Control method, control device and switching power supply

Abstract

The invention discloses a control method, a control device and a switching power supply. The control method comprises the following steps: providing a clock signal; acquiring a trough signal representing that the voltage difference between the two ends of the switching device is at the trough moment; when the switching device is in the turn-off state, judging the working mode of the PFC power supply; before a clock signal arrives, the switch-on moment of a switch device is determined according to the working mode of the PFC power supply: if the PFC power supply is currently in a DCM mode, a switch control unit starts to identify the morning and evening of the set delay time arrival moment and the wave trough signal arrival moment when the clock signal arrives, the switch device is turned on by taking the morning one to turn on the switch device, and the other one to turn off the switch device; the excitation is electric induction excitation; and if the PFC power supply is currently in a CCM mode, the switching device is switched on when a clock signal arrives, and inductance excitation is realized. According to the invention, the PFC power supply can work in different modes and can be applied to wide output power occasions; soft switching of the switching device can be realized, and the power supply efficiency is improved.

Description

Technical Field

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

[0002] AC-DC power supplies usually use active power factor correction (PFC) technology to meet the power conversion requirements of high power factor (PF) and low total harmonic distortion (THD).

[0003] For wide load output situations, traditional CCM (continuous conduction mode) PFC power supplies usually adopt a fixed frequency average current control strategy. Figure 1 This is a block diagram of the average current control mode of an existing CCM PFC power supply, where 101 is the average current loop; 102 is the average current loop reference, which is obtained by multiplying the input voltage sampling and the voltage loop output 104; and 103 is the output voltage loop reference. Its operating principle is as follows: the average inductor current is sampled through the sampling resistor 105, and feedback integration is performed with the average current loop reference 102 to obtain the output of the average current loop 101. A fixed-frequency sawtooth wave is compared with the output of the average current loop 101 and connected to the R terminal of the RS trigger as the switch-off trigger signal. Meanwhile, 106 is a fixed-frequency clock signal, which is connected to the S terminal of the RS trigger as the switch-on trigger signal, thereby realizing average current control of the CCM PFC power supply. Figure 1 The solution has a constant operating frequency of the PFC power supply within the entire input voltage and output power range, and has the characteristics of small PFC inductor current ripple, small total harmonic distortion, and low switch tube current stress. It is mostly used in high power applications. However, the inventors of this application found through research that Figure 1 There are two problems with the control scheme: on the one hand, this control does not distinguish the operating mode of the PFC power supply. Regardless of the mode of the converter, the switching device is turned on when the clock signal arrives, which cannot achieve soft turning-on of the switching device and will increase the loss of the PFC circuit; on the other hand, the input current of the PFC power supply varies sinusoidally within one power frequency cycle, and the input current is large under heavy load and small under light load. Under this control, the frequency of the converter when it is lightly loaded is as high as when it is heavily loaded, which will result in greater loss of the PFC circuit under light load.

[0004] In addition, the CRM (critical conduction mode) PFC power supply is suitable for small and medium power applications. It mostly adopts COT (constant on-time) control or peak current control. Compared with the CCM mode, its biggest feature is that there is no diode reverse recovery and it can achieve soft turn-on of the main power tube. Figure 2The circuit waveform diagram of the existing CRM PFC power supply is shown. The inventor of this application found that Figure 2 The control scheme also has two problems: First, because the average value of the CRM PFC inductor current is half of the peak inductor current, when the converter is under heavy load, the PFC inductor current pulsates greatly, reducing the efficiency of the power supply system and increasing the complexity of the inductor design. Second, the operating frequency of the power supply becomes very high near the zero crossing of the input voltage, resulting in large power losses and reducing the overall efficiency of the circuit, usually requiring frequency limiting.

[0005] It should be noted that the information disclosed in the background technology section above is only intended to deepen the understanding of the overall background technology of this application, and should not be regarded as an admission or in any form of implication that the information constitutes prior art already known to those skilled in the art. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a control method, a control device and a switching power supply, which at least to a certain extent solve one of the technical problems existing in the prior art.

[0007] As a first aspect of the present invention, the technical solution of the control method provided is as follows:

[0008] A control method is applied to a PFC power supply, the PFC power supply comprising: an inductor and a switch device, one end of the inductor being connected to one end of the switch device; wherein: the control method comprises the following steps:

[0009] Provide a clock signal;

[0010] Acquiring a valley signal indicating that the voltage difference across the switching device is at a valley;

[0011] When the switch device is in an off state, determining an operating mode of the PFC power supply;

[0012] Before the clock signal arrives, the turn-on time of the switching device is determined according to the operating mode of the PFC power supply: if the PFC power supply is currently in the DCM mode, the switching control unit begins to identify the earlier of the set delay time arrival time and the valley signal arrival time when the clock signal arrives, and turns on the switching device according to the earlier of the two times to magnetize the inductor; if the PFC power supply is currently in the CCM mode, the switching device is turned on when the clock signal arrives to magnetize the inductor.

[0013] As a second aspect of the present invention, the technical solution of the embodiment of the control device provided is as follows:

[0014] A control device is applied to a PFC power supply, wherein the PFC power supply comprises: an inductor and a switching device, wherein one end of the inductor is connected to one end of the switching device; wherein: the control device comprises:

[0015] A clock signal unit, configured to provide a clock signal;

[0016] A valley detection unit, configured to obtain a valley signal indicating when the voltage difference across the switching device is at a valley;

[0017] a mode recognition unit, configured to determine an operating mode of the PFC power supply when the switch device is in an off state;

[0018] a switch control unit, configured to determine, before the clock signal arrives, a turn-on time of the switch device according to an operating mode of the PFC power supply: if the PFC power supply is currently in a DCM mode, the switch control unit, upon the arrival of the clock signal, begins to identify the earlier of the arrival time of the set delay time and the arrival time of the valley signal, and turns on the switch device according to the earlier of the two, thereby magnetizing the inductor; and if the PFC power supply is currently in a CCM mode, turns on the switch device upon the arrival of the clock signal, thereby magnetizing the inductor.

[0019] Preferably, the mode recognition unit obtains the demagnetization state of the inductor by detecting a change in the voltage of the auxiliary winding of the inductor or according to a change in the current on the inductor, thereby determining the operating mode of the PFC power supply:

[0020] If it is determined that the inductor is always in the demagnetization stage, the mode recognition unit determines that the PFC power supply is currently in the CCM mode;

[0021] If the inductor is first in the demagnetization stage and then in the demagnetization completion stage, when the inductor is in the demagnetization completion stage, the mode recognition unit will determine that the PFC power supply is currently in the DCM mode.

[0022] Preferably, the control device controls the switching device to be turned off by an average current control strategy.

[0023] Preferably, the clock signal unit provides a clock signal with a fixed frequency, or provides a clock signal with a frequency that changes with changes in input voltage phase and output load size.

[0024] Furthermore, the clock signal provided is a variable frequency clock signal, comprising the following units:

[0025] a first signal acquisition unit, configured to use a fixed-amplitude sinusoidal full-wave rectified signal as a first signal, or to divide the fixed-amplitude sinusoidal full-wave rectified signal by the input voltage sampling signal as the first signal, wherein the fixed-amplitude sinusoidal full-wave rectified signal has the same frequency and phase as the input voltage sampling signal;

[0026] a second signal acquisition unit, configured to multiply a first coefficient, the first signal, and the output voltage loop feedback signal; multiply a second coefficient by the output voltage loop feedback signal; and then add the products of the two to obtain the second signal;

[0027] a third signal acquisition unit, configured to multiply the output voltage loop feedback signal by a third coefficient, and then divide the obtained product by the input voltage sampling signal to obtain the third signal;

[0028] a variable frequency function signal generating unit, configured to generate a variable frequency control signal according to the second signal and the third signal, and then generate a clock signal of a corresponding frequency according to the variable frequency control signal;

[0029] Wherein: when the second signal>the third signal, the third signal is used as the frequency conversion control signal; when the second signal≤the third signal, the second signal is used as the frequency conversion control signal.

[0030] Preferably, the valley detection unit obtains the valley signal by directly detecting a change in a voltage difference across the switching device; or obtains the valley signal indirectly by detecting a voltage signal on the inductor and its auxiliary winding.

[0031] Preferably, the delay time should be no less than the resonant period of the inductor and the parasitic capacitance of the switching device.

[0032] Preferably, the switching device is a MOSFET.

[0033] As a third aspect of the present invention, the technical solution of the embodiment of the switching power supply provided is as follows:

[0034] A switching power supply includes a PFC power supply, wherein the PFC power supply includes: an inductor and a switching device, one end of the inductor is connected to one end of the switching device; wherein: the switching power supply further includes the control device described in any one of the second aspects above.

[0035] The beneficial effects of the present invention compared to the prior art are as follows:

[0036] The embodiment of the present invention determines the operating mode of the PFC power supply and then controls the switching of the PFC power supply switching device according to the different operating modes. When the PFC power supply is determined to be in the CCM mode, the switching device is turned on upon the arrival of the clock signal to activate the motor. When the PFC power supply is determined to be in the DCM mode, the timing of the arrival of the set delay time and the arrival of the valley signal is identified upon the arrival of the clock signal, and the earlier of the two is used to activate the switching device to activate the motor. This ensures that the actual operating frequency of the PFC power supply is not much different from the frequency of the variable frequency clock signal. As a result, the PFC power supply operates in the CCM mode under heavy load conditions to achieve relatively high power output and relatively small inductor current ripple. Under light load conditions, the PFC power supply naturally transitions to the DCM mode. Soft-turning on the main power device reduces losses, ultimately achieving high-efficiency operation of the PFC power supply over the full load range. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a control block diagram of an average current type of an existing CCM PFC power supply;

[0038] Figure 2 This is the circuit waveform diagram of the existing CRM PFC power supply;

[0039] Figure 3 1 is a functional block diagram of a PFC power supply including a control device of the present invention;

[0040] Figure 4a for Figure 3 Key signal waveforms when the PFC power supply is in DCM mode;

[0041] Figure 4b for Figure 3 Key signal waveforms when the PFC power supply is in CCM mode;

[0042] Figure 5a A schematic diagram of the process and steps for generating a variable frequency clock for a clock signal unit;

[0043] Figure 5b for Figure 5a Medium frequency conversion control signal waveform. DETAILED DESCRIPTION

[0044] It should be noted that, unless there is any conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0045] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0046] 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 to describe the embodiments of the present application here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes 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 devices.

[0047] 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.

[0048] In addition, the figures of this disclosure are merely schematic diagrams of the present disclosure and are not necessarily drawn to scale. Identical reference numbers in the figures denote identical or similar parts, and therefore repeated descriptions thereof will be omitted. Some of the blocks shown in the figures are functional entities that do not necessarily correspond to physically or logically separate entities. These functional entities may be implemented using software, in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontrollers.

[0049] Based on the technical problems existing in the prior art analyzed in the background art, an embodiment of the present invention provides a control method applied to a PFC power supply. The PFC power supply includes: an inductor and a switching device, one end of the inductor is connected to one end of the switching device. The control method includes the following steps:

[0050] Provide a clock signal;

[0051] Obtaining a valley signal representing the moment when the voltage difference across the switching device is at a valley;

[0052] When the switch device is in the off state, the operating mode of the PFC power supply is determined;

[0053] Before the clock signal arrives, the turn-on time of the switching device is determined according to the working mode of the PFC power supply: if the PFC power supply is currently in the DCM mode, the switch control unit starts to identify the arrival time of the set delay time and the arrival time of the valley signal when the clock signal arrives, and takes the earlier one to turn on the switching device to excite the motor; if the PFC power supply is currently in the CCM mode, the switching device is turned on when the clock signal arrives to excite the motor.

[0054] The above control method enables the PFC power supply to operate in CCM mode under heavy load conditions to achieve relatively large power output and relatively small inductor current pulsation. Under light load conditions, it naturally transitions to DCM mode and reduces losses by soft-turning on the main power devices, ultimately achieving high-efficiency operation of the PFC power supply within the full load range.

[0055] Figure 3 For a block diagram of the PFC power supply including the control device of the present invention, see Figure 3 The PFC power supply includes: an inductor L1 and a switch device Q1, one end of the inductor L1 is connected to one end of the switch device Q1; wherein: the control device includes:

[0056] A clock signal unit 208, configured to provide a clock signal;

[0057] The valley detection unit 210 is used to obtain a valley signal indicating that the voltage difference across the switching device Q1 is at a valley;

[0058] The valley detection unit 210 can be implemented by directly detecting the voltage difference across the switching device, and obtaining a valley signal when the voltage difference changes to the minimum; or indirectly obtaining the valley signal by detecting the voltage signal on the inductor L1 and its auxiliary winding;

[0059] A mode recognition unit 207 is configured to determine an operating mode of the PFC power supply when the switch device Q1 is in an off state;

[0060] Exemplarily, the mode recognition unit 207 determines the current cycle operating mode of the PFC power supply based on the demagnetization state of the inductor L1. For example, the mode recognition unit 207 may determine the demagnetization state of the inductor L1 by detecting a change in the voltage of the auxiliary winding of the inductor L1 or by determining a change in the current on the inductor L1. Specifically, if the inductor L1 is always in the demagnetization stage, the mode recognition unit 207 determines that the PFC power supply is in the CCM mode. If the inductor is first in the demagnetization stage and then in the demagnetization completion stage, when the inductor is in the demagnetization completion stage, the mode recognition unit determines that the PFC power supply is currently in the DCM mode.

[0061] As an example, Figure 3 The mode recognition unit 207 collects the inductor current through the sampling resistor 205 and the inverting amplifier unit 206 and performs mode determination. Specifically, if the output signal of the inverting amplifier unit 206 decreases from a positive value to zero, the PFC power supply is determined to be operating in the DCM mode. If the output voltage signal of the inverting proportional amplifier unit 206 remains positive, the PFC power supply is determined to be operating in the CCM mode. The operating mode determination for this cycle ends when the clock signal from the clock signal unit 208 arrives. The operating mode of the PFC power supply is determined based on whether the inductor L1 current drops to zero before the clock signal arrives. This method is not only simple to implement but also allows for accurate determination.

[0062] The switch control unit 211 is configured to achieve output stability and power factor correction for the power supply by controlling the on and off of the switch device Q1. Specifically, before the clock signal arrives, the switch control unit determines the on-time of the switch device Q1 based on the operating mode of the PFC power supply. If the PFC power supply is currently in the DCM mode, the switch control unit begins to identify the earlier of the set delay time arrival time and the valley signal arrival time when the clock signal arrives, and turns on the switch device Q1 according to the earlier of the two times to excite the inductor. If the PFC power supply is currently in the CCM mode, the switch control unit turns on the switch device Q1 when the clock signal arrives to excite the inductor L1.

[0063] The fixed delay time T1 should be greater than the resonance time of the inductor L1 and the parasitic capacitance of the switching device Q1, so that the valley signal can be detected within the delay time window, thereby reliably achieving soft turning-on of the switching device.

[0064] Figure 3 The PFC power supply can work in different working modes. Figure 4a for Figure 3 Key signal waveforms when the PFC power supply is in DCM mode, Figure 4b for Figure 3 Key signal waveforms when the PFC power supply is in CCM mode; the horizontal axis is time; the vertical axis is: i L1is the current in inductor L1, V Q1,DS is the voltage across the switching device Q1, V Q1_Drv is the driving voltage of the switching device Q1.

[0065] Figure 4a The PFC power supply has the following working stages in one switching cycle when in a stable state:

[0066] Inductor demagnetization stage, i.e., stage 2: the switch control unit 211 determines the turn-on time of the switch device Q1 according to the judgment result of the mode recognition unit 207 on the working mode of the PFC power supply. Figure 4a The current change on the inductor L1 during this stage indicates that the inductor is first in the demagnetization stage with the current decreasing, and then in the demagnetization completion stage with the current crossing zero. Therefore, when the inductor is in the demagnetization completion stage at time t1, the mode recognition unit 207 determines that the PFC power supply is in the DCM mode. The switch control unit 211 needs to be compatible with the frequency of the clock signal of the clock signal unit 208 and the soft turn-on of the switch device. Therefore, at time t2 when the clock signal of the clock signal unit 208 arrives, the fixed delay time T1 is started to be counted and the valley signal of the valley detection unit 210 is waited for: if the valley detection unit 210 has a valley signal, the switch device Q1 is immediately controlled to be turned on; if the valley detection unit 210 has no valley signal, the switch device Q1 is immediately turned on when the fixed delay time T1 expires. Figure 4a During the fixed delay time T1, a valley signal appears at time t3, so the switch device Q1 is immediately controlled to turn on at time t3;

[0067] The electromagnetic excitation stage, namely the first stage, is a stage in which the switching device remains turned on, specifically including the turn-on time t3 of the switching device in this cycle to the turn-off time t4 of the switching device.

[0068] Figure 4b The PFC power supply has the following working stages in one switching cycle when in a stable state:

[0069] Inductor demagnetization stage, i.e., stage 2: the switch control unit 211 determines the turn-on time of the switch device Q1 according to the judgment result of the mode recognition unit 207 on the working mode of the PFC power supply. Figure 4b The current change on the inductor L1 during this stage indicates that the inductor is always in the demagnetization stage. The mode recognition unit 207 determines that the PFC power supply is in the CCM mode, and the switch control unit 211 controls the switch device to turn on at time t5 when the clock signal from the clock signal unit 208 arrives.

[0070] The electromagnetic excitation stage, namely stage 1: the switching device remains turned on during this stage, specifically including the turn-on time t5 of the switching device in this cycle to the turn-off time t6 of the switching device Q1.

[0071] In order to reduce the pulsation of the inductor current, reduce the total harmonic distortion, and reduce the current stress of the switching device, the embodiment of the present invention can use an average current control strategy to control the shutdown of the PFC power supply switching device Q1 to form a complete switching cycle. The background technology of this type of average current controlled switch control unit has been introduced and is summarized here again, including: an output voltage feedback unit for obtaining an output voltage loop feedback signal that represents the output voltage of the PFC power supply; an inductor current reference generation unit for multiplying the output voltage loop feedback signal with the input voltage sampling signal as the inductor current reference; an inductor current feedback unit for obtaining an output current loop feedback signal that represents the current on the inductor; and a switch control unit that compares the output current loop feedback signal with the variable frequency clock signal to generate a shutdown signal for the switching device. An example of the control process can be found in Figure 3 , including: obtaining an average current loop reference 202, which is obtained by multiplying the input voltage sampling and the voltage loop output 204, where 203 is the output voltage loop reference, sampling the inductor L1 current through the sampling resistor 205 and the reverse amplifier unit 206, performing error amplification with the average current loop reference 202, and obtaining an average current loop output 212, comparing the average current loop output 212 with the clock signal (sawtooth wave) of the clock signal unit 208 to generate a shutdown control signal, and the switch control unit 211 controls the shutdown switch device to turn off according to the shutdown control signal, and the inductor L1 begins to demagnetize.

[0072] In order to make the PFC power supply operate in a low-frequency DCM mode under light load and in a high-frequency CCM mode under heavy load, thereby improving the PFC power supply efficiency while taking into account a high PF value and a low THD value of the system, the embodiment of the present invention can set the operating frequency of the PFC power supply to vary with changes in input voltage and load. For the clock signal unit 208, a preferred implementation method for generating a variable frequency signal is shown in FIG5 , wherein:

[0073] 305 is a sinusoidal full-wave rectified signal with a fixed amplitude, which can be obtained by dividing the input instantaneous voltage signal of the PFC power supply by the input voltage peak sampling signal, or by dividing the input instantaneous voltage signal of the PFC power supply by the input voltage effective value sampling signal, or by being generated by a sinusoidal full-wave rectified signal generating circuit and then phase-locked with the full-wave rectified signal of the input instantaneous voltage of the power factor corrector;

[0074] 304 is the peak sampling signal of the input voltage or the effective value sampling signal of the input voltage V in-sense ; Divide the fixed amplitude full-wave sine rectified signal 305 by the voltage loop output 204 to obtain 301, i.e., the first signal V1; Since 205 is a fixed amplitude full-wave sine rectified signal, the amplitude of the first signal V1 will decrease as the input voltage increases; 307 is the output V of the PFC voltage loop fb, set coefficients K1 and K2, where K1 can be between 0.5 and 1.1; K2 can be between 0 and 0.6;

[0075] Set K1, V1, V fb The product of plus V fb The product of K3 and K2 is used as the second signal V2; set the coefficient K3 (the value of K3 can be between 0.5 and 1.8), and multiply K3 by V fb Divide by V in-sense Obtain 303, which is the third signal V3. V3 is smaller at high voltage or light load, and larger at low voltage or heavy load. Finally, the second signal V2 and the third signal V3 are input into the variable frequency function signal generating module: when the second signal V2> the third signal V3, the variable frequency function signal generating module outputs the third signal V3 as the variable frequency control signal; when the second signal V2≤ the third signal V3, the variable frequency function signal generating module outputs the second signal V2 as the variable frequency control signal 306. Then the variable frequency control signal 306 generates a clock signal of corresponding frequency according to the amplitude change of the input signal, wherein the clock signal includes a variable frequency pulse signal and a variable slope sawtooth wave signal corresponding to the variable frequency pulse.

[0076] Figure 5b is the key waveform generated by the clock signal unit 208, where K2 is set to 0, K1 is set to 1, and K3 is set to 0.8. 401 is the signal frequency when the input is high voltage or light load; 402 is the signal frequency when the input is low voltage or heavy load. It can be seen from 5b that this control strategy realizes that within one power frequency cycle, the operating frequency of the PFC power supply is high in the middle and low on both sides. At the same time, the circuit operating frequency is high when it is heavily loaded, and low when it is lightly loaded. The lowest operating frequency is generally set above 20KHz.

[0077] Although the present invention has been described with reference to the embodiments, it should be understood that the terms used are illustrative and exemplary rather than restrictive. Since the present invention can be embodied in many forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope of the appended claims. Therefore, all changes and modifications that fall within the scope of the claims or their equivalents are intended to be covered by the appended claims.

Claims

1. A control method, applied to a PFC power supply, the PFC power supply comprising: An inductor and a switch device, wherein one end of the inductor is connected to one end of the switch device; wherein the control method comprises the following steps: Provide a clock signal; Acquiring a valley signal indicating that the voltage difference across the switching device is at a valley; When the switch device is in an off state, determining an operating mode of the PFC power supply; Before the clock signal arrives, the turn-on time of the switching device is determined according to the operating mode of the PFC power supply: if the PFC power supply is currently in the DCM mode, the switching control unit begins to identify the earlier of the set delay time arrival time and the valley signal arrival time when the clock signal arrives, and turns on the switching device according to the earlier of the two times to magnetize the inductor; if the PFC power supply is currently in the CCM mode, the switching device is turned on when the clock signal arrives to magnetize the inductor.

2. A control device, applied to a PFC power supply, the PFC power supply comprising: An inductor and a switch device, wherein one end of the inductor is connected to one end of the switch device; wherein the control device comprises: A clock signal unit, configured to provide a clock signal; A valley detection unit, configured to obtain a valley signal indicating when the voltage difference across the switching device is at a valley; a mode recognition unit, configured to determine an operating mode of the PFC power supply when the switch device is in an off state; a switch control unit, configured to determine, before the clock signal arrives, a turn-on time of the switch device according to an operating mode of the PFC power supply: if the PFC power supply is currently in a DCM mode, the switch control unit, upon the arrival of the clock signal, begins to identify the earlier of the arrival time of the set delay time and the arrival time of the valley signal, and turns on the switch device according to the earlier of the two, thereby magnetizing the inductor; and if the PFC power supply is currently in a CCM mode, turns on the switch device upon the arrival of the clock signal, thereby magnetizing the inductor.

3. The control device according to claim 2, characterized in that: The mode recognition unit obtains the demagnetization state of the inductor by detecting the change in the auxiliary winding voltage of the inductor or according to the change in the current on the inductor, thereby determining the working mode of the PFC power supply: If it is determined that the inductor is always in the demagnetization stage, the mode recognition unit determines that the PFC power supply is currently in the CCM mode; If the inductor is first in the demagnetization stage and then in the demagnetization completion stage, when the inductor is in the demagnetization completion stage, the mode recognition unit will determine that the PFC power supply is currently in the DCM mode.

4. The control device according to claim 2, characterized in that: The control device controls the switching device to be turned off by an average current control strategy.

5. The control device according to claim 2, characterized in that: The clock signal unit provides a clock signal with a fixed frequency, or provides a clock signal with a frequency that changes with changes in input voltage phase and output load size.

6. The control device according to claim 2, characterized in that: The clock signal provided is a variable frequency clock signal, including the following units: a first signal acquisition unit, configured to use a fixed-amplitude sinusoidal full-wave rectified signal as a first signal, or to divide the fixed-amplitude sinusoidal full-wave rectified signal by the input voltage sampling signal as the first signal, wherein the fixed-amplitude sinusoidal full-wave rectified signal has the same frequency and phase as the input voltage sampling signal; a second signal acquisition unit, configured to multiply a first coefficient, the first signal, and the output voltage loop feedback signal; multiply a second coefficient by the output voltage loop feedback signal; and then add the products of the two to obtain the second signal; a third signal acquisition unit, configured to multiply the output voltage loop feedback signal by a third coefficient, and then divide the obtained product by the input voltage sampling signal to obtain the third signal; a variable frequency function signal generating unit, configured to generate a variable frequency control signal according to the second signal and the third signal, and then generate a clock signal of a corresponding frequency according to the variable frequency control signal; Wherein: when the second signal>the third signal, the third signal is used as the frequency conversion control signal; when the second signal≤the third signal, the second signal is used as the frequency conversion control signal.

7. The control device according to claim 2, characterized in that: The valley detection unit obtains the valley signal by directly detecting the change in the voltage difference across the switching device; or obtains the valley signal indirectly by detecting the voltage signal on the inductor and its auxiliary winding.

8. The control device according to claim 2, characterized in that: The delay time should be no less than the resonant period of the inductor and the parasitic capacitance of the switching device.

9. The control device according to claim 2, characterized in that: The switching device is a MOSFET.

10. A switching power supply, comprising a PFC power supply, the PFC power supply comprising: An inductor and a switching device, one end of the inductor is connected to one end of the switching device; characterized in that: the switching power supply also includes the control device according to any one of claims 2 to 9.

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