Switching power supply applying PFC circuit and control method thereof

Abstract

The invention provides a switching power supply applying a PFC circuit and a control method of the switching power supply. The switching power supply comprises the PFC circuit and an AHB converter which are cascaded, and a PFC controller and an AHB controller which respectively control the working state of the PFC circuit and the working state of the AHB converter, sampling the bus voltage to obtain a first sampling voltage representing the bus voltage, and sampling the output voltage to obtain a second sampling voltage representing the output voltage; and controlling the size of the bus voltage according to the first sampling voltage and the second sampling voltage, so that the ratio of the bus voltage to the output voltage reaches a preset ratio. According to the invention, the bus voltage can be adaptively adjusted so as to optimize the system efficiency and the standby power consumption.

Description

Technical Field

[0001] The present invention relates to the field of lighting, and in particular to a switching power supply using a PFC circuit and a control method thereof. Background Art

[0002] In AC-DC applications with input power greater than 75W, the input current harmonics must meet the Class D requirements of IEC 61000-3-2, and the input of the AC-DC converter needs to have a PFC circuit. The most commonly used PFC circuit in the industry is the boost converter.

[0003] Usually, in order to meet the light load efficiency requirements, the PFC circuit will be turned off under light load. Figure 1 The example of a switching power supply with a PFC circuit cascaded with an AHB converter is shown in the figure. The PFC enable signal is transmitted by an optocoupler to adjust the PFC enable / disable. However, this solution has two disadvantages:

[0004] 1. Increased system cost and number of peripheral devices;

[0005] 2. The output voltage of the PFC circuit cannot be adjusted according to the output voltage and load status, and the PFC circuit can only be enabled or disabled. For example, in a fast charging application, under a 9V output, if the input voltage range of the subsequent DC-DC converter is designed to be narrower, a boost circuit must be used to increase the voltage under low voltage input to meet the input voltage requirements of the subsequent converter. If the PFC circuit has a fixed voltage output, the overall efficiency is not high. Summary of the invention

[0006] The purpose of the present invention is to provide a high-efficiency switching power supply using a PFC circuit and a control method thereof, which can adaptively adjust the bus voltage by feeding back the bus voltage, thereby optimizing system efficiency and standby power consumption.

[0007] The present invention also provides a switching power supply using a PFC circuit, which rectifies an AC voltage to obtain an input voltage, and converts the input voltage to obtain an output voltage, comprising:

[0008] A cascaded PFC circuit and an AHB converter, wherein the PFC circuit converts the input voltage to obtain a bus voltage, and the AHB converter converts the bus voltage to obtain the output voltage; and

[0009] A PFC controller, which performs error amplification on an output feedback voltage of the PFC circuit and a reference voltage to control a switching state of a switch tube in the preceding PFC circuit;

[0010] An AHB controller, used to control the switching state of the switch tube in the AHB converter;

[0011] A sampling circuit, sampling the bus voltage to obtain a first sampling voltage representing the bus voltage, and sampling the output voltage to obtain a second sampling voltage representing the output voltage;

[0012] The magnitude of the bus voltage is adjusted according to the first sampling voltage and the second sampling voltage so that the ratio of the bus voltage to the output voltage reaches a preset ratio.

[0013] Optionally, the AHB controller extracts / injects a first current from an output feedback terminal of the PFC circuit, and the AHB controller controls the magnitude of the first current according to the first sampling voltage and the second sampling voltage to control the magnitude of the bus voltage.

[0014] Optionally, the AHB controller compares the product of the first sampling voltage and the second sampling voltage with a set value, and when the first sampling voltage is greater than the product, the AHB controller controls the first current extracted to decrease or the first current injected to increase; when the first sampling voltage is less than the product, the AHB controller controls the first current extracted to increase or the first current injected to decrease.

[0015] Optionally, the AHB controller includes a first current regulation circuit, including a first operational amplifier and a first adjustment tube, the non-inverting input terminal of the first operational amplifier receives the product of the second sampling voltage and a set value, the inverting input terminal of the first operational amplifier receives the first sampling voltage, the output terminal of the first operational amplifier is connected to the control terminal of the first adjustment tube, the first adjustment tube is connected to the output feedback terminal of the PFC circuit, and the current flowing through the first adjustment tube is the extracted first current.

[0016] Optionally, the PFC controller controls the magnitude of the reference voltage according to the first sampling voltage and the second sampling voltage to control the magnitude of the bus voltage.

[0017] Optionally, the PFC controller compares the product of the first sampling voltage and the second sampling voltage with a set value, and when the first sampling voltage is greater than the product, the PFC controller controls the reference voltage to decrease; when the first sampling voltage is less than the product, the PFC controller controls the reference voltage to increase.

[0018] Optionally, the PFC controller includes a reference voltage regulation circuit, including a second operational amplifier, a second adjustment tube and a first resistor, the non-inverting input terminal of the second operational amplifier receives the product of the second sampling voltage and a set value, the inverting input terminal of the second operational amplifier receives the first sampling voltage, the output terminal of the second operational amplifier is connected to the control terminal of the second adjustment tube, the second adjustment tube and the first resistor are connected in series, and the adjusted reference voltage is obtained according to the voltage on the first resistor.

[0019] Optionally, the AHB converter includes:

[0020] A transformer having a primary winding, a secondary winding and an auxiliary winding;

[0021] The first switch tube and the second switch tube are connected between the input terminal and the reference ground;

[0022] The first inductor and the first capacitor are connected with the primary winding and the second switch tube to form a resonant circuit.

[0023] Optionally, when the first switch tube is turned on, the sampling circuit samples the voltage on the auxiliary winding to obtain the first sampling voltage; when the second switch tube is turned on, the sampling circuit samples the voltage on the auxiliary winding to obtain the second sampling voltage.

[0024] Optionally, the sampling circuit performs voltage-dividing sampling on the bus voltage to obtain the first sampling voltage, the sampling circuit performs voltage-dividing sampling on the output voltage to obtain the second sampling voltage, or the sampling circuit performs voltage-dividing sampling on the voltage on the first capacitor to obtain the second sampling voltage.

[0025] The present invention also provides a control method for a switching power supply using a PFC circuit, wherein an AC voltage is rectified to obtain an input voltage, and the input voltage is converted to obtain an output voltage, comprising a PFC circuit and an AHB converter connected in cascade, and a PFC controller for controlling the working state of the PFC circuit and an AHB controller for controlling the working state of the AHB converter, wherein the PFC circuit converts the input voltage into a bus voltage, and the AHB converter converts the bus voltage into an output voltage;

[0026] Amplifying the error between the output feedback voltage of the PFC circuit and the reference voltage to control the switch state of the main power tube in the previous stage PFC circuit;

[0027] Sampling the bus voltage to obtain a first sampled voltage representing the bus voltage, and sampling the output voltage to obtain a second sampled voltage representing the output voltage;

[0028] The magnitude of the bus voltage is adjusted according to the first sampling voltage and the second sampling voltage so that the ratio of the bus voltage to the output voltage reaches a preset ratio.

[0029] Optionally, a first current is extracted / injected from an output feedback terminal of the PFC circuit, and a magnitude of the first current is adjusted according to the first sampling voltage and the second sampling voltage to control a magnitude of the bus voltage.

[0030] Optionally, the product of the first sampling voltage and the second sampling voltage and a set value is compared; when the first sampling voltage is greater than the product, the first current extracted is controlled to decrease or the first current injected is controlled to increase; when the first sampling voltage is less than the product, the first current extracted is controlled to increase or the first current injected is controlled to decrease.

[0031] Optionally, the reference voltage is controlled according to the first sampling voltage and the second sampling voltage to control the bus voltage.

[0032] Optionally, the product of the first sampling voltage and the second sampling voltage and a set value is compared, and when the first sampling voltage is greater than the product, the reference voltage is controlled to decrease; when the first sampling voltage is less than the product, the reference voltage is controlled to increase.

[0033] Compared with the prior art, the present invention has the following advantages: the bus voltage output by the front-stage PFC circuit can be adaptively feedback-regulated by sampling the bus voltage and the output voltage, the regulation method is flexible, and the regulation function of the present invention can be realized in the back-stage AHB converter without the need for an optocoupler and an additional discrete circuit, thereby optimizing the system efficiency and standby power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The schematic diagram of the existing switching power supply;

[0035] Figure 2 It is the principle diagram of the switching power supply of the present invention;

[0036] Figure 3 This is a flow chart of bus voltage regulation of the present invention;

[0037] Figure 4 A schematic diagram of an embodiment of a regulating circuit;

[0038] Figure 5 is a schematic diagram of another embodiment of a regulating circuit;

[0039] Figure 6 A sampling circuit schematic diagram of the AHB converter of the present invention;

[0040] Figure 7 This is the waveform diagram of the AHB converter of the present invention;

[0041] Figure 8 Another sampling circuit schematic diagram of the AHB converter of the present invention. DETAILED DESCRIPTION

[0042] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made on the spirit and range of the present invention.

[0043] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0044] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportions, in order to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0045] like Figure 2As shown, the schematic diagram of the switching power supply circuit of the present invention is illustrated, including a cascaded EMI filter circuit and a rectifier circuit. The rectifier circuit in the figure is implemented by a rectifier bridge to filter and rectify the AC input voltage AC to obtain the rectified input voltage Vin. The switching power supply also includes a cascaded PFC circuit and an AHB converter, the PFC circuit and the AHB converter are cascaded as a front-stage converter and a rear-stage converter respectively, the PFC circuit converts the rectified input voltage Vin into a bus voltage Vbus, and the harmonics of the input current can be optimized by enabling the PFC circuit. The AHB converter converts the bus voltage into an output voltage Vo to meet the output demand. The PFC circuit generally uses a boost circuit to implement the PFC function, including an inductor L0, a switch tube Q0 and a rectifier tube D0. The inductor L0 is connected between the output end of the rectifier circuit and the connection end of the power tube and the rectifier tube to convert the input voltage into the required bus voltage. When the PFC circuit is enabled, the switch tube Q0 is normally turned on and off, and when the PFC is not enabled, the switch tube Q0 remains off. The AHB converter includes a transformer T1, a first switch tube Q1 and a second switch tube Q2 connected to each other, and a first inductor L1 and a capacitor C1. The first inductor L1, the capacitor C1, the second switch tube Q2 and the primary winding Np of the transformer T1 are connected to form a resonant circuit, and the secondary winding N of the transformer is connected to the output end. The switching power supply also includes a PFC controller and an AHB controller. The PFC controller performs error amplification according to the output feedback voltage FB and the reference voltage representing the bus voltage to control the switching state of the power tube in the PFC circuit so that the feedback voltage reaches the reference voltage (fixed output). The AHB controller is used to control the switching state of the power tube in the AHB converter to convert the bus voltage into the output voltage. As the output voltage changes, the present invention also controls the bus voltage to follow the output voltage change according to the first sampling voltage representing the bus voltage (which can be the output feedback voltage) and the second sampling voltage representing the output voltage. The advantage of using an AHB converter in the post-stage converter of the switching power supply of the present invention is that, compared with an ordinary flyback converter, the AHB converter can realize leakage inductance energy recovery and utilization, zero-voltage turn-on of the main switch tube and zero-current turn-off of the secondary rectifier tube, thereby reducing switching losses and heat generation, and achieving higher efficiency. The transformer excitation inductance and resonant capacitor (first capacitor) both participate in energy storage, which can reduce the size of the transformer, and the stress of the secondary rectifier tube is lower, which can be suitable for application scenarios with high output voltage. Compared with an LLC converter, the output voltage range of the AHB converter can be wider, and it is easier to achieve uniform efficiency at different voltages in applications such as PD chargers.

[0046] Specifically, Figure 2The output terminal of the PFC circuit in the front stage is connected to the series-connected voltage-dividing resistors Rup and Rdown. The common connection terminal of the voltage-dividing resistors R1 and R2 is the output feedback terminal of the PFC circuit. Then there is formula (1): Vbus = FB * (R1 + R2) / R2. Since the feedback voltage FB is controlled to be equal to the reference voltage and usually the voltage-dividing resistors R1 and R2 are fixed, in one control mode of the present invention, the bus voltage is adjusted by adjusting the magnitude of the reference voltage. In another control mode of the present invention, the AHB controller extracts / imparts a first current IFB from the output feedback terminal of the PFC circuit. When the output feedback terminal extracts current, there is formula (2): Vbus = VFB * (R1 + R2) / R2 + IFB * R1. When the output feedback terminal imparts current, there is formula (3): Vbus = VFB * (R1 + R2) / R2 - IFB * R2. When the reference voltage of the feedback output is fixed, the corresponding feedback voltage VFB is also determined. The bus voltage can also be adjusted by adjusting the magnitude of the first current IFB. The present invention samples the bus voltage and the output voltage. According to the bus voltage feedback and the output voltage feedback, by controlling the magnitude of the reference voltage or the magnitude of the first current, the magnitude of the bus voltage is controlled, so that there is a set relationship between the bus voltage and the output voltage. Preferably, the bus voltage and the output voltage are in proportion with a preset proportionality coefficient. For example, Vbus = k * Vo, where k is the preset proportionality coefficient. Under different output voltages, compared with turning on the PFC circuit to control the bus voltage to a fixed value to be compatible with all output voltages, the present invention enables the PFC circuit to adaptively adjust the bus voltage, thereby ensuring that the AHB converter can work normally. The AHB converter has higher efficiency at different voltages, and at the same time, the efficiency of the PFC stage can also be improved, thus greatly improving the overall efficiency of the machine.

[0047] See Figure 3 , which shows the adjustment flowchart of the bus voltage of the present invention. The first step is to sample the bus voltage to obtain a first sampling voltage VS1 representing the bus voltage and sample the output voltage to obtain a second sampling voltage VS2 representing the output voltage; the second step is to judge whether the first sampling voltage VS1 is greater than K times the second sampling voltage, that is, K * VS2. If VS1 > K * VS2, then enter the third step: control the bus voltage to decrease; if VS1 < K * VS2, then enter the fourth step: control the bus voltage to increase. According to this adjustment process, the bus voltage can finally be equal to a certain multiple of the output voltage. The present invention adjusts the bus voltage by feedback of the bus voltage, so that the bus voltage and the output voltage are in a certain multiple relationship, and the adjustment method is flexible, realizing the adaptive adjustment of the bus voltage. When the peripheral parameters of the PFC circuit / AHB converter change, such as the voltage-dividing resistors of the PFC circuit, the turns ratio of the primary and secondary sides, the feedback reference voltage of the PFC circuit, etc., this adjustment method can also be applied, and the adjustment method is more flexible.

[0048] See Figure 4, a schematic diagram of an embodiment of a regulating circuit is shown, the regulating circuit is located in the AHB controller, and is used to extract / inject a first current IFB at the output feedback end of the PFC circuit. Specifically, it includes an operational amplifier U1 and an adjusting tube M1. Taking the extraction of the first current at the output feedback end of the PFC circuit as an example, the drain of the adjusting tube M1 is connected to the output feedback end of the PFC circuit ( Figure 2 Point A in the middle), the in-phase input terminal of the operational amplifier U1 receives the K times second sampling voltage K*VS2, the inverting input terminal of the operational amplifier U1 receives the first sampling voltage VS1, and the output terminal of the operational amplifier U1 is connected to the gate of the adjustment tube M1. The operational amplifier U1 amplifies the error between K*VS2 and VS1 to drive the adjustment tube M1. Here, the adjustment tube M1 takes an NMOS tube as an example. The larger the difference between K*VS2 and VS1, the larger the gate drive voltage of the adjustment tube M1, and the larger the first current IFB generated on the adjustment tube M1. The first current is drawn from the output feedback terminal of the PFC circuit. The larger the first current, the larger the bus voltage, which in turn makes the difference between K*VS2 and VS1 smaller. Finally, the first current is maintained at a certain value, so that VS1 is close to K*VS2. When the first current is injected into the output feedback end of the PFC circuit, the source of the adjustment tube M1 is connected to the output feedback end of the PFC circuit, and the in-phase input end and the inverting input end of the operational amplifier U1 receive the signals VS1 and K*VS2 respectively, so that the bus voltage can be adjusted by adjusting the first current. Specifically, when VS1 is greater than K*VS2, the first current is increased, and when VS1 is less than K*VS2, the first current is reduced. This adjustment method is simple, and the first current can be adaptively adjusted according to the first sampling voltage representing the bus voltage and the second sampling voltage representing the output voltage, thereby adaptively feedback adjusting the bus voltage, so that the bus voltage can follow the output voltage.

[0049] See also Figure 5, illustrates another embodiment schematic diagram of a regulating circuit, which is located in a PFC controller and is used to regulate the reference voltage of the output feedback of the PFC circuit. Specifically, it includes an op amp U2, an adjusting tube M2 and a resistor RS1. The in-phase input terminal of the op amp U2 receives the K-times second sampling voltage K*VS2, the inverting input terminal of the op amp U2 receives the first sampling voltage VS1, the output terminal of the op amp U2 is connected to the gate of the adjusting tube M2, and the op amp U2 amplifies the error between K*VS2 and VS1 to drive the adjusting tube M2. Here, the adjusting tube M2 takes an NMOS tube as an example. The resistor RS1 is connected between the source of the adjusting tube M2 and the ground terminal, and the voltage on the resistor RS1 is the set reference voltage. The larger the difference between K*VS2 and VS1, the larger the gate driving voltage of the adjusting tube M2, the larger the current generated on the adjusting tube M2, the larger the reference voltage on the resistor RS1, and the larger VS1. Finally, the difference between K*VS2 and VS1 becomes smaller, and finally VS1 is close to K*VS2. The regulation method is simple and can adaptively adjust the bus voltage according to the first sampling voltage and the second sampling voltage, so that the bus voltage can follow the output voltage.

[0050] See also Figure 6 , which illustrates a sampling circuit schematic diagram of the AHB converter of the present invention, wherein the AHB converter includes an auxiliary winding Na, a transformer coupling between the auxiliary winding and the AHB converter, an operating waveform of the AHB converter, and a voltage V on the auxiliary winding AUX The waveform of Figure 7 , when the first switch tube Q1 is turned on and the second switch tube Q2 is turned off, V AUX =Na / Np*Vcr, Na / Np is the turns ratio of the primary winding and the auxiliary winding, Vcr≈nVo, when the first switch tube Q1 is turned off and the second switch tube Q2 is turned on, V AUX =-Na / Np*(Vbus-Vcr). The sampling circuit includes connecting voltage-dividing resistors R1 and R2 in series at both ends of the auxiliary winding, and obtaining a sampling voltage Vs through voltage-dividing sampling. When the first switch tube Q1 is turned on and the second switch tube Q2 is turned on, the sampling acquisition unit in the sampling circuit respectively acquires the sampling voltage Vs to obtain the first sampling voltage VS1 and the second sampling voltage VS2, so as to complete the sampling of the bus voltage Vbus and the output voltage Vo. This sampling method can obtain the information of the input voltage and the output voltage respectively only through the auxiliary winding, and the sampling method is simple.

[0051] refer to Figure 7 , which illustrates the waveform of the AHB converter of the present invention. When the control signal GON of the first switch tube Q1 is high and effective, the first switch tube Q1 is controlled to be turned on, the excitation inductor stores energy, the excitation inductor current iLm rises, and the voltage V on the auxiliary winding AUX = -Na / Np*(Vbus-Vcr), the voltage across the first switch tube V DS_Q1When the control signal GAC of the second switch tube Q2 is high and effective, the second switch tube Q2 is controlled to be turned on, the excitation inductor continues to flow, the excitation inductor current iLm decreases, and the voltage V AUX =Na / Np*Vcr, the voltage across the first switch tube V DS_Q1 It is high level. It can be clearly seen from the waveform that in the conduction phase of the first switch tube and the second switch tube, the voltage of the auxiliary winding can be sampled to obtain the bus voltage information and the output voltage information, and then the first sampling voltage and the second sampling voltage representing the bus voltage and the output voltage can be obtained. The sampling method is simple.

[0052] refer to Figure 8 , illustrates another sampling circuit schematic diagram of the AHB converter of the present invention, including a first sampling unit and a second sampling unit. The first sampling unit obtains a first sampling voltage VS1 by voltage-dividing sampling of the bus voltage Vbus, and the second sampling unit obtains a second sampling voltage VS2 by voltage-dividing sampling of the output voltage Vo. This sampling method is relatively simple, but the first sampling voltage and the second sampling voltage are at both ends of the transformer, and the second sampling voltage needs to be isolated and transmitted to the primary side before it can be used to control the bus voltage. The second sampling unit can also obtain a second sampling voltage representing the output voltage by voltage-dividing sampling of the voltage on the first capacitor C1. Sampling is also relatively easy, and there is no need to isolate and transmit the sampling signal.

[0053] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0054] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A switching power supply using a PFC circuit, wherein an AC voltage is rectified to obtain an input voltage, and the input voltage is converted to obtain an output voltage, wherein: include: A cascaded PFC circuit and an AHB converter, wherein the PFC circuit converts the input voltage to obtain a bus voltage, and the AHB converter converts the bus voltage to obtain the output voltage; as well as, A PFC controller, which performs error amplification on an output feedback voltage of the PFC circuit and a reference voltage to control a switching state of a switch tube in the preceding PFC circuit; An AHB controller, used to control the switching state of the switch tube in the AHB converter; A sampling circuit, sampling the bus voltage to obtain a first sampling voltage representing the bus voltage, and sampling the output voltage to obtain a second sampling voltage representing the output voltage; The magnitude of the bus voltage is adjusted according to the first sampling voltage and the second sampling voltage so that the ratio of the bus voltage to the output voltage reaches a preset ratio.

2. The switching power supply according to claim 1, characterized in that: The AHB controller extracts / injects a first current from an output feedback terminal of the PFC circuit, and controls the magnitude of the first current according to the first sampling voltage and the second sampling voltage to control the magnitude of the bus voltage.

3. The switching power supply according to claim 2, characterized in that: The AHB controller compares the product of the first sampling voltage and the second sampling voltage with a set value. When the first sampling voltage is greater than the product, the AHB controller controls the first current extracted to decrease or the first current injected to increase; when the first sampling voltage is less than the product, the AHB controller controls the first current extracted to increase or the first current injected to decrease.

4. The switching power supply according to claim 3, characterized in that: The AHB controller includes a first current regulation circuit, including a first operational amplifier and a first adjustment tube, wherein the non-inverting input terminal of the first operational amplifier receives the product of the second sampling voltage and a set value, the inverting input terminal of the first operational amplifier receives the first sampling voltage, the output terminal of the first operational amplifier is connected to the control terminal of the first adjustment tube, the first adjustment tube is connected to the output feedback terminal of the PFC circuit, and the current flowing through the first adjustment tube is the extracted first current.

5. The switching power supply according to claim 1, characterized in that: The PFC controller controls the magnitude of the reference voltage according to the first sampling voltage and the second sampling voltage to control the magnitude of the bus voltage.

6. The switching power supply according to claim 5, characterized in that: The PFC controller compares the product of the first sampling voltage and the second sampling voltage with a set value. When the first sampling voltage is greater than the product, the PFC controller controls the reference voltage to decrease; when the first sampling voltage is less than the product, the PFC controller controls the reference voltage to increase.

7. The switching power supply according to claim 6, characterized in that: The PFC controller includes a reference voltage adjustment circuit, including a second operational amplifier, a second adjustment tube and a first resistor, wherein the non-inverting input terminal of the second operational amplifier receives the product of the second sampling voltage and a set value, the inverting input terminal of the second operational amplifier receives the first sampling voltage, the output terminal of the second operational amplifier is connected to the control terminal of the second adjustment tube, the second adjustment tube and the first resistor are connected in series, and the adjusted reference voltage is obtained according to the voltage on the first resistor.

8. The switching power supply according to claim 1, characterized in that: The AHB converter comprises: A transformer having a primary winding, a secondary winding and an auxiliary winding; The first switch tube and the second switch tube are connected between the input terminal and the reference ground; The first inductor and the first capacitor are connected with the primary winding and the second switch tube to form a resonant circuit.

9. The switching power supply according to claim 1, characterized in that: When the first switch tube is turned on, the sampling circuit samples the voltage on the auxiliary winding to obtain the first sampling voltage; when the second switch tube is turned on, the sampling circuit samples the voltage on the auxiliary winding to obtain the second sampling voltage.

10. The switching power supply according to claim 1, characterized in that: The sampling circuit performs voltage division sampling on the bus voltage to obtain the first sampling voltage, the sampling circuit performs voltage division sampling on the output voltage to obtain the second sampling voltage, or the sampling circuit performs voltage division sampling on the voltage on the first capacitor to obtain the second sampling voltage.

11. A control method for a switching power supply using a PFC circuit, wherein an AC voltage is rectified to obtain an input voltage, and the input voltage is converted to obtain an output voltage, comprising a PFC circuit and an AHB converter connected in cascade, and a PFC controller for controlling the working state of the PFC circuit and an AHB controller for controlling the working state of the AHB converter, wherein the PFC circuit converts the input voltage into a bus voltage, and the AHB converter converts the bus voltage into an output voltage, characterized in that: Amplifying the error between the output feedback voltage of the PFC circuit and the reference voltage to control the switch state of the main power tube in the previous stage PFC circuit; Sampling the bus voltage to obtain a first sampled voltage representing the bus voltage, and sampling the output voltage to obtain a second sampled voltage representing the output voltage; The magnitude of the bus voltage is adjusted according to the first sampling voltage and the second sampling voltage so that the ratio of the bus voltage to the output voltage reaches a preset ratio.

12. The control method according to claim 11, characterized in that: A first current is extracted / injected from an output feedback terminal of the PFC circuit, and a magnitude of the first current is adjusted according to the first sampling voltage and the second sampling voltage to control a magnitude of the bus voltage.

13. The control method according to claim 12, characterized in that: The product of the first sampling voltage and the second sampling voltage and a set value is compared; when the first sampling voltage is greater than the product, the first current extracted is controlled to decrease or the first current injected is controlled to increase; when the first sampling voltage is less than the product, the first current extracted is controlled to increase or the first current injected is controlled to decrease.

14. The control method according to claim 11, characterized in that: The magnitude of the reference voltage is controlled according to the first sampling voltage and the second sampling voltage to control the magnitude of the bus voltage.

15. The control method according to claim 14, characterized in that: The product of the first sampling voltage and the second sampling voltage and a set value is compared, and when the first sampling voltage is greater than the product, the reference voltage is controlled to decrease; when the first sampling voltage is less than the product, the reference voltage is controlled to increase.

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