Power factor correction circuit

Abstract

The present invention provides a power factor correction circuit, comprising a rectifier and voltage divider circuit, a boost circuit, a control chip, a switch tube circuit, and a zero-crossing bias circuit. The rectifier and voltage divider circuit is connected to a power supply circuit for providing an input voltage. The boost circuit is connected to the rectifier and voltage divider circuit for boosting the input voltage. The control chip includes a first pin, a second pin, a third pin, and a fourth pin. The first pin is connected to the rectifier and voltage divider circuit, and the control chip is configured to output a control signal. The switch tube circuit is respectively connected to the second pin, the fourth pin, and the boost circuit, and is turned on and off according to the control signal. The zero-crossing bias circuit is respectively connected to the second pin and the third pin. The present invention can increase output power.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply circuits, and in particular to a power factor correction circuit. Background Art

[0002] The principle of an active power factor correction circuit is that when the inductor current is equal to or greater than the sinusoidal envelope of the input voltage, the switch is turned off, causing the inductor current to gradually decrease. When the inductor current drops to zero, the switch is turned on, causing the inductor current to gradually increase. Ultimately, the inductor circuit follows the waveform of the input sinusoidal voltage, forming a current with a ripple-shaped envelope. This ripple-shaped envelope current is then rectified to form the output current, thus resetting the input current to a ripple-shaped envelope current, thereby achieving power factor correction. Current domestic power factor correction circuit management chip solutions for switching power supplies reduce the inductor current to zero when it decreases and need to start from zero when it increases. This results in a high peak current and low transmission power. On the other hand, the high inductor current ripple and the resulting RMS current are also high, generating significant noise on the input mains, requiring a large EMI filter to filter out the noise. This drawback limits their application to low power supplies. Summary of the Invention

[0003] The present invention provides a power factor correction circuit, which can improve output power and is suitable for high-power switching power supply circuits.

[0004] In a first aspect, the present invention provides a power factor correction circuit, comprising a rectifier voltage divider circuit, a boost circuit, a control chip, a switch tube circuit and a zero-crossing bias circuit; the rectifier voltage divider circuit is connected to a power supply circuit for providing an input voltage; the boost circuit is connected to the rectifier voltage divider circuit for boosting the input voltage; the control chip comprises a first pin, a second pin, a third pin and a fourth pin, the first pin is connected to the rectifier voltage divider circuit, and the control chip is used to output a control signal; the switch tube circuit is respectively connected to the second pin, the fourth pin and the boost circuit, and is turned on and off according to the control signal; the over The zero bias circuit is connected to the second pin and the third pin respectively; when the switching tube circuit is turned on, the zero-crossing bias circuit is turned on, and the zero-crossing bias circuit and the boost circuit start charging; when the current of the boost circuit reaches the peak current, the control chip sends the control signal to control the switching tube circuit to turn off, and the zero-crossing bias circuit and the boost circuit to discharge; when the voltage of the zero-crossing bias circuit drops to the trigger voltage of the third pin, the control chip sends the control signal to control the switching tube circuit to turn on, wherein when the voltage of the zero-crossing bias circuit drops to the trigger voltage, the current in the boost circuit is not zero.

[0005] Furthermore, the zero-crossing bias circuit includes a charging circuit and a first discharge circuit; the charging circuit is connected to the second pin; the first discharge circuit is respectively connected to the charging circuit, the third pin and the ground terminal; when the charging circuit is turned on, the charging circuit charges the first discharge circuit, and when the charging circuit is turned off, the first discharge circuit discharges through the ground terminal, and when the voltage of the first discharge circuit drops to the trigger voltage, the control chip sends a control signal to control the switching tube circuit and the charging circuit to be turned on.

[0006] Furthermore, the charging circuit includes a first diode, a first resistor and a first capacitor; the positive electrode of the first diode is connected to the second pin, and the negative electrode thereof is respectively connected to one end of the first resistor and one end of the first capacitor, and the other end of the first resistor and the other end of the first capacitor are both connected to the first discharge circuit.

[0007] Furthermore, the first discharge circuit includes a second capacitor and a second resistor; one end of the second capacitor and one end of the second resistor are respectively connected to the charging circuit and the third pin, and the other end of the second capacitor and the other end of the second resistor are both grounded.

[0008] Furthermore, the zero-crossing bias circuit also includes a second discharge circuit, which is respectively connected to the rectifier voltage divider circuit, the second resistor, the second capacitor and the ground terminal, and the second discharge circuit adjusts the discharge speed of the first discharge circuit according to the level of the input voltage.

[0009] Furthermore, the second discharge circuit includes a first switching tube and a third resistor; the base of the first switching tube is connected to the rectifier voltage divider circuit, its emitter is connected to one end of the third resistor, its collector is connected to the ground end, and the other end of the third resistor is respectively connected to the second resistor and the second capacitor.

[0010] Furthermore, the control signal includes a first signal and a second signal, and the switching tube circuit is turned on according to the second signal and turned off according to the first signal, the current envelope signal of the boost circuit and the voltage of the fourth pin, wherein the first signal is a high-level signal and the second signal is a low-level signal.

[0011] Furthermore, the switching tube circuit includes a fourth resistor, a fifth resistor, a second diode and a second switching tube; one end of the fourth resistor is connected to the second pin, and the other end thereof is respectively connected to one end of the fifth resistor and the negative electrode of the second diode, the positive electrode of the second diode and the other end of the fifth resistor are both connected to the gate of the second switching tube, the source of the second switching tube is connected to the boost circuit, and the drain thereof is connected to the ground end.

[0012] Furthermore, the rectifier and voltage divider circuit includes a rectifier circuit and a voltage divider circuit; the rectifier circuit is connected to the power supply circuit, the voltage divider circuit and the boost circuit respectively; and the voltage divider circuit is also connected to the control chip.

[0013] Furthermore, it also includes a current limiting circuit, which is respectively connected to the fourth pin of the control chip and the switching tube circuit, and is used to limit the maximum current of the switching tube circuit to protect the switching tube circuit and form a sinusoidal input current to improve the power factor.

[0014] The power factor correction circuit disclosed in the present invention has a control chip that sends a control signal to control the switching tube circuit and the zero-crossing bias circuit to be turned on. The zero-crossing bias circuit and the switching tube circuit start charging, causing the boost circuit current to increase. When the boost circuit current rises to a peak value, the control chip controls the switching tube circuit and the zero-crossing bias circuit to be turned off, causing the boost circuit current to gradually decrease. At the same time, the zero-crossing bias circuit voltage also decreases synchronously. When the zero-crossing bias circuit voltage drops to a trigger voltage, the control chip controls the switching tube circuit and the zero-crossing bias circuit to be turned on, causing the boost circuit current to increase. That is, the zero-crossing bias circuit can be used to control the off time of the switching tube circuit, so that the boost circuit current will not decrease to zero in high-power applications, and further, the boost circuit current will not start charging from zero during the next charging process, thereby increasing the current volt-second product and improving the output power. The circuit can be applied to high-power switching power supplies. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 is a block diagram of a power factor correction circuit provided by an embodiment of the present invention;

[0017] Figure 2 is a circuit diagram of a power factor correction circuit provided by an embodiment of the present invention;

[0018] Figure 3 4 is a circuit diagram of a zero-crossing bias circuit provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0020] It will be understood that when used in this specification and the appended claims, the terms “include” and “comprising” indicate the presence of described features, integers, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, operations, elements, components and / or groups thereof.

[0021] It should also be understood that the terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the present invention. As used in the specification and appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It should further be understood that the term "and / or" as used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, including and including these combinations.

[0022] Furthermore, directional terms used herein, such as "up," "down," "front," "back," "left," "right," "inside," "outside," and "side," are used solely to refer to the accompanying drawings and the orientation of the product in use. Therefore, these directional terms are intended to illustrate and facilitate understanding of the present invention and are not intended to limit the present invention. Furthermore, in the accompanying drawings, similar or identical structures are denoted by the same reference numerals.

[0023] See also Figures 1 to 3 , Figure 1 shows a block diagram of a power factor correction circuit 100 provided by the present invention, Figure 2 Circuit diagram of the power factor correction circuit 100, Figure 3 3 is a circuit diagram of the zero-crossing bias circuit 30. Figure 1As shown, the power factor correction circuit 100 includes a rectifier voltage divider circuit 10, a boost circuit 50, a control chip 20, a switch tube circuit 40 and a zero-crossing bias circuit 30; the rectifier voltage divider circuit 10 is connected to the power supply circuit 200 for providing an input voltage; the boost circuit 50 is connected to the rectifier voltage divider circuit 10 for boosting the input voltage; the control chip 20 includes a first pin, a second pin, a third pin and a fourth pin, the first pin is connected to the rectifier voltage divider circuit 10 and the control chip 20 for outputting a control signal; the switch tube circuit 40 is respectively connected to the second pin, the fourth pin and the boost circuit 50, and is turned on and off according to the control signal; the zero-crossing bias circuit 30 is respectively The control chip 20 is connected to the second pin and the third pin, and is turned on and off according to the control signal; when the switching tube circuit 40 is turned on, the zero-crossing bias circuit 30 is turned on, and the zero-crossing bias circuit 30 and the boost circuit 50 start charging. When the current of the boost circuit 50 reaches the peak current, the control chip 20 sends the control signal to control the switching tube circuit 40 to turn off, and the zero-crossing bias circuit 30 and the boost circuit 50 discharge. When the voltage of the zero-crossing bias circuit 30 drops to the trigger voltage of the third pin, the control chip 20 sends the control signal to control the switching tube circuit 40 to turn on. When the voltage of the zero-crossing bias circuit 30 drops to the trigger voltage, the current in the boost circuit 50 is not zero.

[0024] Among them, the rectifier and voltage divider circuit 10 may include a rectifier circuit 11 and a voltage divider circuit 12. The rectifier circuit 11 is used to rectify the alternating current input by the power supply circuit 200 to obtain an input voltage. On the one hand, the input voltage is input to the boost circuit 50, and the boost circuit 50 boosts the input current so that the waveform of the input current is a sine wave, and is the same as the waveform of the input voltage. On the other hand, the input voltage enters the control chip 20 from the first pin of the control chip 20 through the voltage divider circuit 12, that is, the first pin is used to detect the input voltage phase. A differential amplifier can be provided inside the control chip 20, and the control chip 20 includes modules such as a differential amplifier, an overvoltage detection module, a zero current detection module, an enable module, a multiplier module, and a current comparator. The differential amplifier is used to regulate the internal controller of the control chip 20 to stabilize the output voltage. The overvoltage detection module is used to detect whether the voltage of the differential amplifier exceeds the operating voltage. When the current through the boost inductor L1 in the boost circuit 50 reverses and the current through the boost circuit 50 reaches zero, the zero current detection module turns on the switch circuit 40. The multiplier has two input terminals: one input terminal inputs the instantaneous line voltage after voltage division, and the other input terminal inputs the signal of the differential amplifier output. If the voltage remains constant, the envelope of the waveform output by the multiplier is a rectified sine wave. The output signal of the multiplier is used as the reference signal for the current comparator. The output of the current comparator is used to control the peak current of the switch circuit 40 in each cycle. The current comparator obtains a voltage signal through a current detection resistor and compares it with the output signal of the multiplier module to determine the shutdown time of the switch circuit 40.

[0025] like Figure 2 As shown, the boost circuit 50 may include a reference circuit composed of the seventh resistor R7 to the tenth resistor R10. The reference circuit inputs the current signal output by the third diode D3 to the sixth pin and the seventh pin, and the differential amplifier is connected to the first pin, the sixth pin and the seventh pin respectively. The differential amplifier outputs the received current signal to the multiplier provided inside the control chip 20. The envelope of the waveform output by the multiplier is a rectified sine wave. The signal output by the multiplier can be used as a reference signal for the current comparator. The current comparator controls the peak current of each cycle of the switch tube circuit 40 according to the reference signal. Figure 2 As shown, the fourteenth resistor R14 to the sixteenth resistor R16 and the sixth capacitor C6 and the seventh capacitor C7 constitute a startup circuit, the fifth diode D5, the sixth diode D6, the eighth capacitor C8 and the seventeenth resistor R17 constitute a secondary rectifier circuit, and the startup circuit and the secondary rectifier circuit are both connected to the fifth pin of the control chip 20, namely the VCC pin, for powering the control chip 20.

[0026] The switch tube circuit 40 is turned on and off according to the control signal sent by the control chip 20. When the switch tube circuit 40 is turned on according to the control signal, the current of the inductor L1 in the boost circuit 50 gradually increases. At the same time, the zero-crossing bias circuit 30 is turned on and starts to charge synchronously. When the inductor L1 reaches its peak current, the control chip 20 controls the switch tube circuit 40 to turn off, the third diode D3 is turned on, and the boost circuit 50 starts to supply power to the subsequent circuit 300. At the same time, the zero-crossing bias circuit 30 is turned off synchronously, and the inductor L1 and the zero-crossing bias circuit 30 both start to discharge. When the current of the zero-crossing bias circuit 30 reaches its peak current, the inductor L1 and the zero-crossing bias circuit 30 are turned off. When the voltage is lower than the trigger voltage of the third pin, the control signal sends a control signal to control the switch tube circuit 40 and the zero-crossing bias circuit 30 to turn on, and the current of the inductor L1 gradually increases. Since the current in the inductor L1 is not zero when the voltage of the zero-crossing bias circuit 30 reaches the trigger voltage, the current in the inductor L1 is not zero. Therefore, when the switch tube circuit 40 is turned on, the current in the inductor L1 is not zero, and the volt-second product of the inductor L1 current increases. The boost circuit 50 starts to supply power to the subsequent circuit 300 when the inductor L1 reaches the peak current to control the switch tube circuit 40 to turn off, thereby improving power transmission and conversion, and thus meeting high-power power requirements.

[0027] See also Figure 2 In one embodiment, the zero-crossing bias circuit 30 includes a charging circuit 31 and a first discharge circuit 32; the charging circuit 31 is connected to the second pin; the first discharge circuit 32 is respectively connected to the charging circuit 31, the third pin and the ground terminal; when the charging circuit 31 is turned on, the charging circuit 31 charges the first discharge circuit 32, and when the charging circuit 31 is turned off, the first discharge circuit 32 discharges through the ground terminal, and when the voltage of the first discharge circuit 32 drops to the trigger voltage, the control chip 20 sends a control signal to control the switching tube circuit 40 and the charging circuit 31 to be turned on.

[0028] Among them, when the switch tube circuit 40 is turned on, the charging circuit 31 is turned on and starts to charge the first discharge circuit 32, and the first discharge circuit 32 is also connected to the third pin. When the switch tube circuit 40 is turned off, the charging circuit 31 is turned off and stops charging the first discharge circuit 32, and the first discharge circuit 32 starts to discharge. When the voltage of the first discharge circuit 32 is less than the trigger voltage, the control chip 20 controls the switch tube circuit 40 to turn on.

[0029] See also Figure 3In one embodiment, the charging circuit 31 includes a first diode D1, a first resistor R1, and a first capacitor C1; the anode of the first diode D1 is connected to the second pin, and the cathode thereof is connected to one end of the first resistor R1 and one end of the first capacitor C1, respectively; the other end of the first resistor R1 and the other end of the first capacitor C1 are both connected to the first discharge circuit 32.

[0030] When the switch circuit 40 is turned on, the first diode D1 is forward-conducted and charges the first discharge circuit 32 through the first capacitor C1 and the first resistor R1. When the switch circuit 40 is turned off, the first diode D1 is reverse-conducted and stops charging the first discharge circuit 32.

[0031] In one embodiment, the first discharge circuit 32 includes a second capacitor C2 and a second resistor R2; one end of the second capacitor C2 and one end of the second resistor R2 are respectively connected to the charging circuit 31 and the third pin, and the other end of the second capacitor C2 and the other end of the second resistor R2 are grounded.

[0032] Among them, when the switching tube circuit 40 is turned on, the charging circuit 31 charges the second capacitor C2. At the same time, a clamping voltage is set inside the third pin, and the voltage of the second capacitor C2 is clamped at the voltage of the clamping voltage. When the switching tube circuit 40 is turned off, the second capacitor C2 is discharged through the second resistor R2, and the first capacitor C1 is discharged through the first resistor R1 until the voltage of the second capacitor C2 is equal to the trigger voltage of the third pin, and the switching tube circuit 40 is turned on again.

[0033] In a further embodiment, the zero-crossing bias circuit 30 further includes a second discharge circuit 33, which is respectively connected to the rectifier voltage divider circuit 10, the second resistor R2, the second capacitor C2 and the ground terminal, and the second discharge circuit 33 adjusts the discharge speed of the first discharge circuit 32 according to the level of the input voltage.

[0034] The second discharge circuit 33 is used to adjust its discharge speed based on the input voltage. When the input AC voltage phase is far from the peak and valley moments and the input AC voltage is low, the inductor L1 stores less energy, and the third diode D3's conduction time is short. For example, at 10°, 170°, 190°, and 350°, i.e., when the voltage is low, the second discharge circuit 33 is turned on. The addition of the second discharge circuit 33 to the first discharge circuit 32 accelerates the discharge speed of the first discharge circuit 32, thereby accelerating the conduction of the switch circuit 40 and shortening the switch circuit 40's off time, thereby preventing the output power from decreasing due to a decrease in input voltage. Since the charging time remains unchanged and the on time remains the same, the circuit operates in continuous mode, increasing power while reducing the peak current of the switch circuit 40.

[0035] In a further embodiment, the second discharge circuit 33 includes a first switching tube Q1 and a third resistor R3; the base of the first switching tube Q1 is connected to the rectifier and voltage divider circuit 10, the emitter thereof is connected to one end of the third resistor R3, and the collector thereof is connected to the ground end, and the other end of the third resistor R3 is respectively connected to the second resistor R2 and the second capacitor C2.

[0036] The first switch tube Q1 can be turned on and off according to the input voltage, and the collector of the first switch tube Q1 is grounded. When the first switch tube Q1 is turned on, the first discharge circuit 32 discharges through the first switch tube Q1.

[0037] In one embodiment, the control signal includes a first signal and a second signal, the switching tube circuit 40 is turned on according to the second signal, and is turned off according to the first signal, the current envelope signal of the boost circuit 50 and the voltage of the fourth pin, wherein the first signal is a high-level signal and the second signal is a low-level signal.

[0038] Among them, when the switch tube circuit 40 receives a high-level signal, it is turned on, and when it receives a low-level signal, the current envelope signal of the boost circuit 50 and the voltage of the fourth pin, it is turned off. When the voltage of the zero-crossing bias circuit 30 is equal to the trigger voltage, the control chip 20 sends a low-level signal.

[0039] In one embodiment, the switching tube circuit 40 includes a fourth resistor R4, a fifth resistor R5, a second diode D2, and a second switching tube Q2; one end of the fourth resistor R4 is connected to the second pin, and the other end thereof is respectively connected to one end of the fifth resistor R5 and the cathode of the second diode D2; the anode of the second diode D2 and the other end of the fifth resistor R5 are both connected to the gate of the second switching tube Q2; the source of the second switching tube Q2 is connected to the boost circuit 50, and the drain thereof is connected to the ground terminal via a nineteenth resistor R19.

[0040] The second switch tube Q2 is turned on and off according to the control signal. When the second switch tube Q2 is turned on, the current of the inductor L1 increases and the third diode D3 is turned off. When the second switch tube Q2 is turned off, the inductor L1 discharges and the third diode D3 is turned on.

[0041] In one embodiment, the rectifier and voltage divider circuit 10 includes a rectifier circuit 11 and a voltage divider circuit 12 ; the rectifier circuit 11 is connected to the power supply circuit 200 , the voltage divider circuit 12 and the boost circuit 50 respectively; the voltage divider circuit 12 is also connected to the control chip 20 .

[0042] Among them, Figure 2 As shown, the rectifier circuit 11 may include a rectifier bridge BD1 and a fifth capacitor C5 for rectifying the input AC power to obtain an input voltage. The voltage divider circuit 12 divides the input voltage and then inputs the divided input voltage to the control chip 20 .

[0043] like Figure 1 As shown, in one embodiment, a current limiting circuit 60 is also included, which is respectively connected to the fourth pin of the control chip 20 and the switching tube circuit 40, and is used to limit the maximum current of the switching tube circuit 40 to protect the switching tube circuit 40 and form a sinusoidal input current to improve the power factor.

[0044] Among them, Figure 2 As shown, the current limiting circuit 60 may include an eighteenth resistor R18 and a nineteenth resistor R19, which are used to limit the peak current of the switching tube circuit 40, thereby protecting the switching tube circuit 40, and at the same time forming a sinusoidal input current to improve the power factor.

[0045] The power factor correction circuit disclosed in the present invention controls the off-time of the switch tube through a zero-crossing bias circuit, thereby controlling the discharge time of the boost circuit, so that the current of the boost circuit does not drop to zero during high-power applications. When the switch tube circuit is turned on next time, the current of the boost circuit does not start to rise from zero, thereby increasing the current volt-second product and thus increasing the output power, and is suitable for high-power power applications.

[0046] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A power factor correction circuit, characterized in that: include: A rectifier and voltage divider circuit is connected to the power supply circuit and is used to provide an input voltage; a boost circuit, connected to the rectifier and voltage divider circuit, for boosting the input voltage; a control chip, comprising a first pin, a second pin, a third pin, and a fourth pin, wherein the first pin is connected to the rectifier voltage divider circuit, and the control chip is used to output a control signal; a switch tube circuit, connected to the second pin, the fourth pin and the boost circuit respectively, and turned on and off according to the control signal; a zero-crossing bias circuit, connected to the second pin and the third pin respectively; When the switching tube circuit is turned on, the zero-crossing bias circuit is turned on, and the zero-crossing bias circuit and the boost circuit start charging. When the current of the boost circuit reaches the peak current, the control chip sends the control signal to control the switching tube circuit to turn off, and the zero-crossing bias circuit and the boost circuit to discharge. When the voltage of the zero-crossing bias circuit drops to the trigger voltage of the third pin, the control chip sends the control signal to control the switching tube circuit to turn on. When the voltage of the zero-crossing bias circuit drops to the trigger voltage, the current in the boost circuit is not zero.

2. The power factor correction circuit according to claim 1, wherein: The zero-crossing bias circuit comprises: a charging circuit connected to the second pin; a first discharging circuit connected to the charging circuit, the third pin and the ground terminal respectively; When the charging circuit is turned on, the charging circuit charges the first discharging circuit. When the charging circuit is turned off, the first discharging circuit discharges through the ground terminal. When the voltage of the first discharging circuit drops to the trigger voltage, the control chip sends a control signal to control the switching tube circuit and the charging circuit to be turned on.

3. The power factor correction circuit according to claim 2, wherein: The charging circuit includes a first diode, a first resistor and a first capacitor; The anode of the first diode is connected to the second pin, and the cathode thereof is connected to one end of the first resistor and one end of the first capacitor respectively. The other end of the first resistor and the other end of the first capacitor are both connected to the first discharge circuit.

4. The power factor correction circuit according to claim 2, wherein: The first discharge circuit includes a second capacitor and a second resistor; One end of the second capacitor and one end of the second resistor are connected to the charging circuit and the third pin respectively, and the other end of the second capacitor and the other end of the second resistor are grounded.

5. The power factor correction circuit according to claim 4, wherein: The zero-crossing bias circuit also includes a second discharge circuit, which is respectively connected to the rectifier voltage divider circuit, the second resistor, the second capacitor and the ground terminal. The second discharge circuit adjusts the discharge speed of the first discharge circuit according to the level of the input voltage.

6. The power factor correction circuit according to claim 5, wherein: The second discharge circuit includes a first switch tube and a third resistor; The base of the first switching tube is connected to the rectifier voltage divider circuit, the emitter thereof is connected to one end of the third resistor, the collector thereof is connected to the ground end, and the other end of the third resistor is connected to the second resistor and the second capacitor respectively.

7. The power factor correction circuit according to claim 1, wherein: The control signal includes a first signal and a second signal. The switching tube circuit is turned on according to the second signal and is turned off according to the first signal, the current envelope signal of the boost circuit and the voltage of the fourth pin, wherein the first signal is a high-level signal and the second signal is a low-level signal.

8. The power factor correction circuit according to claim 1, wherein: The switch tube circuit includes a fourth resistor, a fifth resistor, a second diode and a second switch tube; One end of the fourth resistor is connected to the second pin, and the other end thereof is respectively connected to one end of the fifth resistor and the cathode of the second diode. The anode of the second diode and the other end of the fifth resistor are both connected to the gate of the second switching tube. The source of the second switching tube is connected to the boost circuit, and the drain thereof is connected to the ground end.

9. The power factor correction circuit according to claim 1, wherein: The rectifier and voltage divider circuit includes a rectifier circuit and a voltage divider circuit; The rectifier circuit is connected to the power supply circuit, the voltage divider circuit and the boost circuit respectively; The voltage divider circuit is also connected to the control chip.

10. The power factor correction circuit according to claim 1, wherein: It also includes a current limiting circuit, which is connected to the fourth pin of the control chip and the switching tube circuit respectively, and is used to limit the maximum current of the switching tube circuit to protect the switching tube circuit and form a sinusoidal input current to improve the power factor.

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