Power supply driving circuit of low-temperature plasma surgical equipment

Abstract

The utility model discloses a power supply driving circuit of low-temperature plasma surgical equipment, which comprises a rectifying and filtering circuit, a PWM (Pulse-Width Modulation) waveform generating circuit, a DAC (Digital-to-Analog Converter) converting circuit, a low-voltage direct-current switching power supply, a full-bridge inverter circuit and a high-frequency transformer, wherein an alternating-current power supply is sequentially connected with the rectifying and filtering circuit, the full-bridge inverter circuit and the high-frequency transformer; the PWM waveform generation circuit is connected with the full-bridge inverter circuit, the DAC conversion circuit is connected with the PWM waveform generation circuit, and the AC power supply is connected with the DAC conversion circuit through the low-voltage DC switching power supply. According to the utility model, reliable driving of the alternating-current inverter power supply with the frequency of 200kHz of plasma operation electrode equipment can be realized.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of medical instruments, especially relates to a power supply drive circuit of low temperature plasma operation equipment. BACKGROUND

[0002] The low temperature plasma technology principle is to generate plasma thin layer by 100kHz-1000kHz radio frequency energy excitation medium (NaCl), and the plasma in the thin layer is accelerated by electric field at 40-70 DEG C, and the organic molecular chain in the tissue is broken, and the biological macromolecule such as protein is directly cracked into O2, CO2, N2 and other gases, so that the cutting, punching, ablation, shrinkage and hemostasis and other operations of the tissue are completed, so that minimally invasive surgery is realized.The power supply circuit of the existing low temperature plasma operation equipment cannot realize frequency switching and select the required output frequency.Therefore, how to realize long time efficient and stable output of the required radio frequency energy is the problem to be solved at present. SUMMARY

[0003] In order to solve the above problems, the utility model aims at providing a power supply drive circuit of low temperature plasma operation equipment.

[0004] In order to realize the above-mentioned invention purpose, the utility model adopts the following technical scheme:

[0005] A power supply drive circuit of low temperature plasma operation equipment, it includes rectifier filter circuit, PWM waveform generating circuit, DAC conversion circuit, low voltage DC switching power supply, full bridge inverter circuit, high frequency transformer, alternating current power supply and rectifier filter circuit, full bridge inverter circuit, high frequency transformer are connected in proper order, PWM waveform generating circuit is connected with full bridge inverter circuit, DAC conversion circuit is connected with PWM waveform generating circuit, alternating current power supply is connected with DAC conversion circuit through low voltage DC switching power supply.

[0006] Further, the full-bridge inverter circuit comprises a pulse transformer T2, a pulse transformer T3, a MOS tube Q1, a MOS tube Q2, a MOS tube Q3, a MOS tube Q4, the first signal output end of the PWM waveform generating circuit is connected with the first end of the primary coil T2A of the transformer T2 through the resistance R6 and the capacitor C4, the second end of the primary coil T2A is grounded, the first end and the second end of the secondary coil T2B are connected with the gate of the MOS tube Q1 through the resistance R5 and the resistance R10 respectively, and the second end is connected with the source of the MOS tube Q1, the first end and the second end of the secondary coil T2C are connected with the gate of the MOS tube Q2 through the resistance R4 and the resistance R9 respectively, and the second end is connected with the source of the MOS tube Q2; the second signal output end of the PWM waveform generating circuit is connected with the first end of the primary coil T3A of the transformer T3 through the resistance R15 and the capacitor C10, the second end of the primary coil T3A is grounded, the first end and the second end of the secondary coil T3B are connected with the gate of the MOS tube Q3 through the resistance R14 and the resistance R18 respectively, and the second end is connected with the source of the MOS tube Q3, the first end and the second end of the secondary coil T3C are connected with the gate of the MOS tube Q4 through the resistance R13 and the resistance R16 respectively, and the second end is connected with the source of the MOS tube Q4; the drain of the MOS tube Q1 is connected with the drain of the MOS tube Q2, the source is connected with the drain of the MOS tube Q3, the drain of the MOS tube Q4 is connected with the source of the MOS tube Q2, and the source is connected with the source of the MOS tube Q3; the source of the MOS tube Q2 is connected with the first end of the primary coil of the high-frequency transformer T1 through the inductor L1 and the capacitor C1, the source of the MOS tube Q1 is connected with the second end of the primary coil of the high-frequency transformer T1, and the secondary coil of the high-frequency transformer T1 is connected with the plasma surgical electrode.

[0007] Further, the MOS tube Q1, the MOS tube Q2, the MOS tube Q3 and the MOS tube Q4 are connected with the series-connected resistance and capacitor between the source and the drain.

[0008] Further, the PWM waveform generating circuit comprises a PWM controller U2, a gate drive U1, and an operational amplifier U3, an output terminal of the DAC conversion circuit is connected with a non-inverting input terminal of the operational amplifier U3, an inverting input terminal of the operational amplifier U3 is connected with an output terminal, and the output terminal is connected with an NI terminal of the PWM controller U2, a positive power supply terminal is connected with a first power supply, and a negative power supply terminal is connected with the ground; an IVN terminal and an EAOUT terminal of the PWM controller U2 are connected, an RT terminal is connected with the ground through a resistance R17, an SS terminal is connected with the ground through a capacitor C14, a RAMP terminal and a CT terminal are connected with the ground through a capacitor C15, and the ground is connected with the ground and a PGND terminal; an OUTA terminal and an OUTB terminal are connected with a first signal input terminal and a second signal input terminal of the gate drive U1 respectively, a VCC terminal is connected with a +12V power supply and a resistance R7, and a VC terminal is connected with the ground through a capacitor C8; a first signal output terminal and a second signal output terminal of the gate drive U1 are connected with the transformer T2 and the transformer T3 in the full-bridge inverter circuit respectively, a positive power supply terminal is connected with a second power supply, and a ground terminal is connected with the ground.

[0009] Further, the rectification filter circuit comprises a rectification bridge DB1 and a power supply transformer L2, an alternating current power supply is connected with an input terminal of the power supply transformer L2 through a power supply switch K, a fuse F1, a fuse F2 and an alternating current filter, an output terminal of the power supply transformer L2 is connected with an input terminal of the rectification bridge DB1, a direct current positive output terminal and a direct current negative output terminal of the rectification bridge DB1 are connected with an adjustable resistance R1 and an adjustable resistance R8 respectively, a direct current filter is connected between the adjustable resistance R1 and the adjustable resistance R8, and an output terminal of the direct current filter is connected with the full-bridge inverter circuit.

[0010] Further, the power supply driving circuit of the low-temperature plasma surgical device further comprises an overcurrent and overvoltage protection circuit, the high-frequency transformer is connected with the DAC conversion circuit through the overcurrent and overvoltage protection circuit.

[0011] Still further, the overcurrent and overvoltage protection circuit comprises a current transformer TA1 and a rectification bridge B1, the rectification bridge B1 is composed of a diode D1, a diode D2, a diode D3 and a diode D4, the current transformer TA1 is connected with a line between a primary coil of the high-frequency transformer T1 and the MOS tube Q1, a resistance R19 is connected between output terminals of the current transformer TA1, the output terminals of the current transformer TA1 are connected with input terminals of the rectification bridge B1, output terminals of the rectification bridge B1 are connected with a filter circuit composed of a resistance R22 and a capacitor C17, a voltage division circuit composed of a resistance R23 and a resistance R25, and a resistance R24 and the ILIM terminal of the PWM waveform generating circuit, and a negative output terminal of the rectification bridge B1 is connected with the ground.

[0012] Due to the adoption of the technical scheme, the low-temperature plasma surgical device has the following advantages:

[0013] The power supply driving circuit of the low-temperature plasma surgical equipment first forms an EMC anti-interference circuit through an alternating current filter, then passes through a rectifier bridge and a direct current filter as an initial direct current power supply of the plasma power supply, converts the direct current voltage received from the rectifier bridge into a high-frequency pulsating direct current output voltage, generates a PWM modulation pulse required for controlling the full-bridge topology through a PWM waveform generating circuit, adjusts the quality of plasma generation by adjusting the duty cycle of the PWM pulse to change the output voltage and output current according to the power required by the plasma driving through the output of a group of 0-5V DAC control levels of the host MCU, and forms overvoltage and overcurrent protection through feedback current and feedback voltage detection. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a structural schematic diagram of the power supply driving circuit of the low-temperature plasma surgical equipment of the utility model;

[0015] Figure 2 is a principle diagram of the power supply driving circuit of the low-temperature plasma surgical equipment of the utility model. DETAILED DESCRIPTION

[0016] The technical scheme of the utility model is further described in detail below through the drawings and examples.

[0017] As Figure 1 , 2The power supply driving circuit of the low-temperature plasma surgical device includes a rectifier filter circuit, a PWM waveform generating circuit, a DAC conversion circuit, a low-voltage DC switching power supply, a full-bridge inverter circuit, a high-frequency transformer, 220V AC mains and the rectifier filter circuit, the full-bridge inverter circuit, and the high-frequency transformer are connected in sequence; the PWM waveform generating circuit is connected with the full-bridge inverter circuit, the DAC conversion circuit is connected with the PWM waveform generating circuit, and the AC power supply is connected with the DAC conversion circuit through the low-voltage DC switching power supply; the full-bridge inverter circuit includes a pulse transformer T2, a pulse transformer T3, MOS tubes Q1, Q2, Q3, and Q4, a first signal output end of the PWM waveform generating circuit is connected with a first end of a primary coil T2A of the transformer T2 through a resistor R6 and a capacitor C4, a second end of the primary coil T2A is grounded, a first end and a second end of a secondary coil T2B are respectively connected with a gate of the MOS tube Q1 through a resistor R5 and a resistor R10, and the second end is connected with a source of the MOS tube Q1, a first end and a second end of a secondary coil T2C are respectively connected with a gate of the MOS tube Q2 through a resistor R4 and a resistor R9, and the second end is connected with a source of the MOS tube Q2; a second signal output end is connected with a first end of a primary coil T3A of the transformer T3 through a resistor R15 and a capacitor C10, a second end of the primary coil T3A is grounded, a first end and a second end of a secondary coil T3B are respectively connected with a gate of the MOS tube Q3 through a resistor R14 and a resistor R18, and the second end is connected with a source of the MOS tube Q3, a first end and a second end of a secondary coil T3C are respectively connected with a gate of the MOS tube Q4 through a resistor R13 and a resistor R16, and the second end is connected with a source of the MOS tube Q4; a drain of the MOS tube Q1 is connected with a drain of the MOS tube Q2, a source is connected with a drain of the MOS tube Q3, a drain of the MOS tube Q4 is connected with a source of the MOS tube Q2, and a source is connected with a source of the MOS tube Q3; a source of the MOS tube Q2 is connected with a first end of a primary coil of the high-frequency transformer T1 through an inductor L1 and a capacitor C1, a source of the MOS tube Q1 is connected with a second end of the primary coil of the high-frequency transformer T1, and a secondary coil of the high-frequency transformer T1 is connected with a plasma surgical electrode.

[0018] The source and the drain of the MOS tube Q1 are connected with a resistor R12 and a capacitor C7 in series, the source and the drain of the MOS tube Q2 are connected with a resistor R11 and a capacitor C6 in series, the source and the drain of the MOS tube Q3 are connected with a resistor R21 and a capacitor C16 in series, and the source and the drain of the MOS tube Q4 are connected with a resistor R20 and a capacitor C13 in series.

[0019] The full-bridge inverter circuit above realizes electrical isolation through pulse transformer T2 and pulse transformer T3, minimizes turn-off oscillation through resistor R4, resistor R13, resistor R5 and resistor R14, generates damping through resistor R6 and resistor R15 to eliminate ringing caused by parasitic inductance in pulse transformer T2 and pulse transformer T3, prevents direct current flux imbalance in pulse transformer T2 and pulse transformer T3 through capacitor C4 and capacitor C10, and absorbs the spike pulse of the corresponding MOS tube when the MOS tube is switched on and off through the RC absorption circuit composed of the series connection of resistor and capacitor between the source and drain of MOS tube Q1, MOS tube Q2, MOS tube Q3 and MOS tube Q4. When MOS tube Q1 and MOS tube Q4 are turned on and MOS tube Q2 and MOS tube Q3 are turned off, a positive direct current voltage is obtained at the output end; when MOS tube Q2 and MOS tube Q3 are turned on and MOS tube Q1 and MOS tube Q4 are turned off, a negative direct current voltage is obtained at the output end. The MOS tube switches are alternately switched with a controlled duty cycle.

[0020] The PWM waveform generation circuit above comprises a PWM controller U2, a gate driver U1 and an operational amplifier U3. The output end of the DAC conversion circuit is connected to the non-inverting input end of the operational amplifier U3, the inverting input end of the operational amplifier U3 is connected to the output end and is connected to the NI end (pin 2) of the PWM controller U2, the positive power supply end is connected to a +5V power supply, and the negative power supply end is connected to ground. The IVN end (pin 1) of the PWM controller U2 is connected to the EAOUT end (pin 3), the RT end (pin 5) is connected to the SS end (pin 8) through a resistor R17, the RAMP end (pin 7) and the CT end (pin 6) are connected and are connected to the GND end (pin 10) and the PGND end and are connected to ground through a capacitor C15. The OUTA end (pin 11) and the OUTB end (pin 14) are respectively connected to the first signal input end (pin 2) and the second signal input end (pin 4) of the gate driver U1, the VCC end (pin 15) is connected to a +12V power supply and is connected to the VC end (pin 13) through a resistor R7, and the VC end is connected to ground through a capacitor C8. The first signal output end (pin 7) and the first signal output end (pin 5) of the gate driver U1 are respectively connected to the transformer T2 and the transformer T3 in the full-bridge inverter circuit, the positive power supply end (pin 6) is connected to a +12V power supply, and the ground end (pin 3) is connected to ground.

[0021] The OUTA end (pin 11) and the OUTB end (pin 14) of the PWM controller U2 provide PWM switching pulses, which are alternately output through the OUTA end and the OUTB end and can drive the gates of MOS tube Q1, MOS tube Q2, MOS tube Q3 and MOS tube Q4 through driving resistors R5, R4, R13 and R14 through pulse transformer T2 and pulse transformer T3.

[0022] The rectifier filter circuit comprises a rectifier bridge DB1, a power transformer L2, a 220V AC power supply is connected with the input end of the power transformer L2 through a power switch K, a fuse F1, a fuse F2 and an AC filter, a capacitor C9 is connected between the output ends of the power transformer L2, and the input end of the rectifier bridge DB1, the positive and negative output ends of the rectifier bridge DB1 are connected with one end of an adjustable resistor R1 and one end of an adjustable resistor R8 respectively, a DC filter is connected between the other ends of the adjustable resistor R1 and the adjustable resistor R8, and the output end of the DC filter is connected with the full-bridge inverter circuit; the AC filter is composed of a capacitor C11 connected between a live wire and the ground and a capacitor C12 connected between a zero line and the ground; and the DC filter is composed of a capacitor C2, a capacitor C3, a resistor R2, a resistor R3 and a capacitor C5 connected in parallel.

[0023] The power supply driving circuit of the low-temperature plasma surgical device further comprises an overcurrent and overvoltage protection circuit, the high-frequency transformer is connected with the DAC conversion circuit through the overcurrent and overvoltage protection circuit; the overcurrent and overvoltage protection circuit comprises a current transformer TA1 and a rectifier bridge B1, the rectifier bridge B1 is composed of a diode D1, a diode D2, a diode D3 and a diode D4, the current transformer TA1 is connected in the circuit between the primary coil of the high-frequency transformer T1 and the MOS tube Q1, a resistor R19 is connected between the output ends of the current transformer TA1, the output ends of the current transformer TA1 are connected with the input end of the rectifier bridge B1, the output ends of the rectifier bridge B1 are connected with the PWM waveform generating circuit ILIM end through a filter circuit composed of a resistor R22 and a capacitor C17, a voltage dividing circuit composed of a resistor R23 and a resistor R25, and a resistor R24, and the negative output end of the rectifier bridge B1 is grounded. The current transformer TA1 limits the primary current of the isolation transformer, and prevents the failure of the AC inverter power stage and the failure in the subsequent circuit of the converter.

[0024] The output of the current transformer TA1 is fed back to the ILIM end of the PWM controller U2 through the filter circuit composed of the rectifier bridge B1, the resistor R22 and the capacitor C17. Under the condition of overcurrent, the current limiting function of the PWM controller U2 resets the slow start circuit, causing the output to cycle from on to off until the current decreases.

[0025] The DAC conversion circuit is used for adjusting the parameters of the PWM control loop by outputting a linear voltage signal of 0-5V according to the power required by the plasma driving, and transmitting the DAC signal controlled by the host MCU of the low-temperature plasma surgical device to the emitter follower composed of the operational amplifier U3 and outputting to the NI end of the PWM controller U2, so as to adjust the duty cycle of the PWM output waveform of the PWM controller U2 by controlling the level of the NI end, and change the voltage amplitude and current intensity of the output power by adjusting the duty cycle, and further adjust the quality of the generated plasma.

[0026] The input end of the low-voltage direct-current switching power supply is connected with the output end of the power transformer L2 in the rectifier filter circuit, and the output voltages are +12V, -12V and +5V, which are used for supplying power to the host and each functional module circuit of the low-temperature plasma surgical device.

[0027] The pins of the PWM controller U2 are as follows: the NI end is the inverting input end of the error amplifier; the IVN end is the non-inverting input end of the error amplifier; the EAOUT end is the output end of the error amplifier; the RAMP end is the slope input end; the CT end is the timing capacitor end; the SS end is the soft start end; the RT end is the timing resistor end; the ILIM end is the current control end; the OUTA end is the A output end; the OUTB end is the B output end; the VCC end is the working voltage end; the VC end is the power supply end; the GND end is the ground end; and the PGND end is the power ground end.

[0028] Preferably, the model of the PWM controller U2 is UC3825A, the model of the gate driver U1 is TC1427COA, and the model of the operational amplifier U3 is MAX492.

[0029] The chip UC3825A used by the PWM controller U2 has a maximum frequency of 1M, and the two pulse output ends OUTA and OUTB output alternately, and the frequency of each pulse output end is 1 / 2 of the oscillator frequency, so that the oscillator frequency is set to 400 kHz, and the actual output frequency of the PWM is 200K. The oscillator frequency of the PWM controller U2 can be configured to 400K by configuring the values of the resistor R17 and the capacitor C15, and the capacitor C14 is connected to the SS pin of the PWM controller U2, and controls the slope rising of the pulse width to perform slow start control (realize the soft start function) when the power is turned on.

[0030] In the prior art, the peak voltage outputted by the plasma surgical electrode is 424.2-707V, the pulse duration τ is 1-5µs, the pulse interval time is >10µs and <25.3µs, and the commonly used working frequency is 200 KHz-1000KHz.In the power supply driving circuit of the low-temperature plasma surgical equipment, when the working frequency is configured at 200 KHz, the plasma activation concentration and the blade tip temperature will reach a relatively balanced state, and the working needs of the plasma electrode can be better met.

[0031] The 200kHz full-bridge inverter circuit can generate a peak AC voltage of up to 600V to convert the input DC voltage into a high-frequency AC voltage suitable for exciting the plasma load.

[0032] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A power supply drive circuit for a low temperature plasma surgical apparatus, characterized by: It includes rectifier filter circuit, PWM waveform generating circuit, DAC conversion circuit, low-voltage DC switching power supply, full-bridge inverter circuit, high-frequency transformer, AC power supply and rectifier filter circuit, full-bridge inverter circuit, high-frequency transformer are sequentially connected, PWM waveform generating circuit and full-bridge inverter circuit are connected, DAC conversion circuit and PWM waveform generating circuit are connected, AC power supply is connected with DAC conversion circuit through low-voltage DC switching power supply.

2. The power supply drive circuit for a low temperature plasma surgical apparatus according to claim 1, characterized by: The full-bridge inverter circuit includes pulse transformer T2, pulse transformer T3, MOS tube Q1, MOS tube Q2, MOS tube Q3, MOS tube Q4, the first signal output end of the PWM waveform generating circuit is connected with the first end of the primary coil T2A of the transformer T2 through the resistance R6 and the capacitor C4, the second end of the primary coil T2A is grounded, the first end and the second end of the secondary coil T2B are respectively connected with the gate of the MOS tube Q1 through the resistance R5 and the resistance R10, and the second end is connected with the source of the MOS tube Q1, the first end and the second end of the secondary coil T2C are respectively connected with the gate of the MOS tube Q2 through the resistance R4 and the resistance R9, and the second end is connected with the source of the MOS tube Q2; the second signal output end of the PWM waveform generating circuit is connected with the first end of the primary coil T3A of the transformer T3 through the resistance R15 and the capacitor C10, the second end of the primary coil T3A is grounded, the first end and the second end of the secondary coil T3B are respectively connected with the gate of the MOS tube Q3 through the resistance R14 and the resistance R18, and the second end is connected with the source of the MOS tube Q3, the first end and the second end of the secondary coil T3C are respectively connected with the gate of the MOS tube Q4 through the resistance R13 and the resistance R16, and the second end is connected with the source of the MOS tube Q4; the drain of the MOS tube Q1 is connected with the drain of the MOS tube Q2, the source is connected with the drain of the MOS tube Q3, the drain of the MOS tube Q4 is connected with the source of the MOS tube Q2, and the source is connected with the source of the MOS tube Q3; the source of the MOS tube Q2 is connected with the first end of the primary coil of the high-frequency transformer T1 through the inductor L1 and the capacitor C1, the source of the MOS tube Q1 is connected with the second end of the primary coil of the high-frequency transformer T1, and the secondary coil of the high-frequency transformer T1 is connected with the plasma surgical electrode.

3. The power supply drive circuit for a cryo-plasma surgical apparatus according to claim 2, characterized by: The resistance and the capacitor in series are connected between the source and the drain of the MOS tube Q1, the MOS tube Q2, the MOS tube Q3 and the MOS tube Q4.

4. The power supply drive circuit for a low temperature plasma surgical apparatus according to claim 1 or 3, characterized by: The PWM waveform generating circuit comprises a PWM controller U2, a gate driver U1, and an operational amplifier U3, an output terminal of the DAC conversion circuit is connected with a non-inverting input terminal of the operational amplifier U3, an inverting input terminal of the operational amplifier U3 is connected with an output terminal, and the output terminal is connected with an NI terminal of the PWM controller U2, a positive power supply terminal is connected with a first power supply, and a negative power supply terminal is connected with the ground; an IVN terminal and an EAOUT terminal of the PWM controller U2 are connected, an RT terminal is connected with the ground through a resistance R17, an SS terminal is connected with the ground through a capacitor C14, a RAMP terminal and a CT terminal are connected with the ground through a capacitor C15, and the ground is connected with a GND terminal and a PGND terminal; an OUTA terminal and an OUTB terminal are connected with a first signal input terminal and a second signal input terminal of the gate driver U1 respectively, a VCC terminal is connected with a +12V power supply, and the VCC terminal is connected with a VC terminal through a resistance R7, and the VC terminal is connected with the ground through a capacitor C8; a first signal output terminal and a second signal output terminal of the gate driver U1 are connected with a transformer T2 and a transformer T3 in the full-bridge inverter circuit respectively, a positive power supply terminal is connected with a second power supply, and a ground terminal is connected with the ground.

5. The power supply drive circuit for a cryo-plasma surgical apparatus according to claim 1, characterized by: The rectification filtering circuit comprises a rectification bridge DB1 and a power supply transformer L2, an alternating current power supply is connected with an input terminal of the power supply transformer L2 through a power supply switch K, a fuse F1, a fuse F2, and an alternating current filter, an output terminal of the power supply transformer L2 is connected with an input terminal of the rectification bridge DB1, a direct current positive output terminal and a direct current negative output terminal of the rectification bridge DB1 are connected with one end of an adjustable resistance R1 and an adjustable resistance R8 respectively, a direct current filter is connected between the other end of the adjustable resistance R1 and the adjustable resistance R8, and the direct current filter is connected with the full-bridge inverter circuit.

6. The power supply drive circuit for a cryo-plasma surgical apparatus according to claim 1, characterized by: The high-frequency transformer is connected with the DAC conversion circuit through the overcurrent and overvoltage protection circuit.

7. The power supply drive circuit for a cryo-plasma surgical apparatus according to claim 6, characterized by: The overcurrent and overvoltage protection circuit comprises a current transformer TA1 and a rectification bridge B1, the rectification bridge B1 is composed of a diode D1, a diode D2, a diode D3, and a diode D4, the current transformer TA1 is connected with a line between a primary coil of the high-frequency transformer T1 and the MOS tube Q1, a resistance R19 is connected between output terminals of the current transformer TA1, the output terminals of the current transformer TA1 are connected with input terminals of the rectification bridge B1, output terminals of the rectification bridge B1 are connected with a filter circuit composed of a resistance R22 and a capacitor C17, a voltage division circuit composed of a resistance R23 and a resistance R25, and the PWM waveform generating circuit ILIM terminal, and a negative output terminal of the rectification bridge B1 is connected with the ground.

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