CN113364266B - A single-stage PFC power supply circuit - Google Patents

Abstract

The present invention relates to a single-stage PFC power supply circuit, including an EMI filter circuit, a bridge rectifier circuit, a start-up circuit, a filter circuit, a primary main winding NP of a filter circuit transformer T1 is electrically connected, the start-up circuit is electrically connected to the output end of an auxiliary power supply circuit, the GD pin of a PFC control chip U1 is electrically connected to the IN pin of a single-end to double-end drive circuit, the GDM pin of the single-end to double-end drive circuit is electrically connected to one end of a first drive circuit, the GDA pin of the single-end to double-end drive circuit is electrically connected to one end of a second drive circuit, the other end of the first drive circuit is electrically connected to the gate of a first switch tube Q1, and the second drive circuit is electrically connected to the gate of a second switch tube Q2. This scheme adopts a single-stage PFC voltage conversion circuit of a resonant soft switch, and while correcting the power factor, it realizes isolated step-down conversion from input AC voltage to output DC voltage, reduces switch devices and magnetic components, improves power efficiency, reduces costs, and improves the reliability of power switch devices.

Description

A single-stage PFC power supply circuit

Technical Field

The present invention relates to the technical field of power supply circuits, and in particular to a single-stage PFC power supply circuit.

Background Art

Generally, in high-power (for example, greater than 75W) power supplies, it is necessary to meet the standard requirements for harmonic currents. To make the harmonic currents of the power supply meet the standards, a power factor correction (PFC) part must be added before the DC-DC isolation conversion stage. Therefore, the power supply will be a two-stage voltage conversion structure, with the front stage being a non-isolated active PFC AC to high-voltage DC conversion circuit structure, and the back stage being an isolated high-voltage DC to low-voltage DC conversion circuit structure. This power supply with a two-stage voltage conversion structure has many switching devices and magnetic components, resulting in large switching losses, large line losses, and large core losses, making the power supply efficiency low, the power supply volume large, and the cost high. The switching devices in the non-isolated active PFC circuit of the front stage and the isolated high-voltage DC to low-voltage DC conversion circuit of the back stage generally work in a hard switching state, with large switching losses. Even if the switching devices are allowed to work in a resonant valley switching state, the switching losses are still relatively large, making the power supply inefficient. The isolation transformer in the subsequent isolated high-voltage DC to low-voltage DC conversion circuit has leakage inductance, which resonates with the parasitic capacitance of the switch tube to produce very high voltage spikes, making the voltage stress of the switch tube relatively large. If it is not suppressed, the switch tube will be easily damaged.

It can be seen that the existing power supply circuit with two-stage voltage conversion structure has the following defects:

(1) There are many switching devices and magnetic components, resulting in large switching losses, large line losses, and large core losses;

(2) The efficiency of the power supply is low, the size of the power supply is large, and the cost is high;

(3) The isolation transformer at the rear stage has leakage inductance, which resonates with the parasitic capacitance of the switch tube to produce a very high voltage spike, causing large voltage stress on the switch tube and easily damaging the switch tube.

In order to overcome the above shortcomings, we invented a single-stage PFC power supply circuit.

Summary of the invention

The invention aims to solve the problems of the existing two-stage voltage conversion structure power supply circuit, which has many switch devices and magnetic components, resulting in large switch loss, large line loss, large core loss, low power efficiency, high cost, and easy damage to the switch tube. The specific solution is as follows:

A single-stage PFC power supply circuit includes an EMI filter circuit with one end electrically connected to an external AC power supply and the earth, the other end of the EMI filter circuit is electrically connected to a bridge rectifier circuit and one end of a start-up circuit at the same time, the other end of the bridge rectifier circuit is electrically connected to one end of the filter circuit, the other end of the filter circuit is electrically connected to one end of a primary main winding NP of a transformer T1, the other end of the start-up circuit is electrically connected to the output end of an auxiliary power supply circuit, and the output end of the auxiliary power supply circuit is electrically connected to the VCC power supply pin of a PFC control chip U1, a single-end to double-end drive circuit, and an impedance matching circuit at the same time. The GD pin of the PFC control chip U1 is electrically connected to the IN pin of the single-end to double-end drive circuit, the GDM pin of the single-end to double-end drive circuit is electrically connected to one end of the first drive circuit, the GDA pin of the single-end to double-end drive circuit is electrically connected to one end of the second drive circuit, the other end of the first drive circuit is electrically connected to the gate of the first switch tube Q1, the source of the first switch tube Q1 is electrically connected to one end of the resistors R1 and R2 at the same time, the other end of the resistor R2 is electrically connected to the CS pin of the PFC control chip U1, and the second drive circuit is electrically connected to the gate of the second switch tube Q2. The gate is electrically connected, the source of the second switch tube Q2, the other end of the second drive circuit, and the drain of the first switch tube Q1 are electrically connected to the other end of the primary main winding NP of the transformer T1, the drain of the second switch tube Q2 is electrically connected to one end of the series capacitor C2, the series capacitor C2, the other end of the resistor R1, the auxiliary power supply circuit, the PFC control chip U1, the single-end to double-end drive circuit, and the GND ground pin of the impedance matching circuit are electrically connected to the GND ground terminal of the primary secondary winding NF of the transformer T1, and one end of the impedance matching circuit is electrically connected to the FB pin of the PFC control chip U1. The other end of the impedance matching circuit is electrically connected to one end of the optocoupler chip OP1, the other end of the primary secondary winding NF of the transformer T1 is electrically connected to the auxiliary power supply circuit and one end of the zero current detection circuit at the same time, the other end of the zero current detection circuit is electrically connected to the ZCD pin of the PFC control chip U1, the other end of the optocoupler chip OP1 is electrically connected to one end of the error voltage comparison circuit, the other end of the error voltage comparison circuit is electrically connected to both ends of the output capacitor C3 and the output end of the rectifier circuit, and the input end of the rectifier circuit is electrically connected to both ends of the secondary winding NS of the transformer T1.

Furthermore, the transformer T1 includes a leakage inductance Lr connected in series to one end of the primary main winding NP of the transformer T1 and an excitation inductance Lm connected in parallel to both ends of the primary main winding NP of the transformer T1.

Furthermore, the first switch tube Q1 includes a parasitic capacitor C1 connected in parallel between a source and a drain of the first switch tube Q1.

Furthermore, the starting circuit includes diodes D1 and D2 whose positive electrodes are electrically connected to the AC1 lead and the AC2 lead respectively, and whose negative electrodes are electrically connected to one end of the resistor R3 at the same time, and the other end of the resistor R3 is electrically connected to the output end of the auxiliary power supply circuit.

Furthermore, a compensation circuit is provided between the COMP pin and the FB pin of the PFC control chip U1.

Furthermore, the single-ended to double-ended driving circuit includes a driving control chip U2, the INM pin of the driving control chip U2 is electrically connected to the positive electrode of the diode D4, the resistor R8, and one end of the capacitor C8 at the same time, the other ends of the resistor R8 and the capacitor C8 are electrically connected to one end of the resistor R9 and the positive electrode of the diode D5 at the same time, and serve as the IN pin, the other end of the resistor R9 and the negative electrode of the diode D5 are electrically connected to the capacitor C7 and the INA pin of the driving control chip U2 at the same time, and the other ends of the capacitors C7 and C8 are electrically connected to the GND ground pin of the driving control chip U2 at the same time.

Furthermore, the first drive circuit includes a positive electrode of a diode D3 and one end of a resistor R7 which are electrically connected to the gate of the first switch tube Q1 at the same time, a negative electrode of the diode D3 and the other end of the resistor R7 are electrically connected to one end of a resistor R6 at the same time, and the other end of the resistor R6 is electrically connected to a GDM pin of the single-end to double-end drive circuit.

Further, the second drive circuit includes a positive electrode of a voltage regulator tube ZD1 electrically connected to the other end of the primary main winding NP of the transformer T1 and one end of the secondary of the transformer T2 at the same time, a negative electrode of the voltage regulator tube ZD1 electrically connected to the negative electrode of the voltage regulator tube ZD2, a positive electrode of the voltage regulator tube ZD2 electrically connected to the gate of the second switch tube Q2 and one end of the capacitor C6 at the same time, the other end of the capacitor C6 electrically connected to one end of the resistor R5, the other end of the resistor R5 electrically connected to the other end of the secondary of the transformer T2, one end of the primary of the transformer T2 electrically connected to the GND ground pin of the single-ended to dual-ended drive circuit, the other end of the primary of the transformer T2 electrically connected to one end of the capacitor C5, the other end of the capacitor C5 electrically connected to one end of the resistor R4, and the other end of the resistor R4 electrically connected to the GDA pin of the single-ended to dual-ended drive circuit.

Furthermore, the impedance matching circuit includes a resistor R15 having one end electrically connected to pin 4 of the optocoupler chip OP1, resistors R12 and R13 having one end electrically connected to pin 3 of the optocoupler chip OP1, the other end of the resistor R13 electrically connected to the GND ground, the other end of the resistor R12 electrically connected to the FB pin of the PFC control chip U1 and one end of the resistor R14, and the other ends of the resistors R14 and R15 electrically connected to the output end of the auxiliary power supply circuit.

Further, the error voltage comparison circuit includes one end of resistors R16 and R19 simultaneously connected to the VO+ end of the output capacitor C3, the other end of the resistor R19 is simultaneously electrically connected to one end of resistors R18 and R20 and the reference electrode R of the voltage stabilizing chip U3, the other end of the resistor R20 is simultaneously electrically connected to the anode A of the voltage stabilizing chip U3 and the VO- end of the output capacitor C3, the other end of the resistor R18 is simultaneously electrically connected to one end of the capacitor C11, the other end of the capacitor C11 is simultaneously electrically connected to one end of the resistor R17, the cathode K of the voltage stabilizing chip U3, and pin 2 of the optocoupler chip OP1, and the other end of the resistor R16 is simultaneously electrically connected to the other end of the resistor R17 and pin 1 of the optocoupler chip OP1.

In summary, the technical solution of the present invention has the following beneficial effects:

The present invention solves the problem that the existing power supply circuit of the two-stage voltage conversion structure has many switching devices and magnetic components, resulting in large switching loss, large line loss, large core loss, low power efficiency, high cost, and easy damage to the switch tube. The power supply of this solution adopts a single-stage PFC voltage conversion circuit with resonant soft switching, which can achieve power factor correction while also realizing high-efficiency isolated step-down conversion from input AC voltage to output DC voltage, reducing the switching devices and magnetic components of the power supply, improving power supply efficiency, reducing volume, and reducing cost. The switching device works in a soft switching state, while the leakage inductance energy storage is absorbed, the voltage stress of the switching device is reduced, and the reliability of the power switch device is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only part of the embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative labor.

FIG1 is a block diagram of a single-stage PFC power supply circuit of the present invention;

FIG2 is a circuit diagram of a single-stage PFC power supply circuit of the present invention;

FIG. 3 is a waveform diagram of a single-stage PFC power supply circuit of the present invention.

Description of reference numerals:

100-EMI filter circuit, 110-bridge rectifier circuit, 120-start-up circuit, 130-filter circuit, 140-auxiliary power supply circuit, 150-single-ended to double-ended drive circuit, 160-impedance matching circuit, 170-first drive circuit, 180-second drive circuit, 190-zero current detection circuit, 191-error voltage comparison circuit, 192-rectifier circuit, output capacitor C3, 193-compensation circuit, 194-on-time setting circuit.

DETAILED DESCRIPTION

The technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

As shown in FIGS. 1 and 2, a single-stage PFC power supply circuit includes an EMI filter circuit 100 having one end electrically connected to an external AC power (including a live wire L and a neutral wire N) and the earth (Earth in the figure), the other end of the EMI filter circuit 100 is electrically connected to a bridge rectifier circuit 110 and one end of a start-up circuit 120 at the same time, the other end of the bridge rectifier circuit 110 is electrically connected to one end of a filter circuit 130, the other end of the filter circuit 130 is electrically connected to one end of a primary main winding NP of a transformer T1, the other end of the start-up circuit 120 is electrically connected to the output end of an auxiliary power supply circuit 140, and the output end of the auxiliary power supply circuit 140 is electrically connected to a PFC control core 100. The PFC control chip U1, the single-ended to double-ended driving circuit 150, and the VCC power supply pins of the impedance matching circuit 160 are electrically connected, the GD pin of the PFC control chip U1 is electrically connected to the IN pin of the single-ended to double-ended driving circuit 150, the GDM pin of the single-ended to double-ended driving circuit 150 is electrically connected to one end of the first driving circuit 170, the GDA pin of the single-ended to double-ended driving circuit 150 is electrically connected to one end of the second driving circuit 180, the other end of the first driving circuit 170 is electrically connected to the gate of the first switch tube Q1, the source of the first switch tube Q1 is electrically connected to one end of the resistors R1 and R2 at the same time, the other end of the resistor R2 is electrically connected to the CS pin of the PFC control chip U1 The second driving circuit 180 is electrically connected to the gate of the second switch tube Q2, the source of the second switch tube Q2, the other end of the second driving circuit 180, and the drain of the first switch tube Q1 are electrically connected to the other end of the primary main winding NP of the transformer T1, the drain of the second switch tube Q2 is electrically connected to one end of the series capacitor C2, the series capacitor C2, the other end of the resistor R1, the auxiliary power supply circuit 140, the PFC control chip U1, the single-ended to double-ended driving circuit 150, and the GND ground pin of the impedance matching circuit 160 are electrically connected to the GND ground terminal of the primary secondary winding NF of the transformer T1, and one end of the impedance matching circuit 160 is electrically connected to the PFC control chip The FB pin of U1 is electrically connected, the other end of the impedance matching circuit 160 is electrically connected to one end of the optocoupler chip OP1, the other end of the primary secondary winding NF of the transformer T1 is electrically connected to the auxiliary power supply circuit 140 and one end of the zero current detection circuit 190 at the same time, the other end of the zero current detection circuit 190 is electrically connected to the ZCD pin of the PFC control chip U1, the other end of the optocoupler chip OP1 is electrically connected to one end of the error voltage comparison circuit 191, the other end of the error voltage comparison circuit 191 is electrically connected to both ends of the output capacitor C3 and the output end of the rectifier circuit 192, and the input end of the rectifier circuit 192 is electrically connected to both ends of the secondary winding NS of the transformer T1.

Furthermore, the transformer T1 includes a leakage inductance Lr connected in series to one end of the primary main winding NP of the transformer T1 and an excitation inductance Lm connected in parallel to both ends of the primary main winding NP of the transformer T1.

Furthermore, the first switch tube Q1 includes a parasitic capacitor C1 connected in parallel between a source and a drain of the first switch tube Q1 .

Furthermore, the starting circuit 120 includes diodes D1 and D2 whose positive electrodes are electrically connected to the AC1 lead and the AC2 lead respectively, and the cathodes of the diodes D1 and D2 are electrically connected to one end of the resistor R3 at the same time, and the other end of the resistor R3 is electrically connected to the output end of the auxiliary power supply circuit 140 (that is, the connection point between the cathode of the diode D6 and one end of the capacitor C10).

Further, the model of the PFC control chip U1 is any one of L6562 or OB6563 or NCP1606 or NCP1607 or NCP1608 or NCL30000 or FAN6961 or FL6961, which belongs to the prior art. A compensation circuit 193 is provided between the COMP pin and the FB pin of the PFC control chip U1. The compensation circuit 193 includes a capacitor C9 having one end electrically connected to the COMP pin of the PFC control chip U1, the other end of the capacitor C9 being electrically connected to one end of the resistor R11, and the other end of the resistor R11 being electrically connected to the FB pin of the PFC control chip U1. A conduction time setting circuit 194 is provided on the CT pin of the PFC control chip U1, and the circuit is composed of a capacitor C10 having one end electrically connected to the CT pin and the other end connected to the GND ground.

Furthermore, the single-ended to dual-ended drive circuit 150 includes a drive control chip U2, whose model is any one of MIC4425 or UCC27325 or UCC27525 or NCP81071C, which belongs to the prior art. The INM pin of the drive control chip U2 is electrically connected to the positive electrode of the diode D4, the resistor R8, and one end of the capacitor C8 at the same time. The other ends of the resistor R8 and the capacitor C8 are electrically connected to one end of the resistor R9 and the positive electrode of the diode D5 at the same time, and serve as the IN pin (of the single-ended to dual-ended drive circuit 150). The other end of the resistor R9 and the negative electrode of the diode D5 are electrically connected to the capacitor C7 and the INA pin of the drive control chip U2 at the same time. The other ends of the capacitors C7 and C8 are electrically connected to the GND ground pin of the drive control chip U2 at the same time.

Furthermore, the first drive circuit 170 includes a positive electrode of a diode D3 and one end of a resistor R7 which are electrically connected to the gate of the first switch tube Q1 at the same time, a negative electrode of the diode D3 and the other end of the resistor R7 are electrically connected to one end of a resistor R6 at the same time, and the other end of the resistor R6 is electrically connected to the GDM pin of the single-ended to double-ended drive circuit.

Furthermore, the second drive circuit 180 includes a positive electrode of a Zener diode ZD1 electrically connected to the other end of the primary main winding NP of the transformer T1 and one end of the secondary of the transformer T2, a negative electrode of the Zener diode ZD1 electrically connected to the negative electrode of the Zener diode ZD2, a positive electrode of the Zener diode ZD2 electrically connected to the gate of the second switch tube Q2 and one end of the capacitor C6, the other end of the capacitor C6 electrically connected to one end of the resistor R5, the other end of the resistor R5 electrically connected to the other end of the secondary of the transformer T2, one end of the primary of the transformer T2 electrically connected to the GND ground pin of the single-ended to dual-ended drive circuit 150, the other end of the primary of the transformer T2 electrically connected to one end of the capacitor C5, the other end of the capacitor C5 electrically connected to one end of the resistor R4, and the other end of the resistor R4 electrically connected to the GDA pin of the single-ended to dual-ended drive circuit 150.

Furthermore, the impedance matching circuit 160 includes a resistor R15 having one end electrically connected to pin 4 of the optocoupler chip OP1, resistors R12 and R13 having one end electrically connected to pin 3 of the optocoupler chip OP1, the other end of the resistor R13 electrically connected to the GND ground, the other end of the resistor R12 electrically connected to the FB pin of the PFC control chip U1 and one end of the resistor R14, and the other ends of the resistors R14 and R15 electrically connected to the output end of the auxiliary power supply circuit 140.

Further, the error voltage comparison circuit 191 includes one end of resistors R16 and R19 simultaneously connected to the VO+ end of the output capacitor C3, the other end of the resistor R19 is simultaneously electrically connected to one end of resistors R18 and R20 and the reference electrode R of the voltage regulator chip U3, the other end of the resistor R20 is simultaneously electrically connected to the anode A of the voltage regulator chip U3 and the VO- end of the output capacitor C3, the other end of the resistor R18 is simultaneously electrically connected to one end of the capacitor C11, the other end of the capacitor C11 is simultaneously electrically connected to one end of the resistor R17, the cathode K of the voltage regulator chip U3, and pin 2 of the optocoupler chip OP1, and the other end of the resistor R16 is simultaneously electrically connected to the other end of the resistor R17 and pin 1 of the optocoupler chip OP1.

The working principle and process of the present invention are briefly described as follows:

After the AC mains passes through the EMI filter circuit 100, it passes through the bridge rectifier circuit 110 and the filter circuit 130 to obtain a continuous half-sine wave DC voltage, which is input to the primary winding NP of the isolation transformer T1; the other path passes through the start-up circuit 120 to provide a start-up voltage to the PFC control chip U1. The drive output pin GD of the PFC control chip U1 starts to output a positive pulse with a certain pulse width, and after passing through the single-end to double-end drive circuit 150, a positive pulse is output to turn on the first switch tube Q1, and the primary winding NP of the isolation transformer T1 When the positive pulse output by the driving output pin GD of the PFC control chip U1 becomes zero, the first switch tube Q1 is turned off, and the inductive energy storage of the primary winding NP of the transformer T1 is released, so that the auxiliary power supply circuit 140 and the rectifier tube D7 of the rectifier circuit 192 at the secondary end (i.e., the secondary winding of the transformer T1) start to be turned on, and the auxiliary power supply circuit 140 outputs a voltage to supply power to the PFC control chip U1 and the single-ended to dual-ended drive circuit 150, so that the PFC control chip U1 and the single-ended to dual-ended drive circuit 150 can continue to work. After the rectifier tube D7 of the rectifier circuit 192 connected to the secondary winding NS of the isolation transformer T1 is turned on, the induced voltage of the secondary winding NS charges the output capacitor C3, and the output voltage rises. When the output voltage is higher than the set voltage of the error voltage comparison circuit 191, the light at the transmitting end of the optical coupler OP1 is enhanced, and the resistance of the photosensitive tube at the receiving end is reduced. After passing through the impedance matching circuit 160, the voltage signal received by the FB pin of the PFC control chip U1 is increased, the voltage of the COMP pin of the PFC control chip U1 becomes lower, and the turn-off time of the first switch tube Q1 becomes shorter. The duty cycle of the first switch tube Q1 is reduced, so that the output voltage is reduced. When the output voltage is lower than the set voltage of the error voltage comparison circuit 191, the light at the transmitting end of the optocoupler OP1 is weakened, and the resistance of the photosensitive tube at the receiving end is increased. After the impedance matching circuit 160, the voltage signal received by the FB pin of the PFC control chip U1 is reduced, and the voltage of the COMP pin of the PFC control chip U1 is increased. The off time of the first switch tube Q1 becomes shorter, and the duty cycle of the first switch tube Q1 is increased, so that the output voltage rises, and the output voltage can be maintained stable. The PFC control chip U1 adopts a critical conduction mode (CRM) PFC controller, which adopts a control method of constant on time and variable off time. Under a certain input line voltage and load power, the on time is a constant value, and its value is:

Ton＝(2*L*Pin)/(Vrms) ² , where L is the inductance of the primary winding NP of the transformer T1, Pin is the input power, and Vrms is the effective value of the input voltage. The PFC control chip U1 includes a zero current detection ZCD terminal. The ZCD terminal and the isolation transformer T1 are connected in series with a zero current detection circuit 190. When the inductive energy storage of the primary winding NP of the isolation transformer T1 is converted to the secondary winding NS of the isolation transformer T1 and is completely released to the output terminal to be consumed by the load, the voltage at the ZCD terminal drops to the internal setting level of the PFC control chip U1, so that the drive output pin GD of the PFC control chip U1 starts to output a high level, so that the first switch tube Q1 is turned on, and a new switching cycle is started. Therefore, the first switch tube Q1 is always turned on when the current of the primary winding NP is zero or negative. The first switch tube Q1 works in a critical conduction mode (CRM). The peak value of the inductor current of the primary winding NP changes with the input AC voltage. The peak value of the inductor current of the primary winding NP is:

There is a linear relationship between the inductor current peak and the input voltage. The inductor current peak is always twice the average current, which means that the input average current always follows the input voltage waveform. This critical conduction mode with constant on-time can achieve a natural power factor correction function.

The waveforms during operation are shown in FIG3 , where IL is the current waveform of the primary winding of the transformer T1, and IQ1 is the current waveform flowing through the drain and source of the first switch tube Q1. When the output GD terminal of the PFC control chip U1 outputs a waveform with a constant high-level pulse width, after passing through the single-ended to double-ended drive circuit 150, the output terminal GDM of the single-ended to double-ended drive circuit 150 outputs a pulse with a rising edge delayed from the rising edge of the output pulse of the GD terminal and a falling edge synchronized with the falling edge of the output pulse of the GD terminal, and the output terminal GDA of the single-ended to double-ended drive circuit 150 outputs a pulse with a rising edge delayed from the falling edge of the output pulse of the GD terminal and a falling edge synchronized with the rising edge of the output pulse of the GD terminal, forming a positive pulse alternately output by the GDM terminal and a low-level dead time of tens to hundreds of nanoseconds between adjacent pulses. When the GDM terminal outputs a high-level pulse, the first switch When the tube Q1 is turned on, the GDA terminal outputs a low level, the second switch tube Q2 is turned off, the excitation inductance Lm and the leakage inductance Lr of the primary winding NP of the isolation transformer T1 begin to charge, and the inductor current rises linearly. When the GDM terminal outputs a high level pulse and ends and becomes a low level, the first switch tube Q1 begins to turn off, and the drain-source parasitic diode (not shown in the figure) of the second switch tube Q2 is turned on. The inductor current charges the parasitic capacitance C1 of the first switch tube Q1 and the series capacitance C2 of the switch tube Q2 in a resonant manner. Because the capacity of C2 is relatively large, the drain-source voltage VDS of the first switch tube Q1 slowly rises from zero, and the current IQ1 of the first switch tube Q1 drops rapidly. At this time, the turn-off loss of the first switch tube Q1 is very small. The inductor current of the primary winding NP decreases in resonance. When the inductor current decreases to one nth of the peak current of the secondary winding NS of the isolation transformer (n is the turns ratio of the primary winding NP and the secondary winding NS), the GDA terminal outputs a high-level pulse. The second switch tube Q2 is turned on due to the conduction of the drain-source parasitic diode, so that Q2 flows through a reverse current to achieve zero voltage turn-on. The conduction of the switch tube Q2 makes the large-capacity series capacitor C2 connected in parallel with the parasitic capacitor C1 of the switch tube Q1, because at this time the energy storage induction of the excitation inductance Lm of the primary winding NP is transferred to the secondary winding NS, making the rectifier The rectifier of the circuit is turned on to charge the output capacitor C3. The inductor current of the primary winding NP continues to decrease from one nth of the peak current of the secondary winding NS. In one switching cycle, the terminal voltage of the output capacitor C3 can be regarded as basically unchanged, so the drain-source voltage VDS of the first switch tube Q1 is clamped. This clamping voltage is approximately equal to the instantaneous value of the continuous approximate steamed bun wave obtained by rectification of the AC input voltage at a certain moment plus n times the output voltage. Since the energy of the leakage inductance Lr is not transferred to the output end, it continues to charge the capacitors C1 and C2. The drain-source voltage of the first switch tube Q1 VDS rises very slowly in a resonant manner. After the energy of the leakage inductance Lr is completely transferred to the capacitors C1 and C2, the drain-source voltage VDS of the first switch tube Q1 begins to slowly decrease in a resonant manner. When it drops to the clamping voltage, it remains at this value. When the energy of the secondary winding NS is completely absorbed by the output capacitor C3 or the output load is consumed, the drain-source voltage VDS of the first switch tube Q1 begins to decrease rapidly. At this time, the inductor current of the primary winding NP is already negative, and the first switch tube Q1 also flows through a negative current. The drain-source parasitic diode of the first switch tube Q1 (not shown in the figure) conducts The output GDA end of the single-end to double-end drive circuit outputs a low level to turn off the second switch tube Q2. At this time, the leakage inductance Lr of the primary winding NP resonates with the parasitic capacitance C1 of the first switch tube Q1, and the drain-source voltage VDS of the first switch tube Q1 decreases in a resonant manner until it reaches zero. When the first switch tube Q1 still flows through a negative current, the output end GDM end of the single-end to double-end drive circuit starts to output a high-level pulse, and the first switch tube Q1 can achieve zero voltage turn-on. Subsequently, Lm and Lr are linearly charged again, and a new PWM switching cycle begins again, and the operation is repeated stably. Therefore, a single-stage PFC power supply with a resonant soft switch of the present invention can realize the soft switching operation of all switch tubes (including the first switch tube Q1 and the second switch tube Q2), with low switching loss and high efficiency. At the same time, the leakage inductance energy storage is absorbed, and the voltage stress of the switch device is reduced, so that the power switch device can work reliably.

In summary, the technical solution of the present invention has the following beneficial effects:

The present invention solves the problem that the existing power supply circuit of the two-stage voltage conversion structure has many switching devices and magnetic components, resulting in large switching loss, large line loss, large core loss, low power efficiency, high cost, and easy damage to the switch tube. The power supply of this solution adopts a single-stage PFC voltage conversion circuit with resonant soft switching, which can achieve power factor correction while also realizing high-efficiency isolated step-down conversion from input AC voltage to output DC voltage, reducing the switching devices and magnetic components of the power supply, improving power supply efficiency, reducing volume, and reducing cost. The switching device works in a soft switching state, while the leakage inductance energy storage is absorbed, the voltage stress of the switching device is reduced, and the reliability of the power switch device is improved.

The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims (7)

1. A single-stage PFC power supply circuit, characterized in that: it includes an EMI filter circuit with one end electrically connected to an external AC power supply and the earth, the other end of the EMI filter circuit is electrically connected to a bridge rectifier circuit and one end of a start-up circuit at the same time, the other end of the bridge rectifier circuit is electrically connected to one end of the filter circuit, the other end of the filter circuit is electrically connected to one end of a primary main winding NP of a transformer T1, the other end of the start-up circuit is electrically connected to an output end of an auxiliary power supply circuit, and the output end of the auxiliary power supply circuit is electrically connected to a PFC control chip U1, a single-end to double-end drive circuit, and an impedance matching circuit at the same time. The VCC power supply pin is electrically connected, the GD pin of the PFC control chip U1 is electrically connected to the IN pin of the single-ended to double-ended drive circuit, the GDM pin of the single-ended to double-ended drive circuit is electrically connected to one end of the first drive circuit, the GDA pin of the single-ended to double-ended drive circuit is electrically connected to one end of the second drive circuit, the other end of the first drive circuit is electrically connected to the gate of the first switch tube Q1, the source of the first switch tube Q1 is electrically connected to one end of the resistors R1 and R2 at the same time, the other end of the resistor R2 is electrically connected to the CS pin of the PFC control chip U1, and the second drive circuit is electrically connected to the second switch The gate of the first switch tube Q2 is electrically connected, the source of the second switch tube Q2, the other end of the second drive circuit, and the drain of the first switch tube Q1 are electrically connected to the other end of the primary main winding NP of the transformer T1, the drain of the second switch tube Q2 is electrically connected to one end of the series capacitor C2, the series capacitor C2, the other end of the resistor R1, the auxiliary power supply circuit, the PFC control chip U1, the single-end to double-end drive circuit, and the GND ground pin of the impedance matching circuit are electrically connected to the GND ground terminal of the primary secondary winding NF of the transformer T1, and one end of the impedance matching circuit is electrically connected to the FB of the PFC control chip U1. The pin is electrically connected, the other end of the impedance matching circuit is electrically connected to one end of the optocoupler chip OP1, the other end of the primary secondary winding NF of the transformer T1 is electrically connected to the auxiliary power supply circuit and one end of the zero current detection circuit at the same time, the other end of the zero current detection circuit is electrically connected to the ZCD pin of the PFC control chip U1, the other end of the optocoupler chip OP1 is electrically connected to one end of the error voltage comparison circuit, the other end of the error voltage comparison circuit is electrically connected to both ends of the output capacitor C3 and the output end of the rectifier circuit, and the input end of the rectifier circuit is electrically connected to both ends of the secondary winding NS of the transformer T1; The single-end to double-end drive circuit includes a drive control chip U2, the INM pin of the drive control chip U2 is electrically connected to the positive electrode of the diode D4, the resistor R8, and one end of the capacitor C8 at the same time, the other ends of the resistor R8 and the capacitor C8 are electrically connected to one end of the resistor R9 and the positive electrode of the diode D5 at the same time, and serve as the IN pin, the other end of the resistor R9 and the negative electrode of the diode D5 are electrically connected to the capacitor C7 and the INA pin of the drive control chip U2 at the same time, and the other ends of the capacitors C7 and C8 are electrically connected to the GND ground pin of the drive control chip U2 at the same time; The first driving circuit includes an anode of a diode D3 and one end of a resistor R7 electrically connected to the gate of the first switch tube Q1, a cathode of the diode D3 and the other end of the resistor R7 electrically connected to one end of a resistor R6, and the other end of the resistor R6 electrically connected to the GDM pin of the single-end to double-end driving circuit; The second driving circuit includes a positive electrode of a voltage regulator tube ZD1 electrically connected to the other end of the primary main winding NP of the transformer T1 and one end of the secondary of the transformer T2, a negative electrode of the voltage regulator tube ZD1 electrically connected to the negative electrode of the voltage regulator tube ZD2, a positive electrode of the voltage regulator tube ZD2 electrically connected to the gate of the second switch tube Q2 and one end of the capacitor C6, the other end of the capacitor C6 electrically connected to one end of the resistor R5, the other end of the resistor R5 electrically connected to the other end of the secondary of the transformer T2, one end of the primary of the transformer T2 electrically connected to the GND ground pin of the single-end to double-end driving circuit, the other end of the primary of the transformer T2 electrically connected to one end of the capacitor C5, the other end of the capacitor C5 electrically connected to one end of the resistor R4, and the other end of the resistor R4 electrically connected to the GDA pin of the single-end to double-end driving circuit; The model of the PFC control chip U1 is any one of L6562, OB6563, NCP1606, NCP1607, NCP1608, NCL30000, FAN6961 and FL6961; The driving control chip U2 is any one of MIC4425, UCC27325, UCC27525 and NCP81071C. 2. A single-stage PFC power supply circuit according to claim 1, characterized in that: the transformer T1 includes a leakage inductance Lr connected in series to one end of the primary main winding NP of the transformer T1 and an excitation inductance Lm connected in parallel to both ends of the primary main winding NP of the transformer T1. 3. The single-stage PFC power supply circuit according to claim 1, characterized in that: the first switch tube Q1 includes a parasitic capacitor C1 connected in parallel between the source and the drain of the first switch tube Q1. 4. A single-stage PFC power supply circuit according to claim 1, characterized in that: the starting circuit includes diodes D1 and D2 whose positive electrodes are electrically connected to the AC1 lead and the AC2 lead respectively, and the cathodes of the diodes D1 and D2 are electrically connected to one end of the resistor R3 at the same time, and the other end of the resistor R3 is electrically connected to the output end of the auxiliary power supply circuit. 5. The single-stage PFC power supply circuit according to claim 1, characterized in that a compensation circuit is provided between the COMP pin and the FB pin of the PFC control chip U1. 6. A single-stage PFC power supply circuit according to claim 1, characterized in that: the impedance matching circuit includes a resistor R15 having one end electrically connected to pin 4 of the optocoupler chip OP1, resistors R12 and R13 having one end electrically connected to pin 3 of the optocoupler chip OP1, the other end of the resistor R13 being electrically connected to the GND ground, the other end of the resistor R12 being electrically connected to the FB pin of the PFC control chip U1 and one end of the resistor R14, and the other ends of the resistors R14 and R15 being electrically connected to the output end of the auxiliary power supply circuit. 7. A single-stage PFC power supply circuit according to claim 1, characterized in that: the error voltage comparison circuit includes one end of resistors R16 and R19 simultaneously connected to the VO+ end of the output capacitor C3, the other end of the resistor R19 is simultaneously electrically connected to one end of resistors R18 and R20 and the reference electrode R of the voltage regulator chip U3, the other end of the resistor R20 is simultaneously electrically connected to the anode A of the voltage regulator chip U3 and the VO- end of the output capacitor C3, the other end of the resistor R18 is electrically connected to one end of the capacitor C11, the other end of the capacitor C11 is simultaneously electrically connected to one end of the resistor R17, the cathode K of the voltage regulator chip U3, and the 2nd pin of the optocoupler chip OP1, and the other end of the resistor R16 is simultaneously electrically connected to the other end of the resistor R17 and the 1st pin of the optocoupler chip OP1.