CN114844362A - Control circuit and method of resonant converter - Google Patents

Abstract

The invention provides a control circuit and a method of a resonant converter, wherein the control circuit comprises: the resonant converter comprises a primary side main power switch S1, a primary side main power switch S2, a secondary side rectifier switch S3 and a secondary side rectifier switch S4, and a control circuit of the resonant converter comprises a secondary side drive circuit, an exclusive-OR gate, a pulse synchronization circuit, a phase-locked loop circuit, a frequency division circuit and a primary side drive circuit which are sequentially connected; the secondary side driving circuit is connected with the secondary side rectifying switch S3 and the secondary side rectifying switch S4, and the primary side driving circuit is connected with the primary side main power switch S1 and the primary side main power switch S2. Compared with the prior art, the method can rapidly adjust the switching frequency of the resonant converter to be consistent with the resonant frequency of the resonant circuit, so that the robustness and the application range of the resonant converter are improved.

Description

Control circuit and method of resonant converter

Technical Field

The invention relates to the technical field of resonant converter control, in particular to a control circuit and a control method of a resonant converter.

Background

The main power circuit of a resonant power converter is formed by a resonant circuit, which is usually formed by a combination of a resonant inductor and a resonant capacitor. Such as a common LC resonant converter, LLC resonant converter, etc. The resonant converter needs to set a relatively fixed relationship between the switching frequency and the resonant frequency according to the operating characteristics and performance requirements of the topology of the resonant converter. For example, some resonant converters are expected to operate at a resonant frequency to lower the impedance of the converter and achieve soft switching. Some resonant converters, such as LLC resonant converters, which are intended to operate in a certain frequency range, typically require a switching frequency higher than the resonant frequency in order to operate the power switches of the topology in a soft-switching state.

For a certain resonant converter, the switching frequency can be set and adjusted to be completely consistent with the resonant frequency. However, if the conditions such as temperature and pressure change, the values of the inductance and capacitance in the resonant circuit will also shift. This parameter variation has little effect in low frequency applications. However, in the application of the converter with the switching frequency of 1MHz or above, because the values of the resonant capacitor and the resonant inductor are relatively small, the small device parameter drift can obviously affect the working state and the conversion efficiency of the converter. In addition, in mass production, inductance or capacitance devices with the same nominal value have a certain error range, so that the resonance frequency of the inductance or capacitance devices has a certain deviation. Therefore, for mass production, it is difficult to operate all the inverters in an optimal state for a fixed switching frequency control circuit scheme.

Most of the current common power converter control circuit schemes on the market are Pulse Width Modulation (PWM) control methods, which are not suitable for application in resonant circuits. Still some control schemes are Pulse Frequency Modulation (PFM) and are applied to LLC resonant circuits, and this control scheme has a large range of switching frequency variation and cannot implement a control scheme of locking the resonant frequency.

Disclosure of Invention

The invention mainly aims to provide a control circuit and a control method of a resonant converter, aiming at improving the robustness and the application range of the resonant converter by rapidly adjusting the switching frequency of the resonant converter to be consistent with the resonant frequency of a resonant circuit.

In order to achieve the above object, the present invention provides a control circuit of a resonant converter, including: the resonant converter comprises a primary side main power switch S1, a primary side main power switch S2, a secondary side rectifier switch S3 and a secondary side rectifier switch S4, and a control circuit of the resonant converter comprises a secondary side drive circuit, an exclusive-OR gate, a pulse synchronization circuit, a phase-locked loop circuit, a frequency division circuit and a primary side drive circuit which are sequentially connected; the secondary side driving circuit is connected with the secondary side rectifying switch S3 and the secondary side rectifying switch S4, and the primary side driving circuit is connected with the primary side main power switch S1 and the primary side main power switch S2;

the secondary side driving circuit is used for detecting the resonant frequency of the resonant circuit and driving the secondary side power switches S3 and S4 to be switched on and off;

the exclusive-OR gate is used for sampling and processing the waveform of an S4 gate drive voltage waveform PWMS in the current detection and drive circuit and converting the waveform into a pulse waveform PWM 1;

the pulse synchronization circuit is used for filtering and amplifying the pulse waveform PWM1, converting PWM1 into a direct current signal V1, converting a received driving signal PWM3 of the primary side power switch S1 into a corresponding direct current signal V2, and outputting an adjusting voltage delta V according to the direct current signal V1 and the direct current signal V2;

the frequency dividing circuit is used for performing waveform adjustment on the output signal PWM2 to generate an output signal PWM3 and an output signal PWM4, wherein the output signal PWM3 and the output signal PWM4 have the same frequency, the duty ratio is the same and is slightly smaller than 50%, and the phase difference is 180 degrees;

the phase-locked loop circuit is used for adjusting the output frequency according to the regulating voltage, so that the output signals PWM3 and PWM1 keep the same frequency and the same phase;

the primary side driving circuit is used for amplifying the output signal PWM3 and the output signal PWM4 and driving the primary side power switch S1 and the primary side power switch S2 to work.

The further technical scheme of the invention is that the secondary side driving circuit adopts a driving chip TEA 1995T.

The further technical scheme of the invention is that the secondary side driving chip is powered by an output voltage Vout, and a power supply pin VCC and a ground pin GND of the driving chip are respectively connected with a high level and a low level of the output voltage Vout; the GDA pin, the DSA pin and the SSA pin of the driving chip are respectively connected with the gate, the drain and the source of the secondary side rectifier switch S4, and the GDB pin, the DSB pin and the SSB pin of the driving chip are respectively connected with the gate, the drain and the source of the secondary side rectifier switch S3.

A further technical solution of the present invention is that the pulse synchronization circuit includes an operational amplifier a, an operational amplifier B, and an operational amplifier C, where the operational amplifier a is configured to filter and amplify the pulse waveform PWM1, and convert PWM1 into a direct current signal V1, the operational amplifier B is configured to convert a received drive signal PWM3 of the primary power switch S1 into a corresponding direct current signal V2, and the operational amplifier is configured to compare and perform closed-loop feedback compensation on the direct current signal V1 and the direct current signal V2, and output an adjustment voltage Δ V.

The further technical scheme of the invention is that the phase-locked loop circuit adopts a chip CD4046, and the frequency range set by the chip CD4046 circuit covers the conversion range of the resonant frequency of the resonant converter.

In order to achieve the above object, the present invention further provides a control method of a resonant converter, the method is applied to the control circuit of the resonant converter, and the method includes the following steps:

the secondary side driving circuit detects the resonant frequency of the resonant circuit and drives the secondary side power switches S3 and S4 to be switched on and off;

the exclusive-OR gate samples and processes a gate driving voltage waveform PWMS of S4 in the current detection and driving circuit to convert the gate driving voltage waveform PWMS into a pulse waveform PWM 1;

the pulse synchronization circuit filters and amplifies the pulse waveform PWM1, converts PWM1 into a direct current signal V1, converts the received driving signal PWM3 of the primary side power switch S1 into a corresponding direct current signal V2, and outputs a regulating voltage delta V according to the direct current signal V1 and the direct current signal V2;

the frequency dividing circuit performs waveform adjustment on the output signal PWM2 to generate an output signal PWM3 and an output signal PWM4, wherein the output signal PWM3 and the output signal PWM4 have the same frequency, the duty ratio is the same and is slightly smaller than 50%, and the phase difference is 180 degrees;

the phase-locked loop circuit adjusts the output frequency according to the regulating voltage, so that the output signals PWM3 and PWM1 keep the same frequency and the same phase;

the primary side driving circuit amplifies the output signal PWM3 and the output signal PWM4, and drives the primary side power switch S1 and the primary side power switch S2 to work.

The control circuit and the method of the resonant converter have the advantages that: according to the technical scheme, the switching frequency of the resonant converter can be rapidly adjusted to be consistent with the resonant frequency of the resonant circuit, so that the robustness and the application range of the resonant converter are improved.

Drawings

Fig. 1 is a schematic diagram of a circuit configuration of a control circuit of a resonant converter of the present invention;

FIG. 2 is a schematic diagram of the circuit structure of the driver chip TEA 1995T;

FIG. 3 is a schematic diagram of waveforms for secondary side rectifier switches S3 and S4;

FIG. 4 is a schematic diagram of a PWM shaping circuit;

FIG. 5 is a schematic diagram of the structure of operational amplifiers A and B;

FIG. 6 is a schematic diagram of the structure of an operational amplifier C;

FIG. 7 is a schematic diagram of a phase-locked loop circuit;

FIG. 8 is a schematic diagram of a scheme for generating two PWM drive signals;

fig. 9 is a flowchart illustrating a control method of the resonant converter according to a preferred embodiment of the present invention.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments.

Detailed Description

It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.

The invention provides a control circuit of a resonant converter, which is characterized in that the working state of the resonant circuit can be detected, and the switching frequency of the converter can be automatically adjusted to be consistent with the resonant frequency of the resonant circuit. Therefore, even if the resonant frequency changes due to the change and the offset of the parameters of the components of the resonant circuit, the control circuit can also be rapidly adjusted to enable the resonant circuit to work at the resonant point all the time, so that the robustness and the application range of the resonant converter are improved.

Specifically, referring to fig. 1 to 2, a control circuit of the resonant converter according to the preferred embodiment of the present invention includes a primary side main power switch S1, a primary side main power switch S2, a secondary side rectifier switch S3, and a secondary side rectifier switch S4, where the control circuit of the resonant converter includes a secondary side driving circuit, an xor gate, a pulse synchronization circuit, a phase-locked loop circuit, a frequency dividing circuit, and a primary side driving circuit, which are connected in sequence; the secondary side driving circuit is connected with the secondary side rectifying switch S3 and the secondary side rectifying switch S4, and the primary side driving circuit is connected with the primary side main power switch S1 and the primary side main power switch S2.

In this embodiment, the secondary driving circuit is configured to detect a resonant frequency of the resonant circuit and drive the secondary power switches S3 and S4 to turn on and off, the xor gate is configured to perform waveform sampling and processing on a gate driving voltage waveform PWMS of S4 in the current detection and driving circuit to convert the gate driving voltage waveform PWMS into a pulse waveform PWM1, the pulse synchronization circuit is configured to perform filtering and amplification processing on the pulse waveform PWM1, convert PWM1 into a direct current signal V1, convert the received driving signal PWM3 of the primary power switch S1 into a corresponding direct current signal V2, output an adjustment voltage Δ V according to the direct current signal V1 and the direct current signal V2, and the frequency division circuit is configured to perform waveform adjustment on the output signal 2 to generate the output signal PWM3 and the output signal PWM4, where the output signal PWM3 and the output signal PWM4 have the same frequency and the duty ratio is slightly less than 50%, the phase difference is 180 degrees, the primary side driving circuit is used for amplifying the output signal PWM3 and the output signal PWM4 and driving the primary side power switch S1 and the primary side power switch S2 to work, and the phase-locked loop circuit is used for adjusting the output frequency according to the adjusting voltage so that the output signals PWM3 and PWM1 keep the same frequency and the same phase.

As shown in fig. 1, in this embodiment, the main topology circuit of the resonant converter is an isolated LC resonant circuit, the resonant cavity is formed by an inductor L1 and a capacitor C1, and the resonant inductor L1 may also be formed by or composed of a leakage inductance of the main power transformer T1. S1 and S2 are primary side main power switches, S3 and S4 are secondary side rectifier switches, and the four switches are generally selected from MOSFET power switches. CIN and COUT are input and output filter capacitors. The circuit works optimally in such a way that the frequency of the driving signal emitted by the driving circuit is always consistent with the resonant frequency of the resonant cavity circuit

The four power switches S1, S2, S3 and S4 can all realize soft switching, and the conversion efficiency of the converter is the highest. The output voltage is determined by the input voltage and the primary-secondary transformation ratio of the transformer.

In this embodiment, the secondary driving circuit employs a driver chip TEA 1995T.

As shown in fig. 2, the secondary driving chip is powered by an output voltage Vout, and a power supply pin VCC and a ground pin GND of the driving chip are respectively connected to a high level and a low level of the output voltage Vout; and a GDA pin, a DSA pin and an SSA pin of the driving chip are respectively connected with a gate, a drain and a source of the secondary side rectifier switch S4, and a GDB pin, a DSB pin and an SSB pin of the driving chip are respectively connected with a gate, a drain and a source of the secondary side rectifier switch S3.

In this embodiment, the pulse synchronization circuit includes an operational amplifier a, an operational amplifier B, and an operational amplifier C, where the operational amplifier a is configured to filter and amplify the pulse waveform PWM1, and convert PWM1 into a dc signal V1, the operational amplifier B is configured to convert a received driving signal PWM3 of the primary power switch S1 into a corresponding dc signal V2, and the operational amplifier is configured to compare and perform closed-loop feedback compensation on the dc signal V1 and the dc signal V2, and output an adjustment voltage Δ V.

In this embodiment, the phase-locked loop circuit adopts a chip CD4046, and a frequency range set by the chip CD4046 circuit covers a conversion range of the resonant frequency of the resonant converter.

The specific structure and operation principle of the control circuit of the resonant converter of the present invention will be described in detail with reference to fig. 1 to 8.

The invention provides a switching frequency self-adaptive adjusting scheme for an isolated LC resonant converter, which can ensure that the switching frequency of the converter is always self-adaptively locked at the resonant frequency of an LC resonant cavity. Therefore, even if the parameter value of the resonant circuit drifts or initial errors occur, the control circuit can also quickly detect and adjust, so that the resonant converter is always kept at the optimal working point.

The invention adopts a secondary side driving circuit with current phase detection capability on the secondary side of the resonant converter, wherein a preferred implementation mode of the secondary side driving circuit is to adopt a driving chip TEA 1995T. When the primary power switches S1 and S2 are alternately turned on, a rectified current is generated across the parasitic body diode or parallel diode of the secondary power MOSFET switches S3 and S4. The driving circuit can detect the rectified current and drive the corresponding power switch to be conducted. The waveform of the current flowing through S3 and S4 in the resonant converter shown in fig. 1 is a sine wave, and when it starts to conduct, its current amplitude starts to resonate from 0A to the maximum value, and then decreases to 0A. The drive circuit can detect this zero crossing when it drops to 0A and quickly turn off the drive signal. By using the current detection capability of this drive circuit, the resonance time of the resonance current, that is, the resonance frequency of the resonance circuit can be detected. A typical application circuit of the driver chip is shown in fig. 2. Fig. 3 shows typical waveforms of this circuit, taking the waveform of the S4 switch as an example. The typical waveform of the S3 switch is consistent with this. The operation principle of a typical application circuit of the driving chip shown in fig. 2 is as follows: the driver chip is powered by the output voltage Vout, so the power and ground pins Vcc and GND of the chip are connected to the high and low levels of Vout as shown in fig. 2. GDA is the driving pin of S4, connected to the gate of S4, DSA is connected to the drain of S4, and SSA is connected to the source of S4. The DSA may sample the S4 drain voltage waveform equal to the product of the resonant current flowing through S4 and the S4 on-resistance equivalent. The resonant current waveform can be judged by the voltage waveform detected by the DSA. Similarly, GDB, DSB, SSB are connected to the gate, drain and source of S3, respectively.

As can be seen from the lowermost waveform in fig. 3, the gate drive voltage waveform PWMS of the secondary drive circuit is not a standard pulse square waveform, and the amplitude voltage is also low. The invention adopts an exclusive-or gate circuit to carry out waveform sampling and optimization processing on the driving signal of the pulse width modulation PWM1, and the driving signal is converted into a pulse waveform PWM1 with equal frequency and pulse width, proper level amplitude and more standard waveform shape. The working principle is that the PWMS waveform is compared with a zero level through an exclusive-OR gate, and when the PWMS is a voltage higher than the zero level, the exclusive-OR gate circuit outputs a high level. When PWMS is equal to zero level, the xor gate circuit outputs low level. The output PWM1 waveform is a more standard pulsed square wave than the PWMs waveform, while also retaining the frequency, pulse width, and phase information in the PWMs waveform. A typical circuit is a PWM shaping circuit as shown in fig. 4. The waveform conversion process is shown in fig. 3.

The PWM1 is then fed to a pulse synchronization circuit, which ultimately controls the primary side power switches S1 and S2 to also switch at this resonant frequency. The PWM1 is first converted into a dc signal V1 in the operational amplifier a circuit, the frequency of the pulse corresponding linearly to the voltage amplitude of the dc signal. The same operational amplifier B circuit receives the driving signal PWM3 of the primary power switch S1 and also converts it to a corresponding dc level V2. A typical circuit for the operational amplifiers a and B is shown in fig. 5. In fig. 5, R1 and C1 filter the PWM1, and R2 and R3 amplify it.

The operational amplifier C compares the signals V1 and V2 output by the operational amplifier A and the operational amplifier B and carries out closed loop feedback compensation to output a regulating voltage DeltaV. The purpose is to keep the two consistent, so that the driving signal of S1 keeps consistent with the driving signal of S4 in frequency and phase, and the driving signal of S2 keeps consistent with the driving signal of S3 in frequency and phase. Therefore, the working frequency of the whole resonant converter can be always kept at the resonant frequency, the driving signals of the primary side switch and the secondary side switch can be consistent, the conduction time of the diode in the rectifying circuit is reduced, and the conversion efficiency of the whole converter is improved. A typical circuit for the comparison and feedback compensation operational amplifier C is shown in fig. 6. In fig. 6, R3, C1 and C2 are loop compensation devices.

The voltage difference Δ V output by the operational amplifier C is continuously transmitted to the phase-locked loop circuit. A typical application circuit of the invention employs a phase-locked loop control circuit CD4046, whose frequency range is set to cover the conversion range of the topological resonant frequency. The voltage difference output by the operational amplifier C is sent to pin 9 of CD4046, and CD4046 adjusts its output frequency according to the magnitude of the voltage difference. The PWM1 signal and the PWM3 signal in fig. 1 can be finally maintained at the same frequency and phase after a few switching cycles of fast adjustment by the closed-loop feedback adjustment of the operational amplifier circuit and the pll circuit. The typical application circuit of CD4046 in the present invention is shown in fig. 7, and the output frequency range of the phase-locked loop is set by resistors R1, R2 and capacitor C2. The pin VCO IN receives the voltage difference value Delta V output by the operational amplifier C, and the pin VCO OUT outputs a PWM2 pulse signal.

The PWM2 signal may be passed through a waveform adjustment circuit to generate two PWM output signals, PWM3 and PWM4, as shown in FIG. 8. The two signals have the same frequency and the same duty ratio (the duty ratio is slightly less than 50% in order to leave dead time for the driving signals of S1 and S2), and the phases are 180 degrees apart. The two signals are subjected to power amplification through a driving circuit, and a primary side power switch S1 and a primary side power switch S2 are driven to work.

The invention can keep the driving signals of the secondary side power switches S3 and S4 and the driving signals of the primary side power switches S1 and S2 at the same frequency and the same phase, namely, the frequency of the power switches is locked at the resonant frequency. Even if the resonant frequency of the circuit changes due to drift or initial error of the resonant components of the resonant circuit, the resonant frequency of the circuit changes. The driving circuit on the secondary side of the transformer firstly detects a new resonant frequency, and outputs a new switching frequency through the operational amplifier and the phase-locked loop circuit, so that the switching frequency of the power topology is locked at the new resonant frequency.

The control circuit of the resonant converter has the advantages that: according to the technical scheme, the switching frequency of the resonant converter can be rapidly adjusted to be consistent with the resonant frequency of the resonant circuit, so that the robustness and the application range of the resonant converter are improved.

In order to achieve the above object, the present invention further provides a method for controlling a resonant converter, as shown in fig. 9, a preferred embodiment of the method for controlling a resonant converter of the present invention includes the following steps:

a step S10 of the secondary side driving circuit detecting the resonance frequency of the resonance circuit and driving the secondary side power switches S3 and S4 to turn on and off;

step S20, the exclusive-OR gate samples and processes the gate drive voltage waveform PWMS of S4 in the current detection and drive circuit and converts the sampled and processed voltage waveform into a pulse waveform PWM 1;

step S30, the pulse synchronization circuit filters and amplifies the pulse waveform PWM1, converts PWM1 into a direct current signal V1, converts the received drive signal PWM3 of the primary side power switch S1 into a corresponding direct current signal V2, and outputs an adjustment voltage delta V according to the direct current signal V1 and the direct current signal V2;

step S40, the phase-locked loop circuit adjusts the output frequency according to the regulated voltage, so that the output signals PWM3 and PWM1 keep the same frequency and the same phase;

step S50, the frequency dividing circuit performs waveform adjustment on the output signal PWM2 to generate an output signal PWM3 and an output signal PWM4, wherein the output signal PWM3 and the output signal PWM4 have the same frequency, the same duty ratio and slightly smaller than 50%, and the phase difference is 180 degrees;

and step S60, the primary side driving circuit amplifies the output signal PWM3 and the output signal PWM4, and drives the primary side power switch S1 and the primary side power switch S2 to operate.

The control method of the resonant converter has the advantages that: according to the technical scheme, the switching frequency of the resonant converter can be rapidly adjusted to be consistent with the resonant frequency of the resonant circuit, so that the robustness and the application range of the resonant converter are improved.

The above description is only for the preferred embodiment of the present invention and is not intended to limit the scope of the present invention, and all equivalent structures or flow transformations made by the present specification and drawings, or applied directly or indirectly to other related arts, are included in the scope of the present invention.

Claims (6)

1. A control circuit for a resonant converter, comprising: the resonant converter comprises a primary side main power switch S1, a primary side main power switch S2, a secondary side rectifier switch S3 and a secondary side rectifier switch S4, and a control circuit of the resonant converter comprises a secondary side drive circuit, an exclusive-OR gate, a pulse synchronization circuit, a phase-locked loop circuit, a frequency division circuit and a primary side drive circuit which are sequentially connected; the secondary side driving circuit is connected with the secondary side rectifying switch S3 and the secondary side rectifying switch S4, and the primary side driving circuit is connected with the primary side main power switch S1 and the primary side main power switch S2;

the secondary side driving circuit is used for detecting the resonant frequency of the resonant circuit and driving secondary side power switches S3 and S4 to be switched on and off;

the exclusive-OR gate is used for sampling and processing the waveform of an S4 gate drive voltage waveform PWMS in the current detection and drive circuit and converting the waveform into a pulse waveform PWM 1;

the pulse synchronization circuit is used for filtering and amplifying the pulse waveform PWM1, converting PWM1 into a direct current signal V1, converting a received driving signal PWM3 of the primary side power switch S1 into a corresponding direct current signal V2, and outputting an adjusting voltage delta V according to the direct current signal V1 and the direct current signal V2;

the frequency dividing circuit is used for performing waveform adjustment on the output signal PWM2 to generate an output signal PWM3 and an output signal PWM4, wherein the output signal PWM3 and the output signal PWM4 have the same frequency, the duty ratio is the same and is slightly smaller than 50%, and the phase difference is 180 degrees;

the phase-locked loop circuit is used for adjusting the output frequency according to the regulating voltage, so that the output signals PWM3 and PWM1 keep the same frequency and the same phase; the primary side driving circuit is used for amplifying the output signal PWM3 and the output signal PWM4 and driving the primary side power switch S1 and the primary side power switch S2 to work.

2. The control circuit of the resonant converter according to claim 1, wherein the secondary driving circuit is a driving chip TEA 1995T.

3. The control circuit of the resonant converter according to claim 2, wherein the secondary driving chip is powered by an output voltage Vout, and a power supply pin VCC and a ground pin GND of the driving chip are respectively connected to a high level and a low level of the output voltage Vout; the GDA pin, the DSA pin and the SSA pin of the driving chip are respectively connected with the gate, the drain and the source of the secondary side rectifier switch S4, and the GDB pin, the DSB pin and the SSB pin of the driving chip are respectively connected with the gate, the drain and the source of the secondary side rectifier switch S3.

4. The control circuit of the resonant converter according to claim 3, wherein the pulse synchronization circuit comprises an operational amplifier A, an operational amplifier B and an operational amplifier C, the operational amplifier A is used for filtering and amplifying the pulse waveform PWM1 and converting the PWM1 into the DC signal V1, the operational amplifier B is used for converting the received driving signal PWM3 of the primary side power switch S1 into the corresponding DC signal V2, and the operational amplifier is used for comparing and performing closed-loop feedback compensation on the DC signal V1 and the DC signal V2 and outputting the regulated voltage Δ V.

5. The control circuit of the resonant converter according to claim 1, wherein the phase-locked loop circuit employs a chip CD4046, and the frequency range set by the chip CD4046 circuit covers a conversion range of the resonant frequency of the resonant converter.

6. A method for controlling a resonant converter, the method being applied to a control circuit of a resonant converter according to any one of claims 1 to 5, the method comprising the steps of:

the secondary side driving circuit detects the resonant frequency of the resonant circuit and drives the secondary side power switches S3 and S4 to be switched on and off;

the exclusive-OR gate samples and processes a gate driving voltage waveform PWMS of S4 in the current detection and driving circuit to convert the gate driving voltage waveform PWMS into a pulse waveform PWM 1;

the pulse synchronization circuit filters and amplifies the pulse waveform PWM1, converts PWM1 into a direct current signal V1, converts the received driving signal PWM3 of the primary side power switch S1 into a corresponding direct current signal V2, and outputs a regulating voltage delta V according to the direct current signal V1 and the direct current signal V2;

the frequency dividing circuit performs waveform adjustment on the output signal PWM2 to generate an output signal PWM3 and an output signal PWM4, wherein the output signal PWM3 and the output signal PWM4 have the same frequency, the duty ratio is the same and is slightly smaller than 50%, and the phase difference is 180 degrees;

the phase-locked loop circuit adjusts the output frequency according to the regulating voltage, so that the output signals PWM3 and PWM1 keep the same frequency and the same phase;

the primary side driving circuit amplifies the output signal PWM3 and the output signal PWM4, and drives the primary side power switch S1 and the primary side power switch S2 to work.

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