PFC circuit and power supply

Abstract

The utility model provides a PFC circuit and a power supply. The PFC circuit comprises a power supply circuit, an input circuit, a control circuit and a comparison circuit. The input circuit comprises a first switch tube, a first pole of the first switch tube is connected with the pre-stage circuit, and a second pole of the first switch tube is connected with the power supply circuit; the control circuit comprises a rectification chip and a second switch tube, the rectification chip is respectively connected with a controlled electrode of the first switch tube and a second electrode of the second switch tube, and a first electrode of the second switch tube is connected with a second electrode of the first switch tube; one input end of the comparison circuit is connected between the first pole of the first switch tube and the pre-stage circuit, the other input end of the comparison circuit is connected with the second pole of the first switch tube, and the output end of the comparison circuit is connected with the controlled pole of the second switch tube. According to the utility model, the loss of the power supply and the requirement on heat dissipation can be reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of power supply, in particular to a PFC circuit and a power supply. Background Art

[0002] The traditional PFC circuit is generally composed of two CBB capacitors, a differential mode inductor, a boost inductor and a diode. The voltage drop of the diode is large. When the current passing through is large, the voltage drop will be even greater, resulting in higher losses and reducing the efficiency of the power supply. At the same time, the heat generated by the diode is also high, requiring a larger space for heat dissipation. Utility Model Content

[0003] The utility model provides a PFC circuit and a power supply, aiming to solve the problem that the current power supply has high loss and high heat dissipation requirements.

[0004] In a first aspect, the utility model provides a PFC circuit, which includes a power supply circuit, an input circuit, a control circuit and a comparison circuit; the input circuit includes a first switch tube, a first pole of the first switch tube is connected to a front-stage circuit, and a second pole of the first switch tube is connected to the power supply circuit; the control circuit includes a rectifier chip and a second switch tube, the rectifier chip is respectively connected to a controlled pole of the first switch tube and a second pole of the second switch tube, and a first pole of the second switch tube is connected to the second pole of the first switch tube; an input end of the comparison circuit is connected between the first pole of the first switch tube and the front-stage circuit, the other input end of the comparison circuit is connected to the second pole of the first switch tube, and the output end of the comparison circuit is connected to the controlled pole of the second switch tube.

[0005] Furthermore, the input circuit also includes a first diode and a PFC inductor; the first diode is connected in parallel with the first switch tube, and the anode of the first diode is connected to the front-stage circuit, and the cathode of the first diode is respectively connected to the power supply circuit and an input end of the comparison circuit; one end of the PFC inductor is connected to the front-stage circuit, and the other end of the PFC inductor is respectively connected to the first electrode of the first switch tube and the other input end of the comparison circuit.

[0006] Furthermore, the control circuit further includes a third switch tube, a controlled pole of the third switch tube is connected to the front-stage circuit, a first pole of the third switch tube is grounded, and a second pole of the third switch tube is connected to the PFC inductor.

[0007] Furthermore, the control circuit also includes a first resistor, one end of the first resistor is connected to the second electrode of the second switch tube, and the other end of the first resistor is connected to the rectifier chip.

[0008] Furthermore, the control circuit also includes a second diode and a first capacitor; the anode of the second diode is connected to the first resistor, the cathode of the second diode is respectively connected to one end of the first capacitor and the rectifier chip, and the other end of the first capacitor is connected to the rectifier chip.

[0009] Furthermore, the comparison circuit includes a comparator, a non-inverting input terminal of the comparator is connected to the second pole of the first switch tube, an inverting input terminal of the comparator is connected between the first pole of the first switch tube and the PFC inductor, and an output terminal of the comparator is connected to the controlled pole of the second switch tube.

[0010] Further, the comparison circuit also includes a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor and a seventh resistor; one end of the second resistor is connected to the second electrode of the second switch tube, the other end of the second resistor is connected to one end of the third resistor, the other end of the third resistor is respectively connected to the non-inverting input terminal of the comparator and one end of the fourth resistor, and the other end of the fourth resistor is grounded; one end of the fifth resistor is connected to the PFC inductor, the other end of the fifth resistor is connected to one end of the sixth resistor, the other end of the sixth resistor is respectively connected to the inverting input terminal of the comparator and one end of the seventh resistor, and the other end of the seventh resistor is grounded.

[0011] Furthermore, the first switch tube and the second switch tube are both MOS tubes; the gate of the first switch tube is connected to the rectifier chip, the source of the first switch tube is connected to the front-stage circuit, the drain of the first switch tube is respectively connected to the power supply circuit, the source of the second switch tube and the input end of the comparison circuit, the drain of the second switch tube is connected to the rectifier chip, and the gate of the second switch tube is connected to the output end of the comparison circuit.

[0012] Furthermore, the power supply circuit includes a power supply capacitor, and the power supply capacitor is connected to the input circuit.

[0013] In a second aspect, the utility model further provides a power supply, which includes the PFC circuit described in any one of the above items.

[0014] The power supply disclosed in the utility model includes a PFC circuit, which includes a power supply circuit, an input circuit, a control circuit and a comparison circuit. The front-stage circuit charges the power supply circuit through the input circuit. The controlled electrode of the second switch tube of the control circuit is connected to the output end of the comparison circuit. One input end of the comparison circuit is connected between the first electrode of the first switch tube and the front-stage circuit. The other input end of the comparison circuit is connected to the second electrode of the first switch tube, which is used to detect the voltage difference of the first switch tube and control the conduction and shutdown of the second switch tube according to the voltage difference of the first switch tube. At the same time, the rectifier chip can control the conduction and shutdown of the first switch tube, thereby realizing synchronous rectification. Compared with the diode, the second switch tube has smaller power loss and lower heat dissipation requirements, thereby reducing the power loss and heat dissipation requirements of the power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the utility model, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 It is a circuit diagram of a PFC circuit provided by an embodiment of the utility model. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0018] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, operations, elements, components and / or groups thereof.

[0019] It should also be understood that the terms used in this utility model specification are only for the purpose of describing specific embodiments and are not intended to limit the utility model. As used in the utility model specification and the appended claims, the singular forms of "a", "an" and "the" are intended to include plural forms unless the context clearly indicates otherwise. It should also be further understood that the term "and / or" used in the utility model specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0020] In addition, the directional terms mentioned in the present invention, such as "upper", "lower", "front", "back", "left", "right", "inner", "outer", "side", etc., are only for reference to the directions of the attached drawings and the use status of the product. Therefore, the directional terms used are used to illustrate and understand the present invention, but not to limit the present invention. In addition, in the drawings, structures with similar or identical structures are represented by the same reference numerals.

[0021] See also Figure 1 , Figure 1 is a circuit diagram of a PFC circuit provided by an embodiment of the utility model, such as Figure 1 As shown, the PFC circuit includes a power supply circuit 10, an input circuit 20, a control circuit 30 and a comparison circuit 40; the input circuit 20 includes a first switch tube Q1, a first electrode of the first switch tube Q1 is connected to the front-stage circuit 50, and a second electrode of the first switch tube Q1 is connected to the power supply circuit 10; the control circuit 30 includes a rectifier chip U1 and a second switch tube Q2, the rectifier chip U1 is respectively connected to the controlled electrode of the first switch tube Q1 and the second electrode of the second switch tube Q2, and the first electrode of the second switch tube Q2 is connected to the second electrode of the first switch tube Q1; an input end of the comparison circuit 40 is connected between the first electrode of the first switch tube Q1 and the front-stage circuit 50, the other input end of the comparison circuit 40 is connected to the second electrode of the first switch tube Q1, and the output end of the comparison circuit 40 is connected to the controlled electrode of the second switch tube Q2.

[0022] Specifically, the PFC circuit includes a power supply circuit 10, an input circuit 20, a control circuit 30 and a comparison circuit 40. The power supply circuit 10 may include a storage capacitor EC1. The input circuit 20 is connected to the front-stage circuit 50 and includes a first switch tube Q1. The first pole of the first switch tube Q1 is connected to the front-stage circuit 50, the second pole of the first switch tube Q1 is respectively connected to the power supply circuit 10 and the comparison circuit 40, and the controlled pole of the first switch tube Q1 is connected to the control circuit 30.

[0023] The control circuit 30 includes a rectifier chip U1 and a second switch tube Q2. The controlled pole of the second switch tube Q2 is connected to the comparison circuit 40, and is turned on and off according to the level signal output by the comparison circuit 40. The first pole of the second switch tube Q2 is also connected to the second pole of the first switch tube Q1. The second pole of the second switch tube Q2 is connected to the rectifier chip U1. The rectifier chip U1 is used for synchronous rectification.

[0024] One input end of the comparison circuit 40 is connected between the first electrode of the first switch tube Q1 and the front-stage circuit 50, and the other input end of the comparison circuit 40 is connected to the second electrode of the first switch tube Q1, and is used to detect the voltage difference across the first switch tube Q1. When the voltage difference across the first switch tube Q1 is small, the second switch tube Q2 is controlled to be turned on, and when the voltage difference across the first switch tube Q1 is large, the second switch tube Q2 is controlled to be turned off.

[0025] When the power is just turned on, the input voltage of the front-stage circuit 50 is output to the power supply circuit 10 through the input circuit 20, and the power supply circuit 10 is powered. At this time, there is no difference in the voltage difference across the second switch tube Q2, and the voltage difference across the first switch tube Q1 is small, so the comparison circuit 40 outputs a level signal to control the second switch tube Q2 to be turned on. At the same time, due to the small voltage difference, the power supply circuit 10 cannot power the rectifier chip U1, and the rectifier chip U1 does not start.

[0026] When the voltage difference across the first switch tube Q1 gradually increases, the power supply circuit starts to charge the control circuit 30 until the rectifier chip U1 starts, and when the voltage difference across the first switch tube Q1 increases to a certain value, for example, the voltage difference across the first switch tube Q1 is greater than 100V, the comparison circuit 40 outputs a level signal to control the second switch tube Q2 to turn off, isolate the rectifier chip U1 from the output voltage, and protect the rectifier chip U1.

[0027] When the circuit current reaches the maximum, the voltage difference across the first switch tube Q1 begins to decrease. When the voltage difference across the first switch tube Q1 is less than 100V, the comparison circuit 40 outputs a level signal to control the second switch tube Q2 to turn on, and the rectifier chip U1 detects the voltage across the first switch tube Q1.

[0028] When the voltage difference across the first switch tube Q1 is very small, the rectifier chip U1 uses the source of the first switch tube Q1 as a reference ground. When it detects that the voltage across the drain and source of the first switch tube Q1 drops to a certain value, the rectifier chip U1 turns on the first switch tube Q1.

[0029] When the first switch tube Q1 is turned on, the front-stage circuit 50 charges the power supply circuit 10 through the first switch tube Q1, and gradually reduces when the current reaches the maximum. When the current is less than a certain level, the rectifier chip U1 controls the first switch tube Q1 to disconnect and waits for the next cycle to repeat the above process.

[0030] As a further embodiment, the input circuit 20 further includes a first diode D1 and a PFC inductor L1; the first diode D1 is connected in parallel with the first switch tube Q1, and the anode of the first diode D1 is connected to the front-stage circuit 50, and the cathode of the first diode D1 is respectively connected to the power supply circuit 10 and an input end of the comparison circuit 40; one end of the PFC inductor L1 is connected to the front-stage circuit 50, and the other end of the PFC inductor L1 is respectively connected to the first electrode of the first switch tube Q1 and the other input end of the comparison circuit 40.

[0031] Among them, when the power is just turned on, the front-stage circuit 50 charges the power supply circuit 10 through the first diode D1. When the rectifier chip U1 controls the first switch tube Q1 to turn on, the front-stage circuit 50 charges the power supply circuit 10 through the first switch tube Q1 until the rectifier chip U1 turns off the first switch tube Q1.

[0032] As a further embodiment, the control circuit 30 further includes a third switch tube Q3, a controlled pole of the third switch tube Q3 is connected to the front-stage circuit 50, a first pole of the third switch tube Q3 is grounded, and a second pole of the third switch tube Q3 is connected to the PFC inductor L1.

[0033] The third switch tube Q3 is connected to the feedback circuit in the front-stage circuit 50. When the third switch tube Q3 is turned on, the drain voltage of the third switch tube Q3 will decrease, so that a voltage difference is generated between the drain and source of the first switch tube Q1. As the voltage between the drain and source of the third switch tube Q3 continues to decrease, the voltage difference between the drain and source of the first switch tube Q1 gradually increases, and when the voltage difference is greater than 100V, the comparison circuit 40 controls the second switch tube Q2 to be turned off. When the voltage between the drain and source of the third switch tube Q3 drops to the minimum, the current reaches the maximum, and the feedback circuit turns off the third switch tube Q3, then the voltage difference across the first switch tube Q1 gradually decreases until it is less than 100V, and the comparison circuit 40 controls the second switch tube Q2 to be turned on.

[0034] As a further embodiment, the control circuit 30 further includes a first resistor R1 , one end of the first resistor R1 is connected to the second electrode of the second switch tube Q2 , and the other end of the first resistor R1 is connected to the rectifier chip U1 .

[0035] As a further embodiment, the control circuit 30 also includes a second diode D2 and a first capacitor C1; the positive electrode of the second diode D2 is connected to the first resistor R1, the negative electrode of the second diode D2 is respectively connected to one end of the first capacitor C1 and the rectifier chip U1, and the other end of the first capacitor C1 is connected to the rectifier chip U1.

[0036] When the third switch tube Q3 is turned on, a voltage difference is generated across the first switch tube Q1 , and the power supply circuit 10 charges the first capacitor C1 through the second switch tube Q2 and the second diode D2 . The first capacitor C1 is used to power the rectifier chip U1 .

[0037] As a further embodiment, the comparison circuit 40 includes a comparator U2, a non-inverting input terminal of the comparator U2 is connected to the second pole of the first switch tube Q1, an inverting input terminal of the comparator U2 is connected between the first pole of the first switch tube Q1 and the PFC inductor L1, and an output terminal of the comparator U2 is connected to the controlled pole of the second switch tube Q2.

[0038] The non-inverting input terminal of the comparator U2 is connected to the second electrode of the first switch tube Q1, the inverting input terminal of the comparator U2 is connected between the first electrode of the first switch tube Q1 and the PFC inductor L1, and the output terminal of the comparator U2 is connected to the controlled electrode of the second switch tube Q2. The comparator U2 is used to output a level signal to control the conduction and shutdown of the second switch tube Q2.

[0039] As a further embodiment, the comparison circuit 40 further includes a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6 and a seventh resistor R7; one end of the second resistor R2 is connected to the second electrode of the second switch tube Q2, the other end of the second resistor R2 is connected to one end of the third resistor R3, the other end of the third resistor R3 is respectively connected to the non-inverting input end of the comparator U2 and one end of the fourth resistor R4, and the other end of the fourth resistor R4 is grounded; one end of the fifth resistor R5 is connected to the PFC inductor L1, the other end of the fifth resistor R5 is connected to one end of the sixth resistor R6, the other end of the sixth resistor R6 is respectively connected to the inverting input end of the comparator U2 and one end of the seventh resistor R7, and the other end of the seventh resistor R7 is grounded.

[0040] As a further embodiment, the first switch tube Q1 and the second switch tube Q2 are both MOS tubes; the gate of the first switch tube Q1 is connected to the rectifier chip U1, the source of the first switch tube Q1 is connected to the front-stage circuit 50, the drain of the first switch tube Q1 is respectively connected to the power supply circuit 10, the source of the second switch tube Q2 and the input end of the comparison circuit 40, the drain of the second switch tube Q2 is connected to the rectifier chip U1, and the gate of the second switch tube Q2 is connected to the output end of the comparison circuit 40.

[0041] As a further embodiment, the power supply circuit 10 includes a power supply capacitor, and the power supply capacitor is connected to the input circuit 20 .

[0042] The utility model also provides a power supply, which includes the PFC circuit described in any one of the above embodiments; the PFC circuit includes a power supply circuit 10, an input circuit 20, a control circuit 30 and a comparison circuit 40; the input circuit 20 includes a first switch tube Q1, a first pole of the first switch tube Q1 is connected to a front-stage circuit 50, and a second pole of the first switch tube Q1 is connected to the power supply circuit 10; the control circuit 30 includes a rectifier chip U1 and a second switch tube Q2, the rectifier chip U1 is respectively connected to a controlled pole of the first switch tube Q1 and a second pole of the second switch tube Q2, and a first pole of the second switch tube Q2 is connected to a second pole of the first switch tube Q1; an input end of the comparison circuit 40 is connected between the first pole of the first switch tube Q1 and the front-stage circuit 50, another input end of the comparison circuit 40 is connected to the second pole of the first switch tube Q1, and an output end of the comparison circuit 40 is connected to the controlled pole of the second switch tube Q2.

[0043] Specifically, the PFC circuit includes a power supply circuit 10, an input circuit 20, a control circuit 30 and a comparison circuit 40. The power supply circuit 10 may include a storage capacitor EC1. The input circuit 20 is connected to the front-stage circuit 50 and includes a first switch tube Q1. The first pole of the first switch tube Q1 is connected to the front-stage circuit 50, the second pole of the first switch tube Q1 is respectively connected to the power supply circuit 10 and the comparison circuit 40, and the controlled pole of the first switch tube Q1 is connected to the control circuit 30.

[0044] The control circuit 30 includes a rectifier chip U1 and a second switch tube Q2. The controlled pole of the second switch tube Q2 is connected to the comparison circuit 40, and is turned on and off according to the level signal output by the comparison circuit 40. The first pole of the second switch tube Q2 is also connected to the second pole of the first switch tube Q1. The second pole of the second switch tube Q2 is connected to the rectifier chip U1. The rectifier chip U1 is used for synchronous rectification.

[0045] One input end of the comparison circuit 40 is connected between the first electrode of the first switch tube Q1 and the front-stage circuit 50, and the other input end of the comparison circuit 40 is connected to the second electrode of the first switch tube Q1, and is used to detect the voltage difference across the first switch tube Q1. When the voltage difference across the first switch tube Q1 is small, the second switch tube Q2 is controlled to be turned on, and when the voltage difference across the first switch tube Q1 is large, the second switch tube Q2 is controlled to be turned off.

[0046] When the power is just turned on, the input voltage of the front-stage circuit 50 is output to the power supply circuit 10 through the input circuit 20, and the power supply circuit 10 is powered. At this time, there is no difference in the voltage difference across the second switch tube Q2, and the voltage difference across the first switch tube Q1 is small, so the comparison circuit 40 outputs a level signal to control the second switch tube Q2 to be turned on. At the same time, due to the small voltage difference, the power supply circuit 10 cannot power the rectifier chip U1, and the rectifier chip U1 does not start.

[0047] When the voltage difference across the first switch tube Q1 gradually increases, the power supply circuit starts to charge the control circuit 30 until the rectifier chip U1 starts, and when the voltage difference across the first switch tube Q1 increases to a certain value, for example, the voltage difference across the first switch tube Q1 is greater than 100V, the comparison circuit 40 outputs a level signal to control the second switch tube Q2 to turn off, isolate the rectifier chip U1 from the output voltage, and protect the rectifier chip U1.

[0048] When the circuit current reaches the maximum, the voltage difference across the first switch tube Q1 begins to decrease. When the voltage difference across the first switch tube Q1 is less than 100V, the comparison circuit 40 outputs a level signal to control the second switch tube Q2 to turn on, and the rectifier chip U1 detects the voltage across the first switch tube Q1.

[0049] When the voltage difference across the first switch tube Q1 is very small, the rectifier chip U1 uses the source of the first switch tube Q1 as a reference ground. When it detects that the voltage across the drain and source of the first switch tube Q1 drops to a certain value, the rectifier chip U1 turns on the first switch tube Q1.

[0050] When the first switch tube Q1 is turned on, the front-stage circuit 50 charges the power supply circuit 10 through the first switch tube Q1, and gradually reduces when the current reaches the maximum. When the current is less than a certain level, the rectifier chip U1 controls the first switch tube Q1 to disconnect and waits for the next cycle to repeat the above process.

[0051] The PFC circuit disclosed in the utility model can reduce loss and heat generation by using MOS tubes to replace diodes, and at the same time, it is controlled by a rectifier chip to achieve synchronous rectification, which can reduce power loss and the demand for heat dissipation.

[0052] The above is only a specific implementation of the utility model, but the protection scope of the utility model is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the utility model, and these modifications or replacements should be included in the protection scope of the utility model. Therefore, the protection scope of the utility model should be based on the protection scope of the claims.

Claims

1. A PFC circuit, characterized in that: include: Power supply circuit; An input circuit includes a first switch tube, wherein a first electrode of the first switch tube is connected to a previous stage circuit, and a second electrode of the first switch tube is connected to the power supply circuit; A control circuit, comprising a rectifier chip and a second switch tube, wherein the rectifier chip is respectively connected to a controlled electrode of the first switch tube and a second electrode of the second switch tube, and the first electrode of the second switch tube is connected to the second electrode of the first switch tube; A comparison circuit, wherein one input end of the comparison circuit is connected between the first electrode of the first switching tube and the previous stage circuit, another input end of the comparison circuit is connected to the second electrode of the first switching tube, and an output end of the comparison circuit is connected to the controlled electrode of the second switching tube.

2. The PFC circuit according to claim 1, characterized in that: The input circuit also includes a first diode and a PFC inductor; The first diode is connected in parallel with the first switch tube, and the anode of the first diode is connected to the front-stage circuit, and the cathode of the first diode is connected to the power supply circuit and an input end of the comparison circuit respectively; One end of the PFC inductor is connected to the front-stage circuit, and the other end of the PFC inductor is respectively connected to the first electrode of the first switch tube and the other input end of the comparison circuit.

3. The PFC circuit according to claim 2, characterized in that: The control circuit further includes a third switch tube, a controlled pole of the third switch tube is connected to the front-stage circuit, a first pole of the third switch tube is grounded, and a second pole of the third switch tube is connected to the PFC inductor.

4. The PFC circuit according to claim 2, characterized in that: The control circuit further includes a first resistor, one end of which is connected to the second electrode of the second switch tube, and the other end of which is connected to the rectifier chip.

5. The PFC circuit according to claim 4, characterized in that: The control circuit also includes a second diode and a first capacitor; The anode of the second diode is connected to the first resistor, the cathode of the second diode is respectively connected to one end of the first capacitor and the rectifier chip, and the other end of the first capacitor is connected to the rectifier chip.

6. The PFC circuit according to claim 2, characterized in that: The comparison circuit includes a comparator, a non-inverting input terminal of the comparator is connected to the second pole of the first switch tube, an inverting input terminal of the comparator is connected between the first pole of the first switch tube and the PFC inductor, and an output terminal of the comparator is connected to the controlled pole of the second switch tube.

7. The PFC circuit according to claim 6, characterized in that: The comparison circuit further includes a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor and a seventh resistor; One end of the second resistor is connected to the second electrode of the second switch tube, the other end of the second resistor is connected to one end of the third resistor, the other end of the third resistor is respectively connected to the non-inverting input end of the comparator and one end of the fourth resistor, and the other end of the fourth resistor is grounded; One end of the fifth resistor is connected to the PFC inductor, the other end of the fifth resistor is connected to one end of the sixth resistor, the other end of the sixth resistor is respectively connected to the inverting input terminal of the comparator and one end of the seventh resistor, and the other end of the seventh resistor is grounded.

8. The PFC circuit according to claim 1, wherein: The first switch tube and the second switch tube are both MOS tubes; The gate of the first switch tube is connected to the rectifier chip, the source of the first switch tube is connected to the front-stage circuit, the drain of the first switch tube is respectively connected to the power supply circuit, the source of the second switch tube and the input end of the comparison circuit, the drain of the second switch tube is connected to the rectifier chip, and the gate of the second switch tube is connected to the output end of the comparison circuit.

9. The PFC circuit according to claim 1, wherein: The power supply circuit includes a power supply capacitor, and the power supply capacitor is connected to the input circuit.

10. A power supply, characterized in that: The method comprises a PFC circuit as claimed in any one of claims 1 to 9.

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