CN206364710U - Intelligent half-bridge amendment wave voltage change-over circuit based on PFC Yu LLC resonance - Google Patents

Abstract

The utility model discloses an intelligent half-bridge correction wave voltage conversion circuit based on PFC and LLC resonance, which includes: an input unit; a filter unit; a PFC boost unit; an LLC isolation converter unit, including a first switch tube, The second switching tube, the transformer, the first diode, the second diode and the filter inductor, the source of the first switching tube is connected to the first end of the primary winding of the transformer, and the second end of the primary winding of the transformer passes through the first resonance The capacitor is connected to the front-end ground, the drain of the second switching tube is connected to the first end of the primary winding of the transformer, the first end of the secondary winding of the transformer is connected to the cathode of the first diode, and the second end of the secondary winding of the transformer is connected to The anode of the second diode is connected with the cathode of the second diode to the front end of the filter inductance; an inverter and phase inverting unit. The utility model can improve PF value and output voltage quality.

Description

Intelligent half-bridge modified wave voltage conversion circuit based on PFC and LLC resonance

technical field

The utility model relates to a voltage conversion circuit, in particular to an intelligent half-bridge correction wave voltage conversion circuit based on PFC and LLC resonance.

Background technique

In the prior art, the intelligent buck-boost conversion device from AC to AC is also called a travel plug-in strip. In this device, the voltage conversion circuit is the key circuit, which is a circuit that can realize AC-AC conversion. In the AC-AC conversion, the function of realizing buck-boost and stabilizing voltage and frequency. However, most of the current AC-AC portable equipment market is a non-isolated topology circuit with low PF value, low output voltage quality, and poor safety and reliability.

Utility model content

The technical problem to be solved by the utility model is to provide a safe and reliable intelligent half-bridge correction wave based on PFC and LLC resonance that can improve the PF value of the voltage conversion device and improve the quality of the output voltage. voltage conversion circuit.

In order to solve the above technical problems, the utility model adopts the following technical solutions.

An intelligent half-bridge modified wave voltage conversion circuit based on PFC and LLC resonance, which includes: an input unit for providing DC voltage; a filter unit connected to the output end of the input unit for outputting the input unit The voltage is filtered; a PFC step-up unit is connected to the output end of the filter unit for step-up conversion of the output voltage of the filter unit; an LLC isolation converter unit includes a first switch tube, a second switch tube, A transformer, a first diode, a second diode and a filter inductor, the drain of the first switch tube is connected to the output end of the PFC step-up unit, and the source of the first switch tube is connected to the primary winding of the transformer the first end of the primary winding of the transformer, the second end of the primary winding of the transformer is connected to the front-end ground through the first resonant capacitor, the drain of the second switching tube is connected to the first end of the primary winding of the transformer, and the The source is connected to the front-end ground through a third resistor, and the gates of the first switch tube and the second switch tube are used to load two PWM pulse signals with opposite phases, so that the first switch tube and the second switch tube The two switch tubes are turned on alternately, the middle tap of the secondary winding of the transformer is connected to the rear ground, the first end of the secondary winding of the transformer is connected to the cathode of the first diode, and the The anode is connected to the back-end ground through the second capacitor, the second end of the secondary winding of the transformer is connected to the anode of the second diode, and the cathode of the second diode is connected to the front end of the filter inductor, and the filter The rear end of the inductance is connected to the rear end ground through the third capacitor, and the rear end of the filter inductor and the anode of the first diode are used as the output end of the LLC isolation converter unit; an inverter inverter unit is connected to the LLC isolation The output end of the converter unit, the inverting and inverting unit is used to invert and convert the output voltage of the LLC isolated converter unit to output alternating current.

Preferably, the input unit includes a socket, an insurance, a lightning protection resistor, a common-mode suppression inductor, a safety capacitor and a rectifier bridge. The front end is connected in parallel to the socket, the lightning protection resistor is connected in parallel to the front end of the common mode suppression inductor, and the safety capacitor and the input end of the rectifier bridge are connected in parallel to the rear end of the common mode suppression inductor.

Preferably, the filter unit includes a filter capacitor, and the filter capacitor is connected in parallel to the output terminal of the rectifier bridge.

Preferably, the PFC boost unit includes a boost inductor, a third switch tube, a first rectifier diode and a second electrolytic capacitor, the front end of the boost inductor is connected to the output end of the input unit, and the boost inductor The rear end of the switch is connected to the drain of the third switch tube, the source of the third switch tube is connected to the front ground, the gate of the third switch tube is used to access a PWM control signal, and the third switch tube The drain of the first rectifier diode is connected to the anode of the first rectifier diode, the cathode of the first rectifier diode is used as the output end of the PFC boost unit, and the cathode of the first rectifier diode is connected to the positive pole of the second electrolytic capacitor, and the negative pole of the second electrolytic capacitor Connect to the front end.

Preferably, it also includes an MCU control unit, the grid of the first switch tube, the grid of the second switch tube and the grid of the third switch tube are respectively connected to the MCU control unit, and the MCU control unit is used for respectively Outputting PWM signals to the first switch tube, the second switch tube and the third switch tube to control the on-off states of the first switch tube, the second switch tube and the third switch tube.

Preferably, an AC sampling unit is also included, the AC sampling unit is connected between the input end of the input unit and the MCU control unit, and the AC sampling unit is used to collect the voltage on the AC side of the input unit and feed it back to the MCU control unit.

Preferably, a first sampling resistor is connected between the source of the third switching tube and the front-end ground, the source of the third switching tube is connected to the MCU control unit, and the MCU is controlled by the first sampling resistor. The control unit collects the electrical signal of the source of the third switch tube.

Preferably, the second end of the primary winding of the transformer is connected to the MCU control unit, so that the MCU control unit collects the electrical signal of the primary winding of the transformer.

Preferably, it also includes a DC voltage sampling unit, the DC voltage sampling unit includes a second sampling resistor and a third sampling resistor connected in series in sequence, and the front end of the second sampling resistor is connected to the output terminal of the LLC isolation converter unit , the rear end of the third sampling resistor is connected to the MCU control unit, and the MCU control unit collects the electrical signal output by the LLC isolation converter unit through the second sampling resistor and the third sampling resistor.

Preferably, the inverter and inverter unit includes a fourth switch tube, a fifth switch tube, a third electrolytic capacitor and a fourth electrolytic capacitor, and the drain of the fourth switch tube is connected to the output of the LLC isolation converter unit terminal positive, the source of the fourth switch tube is connected to the drain of the fifth switch tube, the source of the fifth switch tube is connected to the negative output end of the LLC isolation converter unit, and the fourth switch tube The gate and the gate of the fifth switching tube are respectively used to access two PWM pulse signals with opposite phases, the positive pole of the third electrolytic capacitor is connected to the drain of the fourth switching tube, and the negative pole of the third electrolytic capacitor connected to the rear end, the negative pole of the third electrolytic capacitor is also connected to the positive pole of the fourth electrolytic capacitor, the negative pole of the fourth electrolytic capacitor is connected to the source of the fifth switching tube, and the source of the fourth switching tube and the negative pole of the third electrolytic capacitor as the output end of the inverter unit.

In the intelligent half-bridge corrected wave voltage conversion circuit based on PFC and LLC resonance disclosed by the utility model, the DC voltage provided by the input unit is filtered by the filter unit, and the PFC boost unit performs boost conversion, and then transmits it to the LLC isolation converter. unit, in the LLC isolation converter unit, the first switching tube, the second switching tube, the first resonant capacitor, the primary leakage inductance of the transformer and the primary excitation inductance form the LLC resonant circuit, so as to transmit power to the secondary coil of the transformer, It is rectified by the first diode and the second diode into two pulsating levels in opposite directions, and then filtered by the filter inductor, the second capacitor, and the third capacitor into a DC voltage including positive and negative directions, and by changing the transformer The primary-to-secondary turns ratio can adjust the level of the output voltage, thereby realizing step-up or step-down conversion. Based on the above structure, the utility model not only realizes the isolated transmission of the voltage, but also improves the PF value of the step-up/down conversion device, and improves the quality of the output voltage, making the voltage conversion process safer and more reliable.

Description of drawings

FIG. 1 is a schematic diagram of a full-bridge modified wave voltage conversion circuit of the present invention.

Fig. 2 is a schematic circuit diagram of an AC sampling unit in a preferred embodiment of the present invention.

Fig. 3 is a schematic circuit diagram of the MCU control unit in the preferred embodiment of the present invention.

detailed description

Below in conjunction with accompanying drawing and embodiment the utility model is described in more detail.

The utility model discloses an intelligent half-bridge correction wave voltage conversion circuit based on PFC and LLC resonance, which is shown in conjunction with Fig. 1 to Fig. 3, which includes:

An input unit 10, used to provide DC voltage;

A filter unit 20, connected to the output end of the input unit 10, for filtering the output voltage of the input unit 10;

A PFC step-up unit 30, connected to the output end of the filter unit 20, for boosting the output voltage of the filter unit 20;

An LLC isolation converter unit 40, including a first switch tube Q6, a second switch tube Q7, a transformer T1, a first diode D5, a second diode D6 and a filter inductor L3, the first switch tube Q6 The drain of the first switching tube Q6 is connected to the output end of the PFC step-up unit 30, the source of the first switching tube Q6 is connected to the first end of the primary winding of the transformer T1, and the second end of the primary winding of the transformer T1 passes through the first resonant capacitor C4 is connected to the front-end ground, the drain of the second switch tube Q7 is connected to the first end of the primary winding of the transformer T1, the source of the second switch tube Q7 is connected to the front-end ground through the third resistor R2B, and the first switch Q7 is connected to the front-end ground. The gate of a switch tube Q6 and the gate of the second switch tube Q7 are used to load two PWM pulse signals with opposite phases, so that the first switch tube Q6 and the second switch tube Q7 are alternately turned on, and the transformer The middle tap of the secondary winding of T1 is connected to the back-end ground, the first end of the secondary winding of the transformer T1 is connected to the cathode of the first diode D5, and the anode of the first diode D5 passes through the second capacitor C7 connected to the rear end ground, the second end of the secondary winding of the transformer T1 is connected to the anode of the second diode D6, and the cathode of the second diode D6 is connected to the front end of the filter inductor L3, and the filter inductor The rear end of L3 is connected to the rear end ground through the third capacitor C8, and the rear end of the filter inductor L3 and the anode of the first diode D5 are used as the output end of the LLC isolation converter unit 40;

An inverter unit 60 is connected to the output end of the LLC isolation converter unit 40, and the inverter unit 60 is used to invert and convert the output voltage of the LLC isolation converter unit 40 to output AC power.

In the above modified wave voltage conversion circuit, after the DC voltage provided by the input unit 10 is filtered by the filter unit 20, it is boosted and converted by the PFC boost unit 30, and then transmitted to the LLC isolation converter unit 40, where the LLC isolation converter unit 40 Among them, the first switching tube Q6, the second switching tube Q7, the first resonant capacitor C4, the primary leakage inductance of the transformer T1 and the primary excitation inductance form the LLC resonant circuit, so that the power is transmitted to the secondary coil of the transformer T1, through the first The diode D5 and the second diode D6 are rectified into two pulsating levels in opposite directions, and then filtered by the filter inductor L3, the second capacitor C7, and the third capacitor C8 into DC voltages including positive and negative directions, and passed through Changing the primary-to-secondary turns ratio of the transformer T1 can adjust the level of the output voltage, thereby realizing step-up or step-down conversion. Based on the above structure, the utility model not only realizes the isolated transmission of the voltage, but also improves the PF value of the step-up/down conversion device, and also improves the quality of the output voltage, making the voltage conversion process safer and more reliable.

Regarding the input part, the input unit 10 includes a socket, a fuse F2, a lightning protection resistor RV1, a common mode suppression inductor L1, a safety capacitor CX1, and a rectifier bridge DB1, and the fuse F2 is connected in series to the neutral wire or the live wire of the socket , the front end of the common mode suppression inductor L1 is connected in parallel to the socket, the lightning protection resistor RV1 is connected in parallel to the front end of the common mode suppression inductor L1, the safety capacitor CX1 and the input end of the rectifier bridge DB1 are connected in parallel to the common mode suppression inductor Backend of L1.

In order to filter the input voltage, the filter unit 20 includes a filter capacitor C1, and the filter capacitor C1 is connected in parallel to the output terminal of the rectifier bridge DB1.

Regarding the boost part, the PFC boost unit 30 includes a boost inductor L2, a third switch tube Q5, a first rectifier diode D1 and a second electrolytic capacitor C2, and the front end of the boost inductor L2 is connected to the input unit 10 The output terminal of the boost inductor L2 is connected to the drain of the third switching tube Q5, the source of the third switching tube Q5 is connected to the front end, and the gate of the third switching tube Q5 is used for A PWM control signal is connected, the drain of the third switching tube Q5 is connected to the anode of the first rectifier diode D1, the cathode of the first rectifier diode D1 is used as the output end of the PFC boost unit 30, and the first rectifier The cathode of the diode D1 is connected to the positive pole of the second electrolytic capacitor C2, and the negative pole of the second electrolytic capacitor C2 is connected to the terminal ground.

In the above-mentioned PFC boost unit 30, if the filter capacitor C1 outputs a half-wave AC voltage, the PFC enters the boost mode to increase the PF value of the AC-to-AC intelligent step-down conversion topology circuit, and after boosting, it is filtered by the second electrolytic capacitor C2 The voltage is 400V, and the specific boost principle is as follows: when the third switch tube Q5 is turned on, the current on the filter capacitor C1 forms a loop through the boost inductor L2 and the third switch tube Q5 to GND, and the boost inductor L2 stores energy; When the third switching tube Q5 is turned off, an induced electromotive force much higher than the input voltage will be formed on the boost inductor, and the induced electromotive force will be rectified by the freewheeling tube D1 to form a one-way pulse voltage and then sent to the second electrolytic capacitor C2 for further Filtering, filtering into 400V DC voltage. And the third switching tube Q5 increases or decreases the conduction time of the third switching tube Q5 according to the change of the input AC correction wave collected by the control chip, so that the phase of the current and the voltage become consistent to increase the PF value.

As a preferred manner, as shown in FIG. 3 , this embodiment also includes an MCU control unit 80, the gate of the first switch Q6, the gate of the second switch Q7 and the gate of the third switch Q5 The poles are respectively connected to the MCU control unit 80, and the MCU control unit 80 is used to respectively output PWM signals to the first switch tube Q6, the second switch tube Q7 and the third switch tube Q5, so as to control the first switch tube Q6, the second switch tube Q6, and the second switch tube Q6. The switch tube Q7 and the third switch tube Q5 are in an on-off state.

For the convenience of monitoring the electrical signal of the AC side, please refer to Fig. 2, also includes an AC sampling unit 70, the AC sampling unit 70 is connected between the input end of the input unit 10 and the MCU control unit 80, the AC sampling unit 70 It is used to collect the voltage of the AC side of the input unit 10 and feed it back to the MCU control unit 80 .

Further, the AC sampling unit 70 includes an operational amplifier U9B, the two input terminals of the operational amplifier U9B are respectively connected to the input terminals of the input unit 10 through a current limiting resistor, and the output terminal of the operational amplifier U9B is connected to MCU control unit 80 .

In order to facilitate real-time collection of current, a first sampling resistor R2A is connected between the source of the third switching tube Q5 and the front-end ground, and the source of the third switching tube Q5 is connected to the MCU control unit 80, by The first sampling resistor R2A enables the MCU control unit 80 to collect the electrical signal of the source of the third switching transistor Q5.

On this basis, the second end of the primary winding of the transformer T1 is connected to the MCU control unit 80, so that the MCU control unit 80 collects the electrical signal of the primary winding of the transformer T1.

As a preferred manner, in order to collect the DC side electric signal, this embodiment also includes a DC voltage sampling unit 50, the DC voltage sampling unit 50 includes a second sampling resistor R13 and a third sampling resistor R15 connected in series in sequence , the front end of the second sampling resistor R13 is connected to the output end of the LLC isolation converter unit 40, and the rear end of the third sampling resistor R15 is connected to the MCU control unit 80, through the second sampling resistor R13 and the first Three sampling resistors R15 enable the MCU control unit 80 to collect the electrical signal output by the LLC isolation converter unit 40 .

Regarding the inverter part, please refer to FIG. 1, the inverter inverter unit 60 includes a fourth switching tube Q2, a fifth switching tube Q4, a third electrolytic capacitor C3 and a fourth electrolytic capacitor C5, the fourth switching tube The drain of Q2 is connected to the positive pole of the output terminal of the LLC isolation converter unit 40, the source of the fourth switching transistor Q2 is connected to the drain of the fifth switching transistor Q4, and the source of the fifth switching transistor Q4 is connected to The negative electrode of the output end of the LLC isolation converter unit 40, the gate of the fourth switching transistor Q2 and the gate of the fifth switching transistor Q4 are respectively used to access two PWM pulse signals with opposite phases, and the third electrolytic capacitor The anode of C3 is connected to the drain of the fourth switching transistor Q2, the cathode of the third electrolytic capacitor C3 is connected to the back-end ground, and the cathode of the third electrolytic capacitor C3 is also connected to the anode of the fourth electrolytic capacitor C5, the The negative pole of the fourth electrolytic capacitor C5 is connected to the source of the fifth switching transistor Q4 , and the source of the fourth switching transistor Q2 and the negative pole of the third electrolytic capacitor C3 serve as the output end of the inverter unit 60 .

Further, a first resistor R17 is connected between the gate and source of the fourth switching transistor Q2, and a second resistor R23 is connected between the gate and source of the fifth switching transistor Q4.

In the above inverter and phase inverting unit 60, the DC voltage is filtered by the filter inductance L3 to form a loop through the fourth switching tube Q2, the load, and the fourth electrolytic capacitor C4 to supply power to the load to form the first half-period correction wave level; the second The two half-cycle correction wave levels form a loop through the fifth switching tube Q4, the load, and the third electrolytic capacitor C3, so that a complete power frequency correction wave AC voltage is formed on the load. The PWM signal output by the control chip is sent to the GATE poles of the fourth switching tube Q2 and the fifth switching tube Q4 respectively after passing through the driving circuit to PWM2H and PWM2L. The phase and frequency in the inverter inverter circuit work according to the mode set inside the control chip. At the same time, the third electrolytic capacitor C3 and the fourth electrolytic capacitor C4 also have the function of filtering, and can form a filtering circuit with the filtering inductor L3. The control of the inverter circuit is simple, the circuit only uses two MOS tubes, and the cost is low.

The intelligent half-bridge modified wave voltage conversion circuit based on PFC and LLC resonance disclosed by the utility model has a high PF value, can realize the isolation of the power grid and the output terminal, and has very high safety. The output voltage can be automatically adjusted within the full input voltage range, the output frequency can be fixed, and the output voltage is output by a modified wave, which has an automatic shaping function for the AC voltage. In addition, the utility model has a simple circuit, convenient control, and contains voltage and Current sampling circuit can prevent surge voltage and current.

The above is only a preferred embodiment of the utility model, and is not intended to limit the utility model. All modifications, equivalent replacements or improvements made within the technical scope of the utility model should be included in the protection of the utility model. In the range.

Claims (10)

1. A kind of intelligent half-bridge modified wave voltage conversion circuit based on PFC and LLC resonance, it is characterized in that, comprises: an input unit for providing DC voltage; A filter unit, connected to the output end of the input unit, for filtering the output voltage of the input unit; A PFC step-up unit, connected to the output end of the filter unit, used for step-up conversion of the output voltage of the filter unit; An LLC isolated converter unit, including a first switch tube, a second switch tube, a transformer, a first diode, a second diode and a filter inductor, the drain of the first switch tube is connected to the PFC boost The output terminal of the unit, the source of the first switching tube is connected to the first end of the primary winding of the transformer, the second end of the primary winding of the transformer is connected to the front-end ground through the first resonant capacitor, and the The drain is connected to the first end of the primary winding of the transformer, the source of the second switching tube is connected to the front-end ground through a third resistor, and the grid of the first switching tube and the grid of the second switching tube are used to load Two PWM pulse signals with opposite phases, so as to make the first switching tube and the second switching tube conduct alternately, the middle tap of the secondary winding of the transformer is connected to the rear end ground, the first switching tube of the secondary winding of the transformer The end is connected to the cathode of the first diode, the anode of the first diode is connected to the rear end ground through the second capacitor, the second end of the secondary winding of the transformer is connected to the anode of the second diode, The cathode of the second diode is connected to the front end of the filter inductor, the rear end of the filter inductor is connected to the rear ground through a third capacitor, and the rear end of the filter inductor and the anode of the first diode serve as an LLC an output terminal of the isolated converter unit; An inverting and inverting unit connected to the output end of the LLC isolation converter unit, the inverting and inverting unit is used for inverting and converting the output voltage of the LLC isolating converter unit to output alternating current. 2. The intelligent half-bridge modified wave voltage conversion circuit based on PFC and LLC resonance as claimed in claim 1, wherein the input unit includes a socket, an insurance, a lightning protection resistor, a common mode suppression inductor, and a safety capacitor and a rectifier bridge, the insurance is connected in series with the zero line or live line of the socket, the front end of the common mode suppression inductor is connected in parallel with the socket, the lightning protection resistor is connected in parallel with the front end of the common mode suppression inductor, the safety capacitor and The input terminals of the rectifier bridge are connected in parallel to the rear end of the common mode suppression inductor. 3 . The intelligent half-bridge modified wave voltage conversion circuit based on PFC and LLC resonance according to claim 2 , wherein the filter unit includes a filter capacitor connected in parallel to the output terminal of the rectifier bridge. 4 . 4. The intelligent half-bridge modified wave voltage conversion circuit based on PFC and LLC resonance as claimed in claim 1, wherein the PFC boost unit includes a boost inductor, a third switch tube, a first rectifier diode and The second electrolytic capacitor, the front end of the boost inductor is connected to the output terminal of the input unit, the rear end of the boost inductor is connected to the drain of the third switch tube, and the source of the third switch tube is connected to the front end ground , the gate of the third switching tube is used to access a PWM control signal, the drain of the third switching tube is connected to the anode of the first rectifying diode, and the cathode of the first rectifying diode is used as the PFC step-up unit output terminal, and the cathode of the first rectifying diode is connected to the positive pole of the second electrolytic capacitor, and the negative pole of the second electrolytic capacitor is connected to the terminal ground. 5. the intelligent half-bridge modified wave voltage conversion circuit based on PFC and LLC resonance as claimed in claim 4, is characterized in that, also comprises an MCU control unit, the grid of described first switching tube, the second switching tube The grid and the grid of the third switching tube are respectively connected to the MCU control unit, and the MCU control unit is used to respectively output PWM signals to the first switching tube, the second switching tube and the third switching tube to control the first switching tube , the on-off state of the second switch tube and the third switch tube. 6. The intelligent half bridge correction wave voltage conversion circuit based on PFC and LLC resonance as claimed in claim 5, is characterized in that, also comprises an AC sampling unit, and described AC sampling unit is connected to the input terminal of input unit and MCU control Between the units, the AC sampling unit is used to collect the voltage on the AC side of the input unit and feed it back to the MCU control unit. 7. The intelligent half-bridge modified wave voltage conversion circuit based on PFC and LLC resonance as claimed in claim 5, wherein a first sampling resistor is connected between the source of the third switch tube and the front end ground, so The source of the third switch tube is connected to the MCU control unit, and the MCU control unit collects the electrical signal of the source of the third switch tube through the first sampling resistor. 8. the intelligent half bridge correction wave voltage conversion circuit based on PFC and LLC resonance as claimed in claim 5, is characterized in that, the second end of described transformer primary winding is connected with MCU control unit, so that MCU control unit collects transformer The electrical signal of the primary winding. 9. The intelligent half-bridge modified wave voltage conversion circuit based on PFC and LLC resonance as claimed in claim 5, further comprising a DC voltage sampling unit, said DC voltage sampling unit comprising a second sampling unit connected in series in sequence resistor and the third sampling resistor, the front end of the second sampling resistor is connected to the output end of the LLC isolation converter unit, the rear end of the third sampling resistor is connected to the MCU control unit, by the second sampling resistor and The third sampling resistor enables the MCU control unit to collect the electrical signal output by the LLC isolation converter unit. 10. The intelligent half-bridge modified wave voltage conversion circuit based on PFC and LLC resonance as claimed in claim 5, wherein the inverter and phase inverting unit includes a fourth switching tube, a fifth switching tube, a third electrolytic capacitor and a fourth electrolytic capacitor, the drain of the fourth switch tube is connected to the positive pole of the output terminal of the LLC isolation converter unit, the source of the fourth switch tube is connected to the drain of the fifth switch tube, and the drain of the fourth switch tube is connected The sources of the five switching tubes are connected to the negative pole of the output terminal of the LLC isolation converter unit, and the gates of the fourth switching tube and the fifth switching tube are respectively used to access two PWM pulse signals with opposite phases, so The positive pole of the third electrolytic capacitor is connected to the drain of the fourth switch tube, the negative pole of the third electrolytic capacitor is connected to the rear ground, and the negative pole of the third electrolytic capacitor is also connected to the positive pole of the fourth electrolytic capacitor. The negative pole of the fourth electrolytic capacitor is connected to the source of the fifth switching tube, and the source of the fourth switching tube and the negative pole of the third electrolytic capacitor serve as the output terminal of the inverter unit.