Bridgeless PFC device and switching power supply

Abstract

The invention discloses a bridgeless PFC (Power Factor Correction) device and a switching power supply. The bridgeless PFC device comprises a bridgeless PFC circuit, a bus capacitor and a surge suppression circuit, the surge suppression circuit comprises a diode D1, a diode D2, a diode D5, a diode D6, a capacitor C1 and a voltage reduction module; the first input port of the bridgeless PFC circuit, the anode of the diode D1 and the cathode of the diode D2 are connected with the first end of the bridgeless PFC device; the second input port of the bridgeless PFC circuit and the anode of the diode D5 are connected with the second end of the bridgeless PFC device; a first output port of the bridgeless PFC circuit is connected with a cathode of a diode D1, an anode of a diode D6, an output port of the step-down module and one end of a bus capacitor C2; the cathode of the diode D5 is connected with the anode of the diode D6, one end of the capacitor C1 and the input port of the step-down module; the second output port of the bridgeless PFC circuit, the anode of the diode D2, the other end of the capacitor C1, the grounding port of the voltage reduction module and the other end of the bus capacitor C2 are connected with the grounding end of the bridgeless PFC device. According to the invention, the surge current of AC-DC input can be suppressed.

Description

Technical Field

[0001] The present invention belongs to the technical field of power supply, and in particular relates to a bridgeless PFC device and a switching power supply. Background Art

[0002] In order to solve the problems of harmonic pollution and energy waste in the power grid, power factor correction (PFC) circuits are becoming more and more widely used. Bridgeless PFC circuits are receiving more and more attention due to their high efficiency.

[0003] When the PFC circuit starts, the input voltage value is uncertain and the initial voltage on the output filter capacitor is zero, which may cause the output filter capacitor to generate a large input surge current at the moment of charging. The surge current will cause the performance of the power semiconductor device to decay or even damage, reduce the reliability of the converter, and at the same time, cause a great impact on the power supply system.

[0004] The existing solution is usually to insert a thermistor in series in the loop and use a relay to bypass the thermistor after the startup is completed. However, this will increase the size of the power supply equipment and is not conducive to the development of the power supply equipment towards miniaturization and high power density.

[0005] China, with publication number CN111342436B, proposed to suppress surge current by controlling the turn-on time of the thyristor. However, if the input voltage is a DC voltage, the thyristor cannot be naturally turned off when the current passes through zero, so the surge current cannot be suppressed by controlling the turn-on time of the thyristor starting phase.

[0006] Therefore, there is an urgent need for a bridgeless PFC device that can satisfy both AC input surge current suppression and DC input surge current suppression. Summary of the invention

[0007] In view of this, the technical problem to be solved by the present invention is to overcome at least one defect of the above-mentioned prior art, and provide a bridgeless PFC device and a switching power supply, which can achieve AC and DC input surge current suppression without adding thermistors and relays, and can reduce the size of the power supply equipment.

[0008] As a first aspect of the present invention, the technical solution of the embodiment of the bridgeless PFC device provided is as follows: A bridgeless PFC device, comprising: a first terminal for inputting a DC negative voltage or an AC L-line voltage, a second terminal for inputting a DC positive voltage or an AC N-line voltage, a ground terminal, a bridgeless PFC circuit, a bus capacitor and a surge suppression circuit; the surge suppression circuit comprises: a diode D1, a diode D2, a diode D5, a diode D6, a capacitor C1 and a step-down module; the first input port of the bridgeless PFC circuit, the anode of the diode D1 and the cathode of the diode D2 are connected together and used to connect to the first end of the bridgeless PFC device; the second input port of the bridgeless PFC circuit and the anode of the diode D5 are connected at After being connected together, they are used to connect the second end of the bridgeless PFC device; the first output port of the bridgeless PFC circuit is simultaneously connected to the cathode of the diode D1, the anode of the diode D6, the output port of the buck module and one end of the bus capacitor C2; the cathode of the diode D5 is simultaneously connected to the anode of the diode D6, one end of the capacitor C1 and the input port of the buck module; the second output port of the bridgeless PFC circuit, the anode of the diode D2, the other end of the capacitor C1, the ground port of the buck module and the other end of the bus capacitor C2 are connected together and are used to connect the ground end of the bridgeless PFC device; Wherein: the two switch tubes in the power frequency bridge arm of the bridgeless PFC circuit are thyristors. When the bridgeless PFC device is working, after the auxiliary power supply is started, the bridgeless PFC device is first controlled not to work, and the corresponding control strategy is selected according to the current working condition to suppress the surge current: When a positive half-cycle AC signal is input to the first input port and the second input port of the bridgeless PFC circuit, a first control strategy is selected to form a charging circuit by pulse controlling the thyristor in the power frequency bridge arm, so as to slowly charge the voltage of the bus capacitor C2 to be equal to the peak value of the input voltage; When a DC signal is input to the first input port and the second input port of the bridgeless PFC circuit, a second control strategy is selected to control the step-down module so as to slowly charge the voltage of the bus capacitor C2 to be equal to the input voltage; When a negative half-cycle AC signal is input to the first input port and the second input port of the bridgeless PFC circuit, any one of the first control strategy or the second control strategy is selected to slowly charge the voltage of the bus capacitor C2 to be equal to the peak value of the input voltage.

[0009] Preferably, the bridgeless PFC circuit comprises a PFC inductor L1, a high-frequency bridge arm and the power frequency bridge arm, one end of the PFC inductor L1 is a first input port of the bridgeless PFC circuit, the other end of the PFC inductor L1 is connected to the midpoint of the high-frequency bridge arm, the midpoint of the power frequency bridge arm is a second input port of the bridgeless PFC circuit, one end of the high-frequency bridge arm and one end of the power frequency bridge arm are connected together to form a first output port of the bridgeless PFC circuit, and the other end of the high-frequency bridge arm and the other end of the power frequency bridge arm are connected together to form a second output port of the bridgeless PFC circuit.

[0010] Further, when a positive half-cycle AC signal is input to the first input port and the second input port of the bridgeless PFC circuit, the thyristor connected between the first output port of the PFC circuit and the midpoint of the power frequency bridge arm is pulse controlled in the first control strategy; When a negative half-cycle AC signal is input to the first input port and the second input port of the bridgeless PFC circuit, the thyristor connected between the second output port of the PFC circuit and the midpoint of the power frequency bridge arm is pulse controlled in the first control strategy.

[0011] Furthermore, when an AC signal is input to the first input port and the second input port of the bridgeless PFC circuit, a driving pulse is sent to the corresponding thyristor only when the absolute value of the AC signal is in a falling region in each control cycle, thereby ensuring that the corresponding thyristor is turned off at the zero-crossing moment.

[0012] Preferably, the step-down module includes a switch tube Q3, a freewheeling diode D8, and a Buck inductor L2, the drain of the switch tube Q3 is the input port of the step-down module, the source of the switch tube Q3 is simultaneously connected to the cathode of the freewheeling diode D8 and one end of the Buck inductor L2, the other end of the Buck inductor L2 is the output port of the step-down module, and the anode of the freewheeling diode D8 is the ground port of the step-down module.

[0013] Preferably, the switch tube Q3 is a MOS tube.

[0014] Furthermore, in the second control strategy, the driving pulse width of the switch tube Q3 is controlled to gradually increase, so that the voltage of the bus capacitor C2 is slowly charged to be equal to the peak value of the input voltage.

[0015] As a second aspect of the present invention, the technical solution of the embodiment of the switching power supply provided is as follows: A switching power supply, comprising: a bridgeless PFC device as described in any one of the first aspects above.

[0016] The beneficial effects of the present invention are: (1) In the bridgeless PFC device of the embodiment of the present invention, the power frequency bridge arm of the bridgeless PFC circuit is two thyristors. When the bridgeless PFC device is working, after the auxiliary power supply is started, the bridgeless PFC device is first controlled not to work, and a corresponding control strategy is selected according to the current working condition to suppress the surge current, thereby effectively suppressing both the AC input surge current and the DC input surge current; (2) The embodiment of the present invention adopts a bridgeless PFC device, which eliminates the relay to improve efficiency and eliminates the thermistor to enable normal startup at a lower temperature. Therefore, it is more efficient than the traditional solution, has a wider temperature range and better stability; (3) The bridgeless PFC device used in the embodiment of the present invention eliminates the need for relays and thermistors, and is therefore smaller in size than conventional solutions, making it easier to mount and integrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the waveform diagram of AC input voltage; Figure 2 is a principle block diagram of a bridgeless PFC device according to a first embodiment of the present invention; Figure 3 Based on Figure 2 A specific circuit diagram of a block diagram; Figure 4 for Figure 3 Control timing diagram of the circuit when AC input; Figure 5 for Figure 3 Schematic diagram of the current loop of the circuit at DC input. DETAILED DESCRIPTION

[0018] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0019] In order to enable those skilled in the art to better understand the solution of the present application, 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. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0020] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application are described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, the process, method, system, product or equipment comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0021] It should be understood that, in the specification, claims and drawings, when a step is described as being connected to another step, the step may be directly connected to the other step, or be connected to the other step through a third step; when an element / unit is described as being "connected" to another element / unit, the element / unit may be "directly connected" to the other element / unit, or be "connected" to the other element / unit through a third element / unit.

[0022] In addition, the drawings of the present disclosure are only schematic diagrams of the present disclosure and are not necessarily drawn to scale. The same symbols in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented using software, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontrollers.

[0023] Figure 1 is a waveform diagram of the AC input voltage, and the thyristor control strategy in the AC circuit can be: obtain the input AC voltage absolute value decreasing interval according to the input AC voltage waveform diagram, and send a turn-on signal to the thyristor in the input AC voltage absolute value decreasing interval (such as Ts / 4~Ts / 2 interval and 3 / 4Ts~Ts interval, where Ts represents one power frequency cycle), and send a turn-off signal to the thyristor in the input AC voltage absolute value rising interval.

[0024] There are two thyristors in the industrial frequency bridge arm of the bridgeless PFC circuit of the present invention. When the bridgeless PFC device is working, after the auxiliary power supply is started, the bridgeless PFC device is first controlled not to work, and a corresponding control strategy is selected according to the current working conditions to suppress the surge current, thereby effectively suppressing both the AC input surge current and the DC input surge current.

[0025] First embodiment Figure 2It is a principle block diagram of a bridgeless PFC device according to a first embodiment of the present invention, including a diode D1, a diode D2, a bridgeless PFC circuit, a diode D5, a diode D6, a capacitor C1, a bus capacitor C2, and a buck module.

[0026] The terminal L (DC-) is electrically connected to the anode of the diode D1, the cathode of the diode D2, and the first input port A of the bridgeless PFC circuit. The cathode of the diode D1 is electrically connected to the first output port C of the bridgeless PFC circuit, the anode of the diode D6, the output port C' of the buck module, and one end of the bus capacitor C2. The cathode of the diode D6 is electrically connected to the cathode of the diode D5, one end of the capacitor C1, and the input port A' of the buck module. The other end of the output capacitor C2 is electrically connected to the reference ground B' of the buck module, the other end of the capacitor C1, the second output port D of the bridgeless PFC circuit, the anode of the diode D2, and the terminal GND. The terminal N (DC+) is electrically connected to the second input port B of the bridgeless PFC circuit and the anode of the diode D5.

[0027] Among them: there are two thyristors in the power frequency bridge arm of the bridgeless PFC circuit. When the bridgeless PFC device is working, after the auxiliary power supply is started, the bridgeless PFC device is first controlled not to work, and the corresponding control strategy is selected according to the current working conditions to suppress the surge current: When a positive half-cycle AC signal is input to the first input port and the second input port of the bridgeless PFC circuit, the first control strategy is selected to form a charging circuit by pulse controlling the thyristor in the power frequency bridge arm, so as to slowly charge the voltage of the bus capacitor C2 to be equal to the peak value of the input voltage; When a DC signal is input to the first input port and the second input port of the bridgeless PFC circuit, the second control strategy is selected to control the buck module so as to slowly charge the voltage of the bus capacitor C2 to be equal to the input voltage; When a negative half-cycle AC signal is input to the first input port and the second input port of the bridgeless PFC circuit, any one of the first control strategy or the second control strategy is selected to slowly charge the voltage of the bus capacitor C2 to be equal to the peak value of the input voltage.

[0028] Figure 3 Based on Figure 2 A specific circuit diagram of the principle block diagram, the bridgeless PFC circuit includes a PFC inductor L1, a switch tube Q1, a switch tube Q2, a thyristor X1, and a thyristor X2; the step-down module is a Buck circuit, including a switch tube Q3, a freewheeling diode D8 and a Buck inductor L2.

[0029] The terminal L (DC-) is electrically connected to the anode of the diode D1, the cathode of the diode D2, and one end of the PFC inductor L1. The other end of the PFC inductor L1 is electrically connected to the source of the switch tube Q1 and the drain of the switch tube Q2. The terminal N (DC+) is electrically connected to the anode of the thyristor X1, the cathode of the thyristor X2, and the anode of the diode D5. The cathode of the diode D5 is electrically connected to the cathode of the diode D6, one end of the capacitor C1, and the drain of the switch tube Q3. The source of the switch tube Q3 is electrically connected to the cathode of the freewheeling diode D8 and one end of the Buck inductor L2. The cathode of the diode D1 is electrically connected to the drain of the switch tube Q1, the cathode of the thyristor X1, the anode of the diode D6, the other end of the Buck inductor L2, and one end of the bus capacitor C2. The other end of the bus capacitor C2 is electrically connected to the anode of the freewheeling diode D8, the other end of the capacitor C1, the anode of the thyristor X2, the source of the switch tube Q2, the anode of the diode D2, and the terminal GND.

[0030] Figure 3 The working process of the bridgeless PFC device when applied to the switching power supply is divided into four stages, as follows: The first stage is the auxiliary power startup stage. During this stage, the digital control circuit ( Figure 3 This circuit is omitted in the circuit), the bridgeless PFC circuit and the Buck circuit do not work. When the input voltage reaches a certain threshold, the auxiliary voltage works normally; The second stage is the surge current suppression area. In this stage, the bridgeless PFC circuit does not work. At this time, the digital control circuit controls the driving signal of the thyristor or Buck circuit to buffer the voltage of the output capacitor C2 to be equal to the input voltage, thereby achieving the surge current suppression effect. The third stage is the bridgeless PFC circuit startup zone, during which the bridgeless PFC circuit begins soft start; The fourth stage is the working area of ​​the bridgeless PFC circuit, during which the bridgeless PFC circuit works normally.

[0031] When an AC signal is input in the above-mentioned second stage, the pulse control of the thyristor can be realized through the digital control circuit, and the voltage of the output capacitor C2 can be slowly charged to be equal to the peak value of the input voltage, thereby realizing the effect of the AC surge suppression circuit; when a DC signal is input, the switch tube Q3 of the Bcuk circuit can be controlled by the digital control circuit, and the voltage of the output capacitor C2 can be slowly charged to be equal to the input voltage, thereby realizing the effect of the DC surge suppression circuit.

[0032] Figure 4 for Figure 3 The circuit works when the positive half-cycle voltage of AC is input. The first control strategy is used to suppress the surge current. The thyristor in the power frequency bridge arm is controlled. For details, please refer to Figure 4, where Vin represents the input voltage waveform, Vgs represents the pulse drive signal of the thyristor, Uo represents the voltage on the output capacitor C2, i rush It represents the input surge current. At the initial moment, the bridgeless PFC circuit and the Buck circuit do not work (the switch tubes Q1, Q2, and Q3 are turned off, and the thyristors X1 and X2 are cut off). In order to suppress the surge current, after the auxiliary power supply starts working, the input AC voltage and the output voltage are detected, and the voltage difference between the input voltage and the output voltage is calculated. The input AC voltage can be divided into an absolute value rising interval and an absolute value falling interval. Under the action of the digital control circuit, the thyristor X2 is pulsed on for a time period of T1 in the absolute value falling interval of the input AC voltage. At this time, the thyristor X2 is turned on, and the output capacitor C2 is charged. The charging current path is terminal L (DC-) → diode D1 → output capacitor C2 → thyristor X2 → terminal N (DC+). The voltage of the output capacitor C2 gradually increases, and at the same time, the input voltage gradually decreases. When the voltage of the output capacitor C2 is higher than the input voltage, that is, the cathode voltage of the thyristor X2 is greater than the anode voltage, the thyristor is cut off, and the charging circuit of the output capacitor C2 is disconnected and charged. The single charging is completed. At this time, the voltage of the output capacitor C2 is U1. Among them, the smaller the voltage difference between the input voltage and the output voltage, the smaller the conduction phase difference of the thyristor, the smaller the surge current, and the longer the time required for the output capacitor to be pre-charged to the same level as the input voltage peak, so that the startup time can be controlled to meet different application requirements.

[0033] When the input AC negative cycle is used, the first control strategy is also used to suppress the surge current. Since the AC input is symmetrical, the thyristor controlled at this time is X1. Specifically, the thyristor X1 is pulsed on for a duration of T2 in the absolute value drop interval of the input AC voltage. At this time, the thyristor X1 is turned on, and the output capacitor C2 is charged. The charging current path is terminal N (DC+) → thyristor X1 → output capacitor C2 → diode D2 → terminal L (DC-). The voltage of the output capacitor C2 gradually increases, and at the same time, the absolute value of the input voltage gradually decreases. When the cathode voltage of the thyristor X1 is greater than the anode voltage, the thyristor is turned off, and the charging circuit of the output capacitor C2 is disconnected and charged. The single charge is completed. At this time, the voltage of the output capacitor C2 is U2, and U2>U1. The absolute value of the input AC voltage corresponding to the thyristor turn-on moment increases successively with the order of the turn-on time points, so that the voltage of the output capacitor C2 can gradually increase to the maximum amplitude of the input AC voltage.

[0034] Figure 5 for Figure 3 The circuit is a schematic diagram of the current loop of the DC input. The second control strategy is used to suppress the surge current. The control is for the step-down module. For details, please refer to Figure 5, where L (DC-) is the negative input terminal of the DC, and L (DC+) is the positive input terminal of the DC. At the initial moment, the bridgeless PFC circuit and the Buck circuit do not work (switch tubes Q1, Q2, and Q3 are turned off, thyristors X1 and X2 are turned off, diode D5 is turned on, diode D6 is turned off, and diode D2 is turned on). To suppress the startup surge current, the current charges capacitor C1 through diodes D5 and D2. After the auxiliary power supply starts working, the digital control circuit controls the driving pulse width of the switch tube Q3. When the switch tube Q3 is turned on, the voltage on capacitor C1 excites the Buck inductor L2 and charges the output capacitor C2. When the switch tube Q3 is turned off, the freewheeling tube D8 is turned on, and the Buck inductor L2 charges the output capacitor C2. As the driving pulse width of the switch tube Q3 increases, the voltage of the output capacitor C2 gradually increases, and finally equals the input voltage, achieving the startup DC input surge suppression effect. The longer the driving pulse width of the switch tube Q3 gradually increases, the better the DC input surge suppression effect is.

[0035] It should be noted that Figure 3 The circuit can also be used in the negative half cycle of the input AC Figure 5 The current loop in the output capacitor C2 buffers the voltage to be equal to the input voltage, thereby achieving the inrush current suppression effect. At this time, the second control strategy is used to suppress the inrush current, and the step-down module is controlled.

[0036] The bridgeless PFC device of the present invention can effectively suppress AC and DC input surge currents, has a controllable startup time, and can meet different application requirements. It is more efficient than traditional solutions, has a wider and more stable temperature range, and is smaller in size than traditional solutions, making it easier to mount and integrate.

[0037] Second embodiment This embodiment provides a switching power supply, which includes any bridgeless PFC device in the first embodiment.

[0038] A switching power supply of this embodiment includes any one of the bridgeless PFC devices in the first embodiment, and can achieve AC and DC input surge current suppression without adding thermistors and relays, thereby reducing the size of the switching power supply equipment.

[0039] The description of the above embodiments is only used to help understand the inventive concept of the present invention and is not intended to limit the present invention. For ordinary technicians in this technical field, any modifications, equivalent substitutions, improvements, etc. made without departing from the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A bridgeless PFC device, characterized in that: It includes a first terminal for inputting a DC negative voltage or an AC L-line voltage, a second terminal for inputting a DC positive voltage or an AC N-line voltage, a ground terminal, a bridgeless PFC circuit, a bus capacitor and a surge suppression circuit; The surge suppression circuit includes: a diode D1, a diode D2, a diode D5, a diode D6, a capacitor C1 and a buck module; the first input port of the bridgeless PFC circuit, the anode of the diode D1 and the cathode of the diode D2 are connected together to connect the first end of the bridgeless PFC device; the second input port of the bridgeless PFC circuit and the anode of the diode D5 are connected together to connect the second end of the bridgeless PFC device; the first output port of the bridgeless PFC circuit is simultaneously connected to the cathode of the diode D1, the anode of the diode D6, the output port of the buck module and one end of the bus capacitor C2; the cathode of the diode D5 is simultaneously connected to the anode of the diode D6, one end of the capacitor C1 and the input port of the buck module; the second output port of the bridgeless PFC circuit, the anode of the diode D2, the other end of the capacitor C1, the ground port of the buck module and the other end of the bus capacitor C2 are connected together to connect the ground end of the bridgeless PFC device; Wherein: the two switch tubes in the power frequency bridge arm of the bridgeless PFC circuit are thyristors. When the bridgeless PFC device is working, after the auxiliary power supply is started, the bridgeless PFC device is first controlled not to work, and the corresponding control strategy is selected according to the current working condition to suppress the surge current: When a positive half-cycle AC signal is input to the first input port and the second input port of the bridgeless PFC circuit, a first control strategy is selected to form a charging circuit by pulse controlling the thyristor in the power frequency bridge arm, so as to slowly charge the voltage of the bus capacitor C2 to be equal to the peak value of the input voltage; When a DC signal is input to the first input port and the second input port of the bridgeless PFC circuit, a second control strategy is selected to control the step-down module so as to slowly charge the voltage of the bus capacitor C2 to be equal to the input voltage; When a negative half-cycle AC signal is input to the first input port and the second input port of the bridgeless PFC circuit, any one of the first control strategy or the second control strategy is selected to slowly charge the voltage of the bus capacitor C2 to be equal to the peak value of the input voltage.

2. The bridgeless PFC device according to claim 1, characterized in that: The bridgeless PFC circuit includes a PFC inductor L1, a high-frequency bridge arm and the power frequency bridge arm, one end of the PFC inductor L1 is a first input port of the bridgeless PFC circuit, the other end of the PFC inductor L1 is connected to the midpoint of the high-frequency bridge arm, the midpoint of the power frequency bridge arm is a second input port of the bridgeless PFC circuit, one end of the high-frequency bridge arm and one end of the power frequency bridge arm are connected together to form a first output port of the bridgeless PFC circuit, and the other end of the high-frequency bridge arm and the other end of the power frequency bridge arm are connected together to form a second output port of the bridgeless PFC circuit.

3. The bridgeless PFC device according to claim 2, characterized in that: When a positive half-cycle AC signal is input to the first input port and the second input port of the bridgeless PFC circuit, the thyristor connected between the first output port of the PFC circuit and the midpoint of the power frequency bridge arm is pulse controlled in the first control strategy; When a negative half-cycle AC signal is input to the first input port and the second input port of the bridgeless PFC circuit, the thyristor connected between the second output port of the PFC circuit and the midpoint of the power frequency bridge arm is pulse controlled in the first control strategy.

4. The bridgeless PFC device according to claim 3, characterized in that: When an AC signal is input to the first input port and the second input port of the bridgeless PFC circuit, a driving pulse is sent to the corresponding thyristor only when the absolute value of the AC signal is in a falling region in each control cycle, thereby ensuring that the corresponding thyristor is turned off at the zero-crossing moment.

5. The bridgeless PFC device according to claim 1, characterized in that: The buck module includes a switch tube Q3, a freewheeling diode D8, and a Buck inductor L2. The drain of the switch tube Q3 is the input port of the buck module, the source of the switch tube Q3 is simultaneously connected to the cathode of the freewheeling diode D8 and one end of the Buck inductor L2, the other end of the Buck inductor L2 is the output port of the buck module, and the anode of the freewheeling diode D8 is the ground port of the buck module.

6. The bridgeless PFC device according to claim 5, characterized in that: The switch tube Q3 is a MOS tube.

7. The bridgeless PFC device according to claim 5, characterized in that: In the second control strategy, the driving pulse width of the switch tube Q3 is controlled to gradually increase, so that the voltage of the bus capacitor C2 is slowly charged to be equal to the peak value of the input voltage.

8. A switching power supply, characterized in that: The bridgeless PFC device comprises the bridgeless PFC device according to any one of claims 1 to 7.

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