CN115995980A

CN115995980A - Power supply circuit of high-insulation soft switch

Info

Publication number: CN115995980A
Application number: CN202211558035.8A
Authority: CN
Inventors: 张朋; 王仕城
Original assignee: Beijing Suoying Electric Technology Co ltd
Current assignee: Beijing Suoying Electric Technology Co ltd
Priority date: 2022-12-06
Filing date: 2022-12-06
Publication date: 2023-04-21

Abstract

The embodiment of the application discloses a power circuit of a high-insulation soft switch. The circuit includes: the direct current-direct current conversion circuit comprises an input power supply, an input filter capacitor, a transformer, a resonance capacitor, a voltage doubling rectifying circuit and an output filter capacitor; the input power supply is connected with the input filter capacitor, the transformer is connected with the resonance capacitor and the voltage doubling rectifying circuit, the output filter capacitor is connected with the voltage doubling rectifying circuit, the leakage inductance of the adverse parameter of the transformer is used as resonance inductance, and the transformer is connected with the resonance capacitor, so that the secondary rectifying diode is turned off at zero current, and the efficiency is improved; the transformer is utilized to realize soft switching, so that electromagnetic interference is reduced; and the power supply circuit of the power supply circuit adopts open-loop operation, has a simple structure, is not provided with devices on the premise of improving the performance compared with other circuits, has low cost and is convenient for large-scale use.

Description

Power supply circuit of high-insulation soft switch

Technical Field

The application relates to the field of power electronics, in particular to a power circuit of a high-insulation soft switch.

Background

The insulated gate bipolar transistor (I nsu l atedGateBi po l arTrans I stor, I GBT) has the characteristics of high voltage resistance, high current and low conduction voltage drop, and is widely applied to high-voltage and high-power occasions.

In the prior art, in the scheme of the I GBT driving power supply, no matter in topological types such as forward, flyback, push-pull or half-bridge, a switching device of the I GBT driving power supply belongs to a hard switch, namely, the I GBT driving power supply is turned on and off under the condition that the voltage and the current of the switching device are not zero, so that the efficiency is reduced due to switching loss, and electromagnetic interference caused by high voltage change rate and voltage change rate affects sensitive driving signals, and potential safety hazards are increased. In addition, in the manufacturing process of the transformers with the topologies, high coupling coefficients are required so as to reduce leakage inductance and reduce peaks caused by switching. The high coupling coefficient will increase the turn-to-turn capacitance of the transformer, and increase the common mode interference, which is also unfavorable for the normal operation of the driving circuit.

Disclosure of Invention

The embodiment of the application provides a power circuit of a high-insulation soft switch, which is used for improving the compressive strength and reducing the loss and the electromagnetic interference.

The application provides a power supply circuit of high insulation soft switch, includes: the direct current-direct current conversion circuit comprises an input power supply, an input filter capacitor, a transformer, a resonance capacitor, a voltage doubling rectifying circuit and an output filter capacitor;

the input power supply is connected with the input filter capacitor, the transformer is connected with the resonance capacitor and the voltage doubling rectifying circuit, and the output filter capacitor is connected with the voltage doubling rectifying circuit;

the input filter capacitor is used for providing energy;

the voltage doubling rectifying circuit is used for converting alternating current into direct current;

the output filter capacitor is used for filtering the output voltage.

Optionally, the dc-dc conversion circuit further includes a primary side switching tube, and the primary side switching tube includes a first switching tube and a second switching tube; the input filter capacitor comprises a first capacitor and a second capacitor; the first capacitor is connected in series with the first switching tube, and the second capacitor is connected in series with the second switching tube;

the first capacitor and the second capacitor are connected in series to form an input filter capacitor;

the first capacitor is used for providing energy when the first switching tube is conducted;

the second capacitor is used for providing energy when the second switching tube is conducted.

Optionally, the resonant capacitor comprises a first resonant capacitor and a second resonant capacitor, and the transformer comprises an excitation inductance and a leakage inductance;

the exciting inductor is used for providing energy for zero-voltage switching of the primary side switching tube;

the first resonance capacitor and the second resonance capacitor are connected in parallel to form the resonance capacitor;

and the resonance capacitor is connected with the leakage inductance in series to form the series-parallel resonance circuit.

Optionally, the transformer is wound by using a multi-slot framework.

Optionally, the voltage doubling rectifying circuit includes a resonant capacitor, a first diode and a second diode.

Optionally, the circuit further comprises a square wave generating circuit for generating a square wave signal of a fixed frequency.

Optionally, the square wave generating circuit includes: a dual D flip-flop including a first flip-flop and a second flip-flop;

the first trigger is used for forming a square wave generator, and square waves are generated through the square wave generator;

the second trigger is configured to divide the square wave generated by the square wave transmitter by two, so as to output a square wave signal with a fixed frequency, where the duty cycle of the square wave signal is 0.5.

Optionally, the circuit further includes a half-bridge driving chip, configured to generate a pulse modulation signal based on the square wave signal, where the pulse modulation signal provides driving for the dc-dc conversion circuit.

Optionally, the frequency of the pulse modulation signal is the same as the frequency of the square wave signal; the pulse modulation signal is a pulse modulation signal with dead zone time delay.

Optionally, the circuit further comprises a negative pressure output circuit, wherein the negative pressure output circuit comprises a positive voltage output capacitor, a negative voltage output capacitor, a zener diode and a divider resistor;

the positive voltage output capacitor is connected in series with the negative voltage output capacitor, the zener diode is connected in parallel with the negative voltage output capacitor, and the voltage dividing resistor is connected in series with the zener diode;

the positive voltage output capacitor is used for filtering positive voltage;

the negative voltage output capacitor is used for filtering negative voltage;

the zener diode is used for stabilizing the negative voltage;

the divider resistor is used for providing a current path for the zener diode.

The embodiment of the application discloses a power circuit of a high-insulation soft switch. The circuit includes: the direct current-direct current conversion circuit comprises an input power supply, an input filter capacitor, a transformer, a resonance capacitor, a voltage doubling rectifying circuit and an output filter capacitor; the input power supply is connected with the input filter capacitor, the transformer is connected with the resonance capacitor and the voltage doubling rectifying circuit, and the output filter capacitor is connected with the voltage doubling rectifying circuit; an input filter capacitor for providing energy; the voltage doubling rectifying circuit is used for converting alternating current into direct current; and the output filter capacitor is used for filtering the output voltage. Therefore, by using the scheme provided by the embodiment of the application, the leakage inductance of the adverse parameter of the transformer is used as the resonance inductance, and the secondary rectifier diode is turned off in zero current through the connection of the transformer and the resonance capacitor, so that the efficiency is improved; the transformer is utilized to realize soft switching, so that electromagnetic interference is reduced; and the power supply circuit of the power supply circuit adopts open-loop operation, has a simple structure, is not provided with devices on the premise of improving the performance compared with other circuits, has low cost and is convenient for large-scale use.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments described in the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic structural diagram of a power circuit of a high-insulation soft switch according to an embodiment of the present application;

fig. 2 is a schematic diagram of a dc-dc conversion circuit according to an embodiment of the present application;

fig. 3 is a schematic structural diagram of a dual-groove framework according to an embodiment of the present disclosure;

fig. 4 is a schematic diagram of another dc-dc conversion circuit according to an embodiment of the present disclosure;

fig. 5 is a schematic diagram of another dc-dc conversion circuit according to an embodiment of the present disclosure;

fig. 6 is a schematic diagram of another dc-dc conversion circuit according to an embodiment of the present disclosure;

fig. 7 is a schematic diagram of a square wave generating circuit according to an embodiment of the present application;

fig. 8 is a schematic diagram of a half-bridge driving chip according to an embodiment of the present application;

fig. 9 is a schematic diagram of a negative pressure generating circuit according to an embodiment of the present application.

Detailed Description

For easy understanding, first, an application scenario of the embodiment of the present application will be described.

With global climate change forming a major threat to human society, more and more countries are raising "carbon neutralization" to national strategy, and carbon-free future prospects are proposed. In 2020, china announced the target landscape of carbon arrival peaks and carbon neutralization based on the role of promoting the inherent requirements for sustainable development and the responsibility for constructing human fate communities.

Under the background, new energy fields such as new energy automobiles, photovoltaics, wind power, energy storage and other industries are vigorously developed. The application of the new energy source in any aspect is not conducted. Power electronics is a huge discipline, with complex classes and numerous branches. However, in any field, the topology is not separated from the semiconductor switching device, so that the performance of the switching device plays a decisive role in the performance of the device. Common switching devices are metal-oxide semiconductor field effect transistors (MOSFET), igbt, thyristors, etc. The IGBT has the characteristics of high withstand voltage, high current and low conduction voltage drop, and is widely applied to high-voltage and high-power occasions.

GBT is a voltage-type fully controlled device that is turned on or off by applying a voltage between its G and E poles. Reasonable driving circuit is the key of controlling I GBT safety to switch on and off, and an excellent driving circuit brings great improvement to the functions, reliability and other aspects of power electronic equipment.

There are bootstrap capacitor, pulse transformer and isolated power supply modes common in GBT drive schemes. The bootstrap capacitor is charged by using the bootstrap diode and the switch conduction of the main circuit for the conduction of the I GBT, and has the characteristics of simple structure and low cost. But the circuit is non-isolated and the operating state depends on the duty cycle and on-time of the main circuit. Therefore, in high voltage and high power applications, the scheme has safety risks and is rarely adopted.

The pulse transformer type is to isolate and amplify the driving signal by utilizing the characteristics of the transformer, and generally adopts a forward or push-pull structure. Although the driving circuit can realize isolation, the quality of a driving signal is seriously dependent on the working state of the driving circuit.

The isolation power supply is a stable power supply which is specially used for providing energy for I GBT on/off by using a DC-DC isolation topology, and the driving signals are transmitted in an optocoupler, capacitor or magnetic isolation mode, so that the driving signals and the isolation power supply are completely decoupled and do not interfere with each other, and the isolation power supply is flexible in application, safe and reliable.

Therefore, in the application of high power and high voltage, an isolated power supply is often used to supply energy for driving the IGBT switch based on the consideration of reliability and safety of the device. At present, the adopted I GBT driving power supply schemes in the market have topological types such as forward, flyback, push-pull, half-bridge and the like. The topology has the characteristics of simple structure and low cost, and is applied in a large scale. But each suffers from some drawbacks due to their topological nature. If the topology is forward, an additional magnetic reset circuit must be added to work normally; the flyback topology has the defects that the stress on the switching tube is large, the interference is serious, and the switching tube needs to work in a closed loop state, which clearly increases the complexity of the circuit.

The present application thus proposes a power supply circuit of a high insulation soft switch. The circuit has the characteristics of high voltage withstand level and low electromagnetic interference, is simple and easy to realize, and is stable and reliable. The circuit works under the condition of open loop fixed switching frequency, and can work under the state of soft switching by adjusting the parameters of leakage inductance and resonance capacitance of the transformer. As shown in FIG. 1, the circuit specifically comprises a square wave generating circuit, a half-bridge driving chip, a direct current-direct current conversion circuit and a negative pressure generating circuit. The square wave generating circuit generates a square wave signal with fixed frequency, the square wave signal is input to the half-bridge driving chip, and therefore a group of pulse modulation signals are generated, the pulse modulation signals drive the direct current-direct current conversion circuit, and the direct current-direct current conversion circuit inputs the converted direct current into the negative pressure generating circuit.

Referring to fig. 2, a schematic diagram of a dc-dc conversion circuit according to an embodiment of the present application is shown.

The schematic diagram of the dc-dc conversion circuit provided in the embodiment of the present application includes: input power V _in The transformer comprises an input filter capacitor, a transformer, a resonant capacitor, a voltage doubling rectifying circuit and an output filter capacitor C3.

The input power supply is connected with the input filter capacitor, the transformer is connected with the resonance capacitor and the voltage doubling rectifying circuit, and the output filter capacitor is connected with the voltage doubling rectifying circuit. An input filter capacitor for providing energy; the voltage doubling rectifying circuit is used for converting alternating current into direct current; and the output filter capacitor C3 is used for filtering the output voltage.

Specifically, the power supply V is input _in The voltage value is a fixed voltage value, and can be 15V, 24V and the like which are commonly used, and it is to be noted that the voltage value of the input voltage is not limited in the application, and a proper fixed voltage value can be selected according to practical situations.

Specifically, the output filter capacitor C3 plays a role of filtering and energy supporting in the circuit.

In the embodiment of the application, the direct current-direct current conversion circuit further comprises a primary side switching tube, wherein the primary side switching tube comprises a first switching tube MOS1 and a second switching tube MOS2; the input filter capacitor comprises a first capacitor C1 and a second capacitor C2; the first capacitor C1 is connected with the first switching tube MOS1 in series, and the second capacitor C2 is connected with the second switching tube MOS2 in series.

The first capacitor C1 and the second capacitor C2 are connected in series to form an input filter capacitor, the first capacitor C1 supplies energy when the first switching tube MOS1 is conducted, and the second capacitor C2 supplies energy when the second switching tube MOS2 is conducted.

In the embodiment of the present application, the transformer T1 is a high-frequency transformer, and plays roles of voltage conversion and isolation. The transformer T1 transmits electric energy by utilizing the principle of electromagnetic induction, and realizes the function of voltage conversion by adjusting the turn ratio of the primary and secondary. The primary and secondary of the transformer are not directly connected by a circuit, but energy is transferred by electromagnetic induction, so that the two ends of the transformer are isolated. The transformer T1 comprises an excitation inductance LM and a leakage inductance Lr; the excitation inductance LM energizes the zero voltage switch (Zero Vo ltage Switch, ZVS) of the primary side switching tube.

Specifically, parasitic capacitance Cds exist between the drain electrode and the source electrode of the MOS transistor, the MOS transistor needs to release energy stored in the Cds in the opening process, and switching loss, namely hard switching, is generated when voltage and current overlap. ZVS is that before the MOS transistor is turned on, the voltage of Cds is already zero, so no loss occurs. In the embodiment of the application, in the process of alternately conducting MOS1 and MOS2, a + -1/2 Vin square wave voltage is applied to two ends of the transformer, namely, two ends of the LM. For example, when MOS1 is on and MOS2 is off, the transformer input voltage is +1/2 Vin, and the current flowing through LM will rise linearly. At this time, MOS1 is turned off, and LM will charge the Cds of MOS1 and discharge the Cds of MOS2 because inductor current cannot be suddenly changed. During the dead time, cds of MOS2 discharge to 0. At this time, MOS2 is turned on, i.e., zero voltage turn-on is realized.

In the embodiment of the application, the transformer T1 may use a multi-slot framework to generate leakage inductance, so as to improve the withstand voltage level. As shown in the double-slot skeleton structure schematic diagram in fig. 3, a retaining wall is provided in the central area of the winding, and the primary winding and the secondary winding of the transformer are wound on two sides of the retaining wall respectively, so as to improve the insulation level between the primary winding and the secondary winding. The primary and secondary windings on both sides of the retaining wall can generate larger leakage inductance compared with the primary and secondary windings which are uniformly wound on the transformer framework. Leakage inductance of the transformer, turn-to-turn coupling capacitance is usually an unfavorable parasitic parameter in the circuit, and adverse factors such as switch peaks, high-frequency interference, common-mode voltage and the like which influence the normal operation of the circuit can be generated. The invention effectively utilizes the leakage inductance of the transformer, realizes the soft switching process, can improve the efficiency, increases the switching frequency, reduces the volume and simultaneously reduces the electromagnetic interference. The transformer is wound by utilizing the multi-slot framework, so that the coupling capacitance is reduced, and the insulation performance is enhanced.

In the embodiment of the application, the resonant capacitor comprises a first resonant capacitor Cr1 and a second resonant capacitor Cr2, and the first resonant capacitor and the second resonant capacitor are connected in parallel to form a resonant capacitor; the resonance capacitor is connected in series with the leakage inductance Lr to form an LC series-parallel resonance circuit. The leakage inductance of the adverse parameter of the transformer is used as Lr, a soft switching process is realized, the secondary rectifier diode can be turned off in zero current, and the efficiency is improved.

When the current is in the positive flow direction, cr1 and the output filter capacitor C3 are connected in series and then connected in parallel with Cr 2. Because C3 is an energy storage capacitor, the capacitance value of C3 is usually much larger than that of Cr1, so that after Cr1 and C3 are connected in series, the capacitance value is close to C3. When the current flows in the opposite direction, cr2 and C3 are connected in series, and the capacitance value is close to C3 after Cr2 and C3 are connected in series, so that the capacitor can be approximately equivalent to Cr1 and Cr2 which are connected in parallel to form a resonance capacitor, and the resonance capacitor and Lr are connected in series to form a series-parallel resonance circuit.

In the embodiment of the present application, cr1 and Cr2 form a voltage doubler rectifier circuit with the first diode D1 and the second diode D2.

In one possible implementation, as shown in fig. 4, another dc-dc conversion circuit is provided in an embodiment of the present application.

The difference between fig. 4 and fig. 2 is that the voltage doubler becomes bridge rectification, and the resonance capacitance Cr becomes 1 branch. If the same voltage output is to be achieved in fig. 4 as in fig. 2, the turn ratio of the transformer T1 needs to be changed to 1/2.

Another dc-dc conversion circuit shown in fig. 4 includes: an input voltage source VDC2, an input filter capacitor, a transformer T1, a first switch tube MOS1, a second switch tube MOS2, a resonance capacitor Cr, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, and an output filter capacitor C3.

Specifically, the first capacitor C1 and the second capacitor C2 are connected in series to form an input filter capacitor; the first switching tube MOS1 and the second switching tube MOS2 are connected with a transformer and used for power conversion; lr is equivalent leakage inductance of the transformer T1 and forms a series resonance network with a resonance capacitor Cr; lm is the exciting inductance of the transformer T1, and provides energy for realizing the ZVS of the MOS transistor; the first diode D1, the second diode D2, the third diode D3, and the fourth diode D4 constitute a bridge rectifier circuit for converting the alternating current output from the transformer into direct current.

In one possible implementation, as shown in fig. 5, another dc-dc conversion circuit is provided in an embodiment of the present application.

Fig. 5 is another dc-dc conversion circuit, specifically a primary resonant symmetrical half-bridge circuit, and compared with fig. 2, the dc-dc conversion circuit provided in fig. 5 shifts the resonant capacitor Cr to the primary side, and the secondary side is bridge rectification, so that the turn ratio of the transformer T1 needs to be changed to 1/2 to achieve the same output voltage in fig. 2.

Another dc-dc conversion circuit shown in fig. 5 includes: an input voltage source VDC3, an input filter capacitor, a transformer T1, a first switch tube MOS1, a second switch tube MOS2, a resonance capacitor Cr, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, and an output filter capacitor C3.

In one possible implementation, as shown in fig. 6, another dc-dc conversion circuit is provided in an embodiment of the present application.

Fig. 6 shows another dc-dc conversion circuit, specifically a primary resonant asymmetrical half-bridge circuit, in which the number of input filter capacitors is adjusted to one, the resonant capacitor Cr is shifted to the primary side, and the secondary side is bridge rectified, and the circuit needs to change the turn ratio of the transformer to 1/2 of the original one in order to achieve the same output voltage in the circuit shown in fig. 2.

Another dc-dc conversion circuit shown in fig. 6 includes: an input voltage source VDC2, an input filter capacitor, a transformer T1, a first switch tube MOS1, a second switch tube MOS2, a resonance capacitor Cr, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, and an output filter capacitor C3.

It should be noted that the application is not limited to MOS-driven devices, and devices such as 555 timers or other power management chips may be used to generate MOS-driven devices.

It should be noted that fig. 2, fig. 4 to fig. 6 of the drawings illustrate embodiments of the present application. "means the direction of current flow.

Referring to fig. 7, a schematic diagram of a square wave generating circuit according to an embodiment of the present application is shown.

The schematic diagram of the square wave generating circuit provided in the embodiment of the application includes: the dual D flip-flop comprises a dual D flip-flop, a first capacitor C1, a second capacitor C2, a third capacitor C3, a first resistor R1, a second resistor R2, a first diode D1 and a second diode D2.

And the square wave generating circuit is used for generating a square wave signal with fixed frequency.

Specifically, CD4013 is a dual D flip-flop that is composed of two identical, independent data flip-flops. Each flip-flop has independent data (D), set (S), reset (R), clock input (CP), output (Q and

) Pins.

The first flip-flop of CD4013 forms a group with R1, C1 and D1 and R2, C2 and D2A square wave generator. When initially powered up, Q1 outputs a low level,

outputting a high level, and charging C1 through R1; when C1 charges to the trigger level of S1, the trigger output is inverted, Q1 is high, it will charge C2 through R2, C1 will discharge rapidly through D1; when C2 charges to the trigger level of R1, the flip-flop will again invert, C1 charges, and C2 discharges. Repeatedly, the first flip-flop of CD4013 will output a square wave signal, the frequency and duty cycle of which are determined by the parameters of R1, C1, R2, C2.

The second flip-flop of CD4013 has the function of dividing the square wave generated by the first flip-flop by two, the clock signal CP2 of the second flip-flop being input as the first flip-flop signal output

It will output a square wave signal with a fixed frequency and a duty cycle of 0.5.

Referring to fig. 8, a schematic diagram of a half-bridge driving chip according to an embodiment of the present application is shown.

The schematic diagram of the half-bridge driving chip provided in the embodiment of the application includes: half-bridge driver chip, decoupling capacitor C1, capacitor C2, diode D1.

Specifically, D1 and C2 are bootstrap circuits formed by the same chip, and power supply is provided for the output HO of the upper tube; HO and LO are chip outputs and provide driving signals for MOS tubes in the DC-DC conversion circuit.

Specifically, the square wave signal generated by the square wave generating circuit is input into the half-bridge driving chip, so that a group of pulse modulation signals (Pu l se Width Modu l at ion, PWM) with dead time delay and the frequency equal to that of the input square wave signal are generated. The set of signals provides drive for the DC-DC conversion circuit to operate normally.

Referring to fig. 9, a schematic diagram of a negative voltage generating circuit according to an embodiment of the present application is shown.

The schematic diagram of the negative voltage generating circuit provided in the embodiment of the application includes: positive voltage output capacitance, negative voltage output capacitance, zener diode and divider resistor.

Specifically, the positive voltage output capacitor is connected in series with the negative voltage output capacitor, the zener diode is connected in parallel with the negative voltage output capacitor, and the voltage dividing resistor is connected in series with the zener diode. The positive voltage output capacitor is used for filtering positive voltage; the negative voltage output capacitor is used for filtering negative voltage; a zener diode for stabilizing a negative voltage; and the voltage dividing resistor is used for providing a current path for the zener diode.

The terms "first," "second," "third," "fourth" and the like in the description and in the claims of this application and in the above-described figures, if any, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments described herein may be implemented in other sequences than those illustrated or otherwise described herein. Furthermore, the terms "comprise" and "have," as well as any variations thereof, are intended to cover a non-exclusive inclusion.

The units described as separate units may or may not be physically separate, and units shown as units may or may not be physical units, may be located in one place, or may be distributed over a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

The objects, technical solutions and advantageous effects of the present invention have been described in further detail in the above embodiments, and it should be understood that the above are only embodiments of the present invention.

The above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A power circuit of a high insulation soft switch, the circuit comprising: the direct current-direct current conversion circuit comprises an input power supply, an input filter capacitor, a transformer, a resonance capacitor, a voltage doubling rectifying circuit and an output filter capacitor;

the input filter capacitor is used for providing energy;

the output filter capacitor is used for filtering the output voltage.

2. The circuit of claim 1, wherein the dc-dc conversion circuit further comprises a primary side switching tube comprising a first switching tube and a second switching tube; the input filter capacitor comprises a first capacitor and a second capacitor; the first capacitor is connected in series with the first switching tube, and the second capacitor is connected in series with the second switching tube;

3. The circuit of claim 1, wherein the resonant capacitance comprises a first resonant capacitance and a second resonant capacitance, and the transformer comprises an excitation inductance and a leakage inductance;

4. A circuit according to claim 3, wherein the transformer is wound using a multi-slot bobbin.

5. The circuit of claim 1, wherein the voltage doubler rectifier circuit comprises a resonant capacitor, a first diode, and a second diode.

6. The circuit of claim 1, further comprising a square wave generating circuit for generating a square wave signal of a fixed frequency, the square wave signal having a duty cycle of 0.5.

7. The circuit of claim 6, wherein the square wave generation circuit comprises: a dual D flip-flop including a first flip-flop and a second flip-flop;

the second trigger is used for dividing the square wave generated by the square wave transmitter by two so as to output a square wave signal with fixed frequency.

8. The circuit of claim 6, further comprising a half-bridge driver chip for generating a pulse modulated signal based on the square wave signal, wherein the pulse modulated signal provides drive for the dc-dc conversion circuit.

9. The circuit of claim 8, wherein the frequency of the pulse modulated signal is the same as the frequency of the square wave signal; the pulse modulation signal is a pulse modulation signal with dead zone time delay.

10. The circuit of claim 1, further comprising a negative voltage yield circuit comprising a positive voltage output capacitance, a negative voltage output capacitance, a zener diode, and a divider resistor;

the positive voltage output capacitor is used for filtering positive voltage;

the negative voltage output capacitor is used for filtering negative voltage;

the zener diode is used for stabilizing the negative voltage;

the divider resistor is used for providing a current path for the zener diode.