes: a first push-pull MOS tube and a second push-pull MOS tube; the first primary winding is electrically connected to the drain of the first push-pull MOS tube, and the second primary winding is electrically connected to the drain of the second push-pull MOS tube; the gate of the first push-pull MOS tube and the gate of the second push-pull MOS tube receive a square wave signal with a dead zone and a phase shift of 180°, and the source of the first push-pull MOS tube and the source of the second push-pull MOS tube are both grounded.

[0007] Preferably, the driving resistor includes: a first resistor and a second resistor; the power MOS tube includes: a first power MOS tube and a second power MOS tube; when the first power MOS tube and the second power MOS tube have a common source, the number of the secondary windings is one; when the first power MOS tube and the second power MOS tube do not have a common source, the number of the secondary windings is two, recorded as: a first secondary winding and a second secondary winding.

[0008] Preferably, the first resistor is connected in series between the like-name end of the first secondary winding and the gate of the first power MOS tube; the source of the first power MOS tube is electrically connected to the unlike-name end of the first secondary winding; the second resistor is connected in series between the unlike-name end of the second secondary winding and the gate of the second power MOS tube; the source of the second power MOS tube is electrically connected to the like-name end of the second secondary winding.

[0009] Preferably, the turns ratio of the primary and secondary sides of the driving transformer is set to , the primary winding excitation inductance of the drive transformer The value of needs to satisfy the following formula:

[0010]

[0011] in, is the dead time between driving the first push-pull MOS tube and the second push-pull MOS tube, is the gate-source capacitance of the first power MOS tube, The gate-source capacitance of the second power MOS tube, The drain-source capacitance of the first push-pull MOS tube, is the drain-source capacitance of the second push-pull MOS tube, is the duty cycle of the first push-pull MOS tube V1, is the switching cycle.

[0012] Preferably, it also includes: four signal-type MOS tubes, which are respectively recorded as: a first MOS tube, a second MOS tube, a third MOS tube and a fourth MOS tube; the same-name end of the first secondary winding is electrically connected to the gate of the first MOS tube, the drain of the second MOS tube and one end of the first resistor, the opposite-name end of the first secondary winding is electrically connected to the drain of the first MOS tube and the gate of the second MOS tube, the gate of the first power MOS tube is electrically connected to the other end of the first resistor, and the source of the first power MOS tube is electrically connected to the source of the first MOS tube and the source of the second MOS tube; the opposite-name end of the second secondary winding is electrically connected to the gate of the third MOS tube, the drain of the fourth MOS tube and one end of the second resistor, the same-name end of the second secondary winding is electrically connected to the drain of the third MOS tube and the gate of the fourth MOS tube, the gate of the second power MOS tube is electrically connected to the other end of the second resistor, and the source of the second power MOS tube is electrically connected to the source of the third MOS tube and the source of the fourth MOS tube.

[0013] Preferably, the gate voltage turn-on thresholds of the first MOS tube, the second MOS tube, the third MOS tube and the fourth MOS tube are all lower than the gate voltage turn-on thresholds of the first power MOS tube and the second power MOS tube.

[0014] Preferably, when the first power MOS tube and the second power MOS tube are in a common source form, the soft switch isolation drive circuit further includes: a fifth MOS tube and a sixth MOS tube; one end of the secondary winding is electrically connected to one end of the first resistor, the drain of the fifth MOS tube and the gate of the sixth MOS tube; the other end of the secondary winding is electrically connected to one end of the second resistor, the drain of the sixth MOS tube and the gate of the fifth MOS tube; the gate of the first power MOS tube is electrically connected to the other end of the first resistor, and the source of the first power MOS tube is electrically connected to the source of the fifth MOS tube, the source of the sixth MOS tube and the source of the second power MOS tube; the gate of the second power MOS tube is electrically connected to the other end of the second resistor.

[0015] Preferably, the first power MOS tube and the second power MOS tube are positive voltage driven.

[0016] Preferably, the drain of the first power MOS tube and the drain of the second power MOS tube are both connected to a power circuit to control power conversion of the power circuit.

[0017] The soft switching isolation drive circuit provided in the present application is suitable for a topology with a fixed duty cycle close to 50%. By adjusting the excitation inductance of the driving transformer and the dead time of the push-pull MOS tube, the soft switching of the push-pull MOS tube is realized and the voltage stress of the push-pull MOS tube is reduced, thereby effectively reducing the driving loss, reducing the heat, and improving the working efficiency of the switching power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the conventional technology, the drawings required for use in the embodiments or the conventional technology descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 This is a schematic diagram of the positive and negative voltage soft switch isolation drive circuit according to an embodiment of the present application.

[0020] Figure 2 for Figure 1 The driving circuit waveform diagram.

[0021] Figure 3 This is a schematic diagram of a positive pressure soft switch isolation drive circuit according to an embodiment of the present application.

[0022] Figure 4 This is a schematic diagram of a positive pressure soft switch isolation drive circuit according to another embodiment of the present application. DETAILED DESCRIPTION

[0023] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0024] It can be understood that the “connection” in the following embodiments should be understood as “electrical connection”, “communication connection”, etc. if the connected circuits, modules, units, etc. have electrical signals or data transmission between each other.

[0025] like Figure 1 As shown, this embodiment provides a soft switch isolation driving circuit, including: a driving transformer T, a push-pull MOS tube 1, a power MOS tube 2, a driving resistor 3 and an input capacitor C.

[0026] The primary winding of the driving transformer T is connected in series between the push-pull MOS tube 1 and the input capacitor C; one end of the driving resistor 3 is electrically connected to the secondary winding of the driving transformer T, and the other end of the driving resistor 3 is electrically connected to the power MOS tube 2.

[0027] Preferably, the primary winding includes: a first primary winding and a second primary winding; the push-pull MOS transistor 1 includes: a first push-pull MOS transistor V1 and a second push-pull MOS transistor V2.

[0028] One end of the first primary winding is electrically connected to the drain of the first push-pull MOS tube V1, and the other end of the first primary winding is electrically connected to one end of the input capacitor C; one end of the second primary winding is electrically connected to the drain of the second push-pull MOS tube V2, and the other end of the second primary winding is electrically connected to one end of the input capacitor C; the gate of the first push-pull MOS tube V1 and the gate of the second push-pull MOS tube V2 receive a square wave signal with a dead zone and a phase shift of 180°, and the source of the first push-pull MOS tube V1 and the source of the second push-pull MOS tube V2 are both grounded; the other end of the input capacitor C is grounded.

[0029] Here, the square wave signal is generated by the control circuit module as the initial driving signal of the first push-pull MOS tube V1 and the second push-pull MOS tube V2. As an example, two square wave signals with a fixed duty cycle close to 50% and a phase shift of 180° are respectively given to the first push-pull MOS tube V1 and the second push-pull MOS tube V2, which are recorded as: the driving signal Pulse_A of the first push-pull MOS tube V1 and the driving signal Pulse_B of the second push-pull MOS tube V2. Preferably, the duty cycles of the driving signal Pulse_A and the driving signal Pulse_B are equal.

[0030] Preferably, the driving resistor 3 includes: a first resistor R1 and a second resistor R2; the power MOS tube 2 includes: a first power MOS tube V3 and a second power MOS tube V4.

[0031] When the first power MOS tube V3 and the second power MOS tube V4 share a common source, the number of the secondary windings is one; when the first power MOS tube V3 and the second power MOS tube V4 do not share a common source, the number of the secondary windings is two, which are recorded as: the first secondary winding and the second secondary winding.

[0032] exist Figure 1 In the embodiment, the first resistor R1 is connected in series between the same-name end of the first secondary winding and the gate of the first power MOS tube V3; the source of the first power MOS tube V3 is electrically connected to the opposite-name end of the first secondary winding; the second resistor R2 is connected in series between the opposite-name end of the second secondary winding and the gate of the second power MOS tube V4; the source of the second power MOS tube V4 is electrically connected to the same-name end of the second secondary winding.

[0033] Figure 1The soft switch isolation drive circuit shown is a square wave complementary lossless isolation drive circuit with a phase shift of 180° and a duty cycle of nearly 50%. When the turns ratio of the primary and secondary sides of the driving transformer T is 1:1:1:1, as shown in FIG. Figure 2 As shown, the specific working mode of the circuit is:

[0034] (1) During the time [t0, t1], the drive signal Pulse_A is high and the drive signal Pulse_B is low. The first push-pull MOS transistor V1 is turned on and the second push-pull MOS transistor V2 is turned off. The drain current V1_Id of the first push-pull MOS transistor V1 increases linearly and reaches the maximum value at time t1. The first power MOS transistor V3 is turned on and the second power MOS transistor V4 is turned off, and a power transmission process begins.

[0035] (2) During the time [t1, t2], the drive signal Pulse_A becomes low, and the first push-pull MOS tube V1 and the second push-pull MOS tube V2 are both turned off. During the dead time, the excitation inductance of the drive transformer T It resonates with the gate capacitance of the first power MOS tube V3 and the second power MOS tube V4, redistributes the energy between the gates, causes the output parasitic capacitance of the first push-pull MOS tube V1 to be charged and the output parasitic capacitance of the second push-pull MOS tube V2 to be discharged, so that the gate voltage V4_GS of the second power MOS tube V4 reaches the winding supply voltage VCC at time t2, and the gate voltage of the first power MOS tube V3 reaches -VCC at time t2. During the dead time, the drain-source voltage V1_DS of the first push-pull MOS tube V1 gradually rises and finally reaches the voltage of 2*VCC.

[0036] (3) During the time [t2, t3], the drive signal Pulse_B becomes high at time t2. Since the voltage across the push-pull drive transformer winding is VCC at time t2, the second push-pull MOS tube V2 can achieve ZVS conduction. The drain current of the second push-pull MOS tube V2 increases linearly and reaches the maximum value at time t3. The second power MOS tube V4 is turned on and the first power MOS tube V3 is turned off, starting another power transmission process.

[0037] (4) During the time [t3, t4], the drive signal Pulse_B becomes low, and the first push-pull MOS tube V1 and the second push-pull MOS tube V2 are both turned off. At this time, the excitation inductance of the driving transformer T Resonate with the gate capacitance of the first power MOS tube V3 and the second power MOS tube V4, redistribute the energy between the gates, cause the output parasitic capacitance of the first push-pull MOS tube V1 to discharge and the output parasitic capacitance of the second push-pull MOS tube V2 to charge, so that the voltage across the winding of the push-pull drive transformer reaches VCC; turn on the first push-pull MOS tube V1 at time t4, and realize ZVS turn-on of the first push-pull MOS tube V1. So far, a switching cycle working process ends.

[0038] The turns ratio of the primary and secondary sides of the drive transformer is set to , during the dead time, the excitation inductance of the drive transformer T Resonate with the gate capacitance of the first power MOS tube V3 and the second power MOS tube V4, redistribute the energy between the gates, and complete the charge transfer within the dead time, as shown below:

[0039]

[0040]

[0041] Here, 2×VCC is because the gate voltage of the power MOS tube (i.e., GS voltage) changes from -VCC to +VCC. is the duty cycle of the first push-pull MOS tube V1, is the switching cycle of the soft switching isolation drive circuit, is the primary excitation current of the driving transformer T. From the above two formulas, it can be deduced that the primary winding excitation inductance of the driving transformer T is The value of needs to satisfy the following formula:

[0042]

[0043] in, is the dead time between driving the first push-pull MOS tube and the second push-pull MOS tube, is the gate-source capacitance of the first power MOS tube, The gate-source capacitance of the second power MOS tube, The drain-source capacitance of the first push-pull MOS tube, is the drain-source capacitance of the second push-pull MOS tube.

[0044] The soft switch isolation driving circuit provided in this embodiment is suitable for topologies with a fixed duty cycle close to 50% (such as full-bridge / half-bridge LLC topology, BUCK cascade push-pull topology, etc.), by adjusting the excitation inductance of the driving transformer T And the dead time of the push-pull MOS tube, realize the soft switching of the push-pull MOS tube and reduce the voltage stress of the push-pull MOS tube, effectively reduce the driving loss, reduce the heat, and improve the working efficiency of the switching power supply.

[0045] exist Figure 1 In the circuit shown, the gate waveforms obtained by the first power MOS tube V3 and the second power MOS tube V4 are in the positive and negative voltage driving form. Since the reverse flow of current consumes part of the energy during the conversion from negative voltage to positive voltage, Figure 1 On the basis of the above, MOS tubes are added to improve the first power MOS tube V3 and the second power MOS tube V4 to become positive voltage drive. The specific circuit form is as follows Figure 3 That is, Figure 3 The first power MOS tube V3 and the second power MOS tube V4 are driven by positive voltage.

[0046] Figure 3 The four MOS tubes added in the embodiment are respectively recorded as: a first MOS tube V31, a second MOS tube V32, a third MOS tube V41 and a fourth MOS tube V42.

[0047] As an example, the four MOS tubes are all signal-type positive voltage clamped MOS tubes; preferably, the gate voltage turn-on thresholds of the first MOS tube V31, the second MOS tube V32, the third MOS tube V41 and the fourth MOS tube V42 are all lower than the gate voltage turn-on threshold of the first power MOS tube V3; the gate voltage turn-on thresholds of the first MOS tube V31, the second MOS tube V32, the third MOS tube V41 and the fourth MOS tube V42 are all lower than the gate voltage turn-on threshold of the second power MOS tube V4.

[0048] The same-name end of the first secondary winding is electrically connected to the gate of the first MOS transistor V31, the drain of the second MOS transistor V32 and one end of the first resistor R1, the opposite-name end of the first secondary winding is electrically connected to the drain of the first MOS transistor V31 and the gate of the second MOS transistor V32, the gate of the first power MOS transistor V3 is electrically connected to the other end of the first resistor R1, and the source of the first power MOS transistor V3 is electrically connected to the source of the first MOS transistor V31 and the source of the second MOS transistor V32.

[0049] The opposite-name end of the second secondary winding is electrically connected to the gate of the third MOS tube V41, the drain of the fourth MOS tube V42 and one end of the second resistor R2, the same-name end of the second secondary winding is electrically connected to the drain of the third MOS tube V41 and the gate of the fourth MOS tube V42, the gate of the second power MOS tube V4 is electrically connected to the other end of the second resistor R2, and the source of the second power MOS tube V4 is electrically connected to the source of the third MOS tube V41 and the source of the fourth MOS tube V42.

[0050] Figure 3 The working process of the positive voltage soft switch isolation driving circuit shown is as follows: when the same-name end of the first secondary winding of the driving transformer T is positive, the first MOS tube V31 is turned on, the positive voltage is applied between the gate source of the first power MOS tube V3, and the first power MOS tube V3 is turned on; when the opposite-name end of the first secondary winding is positive, the second MOS tube V32 is turned on, the gate source of the first power MOS tube V3 is short-circuited through the first resistor R1, and the first power MOS tube V3 is turned off. When the opposite-name end of the second secondary winding of the driving transformer T is positive, the third MOS tube V41 is turned on, the positive voltage is applied between the gate source of the second power MOS tube V4, and the second power MOS tube V4 is turned on; when the same-name end of the second secondary winding is positive, the fourth MOS tube V42 is turned on, the gate source of the second power MOS tube V4 is short-circuited through the second resistor R2, and the second power MOS tube V4 is turned off.

[0051] When the first power MOS tube V3 and the second power MOS tube V4 share a source, Figure 3 The circuit shown can be simplified to Figure 4 , saving a secondary winding and two signal MOS tubes. It can be understood that Figure 4 The first power MOS tube V3 and the second power MOS tube V4 are driven by positive voltage.

[0052] exist Figure 4In the embodiment, the number of the secondary winding is one, and the two signal MOS transistors are respectively recorded as: a fifth MOS transistor V51 and a sixth MOS transistor V61. The opposite-name end of the secondary winding is electrically connected to one end of the first resistor R1, the drain of the fifth MOS transistor V51, and the gate of the sixth MOS transistor V61; the same-name end of the secondary winding is electrically connected to one end of the second resistor R2, the drain of the sixth MOS transistor V61, and the gate of the fifth MOS transistor V51; the gate of the first power MOS transistor V3 is electrically connected to the other end of the first resistor R1, and the source of the first power MOS transistor V3 is electrically connected to the source of the fifth MOS transistor V51, the source of the sixth MOS transistor V61, and the source of the second power MOS transistor V4; the gate of the second power MOS transistor V4 is electrically connected to the other end of the second resistor R2.

[0053] Figure 4 The working process of the positive voltage soft switch isolation driving circuit shown is as follows: when the same-name end of the secondary winding of the driving transformer T is positive, the fifth MOS tube V51 is turned on, a positive voltage is applied between the gate and source of the second power MOS tube V4, the second power MOS tube V4 is turned on, the gate and source of the first power MOS tube V3 are short-circuited through the first resistor R1, and the first power MOS tube V3 is turned off; when the opposite-name end of the secondary winding is positive, the sixth MOS tube V61 is turned on, a positive voltage is applied between the gate and source of the first power MOS tube V3, the first power MOS tube V3 is turned on, the gate and source of the second power MOS tube V4 are short-circuited through the second resistor R2, and the second power MOS tube V4 is turned off.

[0054] Understandably, Figure 1 , Figure 3 and Figure 4 In the circuit, the drain of the first power MOS tube V3 and the drain of the second power MOS tube V4 are both connected to the power circuit to control the power conversion of the power circuit. As an example, the power circuit may include a capacitor, a transformer, and the like.

[0055] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A soft switch isolation drive circuit, characterized in that: include: Driving transformer, push-pull MOS tube, power MOS tube, driving resistor and input capacitor; The primary winding of the driving transformer is connected in series between the push-pull MOS tube and the input capacitor; one end of the driving resistor is electrically connected to the secondary winding of the driving transformer, and the other end of the driving resistor is electrically connected to the power MOS tube.

2. The soft switch isolation drive circuit according to claim 1, characterized in that: The primary winding comprises: a first primary winding and a second primary winding; The push-pull MOS tube comprises: a first push-pull MOS tube and a second push-pull MOS tube; The first primary winding is electrically connected to the drain of the first push-pull MOS tube, and the second primary winding is electrically connected to the drain of the second push-pull MOS tube; the gate of the first push-pull MOS tube and the gate of the second push-pull MOS tube receive a square wave signal with a dead zone and a phase shift of 180°, and the source of the first push-pull MOS tube and the source of the second push-pull MOS tube are both grounded.

3. The soft switch isolation driving circuit according to claim 2, characterized in that: The driving resistor comprises: a first resistor and a second resistor; The power MOS tube comprises: a first power MOS tube and a second power MOS tube; When the first power MOS tube and the second power MOS tube share a common source, the number of the secondary winding is one; When the first power MOS tube and the second power MOS tube do not have a common source, the number of the secondary windings is two, which are recorded as: a first secondary winding and a second secondary winding.

4. The soft switch isolation drive circuit according to claim 3, characterized in that: The first resistor is connected in series between the same-name end of the first secondary winding and the gate of the first power MOS tube; the source of the first power MOS tube is electrically connected to the opposite-name end of the first secondary winding; The second resistor is connected in series between the opposite-name end of the second secondary winding and the gate of the second power MOS tube; the source of the second power MOS tube is electrically connected to the same-name end of the second secondary winding.

5. The soft switch isolation drive circuit according to claim 4, characterized in that: The turns ratio of the primary and secondary sides of the driving transformer is , the primary winding excitation inductance of the drive transformer The value of is: in, is the dead time between driving the first push-pull MOS tube and the second push-pull MOS tube, The drain-source capacitance of the first push-pull MOS tube, is the drain-source capacitance of the second push-pull MOS tube, is the gate-source capacitance of the first power MOS tube, The gate-source capacitance of the second power MOS tube, is the duty cycle of the first push-pull MOS tube V1, is the switching cycle.

6. The soft switch isolation drive circuit according to claim 3, characterized in that: Also includes: A first MOS tube, a second MOS tube, a third MOS tube and a fourth MOS tube; The same-name end of the first secondary winding is electrically connected to the gate of the first MOS transistor, the drain of the second MOS transistor and one end of the first resistor, the opposite-name end of the first secondary winding is electrically connected to the drain of the first MOS transistor and the gate of the second MOS transistor, the gate of the first power MOS transistor is electrically connected to the other end of the first resistor, and the source of the first power MOS transistor is electrically connected to the source of the first MOS transistor and the source of the second MOS transistor; The opposite-name end of the second secondary winding is electrically connected to the gate of the third MOS tube, the drain of the fourth MOS tube and one end of the second resistor, the same-name end of the second secondary winding is electrically connected to the drain of the third MOS tube and the gate of the fourth MOS tube, the gate of the second power MOS tube is electrically connected to the other end of the second resistor, and the source of the second power MOS tube is electrically connected to the source of the third MOS tube and the source of the fourth MOS tube.

7. The soft switch isolation driving circuit according to claim 6, characterized in that: The gate voltage turn-on thresholds of the first MOS tube, the second MOS tube, the third MOS tube and the fourth MOS tube are all lower than the gate voltage turn-on thresholds of the first power MOS tube and the second power MOS tube.

8. The soft switch isolation driving circuit according to claim 3, characterized in that: When the first power MOS tube and the second power MOS tube are in a common source form, the soft switch isolation drive circuit further includes: a fifth MOS tube and a sixth MOS tube; One end of the secondary winding is electrically connected to one end of the first resistor, the drain of the fifth MOS transistor and the gate of the sixth MOS transistor; the other end of the secondary winding is electrically connected to one end of the second resistor, the drain of the sixth MOS transistor and the gate of the fifth MOS transistor; The gate of the first power MOS tube is electrically connected to the other end of the first resistor, and the source of the first power MOS tube is electrically connected to the source of the fifth MOS tube, the source of the sixth MOS tube and the source of the second power MOS tube; The gate of the second power MOS tube is electrically connected to the other end of the second resistor.

9. The soft switch isolation drive circuit according to any one of claims 5 to 8, characterized in that: The first power MOS tube and the second power MOS tube are driven by positive voltage.

10. The soft switch isolation drive circuit according to any one of claims 4 to 8, characterized in that: The drain of the first power MOS tube and the drain of the second power MOS tube are both connected to a power circuit to control power conversion of the power circuit.

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