Switching power supply and control method

Abstract

The invention provides a switching power supply and a control method. The control method comprises the following steps: when the switching power supply works in a light load state, detecting whether a PFC circuit works or not; if not, acquiring a first feedback signal containing the input voltage information and a second feedback signal containing the output voltage information; and according to the ratio of the first feedback signal to the second feedback signal, the pre-stage PFC circuit is controlled to start working, so that the minimum value of the bus voltage is adaptively adjusted along with the output of the post-stage asymmetric half-bridge flyback circuit. The control method provided by the invention is suitable for the switching power supply formed by carrying the PFC circuit and the asymmetric half-bridge flyback circuit, and the PFC circuit is controlled in real time according to the input and output of the asymmetric half-bridge flyback circuit under the light-load working condition; the output of the PFC circuit under the control of burst mode is adaptively adjusted along with the output of the asymmetric half-bridge flyback circuit, and the lower limit value of the output of the PFC circuit is smaller, so that the light-load power consumption is reduced.

Description

Technical Field

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

[0002] In adapter applications with input power greater than 75W, the input current harmonics must meet the Class D requirements of IEC 61000-3-2, so the adapter is often equipped with a pre-stage PFC. In order to improve the light-load efficiency of the adapter, when the output load drops to a certain value, the pre-stage PFC circuit will enter the burst mode (intermittent working mode). Figure 1 As shown in the figure, the front-stage PFC circuit works continuously for several switching cycles, and the bus voltage gradually increases. When the bus voltage increases to a certain value, the front-stage PFC circuit stops working, and the stop time is relatively long. After the front-stage PFC circuit stops working, the bus voltage gradually decreases until the bus voltage drops to a certain value, and the front-stage PFC circuit starts working again, and this is repeated. This working mode is called Burst mode.

[0003] However, recently EU ERP lot6 has put forward higher requirements on the light-load power consumption and no-load power consumption of the adapter. Therefore, controlling the pre-stage PFC circuit to enter the burst mode under light load to reduce power consumption according to the above operation cannot meet the higher requirements. Therefore, a technical solution is urgently needed to reduce the light-load power consumption of the adapter. Summary of the invention

[0004] In order to solve the technical problem that the technical solution for reducing the light-load power consumption of the adapter in the prior art needs to be optimized, the present invention proposes a switching power supply and a control method, wherein the switching power supply includes a front-stage PFC circuit and a rear-stage asymmetric half-bridge flyback circuit, wherein the front-stage PFC circuit converts the power supply voltage into a bus voltage, and the rear-stage asymmetric half-bridge flyback circuit converts the bus voltage as an input voltage into an output voltage, and the control method includes the steps of:

[0005] When the switching power supply is operating in a light load state, detecting whether the front-stage PFC circuit is operating;

[0006] If not, obtaining a first feedback signal and a second feedback signal, wherein the first feedback signal includes the input voltage information, and the second feedback signal includes the output voltage information;

[0007] The front-stage PFC circuit is controlled to start working according to the ratio of the first feedback signal to the second feedback signal.

[0008] Further, when the ratio represents that the ratio of the input voltage to the output voltage is less than a first preset coefficient, the front-stage PFC circuit is controlled to start working;

[0009] Among them, the first preset coefficient satisfies: K1=(k1+1)*N, K1 is the first preset coefficient, k1 is greater than zero, and N is the turns ratio of the primary and secondary windings of the subsequent asymmetric flyback circuit.

[0010] Furthermore, it also includes:

[0011] If yes, obtain a first feedback signal and a second feedback signal, wherein the first feedback signal includes the input voltage information, and the second feedback signal includes the output voltage information;

[0012] The front-stage PFC circuit is controlled to stop working according to the ratio of the first feedback signal to the second feedback signal.

[0013] Further, when the ratio represents that the ratio of the input voltage to the output voltage is greater than a second preset coefficient, the front-stage PFC circuit is controlled to stop working;

[0014] The second preset coefficient satisfies: K2=(k2+1)*N, K2 is the second preset coefficient, and k2 is greater than k1.

[0015] Furthermore, it also includes:

[0016] If yes, obtaining a third feedback signal, wherein the third feedback signal represents the input voltage;

[0017] According to the third feedback signal and the preset upper limit threshold, the front-stage PFC circuit is controlled to stop working.

[0018] Further, when the third feedback signal is greater than the preset upper limit threshold, the front-stage PFC circuit is controlled to stop working.

[0019] In one embodiment, obtaining the first feedback signal and the second feedback signal comprises the steps of:

[0020] The first feedback signal and the second feedback signal are obtained through the auxiliary winding, the first feedback signal represents the voltage across the primary winding when the primary winding is magnetized, and the second feedback signal represents the voltage across the primary winding when the secondary winding is demagnetized.

[0021] In one embodiment, when the ratio represents that the ratio of the input voltage to the output voltage is less than a first preset coefficient, controlling the pre-stage PFC circuit to start working includes the steps of:

[0022] When the ratio of the first feedback signal to the second feedback signal is less than k1, the front-stage PFC circuit is controlled to start working;

[0023] When the ratio represents that the ratio of the input voltage to the output voltage is greater than a second preset coefficient, controlling the front-stage PFC circuit to stop working comprises the steps of:

[0024] When the ratio of the first feedback signal to the second feedback signal is greater than k2, the front-stage PFC circuit is controlled to stop working.

[0025] A switching power supply, the switching power supply comprising a front-stage PFC circuit, a rear-stage asymmetric half-bridge flyback circuit, a front-stage controller, and a rear-stage controller, wherein the front-stage controller controls the front-stage PFC circuit to convert a power supply voltage into a bus voltage, and the rear-stage controller controls the rear-stage asymmetric half-bridge flyback circuit to convert the bus voltage as an input voltage into an output voltage.

[0026] When the switching power supply operates in a light-load state and the front-stage PFC circuit stops operating, the rear-stage controller outputs a first control signal according to a ratio of a first feedback signal to a second feedback signal, wherein the first feedback signal includes the input voltage information, and the second feedback signal includes the output voltage information;

[0027] The front-stage controller controls the front-stage PFC circuit to start working according to the first control signal.

[0028] Further, when the ratio represents that the ratio of the input voltage to the output voltage is less than a first preset coefficient, the first control signal is output;

[0029] Among them, the first preset coefficient satisfies: K1=(k1+1)*N, K1 is the first preset coefficient, k1 is greater than zero, and N is the turns ratio of the primary and secondary windings of the subsequent asymmetric flyback circuit.

[0030] Furthermore, when the switching power supply operates in a light-load state and the front-stage PFC circuit operates, the rear-stage controller outputs a second control signal according to a ratio of the first feedback signal to the second feedback signal;

[0031] The front-stage controller controls the front-stage PFC circuit to stop working according to the second control signal.

[0032] Further, when the ratio represents that the ratio of the input voltage to the output voltage is greater than a second preset coefficient, the second control signal is output;

[0033] The second preset coefficient satisfies: K2=(k2+1)*N, K2 is the second preset coefficient, and k2 is greater than k1.

[0034] Furthermore, the post-stage controller includes:

[0035] A judgment module, outputting a judgment signal according to an output feedback signal and a reference signal, wherein the output feedback signal represents the output voltage, and the judgment signal in a valid state represents that the switching power supply is operating in a light-load state;

[0036] an enabling module, outputting a first enabling signal or a second enabling signal according to a ratio of the first feedback signal to the second feedback signal, wherein the first enabling signal is output when the ratio of the input voltage to the output voltage is less than a first preset coefficient, and the second enabling signal is output when the ratio of the input voltage to the output voltage is greater than a second preset coefficient;

[0037] A logic module performs logic processing on the valid state judgment signal and the first enable signal to output the first control signal, or performs logic processing on the valid state judgment signal and the second enable signal to output the second control signal.

[0038] Further, when the switching power supply operates in a light-load state and the front-stage PFC circuit operates, the rear-stage controller outputs a second control signal according to a third feedback signal and a preset upper limit threshold, and the third feedback signal represents the input voltage;

[0039] The front-stage controller controls the front-stage PFC circuit to stop working according to the second control signal;

[0040] When the third feedback signal is greater than the preset upper limit threshold, the second control signal is output.

[0041] In the control method proposed in the present invention: when the switching power supply operates under light load conditions, the moment when the front-stage PFC circuit starts to work varies with the change in the output of the rear-stage asymmetric half-bridge flyback circuit, that is, the lower limit of the bus voltage is adaptively adjusted following the output voltage, and when the output voltage decreases, the lower limit of the bus voltage will also decrease accordingly to further reduce the light-load power consumption. At the same time, under the same output voltage, the lower limit of the bus voltage in this control method is often smaller than the fixed lower limit Vth1 in the prior art, so that the solution proposed in the present invention can make the lower limit of the output of the front-stage PFC circuit lower, thereby further reducing the light-load power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 For the existing burst mode control;

[0043] Figure 2 A control method proposed by the present invention;

[0044] Figure 3 Another control method proposed by the present invention;

[0045] Figure 4 An embodiment for obtaining a first feedback signal and a second feedback signal;

[0046] Figure 5 for Figure 4 The working waveform diagram of the embodiment shown;

[0047] Figure 6 for Figure 2 The control method shown is compared with the results of the prior art;

[0048] Figure 7 for Figure 3 The control method shown is compared with the results of the prior art;

[0049] Figure 8 Another embodiment for obtaining a first feedback signal and a second feedback signal;

[0050] Fig. 9 It is the structural block diagram of the switching power supply;

[0051] Fig.10 It is the structural block diagram of the post-stage controller;

[0052] Fig.11 This is the specific structure diagram of the post-stage controller. DETAILED DESCRIPTION

[0053] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0054] The switching power supply with an asymmetric half-bridge flyback circuit in the PFC circuit is suitable for a wide range of output. When the switching power supply operates under light load conditions, in order to reduce light load power consumption, the PFC circuit will enter the burst mode (intermittent working mode). Figure 1 As shown in the figure, in burst mode, the PFC circuit works for several switching cycles continuously, and the bus voltage gradually increases; when the bus voltage increases to Vth2, the PFC circuit stops working, and the stop time is relatively long; when the PFC circuit stops working, the bus voltage gradually decreases until the bus voltage drops to Vth1, and the PFC circuit starts working again, and so on. Among them, Vth1 and Vth2 are relatively close.

[0055] However, under the existing burst mode control, no matter what the output of the switching power supply is, the variation range of the PFC circuit output is always Vth1-Vth2, and the power consumption reduction is limited. Therefore, there is still room for optimization in the specific control process of the existing burst mode to further reduce the light load power consumption.

[0056] In view of the above problems, the present invention proposes a control method for a switching power supply to further reduce the light-load power consumption of the switching power supply, wherein the switching power supply is equipped with a front-stage PFC circuit and a rear-stage asymmetric half-bridge flyback circuit, the front-stage PFC circuit boosts the power supply voltage to convert it into a bus voltage, and the rear-stage asymmetric half-bridge flyback circuit converts the bus voltage as an input voltage into an output voltage, and the control method comprises the steps of:

[0057] When the switching power supply is working in a light load state, detect whether the previous PFC circuit is working;

[0058] If not, obtaining a first feedback signal and a second feedback signal, the first feedback signal comprising input voltage information, and the second feedback signal comprising output voltage information;

[0059] According to the ratio of the first feedback signal to the second feedback signal, the front-stage PFC circuit is controlled to start working, so as to achieve adaptive change of the lower limit value of the bus voltage along with the output voltage.

[0060] Specifically, when the ratio of the first feedback signal to the second feedback signal represents that the ratio of the input voltage to the output voltage is less than the first preset coefficient K1, the front-stage PFC circuit is controlled to start working. The first preset coefficient K1 satisfies: K1 = (1 + k1) * N, where k1 > 0, and N is the turns ratio of the primary and secondary windings in the rear-stage asymmetric flyback circuit.

[0061] Further, such as Figure 2 As shown, if it is detected that the front-stage PFC circuit is working, a first feedback signal containing input voltage information and a second feedback signal containing output voltage information are obtained; according to the ratio of the first feedback signal and the second feedback signal, the front-stage PFC circuit is controlled to stop working. Specifically, when the ratio of the first feedback signal and the second feedback signal represents that the ratio of the input voltage to the output voltage is greater than the second preset coefficient K2, the front-stage PFC circuit is controlled to stop working; wherein the second preset coefficient K2 satisfies: K2=(1+k2)*N, k2>k1. Therefore, the output range (the range of bus voltage variation) of the front-stage PFC circuit is: (1+k1)*N*output voltage~(1+k2)*N*output voltage, and when the output voltage decreases, the lower limit value of the output of the front-stage PFC circuit decreases accordingly, further reducing the light-load power consumption.

[0062] Further, such as Figure 3As shown, if it is detected that the front-stage PFC circuit is working, a third feedback signal representing the input voltage is obtained; according to the third feedback signal and the preset upper limit threshold, the front-stage PFC circuit is controlled to stop working. Specifically, when the third feedback signal is greater than the preset upper limit threshold, the front-stage PFC circuit is controlled to stop working. Among them, the preset upper limit threshold is a fixed value set in advance, and the preset upper limit threshold represents that the upper limit value of the bus voltage is greater than the product of the first preset coefficient K1 and the maximum output voltage. Therefore, the output range of the front-stage PFC circuit is: (1+k1)*N*output voltage~preset upper limit threshold. When the output voltage decreases, the lower limit value of the output of the front-stage PFC circuit decreases accordingly, further reducing the light load power consumption.

[0063] The control method proposed by the present invention is described in detail below in conjunction with specific embodiments.

[0064] In the first embodiment, if Figure 4 As shown, the first feedback signal and the second feedback signal are obtained through the auxiliary winding. Specifically, when the first switch tube M1 is turned on and the primary winding is magnetized, the voltage Vbus-Vcr across the primary winding is obtained through the auxiliary winding, and Vbus-Vcr is the first feedback signal. The bus voltage Vbus is the input voltage of the subsequent asymmetric flyback circuit, that is, the obtained first feedback signal contains information about the input voltage; when the second switch tube M2 is turned on and the secondary winding is demagnetized, the voltage Vcr across the primary winding is obtained through the auxiliary winding, and Vcr is the second feedback signal, and Vcr can represent the output voltage Vo (Vcr=Np / Ns*Vo). As shown Figure 5 As shown, when the first switch tube M1 is turned on, the auxiliary winding voltage Vaux=Na / Np*(Vbus-Vcr), and when the second switch tube M2 is turned on, the auxiliary winding voltage Vaux=Na / Np*Vcr. Therefore, Vbus-Vcr and Vcr can be obtained through the auxiliary winding. Thereafter, the front-stage PFC circuit is controlled to start working or stop working according to the ratio of Vbus-Vcr and Vcr in real time. Specifically, when (Vbus-Vcr) / Vcr<k1, the front-stage PFC circuit is controlled to start working, and the bus voltage Vbus gradually rises when the front-stage PFC circuit works; when (Vbus-Vcr) / Vcr>k2, the front-stage PFC circuit is controlled to stop working, and the bus voltage Vbus gradually decreases when the front-stage PFC circuit stops working. Therefore, the output range of the front-stage PFC circuit is (1+k1)*N*Vo~(1+k2)*N*Vo, where N represents the turns ratio of the primary winding to the secondary winding. It can be seen from this that when the output of the previous PFC circuit changes, Vbus≥(1+k1)*N*Vo, that is, Vbus≥(1+k1)*Vcr, so Vbus is always greater than Vcr. The primary winding can be magnetized normally under light load conditions, and the entire switching power supply can still work normally while further reducing power consumption.

[0065] like Figure 6 As shown, curve ① is the prior art that does not consider the size of the output voltage Vo under light load conditions, and uniformly controls the output range of the front-stage PFC circuit to be Vth1~Vth2, where the difference between Vth1 and Vth2 is small. For example, under light load conditions, when the output voltage Vo is 10V, the output range of the front-stage PFC circuit is controlled to be Vth1~Vth2. Under light load conditions, when the output voltage Vo is 20V, the output range of the front-stage PFC circuit is still controlled to be Vth1~Vth2. Curve ② is under light load conditions, when the output voltage Vo1 is 10V, the output range of the front-stage PFC circuit is (1+k1)*N*Vo1~(1+k2)*N*Vo1. If N=10, k1=0.5, k2=1, then the output range of the front-stage PFC circuit is 150V~200V. Curve ③ is the output range of the front-stage PFC circuit under light load conditions when the output voltage Vo2 is 8V, which is (1+k1)*N*Vo2~(1+k2)*N*Vo2. If N=10, k1=0.5, k2=1, then the output range of the front-stage PFC circuit is 120V~160V. Comparing curve ① with curve ② or comparing curve ① with curve ③, it can be seen that compared with the prior art, the fluctuation range of the output of the front-stage PFC circuit is larger, and the output lower limit of the front-stage PFC circuit is smaller, so the light-load power consumption is further reduced. Comparing curve ② with curve ③, it can be seen that the output of the front-stage PFC circuit in the present invention will be adaptively adjusted as the output voltage changes, and the output lower limit of the front-stage PFC circuit will decrease as the output voltage decreases, thereby further reducing the light-load power consumption.

[0066] In addition, in the first embodiment, when the switching power supply operates in a light-load condition and the front-stage PFC circuit operates, the front-stage PFC circuit can also be controlled to stop operating according to the magnitude relationship between the input voltage and the preset upper limit threshold. Therefore, the output range of the front-stage PFC circuit is (1+k1)*N*Vo~preset upper limit threshold, where N represents the turns ratio of the primary winding to the secondary winding. Specifically, Figure 7As shown, curve ① is the prior art that does not consider the size of the output voltage Vo under light load conditions, and uniformly controls the output range of the front-stage PFC circuit to be Vth1~Vth2, where the difference between Vth1 and Vth2 is small. For example, under light load conditions, when the output voltage Vo is 10V, the output range of the front-stage PFC circuit is controlled to be Vth1~Vth2. Under light load conditions, when the output voltage Vo is 20V, the output range of the front-stage PFC circuit is still controlled to be Vth1~Vth2. Curve ② is under light load conditions, when the output voltage Vo1 is 10V, the output range of the front-stage PFC circuit is (1+k1)*N*Vo1~Vth3. If N=10, k1=0.5, k2=1, Vth3=220V, then the output range of the front-stage PFC circuit is 150V~220V. Curve ③ is the output range of the front-stage PFC circuit under light load conditions when the output voltage Vo2 is 8V, which is (1+k1)*N*Vo2~Vth3. If N=10, k1=0.5, k2=1, and Vth3=220V, then the output range of the front-stage PFC circuit is 120V~220V. Obviously, by comparing curve ① with curve ② or comparing curve ① with curve ③, it can be seen that the fluctuation range of the output of the front-stage PFC circuit in the present invention is larger, and the output lower limit of the front-stage PFC circuit is smaller, so the light-load power consumption is further reduced. Comparing curve ② with curve ③, it can be seen that the output lower limit of the front-stage PFC circuit will be adaptively adjusted as the output voltage changes, and the output lower limit of the front-stage PFC circuit will decrease as the output voltage decreases, thereby further reducing the light-load power consumption.

[0067] In the second embodiment, if Figure 8 As shown, a first voltage-dividing sampling circuit is formed by resistors R1 and R2 to obtain a first feedback signal representing the bus voltage, and the first feedback signal is R2*Vbus / (R1+R2); a second voltage-dividing sampling circuit is formed by resistors R3 and R4 to obtain a second feedback signal representing the output voltage, and the second feedback signal is R4*VO / (R3+R4). Therefore, when the switching power supply operates under light load conditions and the front-stage PFC circuit stops working, if the ratio of the first feedback signal to the second feedback signal is less than In addition, when the switching power supply is operating under light load conditions and the front-stage PFC circuit stops working, the first feedback signal and the second feedback signal are obtained in real time. If the ratio of the first feedback signal to the second feedback signal is greater than Then the front-stage PFC circuit is controlled to stop working. Therefore, the output range of the front-stage PFC circuit is (1+k1)*N*Vo~(1+k2)*N*Vo. Similarly, when the switching power supply is operating under light load conditions and the front-stage PFC circuit is operating, the third feedback signal representing the bus voltage Vbus can also be obtained in real time, and the front-stage PFC circuit is controlled to stop working according to the size relationship between the third feedback signal and the preset upper limit threshold. Among them, the preset upper limit threshold is a fixed value set in advance, and the preset upper limit threshold represents that the upper limit value of the bus voltage is greater than the product of the first preset coefficient K1 and the maximum output voltage. Therefore, the output range of the front-stage PFC circuit is (1+k1)*N*Vo~preset upper limit threshold, and N represents the turns ratio of the primary winding to the secondary winding.

[0068] In summary, when the switching power supply operates under light load conditions, the moment when the front-stage PFC circuit starts to work varies with the change in the output of the rear-stage asymmetric half-bridge flyback circuit, that is, the lower limit of the bus voltage is adaptively adjusted following the output voltage, and when the output voltage decreases, the lower limit of the bus voltage will also decrease accordingly to further reduce the light-load power consumption. At the same time, under the same output voltage, the lower limit of the bus voltage in this control method is often smaller than the fixed lower limit Vth1 in the prior art, so that the optimized solution of the present invention can make the lower limit of the output of the front-stage PFC circuit lower, thereby further reducing the light-load power consumption.

[0069] In addition, the present invention also provides a control circuit of a switching power supply, such as Fig. 9 As shown, the switching power supply includes a front-stage PFC circuit and a rear-stage asymmetric flyback circuit, and the control circuit includes a front-stage controller and a rear-stage controller. The front-stage controller controls the front-stage PFC circuit to convert the power supply voltage into a bus voltage, and the rear-stage controller controls the asymmetric half-bridge flyback circuit to convert the bus voltage into an output voltage, wherein:

[0070] When the switching power supply operates in a light-load state and the front-stage PFC circuit stops working, the rear-stage controller obtains a first feedback signal and a second feedback signal, and outputs a first control signal according to a ratio of the first feedback signal to the second feedback signal, wherein the first feedback signal includes input voltage information, and the second feedback signal includes output voltage information;

[0071] The front-stage controller controls the front-stage PFC circuit to start working according to the first control signal.

[0072] Specifically, when the ratio of the first feedback signal to the second feedback signal represents that the ratio of the input voltage to the output voltage is less than the first preset coefficient K1, the post-stage controller outputs the first control signal. The first preset coefficient K1 satisfies: K1 = (1 + k1) * N, where k1 > 0, and N is the turns ratio of the primary and secondary windings in the post-stage asymmetric flyback circuit.

[0073] Furthermore, when the switching power supply operates in a light-load state and the front-stage PFC circuit operates, the rear-stage controller obtains the first feedback signal and the second feedback signal from the rear-stage asymmetric flyback circuit in real time, and outputs the second control signal according to the ratio of the first feedback signal and the second feedback signal; the front-stage controller controls the front-stage PFC circuit to stop working according to the second control signal. Specifically, when the ratio of the first feedback signal and the second feedback signal represents that the ratio of the input voltage to the output voltage is greater than the second preset coefficient K2, the front-stage controller outputs the second control signal. Among them, the second preset coefficient K2 satisfies: K2=(1+k2)*N, k2>k1. Therefore, the output range (the range of bus voltage change) of the front-stage PFC circuit is: (1+k1)*N*output voltage~(1+k2)*N*output voltage. When the output voltage decreases, the lower limit value of the output of the front-stage PFC circuit decreases accordingly, further reducing the light-load power consumption.

[0074] Furthermore, when the switching power supply is operating in a light-load state and the front-stage PFC circuit is operating, the rear-stage controller outputs a second control signal according to the third feedback signal representing the input voltage and the preset upper limit threshold, and the front-stage controller controls the front-stage PFC circuit to stop operating according to the second control signal. Specifically, when the third feedback signal is greater than or equal to the preset upper limit threshold, the rear-stage controller outputs the second control signal. Therefore, the output range of the front-stage PFC circuit is: (1+k1)*N*output voltage~preset upper limit threshold, and when the output voltage decreases, the lower limit value of the output of the front-stage PFC circuit decreases accordingly, further reducing the light-load power consumption.

[0075] Specifically, the post-controller can be Figure 4 As shown, the first feedback signal and the second feedback signal are obtained through the auxiliary winding, or as shown Figure 8 As shown, the first feedback signal is obtained by the first voltage-dividing sampling circuit, and the second feedback signal is obtained by the second voltage-dividing sampling circuit.

[0076] like Fig.10 As shown, in one embodiment, the post-stage controller includes:

[0077] A judgment module, wherein the judgment module outputs a judgment signal according to the output feedback signal and the reference signal, wherein the judgment signal in a valid state indicates that the switching power supply is operating in a light-load state;

[0078] An enable mode, outputting a first enable signal or a second enable signal according to a ratio of a first feedback signal to a second feedback signal, outputting a first enable signal when the ratio represents that the ratio of an input voltage to an output voltage is less than a first preset coefficient, and outputting a second enable signal when the ratio represents that the ratio of an input voltage to an output voltage is greater than a second preset coefficient;

[0079] The logic module outputs a first control signal after logic processing of the judgment signal of the effective state and the first enable signal, or outputs a second control signal after logic processing of the judgment signal of the effective state and the second enable signal. The driving module in the front-stage controller drives the main switch tube in the front-stage PFC circuit to turn on according to the first control signal / drives the main switch tube in the front-stage PFC circuit to turn off according to the second control signal.

[0080] Specifically, Fig.11 As shown, the judgment module includes a comparator U1, a comparator U2 and a first SR trigger, the positive input end of the comparator U1 receives the first reference signal Vcomp_L, the reverse input end is connected to the positive input end of the comparator U2 and receives the output feedback signal Vcomp, and the output end is connected to the set end of the first SR trigger, the reverse input end of the comparator U2 receives the second reference signal Vcomp_H, and the output end is connected to the reset end of the first SR trigger, and the second reference signal Vcomp_H is greater than the first reference signal Vcomp_L. The enabling module includes a comparator U3, a comparator U4 and a second SR trigger, the positive input end of the comparator U3 receives k1*Vcr, the reverse input end is connected to the positive input end of the comparator U4 and receives Vbus-Vcr, and the output end is connected to the set end of the second SR trigger, the reverse input end of the comparator U4 receives k2*Vcr, and the output end is connected to the reset end of the second SR trigger. The logic module includes an AND gate U5, the first input end of the AND gate U5 is connected to the output end of the first SR trigger, and the second input end is connected to the output end of the second SR trigger. When Vcomp is less than Vcomp_L, the first SR trigger outputs a high-level judgment signal Q1; when Vbus-Vcr is less than k1*Vcr, the second SR trigger outputs a high-level enable signal Q2, and the AND gate U5 outputs a high-level control signal PFC_ON, and the driver unit in the front-stage controller drives the switch tube Q1 to turn on according to the control signal PFC_ON. When Vcomp is less than Vcomp_L, the first SR trigger outputs a high-level judgment signal Q1; when Vbus-Vcr is greater than k2*Vcr, the second SR trigger outputs a low-level enable signal Q2, and the AND gate U5 outputs a low-level control signal PFC_OFF, and the driver unit in the front-stage controller drives the switch tube Q1 to turn off according to the control signal PFC_OFF.

[0081] In summary, when the switching power supply operates under light-load conditions, the moment when the front-stage PFC circuit starts to work varies with the change in the output of the rear-stage asymmetric half-bridge flyback circuit, that is, the lower limit of the bus voltage is adaptively adjusted following the output voltage, and when the output voltage decreases, the lower limit of the bus voltage will also decrease accordingly to further reduce the light-load power consumption. At the same time, under the same output voltage, the lower limit of the bus voltage in this control method is often smaller than the fixed value Vth1 in the prior art, so that the optimized solution of the present invention can make the lower limit of the output of the front-stage PFC circuit lower, thereby further reducing the light-load power consumption.

[0082] It should be noted that Fig.11 The post-stage controller obtains the first feedback signal and the second feedback signal through the auxiliary winding, and outputs the second control signal according to the ratio of the first feedback signal and the second feedback signal. However, those skilled in the art can also apply this specific structure to the working principle of outputting the second control signal according to the third feedback signal and the preset upper limit threshold. In addition, the pre-stage controller can also control the pre-stage PFC circuit to stop working in a variety of ways, such as adding a large pull-down current to the FB pin of the pre-stage controller to trigger the undervoltage protection of the switching power supply, thereby shutting down the pre-stage PFC circuit; or directly controlling Vcc to stop supplying power to the pre-stage controller.

[0083] It should be noted that the specific implementation and corresponding illustrations given are merely a way of describing the implementation method of the present invention, and do not limit the specific structure of the implementation scheme of the present invention. Various changes or modifications can be made to these implementation schemes without departing from the principle and essence of the present invention, but these changes and modifications fall within the scope of protection of the present invention.

[0084] 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.

[0085] 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 control method for a switching power supply, the switching power supply comprising a front-stage PFC circuit and a rear-stage asymmetric half-bridge flyback circuit, the front-stage PFC circuit converts a power supply voltage into a bus voltage, and the rear-stage asymmetric half-bridge flyback circuit converts the bus voltage as an input voltage into an output voltage, characterized in that: The control method comprises the steps of: When the switching power supply is operating in a light load state, detecting whether the front-stage PFC circuit is operating; If not, obtaining a first feedback signal and a second feedback signal, wherein the first feedback signal includes the input voltage information, and the second feedback signal includes the output voltage information; The front-stage PFC circuit is controlled to start working according to the ratio of the first feedback signal to the second feedback signal.

2. The control method according to claim 1, characterized in that: When the ratio represents that the ratio of the input voltage to the output voltage is less than a first preset coefficient, controlling the pre-stage PFC circuit to start working; Among them, the first preset coefficient satisfies: K1=(k1+1)*N, K1 is the first preset coefficient, k1 is greater than zero, and N is the turns ratio of the primary and secondary windings of the subsequent asymmetric flyback circuit.

3. The control method according to claim 2, characterized in that: Also includes: If yes, obtain a first feedback signal and a second feedback signal, wherein the first feedback signal includes the input voltage information, and the second feedback signal includes the output voltage information; The front-stage PFC circuit is controlled to stop working according to the ratio of the first feedback signal to the second feedback signal.

4. The control method according to claim 3, characterized in that: When the ratio represents that the ratio of the input voltage to the output voltage is greater than a second preset coefficient, controlling the front-stage PFC circuit to stop working; The second preset coefficient satisfies: K2=(k2+1)*N, K2 is the second preset coefficient, and k2 is greater than k1.

5. The control method according to claim 2, characterized in that: Also includes: If yes, obtaining a third feedback signal, wherein the third feedback signal represents the input voltage; According to the third feedback signal and the preset upper limit threshold, the front-stage PFC circuit is controlled to stop working.

6. The control method according to claim 5, characterized in that: When the third feedback signal is greater than the preset upper limit threshold, the front-stage PFC circuit is controlled to stop working.

7. The control method according to claim 4, characterized in that: Acquiring the first feedback signal and the second feedback signal comprises the steps of: The first feedback signal and the second feedback signal are obtained through the auxiliary winding, the first feedback signal represents the voltage across the primary winding when the primary winding is magnetized, and the second feedback signal represents the voltage across the primary winding when the secondary winding is demagnetized.

8. The control method according to claim 7, characterized in that: When the ratio represents that the ratio of the input voltage to the output voltage is less than a first preset coefficient, controlling the pre-stage PFC circuit to start working includes the steps of: When the ratio of the first feedback signal to the second feedback signal is less than k1, the front-stage PFC circuit is controlled to start working; When the ratio represents that the ratio of the input voltage to the output voltage is greater than a second preset coefficient, controlling the front-stage PFC circuit to stop working comprises the steps of: When the ratio of the first feedback signal to the second feedback signal is greater than k2, the front-stage PFC circuit is controlled to stop working.

9. A switching power supply, comprising a front-stage PFC circuit, a rear-stage asymmetric half-bridge flyback circuit, a front-stage controller, and a rear-stage controller, wherein the front-stage controller controls the front-stage PFC circuit to convert the power supply voltage into a bus voltage, and the rear-stage controller controls the rear-stage asymmetric half-bridge flyback circuit to convert the bus voltage as an input voltage into an output voltage, characterized in that: When the switching power supply operates in a light-load state and the front-stage PFC circuit stops operating, the rear-stage controller outputs a first control signal according to a ratio of a first feedback signal to a second feedback signal, wherein the first feedback signal includes the input voltage information, and the second feedback signal includes the output voltage information; The front-stage controller controls the front-stage PFC circuit to start working according to the first control signal.

10. The switching power supply according to claim 9, characterized in that: When the ratio represents that the ratio of the input voltage to the output voltage is less than a first preset coefficient, outputting the first control signal; Among them, the first preset coefficient satisfies: K1=(k1+1)*N, K1 is the first preset coefficient, k1 is greater than zero, and N is the turns ratio of the primary and secondary windings of the subsequent asymmetric flyback circuit.

11. The switching power supply according to claim 10, characterized in that: When the switching power supply operates in a light-load state and the front-stage PFC circuit operates, the rear-stage controller outputs a second control signal according to a ratio of the first feedback signal to the second feedback signal; The front-stage controller controls the front-stage PFC circuit to stop working according to the second control signal.

12. The switching power supply according to claim 11, characterized in that: When the ratio represents that the ratio of the input voltage to the output voltage is greater than a second preset coefficient, outputting the second control signal; The second preset coefficient satisfies: K2=(k2+1)*N, K2 is the second preset coefficient, and k2 is greater than k1.

13. The switching power supply according to claim 12, characterized in that: The post-stage controller comprises: A judgment module, outputting a judgment signal according to an output feedback signal and a reference signal, wherein the output feedback signal represents the output voltage, and the judgment signal in a valid state represents that the switching power supply is operating in a light-load state; an enabling module, outputting a first enabling signal or a second enabling signal according to a ratio of the first feedback signal to the second feedback signal, wherein the first enabling signal is output when the ratio of the input voltage to the output voltage is less than a first preset coefficient, and the second enabling signal is output when the ratio of the input voltage to the output voltage is greater than a second preset coefficient; A logic module performs logic processing on the valid state judgment signal and the first enable signal to output the first control signal, or performs logic processing on the valid state judgment signal and the second enable signal to output the second control signal.

14. The switching power supply according to claim 9, characterized in that: When the switching power supply operates in a light-load state and the front-stage PFC circuit operates, the rear-stage controller outputs a second control signal according to a third feedback signal and a preset upper limit threshold, wherein the third feedback signal represents the input voltage; The front-stage controller controls the front-stage PFC circuit to stop working according to the second control signal; When the third feedback signal is greater than the preset upper limit threshold, the second control signal is output.

Images