Power factor improvement circuit

Abstract

The embodiment of the invention provides a power factor improvement circuit, and relates to the technical field of power supply circuits. In the power factor improvement circuit, a first switch unit, a first one-way conduction unit and a first inductance branch are used as a whole and have a voltage reduction function, and the first inductance branch, a second switch unit and a second one-way conduction unit form a traditional power factor improvement circuit, namely, voltage reduction is carried out firstly and then the traditional power factor improvement circuit is used for boosting. The output voltage of the power factor improvement circuit can be 1.41 times lower than the input voltage. In addition, synchronous switching of the first switching unit and the second switching unit can improve the power factor.

Description

Technical Field

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

[0002] In recent years, home appliances and various products other than home appliances have also been required to comply with harmonic standards, so power factor improvement circuits are widely used. Figure 1 As shown, usually a boost circuit is used to improve the power factor. The input voltage is AC, and DC is output after rectification and boosting. However, if the output voltage of the inverter intermediate voltage is controlled below 1.41 times the input voltage, the input current waveform will be distorted and cannot pass the harmonic standard.

[0003] In other words, the current power factor improvement circuit cannot achieve voltage reduction. When the motor is driven at a low frequency such as an inverter, a Vdc exceeding the necessary value needs to be applied, consuming excess power and generating leakage current.

[0004] How to enable the power factor improvement circuit to achieve the function of lower voltage output is the technical problem to be solved by this application. Summary of the invention

[0005] The purpose of the present application is to provide a power factor improvement circuit to solve the technical problem in the prior art of how to enable the power factor improvement circuit to achieve a function of lower voltage output.

[0006] To achieve the above objectives, the embodiments of the present application adopt the following technical solutions.

[0007] In a first aspect, an embodiment of the present application provides a power factor improvement circuit, including a controller, a first switch unit, a first unidirectional conduction unit, a first inductor branch, a second switch unit, and a second unidirectional conduction unit;

[0008] The first end of the first switch unit is connected to the first end of the first unidirectional conductive unit, the second end of the first switch unit is used to connect to the first pole of the DC power supply, and the second end of the first unidirectional conductive unit is used to connect to the second pole of the DC power supply;

[0009] The first end of the first unidirectional conduction unit is connected to the first end of the first inductor branch, the second end of the first inductor branch is connected to the first end of the second switch unit and the first end of the second unidirectional conduction unit, the second end of the second switch unit is connected to the second end of the first unidirectional conduction unit; the second end of the second unidirectional conduction unit and the second end of the second switch unit obtain an output voltage;

[0010] The controller is used to make the first switch unit and the second switch unit switch synchronously in a first voltage output state; and to make the first switch unit continuously turned on and control the second switch unit through a PWM signal in a second voltage output state.

[0011] Compared with the prior art, the power factor improvement circuit of the first aspect has the following beneficial effects:

[0012] The first switch unit, the first unidirectional conduction unit and the first inductor branch have a step-down function as a whole. The first inductor branch, the second switch unit and the second unidirectional conduction unit form a traditional power factor improvement circuit, that is, the voltage is first stepped down and then the voltage is stepped up by the traditional power factor improvement circuit, that is, the output voltage is lower than the traditional power factor improvement circuit. Specifically, the output voltage of the traditional power factor improvement circuit is 1.41 times higher than the input voltage, and the output voltage of the power factor improvement circuit of the first aspect can be lower than 1.41 times the input voltage. In addition, the first switch unit and the second switch unit are switched synchronously to improve the power factor.

[0013] Optionally, the first inductor branch includes a first inductor and a current detection module; the first inductor and the current detection module are connected in series, and the current detection module is used to transmit current information of the first inductor to the controller.

[0014] The controller controls the on and off of the first switch unit and the second switch unit according to the current information provided by the current detection module.

[0015] Optionally, the power factor improvement circuit includes the DC power supply, the DC power supply is an AC-DC module, a first voltage detection module is provided between two input ends of the AC-DC module, a second voltage detection module is provided between the second end of the second unidirectional conduction unit and the second end of the second switch unit, the first voltage detection module is used to transmit voltage information of the two input ends of the AC-DC module to the controller, and the second voltage detection module is used to transmit voltage information of the output voltage to the controller;

[0016] The controller is used to control the first switch unit and the second switch unit according to the current information, the voltage information of the two input terminals of the AC-DC module and the voltage information of the output voltage.

[0017] Optionally, the controller synchronizes the phases of the voltages at two input terminals of the AC-DC converter with the input current through PI control so as to improve the power factor, and the input current is the input current of the AC-DC converter.

[0018] Optionally, the AC-to-DC module is a full-bridge rectifier circuit including four diodes.

[0019] Optionally, the first switch unit includes a first switch device and a first drive circuit; a first end of the first switch device is connected to a first end of the first unidirectional conduction unit, and a second end of the first switch device is used to connect to a first pole of a DC power supply; the controller controls the conduction or cutoff of the first switch device through the first drive circuit;

[0020] The second switch unit includes a second switch device and a second drive circuit; the first end of the second switch device is connected to the second end of the first inductor branch, and the second end of the second switch device is connected to the second end of the first unidirectional conduction unit; the controller controls the conduction or cutoff of the second switch device through the second drive circuit.

[0021] Optionally, the first unidirectional conductive unit and the second unidirectional conductive unit both include diodes;

[0022] The second end of the first unidirectional conductive unit is a cathode and connected to the negative electrode of the DC power supply, the first end of the second unidirectional conductive unit is an anode and the second end of the second unidirectional conductive unit is the positive electrode of the output voltage.

[0023] In a second aspect, an embodiment of the present application provides a power factor improvement circuit, including a controller, a boost module and a buck module;

[0024] The boost module is used to input a DC voltage and output a first voltage to the buck module, and the buck module is used to obtain a second voltage according to the first voltage; the second voltage is less than or equal to the first voltage;

[0025] The controller is used to control the boost module and the buck module using the same PWM signal in a first voltage output state; and to keep the buck module turned on continuously and control the boost module through the PWM signal in a second voltage output state.

[0026] Compared with the prior art, the power factor improvement circuit of the second aspect has the following beneficial effects:

[0027] By first stepping up the voltage and then stepping down the voltage, a lower output voltage can be achieved compared to the traditional power factor improvement circuit. The first switch unit and the second switch unit switch synchronously to improve the power factor.

[0028] Optionally, the boost module includes a first inductor, a first switch unit, a first unidirectional conduction unit and a first capacitor;

[0029] The first end of the first inductor is used to connect to the first pole of the DC power supply, the second end of the first inductor is connected to the first end of the first switch unit and the first end of the first unidirectional conduction unit, and the second end of the first switch unit is used to connect to the second pole of the DC power supply; the second end of the first unidirectional conduction unit is connected to the first end of the first capacitor, and the second end of the first capacitor is connected to the second end of the first switch unit;

[0030] A voltage between the first end of the first capacitor and the second end of the first capacitor is the first voltage;

[0031] The step-down module includes a second switch unit, a second inductor, a second unidirectional conductive unit and a second capacitor;

[0032] A first end of the second switch unit is connected to a first end of the first capacitor, a second end of the second switch unit is connected to a first end of the second inductor and a first end of the second unidirectional conduction unit, and a second end of the second unidirectional conduction unit is connected to a second end of the first capacitor; a second end of the second inductor is connected to a first end of the second capacitor, and a second end of the second capacitor is connected to a second end of the second unidirectional conduction unit;

[0033] A voltage between the first end of the second capacitor and the second end of the second capacitor is the second voltage;

[0034] The controller is used to control the first switch unit and the second switch unit using the same PWM signal in a first voltage output state; and to keep the second switch unit turned on continuously and control the first switch unit through the PWM signal in a second voltage output state.

[0035] Optionally, the DC power supply includes a full-bridge rectifier circuit; a first voltage detection module is provided at the input end of the full-bridge rectifier circuit; a third voltage detection module is provided between the first end of the first capacitor and the second end of the first capacitor; a second voltage detection module is provided between the first end of the second capacitor and the second end of the second capacitor; and a current detection module is connected in series with the first switch unit;

[0036] The controller controls the first voltage and the second voltage respectively according to the voltage information of the first voltage detection module, the voltage information of the second voltage detection module and the current information of the current detection module, obtains two power supplies of the first voltage and the second voltage, and provides the two power supplies to loads with two voltage requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1 It is a schematic diagram of a power factor improvement circuit in the prior art;

[0039] Figure 2 A schematic diagram of a power factor improvement circuit provided in an embodiment of the present application;

[0040] Figure 3 A schematic diagram of an AC-DC converter provided in an embodiment of the present application as a power factor improvement circuit;

[0041] Figure 4 A schematic diagram of a power factor improvement circuit composed of a transistor, an inductor, etc. provided in an embodiment of the present application;

[0042] Figure 5 A schematic diagram of making an input voltage and an input current in phase provided by an embodiment of the present application;

[0043] Figure 6 A schematic diagram of a control principle provided in an embodiment of the present application;

[0044] Figure 7 A schematic diagram of a power factor improvement circuit for first boosting and then reducing voltage provided in an embodiment of the present application;

[0045] Figure 8 A schematic diagram of a power factor improvement circuit composed of an inductor, a transistor, a capacitor, etc. provided in an embodiment of the present application.

[0046] Description of reference numerals:

[0047] 101 First switch unit

[0048] 102 first one-way conduction unit

[0049] 103 First inductor branch

[0050] 104 Second switch unit

[0051] 105 The second one-way conduction unit

[0052] 106 DC power supply DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. The described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described in the drawings here can be arranged and designed in various different configurations.

[0054] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0055] In the description of this application, it should be noted that relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. The term "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium.

[0056] The existing power factor improvement circuit can only output a voltage that is 1.41 times higher than the input voltage, and cannot output a smaller voltage.

[0057] To overcome the above problems, see Figure 2 The embodiment of the present application provides a power factor improvement circuit, which includes a first switch unit 101, a first unidirectional conduction unit 102, a first inductor branch 103, a second switch unit 104, a second unidirectional conduction unit 105 and a controller, which is not shown in the figure. Figure 2 , the various parts of the power factor improvement circuit have the following connection relationship:

[0058] The first end of the first switch unit 101 is connected to the first end of the first unidirectional conductive unit 102, the second end of the first switch unit 101 is used to connect to the first pole of the DC power supply 106, and the second end of the first unidirectional conductive unit 102 is used to connect to the second pole of the DC power supply 106; the first pole and the second pole of the DC power supply 106 are respectively positive and negative, the first pole of the DC power supply 106 is positive and the second pole is negative, or the first pole of the DC power supply 106 is negative and the second pole is positive;

[0059] The first end of the first unidirectional conduction unit 102 is connected to the first end of the first inductor branch 103, the second end of the first inductor branch 103 is connected to the first end of the second switch unit 104 and the first end of the second unidirectional conduction unit 105, the second end of the second switch unit 104 is connected to the second end of the first unidirectional conduction unit 102; the second end of the second unidirectional conduction unit 105 and the second end of the second switch unit 104 obtain an output voltage OUT.

[0060] The states of the controller control voltage output include:

[0061] In the first voltage output state, the first switch unit 101 and the second switch unit 104 are switched synchronously;

[0062] In the second voltage output state, the first switch unit 101 is continuously turned on and the second switch unit 104 is controlled by the PWM signal.

[0063] The first switch unit, the first unidirectional conduction unit and the first inductor branch form a module with a step-down function, and the first inductor branch, the second switch unit and the second unidirectional conduction unit form a module with a step-up function. In the first voltage output state, the two modules work simultaneously, that is, step-down first and then step-up. In the second voltage output state, the module with the step-down function does not work, that is, only the module with the step-up function works, and the output voltage obtained in the first voltage output state is lower than the output voltage obtained in the second voltage output state.

[0064] like Figure 3 The DC power supply 106 may include an AC to DC module. The DC power supply 106 inputs AC power and then converts the AC power into DC power to provide to the power factor improvement circuit.

[0065] The output voltage obtained in the first voltage output state may be lower than 1.41 times the AC voltage, and the output voltage obtained in the second voltage output state may be higher than 1.41 times the AC voltage. The AC voltage refers to the effective voltage of the AC.

[0066] Figure 4 A power factor improvement circuit composed of transistors, inductors, etc. is demonstrated.

[0067] like Figure 4 The AC-to-DC module may include four diodes, which are D1, D2, D3, and D4 in the figure, and the four diodes form a full-bridge rectifier circuit.

[0068] The first unidirectional conductive unit 102 and the second unidirectional conductive unit 105 can both be implemented by fast recovery diodes, namely the diodes D5 and D6 in the figure. In one implementation, the second end of the first unidirectional conductive unit 102 is a cathode and the second end of the first unidirectional conductive unit 102 is connected to the negative electrode of the DC power supply 106, the first end of the second unidirectional conductive unit 105 is an anode and the second end of the second unidirectional conductive unit 105 is the positive electrode of the output voltage. Another implementation is to swap the cathode and anode, and interchange the negative electrode and the positive electrode.

[0069] The first switch unit 101 may include a first switch device SW1 and a first drive circuit; the first end of the first switch device SW1 is connected to the first end of the first unidirectional conduction unit 102, and the second end of the first switch device SW1 is used to connect to the first pole of the DC power supply 106. The controller can control the conduction or cut-off of the first switch device SW1 through the first drive circuit, and the conduction and cut-off of the first switch device SW1 control the opening and closing of the first switch unit 101. The first drive circuit enables the controller with a lower voltage to control the first switch device SW1 with a higher voltage and higher power.

[0070] The second switch unit 104 may include a second switch device SW2 and a second drive circuit; the first end of the second switch device SW2 is connected to the second end of the first inductor L1 branch 103, and the second end of the second switch device SW2 is connected to the second end of the first unidirectional conduction unit 102; the controller controls the conduction or cut-off of the second switch device SW2 through the second drive circuit, and the conduction and cut-off of the second switch device SW2 control the on and off of the second switch unit 104. The second drive circuit enables the controller with a lower voltage to control the second switch device SW2 with a higher voltage and higher power.

[0071] Figure 4 A layout of signal collection points is also shown. Regarding the collected signals, there are current detection and voltage detection. The current detection module can be connected in series with the first inductor L1 to detect the current of the first inductor L1, the voltage detection module can be connected in parallel with the input end of the AC-DC module to detect the input voltage of the AC-DC module, and the voltage detection module can also be connected in parallel with the output end of the entire power factor improvement circuit to detect the output voltage of the entire power factor improvement circuit.

[0072] The first inductor branch 103 may include a first inductor L1 and a current detection module. The first inductor and the current detection module are connected in series, and the current detection module is used to transmit current information of the first inductor L1 to the controller.

[0073] A first voltage detection module may be provided between the two input terminals of the AC-DC converter module, and a second voltage detection module may be provided between the second terminal of the second unidirectional conduction unit and the second terminal of the second switch unit. The first voltage detection module is used to transmit voltage information of the two input terminals of the AC-DC converter module to the controller, and the second voltage detection module is used to transmit voltage information of the output voltage to the controller, and the controller is used to control the first switch unit 101 and the second switch unit 104 according to the current information and the voltage information.

[0074] The controller can be configured to synchronize the phase of the voltage at the two input terminals of the AC-DC converter with the input current through PI control. Figure 5 , thereby improving the power factor. The input current is the input current of the AC to DC module. Figure 6 The control principle is demonstrated. The first voltage output state is Figure 6 The control mode below, the second voltage output state is Figure 6 The difference between the two control modes below is that the second voltage output state only provides a PWM signal for the second switch device SW2. The output voltage and the set voltage are calculated and input to the automatic voltage regulator (Automatic Voltage Regulator, AVR), and then the output result of the automatic voltage regulator is calculated with the input current, and then the result is calculated with the inductor current and input to the alternating current voltage regulator (Alternating Current Voltage Regulator) to generate a PWM signal.

[0075] See also Figure 7 The embodiment of the present application also provides another power factor improvement circuit, which adopts the method of first boosting and then bucking, and can also achieve an output voltage lower than 1.41 times the input voltage. The power factor improvement circuit includes a controller, a boost module 201 and a buck module 202.

[0076] The boost module 201 is used to input a DC voltage and output a first voltage to the buck module 202. The buck module 202 is used to obtain a second voltage according to the first voltage; the second voltage is less than or equal to the first voltage.

[0077] The states of the controller control voltage output include:

[0078] In the first voltage output state, the controller uses the same PWM signal to control the boost module 201 and the buck module 202, first boosting the voltage and then bucking the voltage, which can also achieve an output voltage lower than 1.41 times the input voltage;

[0079] In the second voltage output state, the controller keeps the buck module 202 turned on and controls the boost module 201 through the PWM signal, so that an output voltage 1.41 times higher than the input voltage is achieved even if the buck module 202 is not working.

[0080] Figure 8 An implementation method of the power factor improvement circuit composed of an inductor, a transistor, a capacitor, etc. is shown. The DC voltage can be obtained through a full-bridge rectifier circuit, and a first voltage detection module can be set at the input end of the full-bridge rectifier circuit.

[0081] like Figure 8 , the boost module 201 may include a first inductor L1, a first switch unit 101, a first unidirectional conduction unit 102 and a first capacitor C1. The first switch unit 101 may include a first switch device SW1 and a first drive circuit, and the first switch unit 101 may be connected in series with a current detection module. The first unidirectional conduction unit 102 may include a fast recovery diode D5. The voltage between the first end of the first capacitor C1 and the second end of the first capacitor C1 is a first voltage Vdc1, and a third voltage detection module may be provided between the first end of the first capacitor C1 and the second end of the first capacitor C1.

[0082] The step-down module 202 may include a second switch unit 104, a second inductor L2, a second unidirectional conduction unit 105, and a second capacitor C2. The second switch unit 104 may include a second drive circuit and a second switch device SW2. The second unidirectional conduction unit 105 may include a fast recovery diode D6. The voltage between the first end of the second capacitor C2 and the second end of the second capacitor C2 is a second voltage Vdc2, and a second voltage detection module may be provided between the first end of the second capacitor C2 and the second end of the second capacitor C2.

[0083] The states of the controller control voltage output include:

[0084] In the first voltage output state, the controller uses the same PWM signal to control the first switch device SW1 and the second switch device SW2;

[0085] In the second voltage output state, the controller keeps the second switch device SW2 turned on continuously and controls the first switch device SW1 through the PWM signal.

[0086] The controller can be configured to control the first voltage and the second voltage respectively according to the voltage information of the first voltage detection module, the voltage information of the second voltage detection module and the current information of the current detection module, so as to obtain two power supplies of the first voltage and the second voltage, thereby being able to meet the loads with two voltage requirements.

[0087] The power factor improvement circuit provided by the present application can flexibly control different voltages, obtain a larger voltage range, and further control the motor by the voltage size. Compared with the traditional power factor improvement circuit that needs to obtain a larger voltage and then consume power to obtain a smaller voltage, the power factor improvement circuit reduces unnecessary power consumption. It can be achieved with only a simple switching mode, and also solves the problem of power factor.

[0088] The above-described device and system embodiments are merely illustrative, and some or all of the modules may be selected according to actual needs to achieve the purpose of the present embodiment. A person skilled in the art may understand and implement the present embodiment without creative effort.

[0089] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A power factor improvement circuit, characterized in that: It includes a controller, a first switch unit, a first unidirectional conduction unit, a first inductor branch, a second switch unit and a second unidirectional conduction unit; The first end of the first switch unit is connected to the first end of the first unidirectional conductive unit, the second end of the first switch unit is used to connect to the first pole of the DC power supply, and the second end of the first unidirectional conductive unit is used to connect to the second pole of the DC power supply; The first end of the first unidirectional conduction unit is connected to the first end of the first inductor branch, the second end of the first inductor branch is connected to the first end of the second switch unit and the first end of the second unidirectional conduction unit, the second end of the second switch unit is connected to the second end of the first unidirectional conduction unit; an output voltage is obtained between the second end of the second unidirectional conduction unit and the second end of the second switch unit; The controller is used to make the first switch unit and the second switch unit switch synchronously in a first voltage output state; and to make the first switch unit continuously turned on and control the second switch unit through a PWM signal in a second voltage output state.

2. The power factor improvement circuit according to claim 1, characterized in that: The first inductor branch includes a first inductor and a current detection module; the first inductor and the current detection module are connected in series, and the current detection module is used to transmit current information of the first inductor to the controller.

3. The power factor improvement circuit according to claim 2, characterized in that: The power factor improvement circuit includes the DC power supply, which is an AC-DC module, a first voltage detection module is provided between two input ends of the AC-DC module, a second voltage detection module is provided between the second end of the second unidirectional conduction unit and the second end of the second switch unit, the first voltage detection module is used to transmit voltage information of the two input ends of the AC-DC module to the controller, and the second voltage detection module is used to transmit voltage information of the output voltage to the controller; The controller is used to control the first switch unit and the second switch unit according to the current information, the voltage information of the two input terminals of the AC-DC module and the voltage information of the output voltage.

4. The power factor improvement circuit according to claim 3, characterized in that: The controller synchronizes the phases of the voltages at the two input terminals of the AC-DC converter with the input current through PI control, and the input current is the input current of the AC-DC converter.

5. The power factor improvement circuit according to claim 3, characterized in that: The AC-to-DC module is a full-bridge rectifier circuit including four diodes.

6. The power factor improvement circuit according to claim 1, characterized in that: The first switch unit comprises a first switch device (SW1) and a first drive circuit; a first end of the first switch device (SW1) is connected to a first end of the first unidirectional conduction unit, and a second end of the first switch device (SW1) is used to connect to a first pole of a DC power supply; the controller controls the conduction or cutoff of the first switch device (SW1) through the first drive circuit; The second switch unit comprises a second switch device (SW2) and a second drive circuit; a first end of the second switch device (SW2) is connected to a second end of the first inductor branch, and a second end of the second switch device (SW2) is connected to a second end of the first unidirectional conduction unit; the controller controls the conduction or cutoff of the second switch device (SW2) through the second drive circuit.

7. The power factor improvement circuit according to claim 1, characterized in that: The first unidirectional conductive unit and the second unidirectional conductive unit both include diodes; The second end of the first unidirectional conductive unit is a cathode and connected to the negative electrode of the DC power supply, the first end of the second unidirectional conductive unit is an anode and the second end of the second unidirectional conductive unit is the positive electrode of the output voltage.

8. A power factor improvement circuit, characterized in that: It includes a controller, a boost module and a buck module; The boost module is used to input a DC voltage and output a first voltage to the buck module, and the buck module is used to obtain a second voltage according to the first voltage; the second voltage is less than or equal to the first voltage; The controller is used to control the boost module and the buck module using the same PWM signal in a first voltage output state; and to keep the buck module turned on continuously and control the boost module through the PWM signal in a second voltage output state.

9. The power factor improvement circuit according to claim 8, characterized in that: The boost module includes a first inductor, a first switch unit, a first unidirectional conduction unit and a first capacitor; The first end of the first inductor is used to connect to the first pole of the DC power supply, the second end of the first inductor is connected to the first end of the first switch unit and the first end of the first unidirectional conduction unit, and the second end of the first switch unit is used to connect to the second pole of the DC power supply; the second end of the first unidirectional conduction unit is connected to the first end of the first capacitor, and the second end of the first capacitor is connected to the second end of the first switch unit; A voltage between the first end of the first capacitor and the second end of the first capacitor is the first voltage; The step-down module includes a second switch unit, a second inductor, a second unidirectional conductive unit and a second capacitor; A first end of the second switch unit is connected to a first end of the first capacitor, a second end of the second switch unit is connected to a first end of the second inductor and a first end of the second unidirectional conduction unit, and a second end of the second unidirectional conduction unit is connected to a second end of the first capacitor; a second end of the second inductor is connected to a first end of the second capacitor, and a second end of the second capacitor is connected to a second end of the second unidirectional conduction unit; A voltage between the first end of the second capacitor and the second end of the second capacitor is the second voltage; The controller is used to control the first switch unit and the second switch unit using the same PWM signal in a first voltage output state; and to keep the second switch unit turned on continuously and control the first switch unit through the PWM signal in a second voltage output state.

10. The power factor improvement circuit according to claim 9, characterized in that: The DC power supply includes a full-bridge rectifier circuit; a first voltage detection module is provided at the input end of the full-bridge rectifier circuit; a third voltage detection module is provided between the first end of the first capacitor and the second end of the first capacitor; a second voltage detection module is provided between the first end of the second capacitor and the second end of the second capacitor; and a current detection module is connected in series with the first switch unit; The controller controls the first voltage and the second voltage respectively according to the voltage information of the first voltage detection module, the voltage information of the second voltage detection module and the current information of the current detection module, obtains two power supplies of the first voltage and the second voltage, and provides the two power supplies to loads with two voltage requirements.

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