Control method, control circuit and switching power supply for switching power supply

Abstract

The application discloses a control method and control circuit of a switching power supply and the switching power supply. The operation mode of the switching power supply is controlled in a first mode and a second mode according to an output feedback signal of the switching power supply. One working cycle of the first mode comprises one critical mode switching cycle, and one working cycle of the second mode comprises N critical mode switching cycles and one intermittent mode switching cycle. When one working cycle of the current second mode enters a next working cycle or the current second mode enters the first mode, the parasitic capacitance of a main switch tube is discharged by turning on an auxiliary switch tube once before the next working cycle or the first mode starts, so that the zero-voltage conduction of the main switch tube is realized. The technical scheme of the application can well realize the control of the zero-voltage conduction of the asymmetric half-bridge switching power supply, and the effect is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronics, in particular to a control method of a switching power supply, a control circuit and the switching power supply. BACKGROUND

[0002] In the application process of the switching power supply, when the power of the load changes, the working mode of the switching power supply will be switched accordingly to obtain better system efficiency, for example, when the load power decreases, the switching power supply will enter the discontinuous conduction mode from the critical conduction mode; when the load power increases, the switching power supply will enter the critical conduction mode from the discontinuous conduction mode.

[0003] The asymmetric half-bridge switching power supply includes two switching tubes constituting a half-bridge, and the input energy is converted into the desired output energy by controlling the conduction / cutoff of the switching tubes, but the switching tubes usually have a parasitic capacitance, and the conduction of the switching tube will generate a large switching loss when the charge of the parasitic capacitance is not zero. In the mode switching process, such as in the case of entering the critical conduction mode, the parasitic capacitance charge of the switching tube is discharged as much as possible before conduction to realize zero-voltage conduction, but how to realize zero-voltage conduction is a technical problem. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a control method of a switching power supply, a control circuit and the switching power supply to solve the technical problem of how to realize zero-voltage conduction in the prior art.

[0005] The technical solution of the present application is to provide a control circuit of a switching power supply, the switching power supply including a main switching tube and an auxiliary switching tube constituting a half-bridge, comprising: an error amplifier circuit receiving an output feedback signal of the switching power supply to obtain an error compensation signal; a switching control circuit receiving the error compensation signal to set a first current curve and a first frequency curve accordingly, the switching control circuit receiving an inductor current sampling signal and a working frequency signal of the switching power supply, and controlling the switching state of the main switching tube and the auxiliary switching tube according to the comparison of the inductor current sampling signal and the first current curve and the comparison of the working frequency signal and the first frequency curve.

[0006] Preferably, the first current curve is a preset inductor current signal change curve with the error compensation signal; and the first frequency curve is a preset system working frequency change curve with the error compensation signal.

[0007] Preferably, the switch control circuit comprises a current curve setting circuit and a frequency curve setting circuit, the operating mode of the switch power supply is set according to the error compensation signal, the first current curve is set according to the operating mode of the switch power supply by the current curve setting circuit, and the first frequency curve is set according to the control mode of the switch power supply by the frequency curve setting circuit.

[0008] The operating mode of the switch power supply comprises a first mode and a second mode, one working cycle of the first mode comprises one critical mode switching cycle, and the second mode comprises N critical mode switching cycles and one discontinuous mode switching cycle.

[0009] Preferably, the switch control circuit comprises a first comparison circuit and a second comparison circuit, when the switch power supply works in a certain mode, the first comparison circuit compares the inductor current sampling signal of the switch power supply with the first current curve to control the switching state of the main switch tube, and the second comparison circuit compares the working frequency signal of the switch power supply with the first frequency curve to control the switching state of the auxiliary switch tube.

[0010] Preferably, the switch power supply comprises a primary winding, a secondary winding and an auxiliary winding, the control circuit further comprises an input end receiving the voltage between any winding of the primary winding, the secondary winding and the auxiliary winding,

[0011] The control circuit determines the zero-crossing time of the drain-source voltage of the main switch tube according to the voltage received by the input end, so as to control the switching state of the main switch tube and the auxiliary switch tube.

[0012] Preferably, the control circuit further comprises a logic circuit, a first driver and a second driver, the logic circuit generates the switching control signals of the main switch tube and the auxiliary switch tube according to the comparison results of the first comparison circuit and the second comparison circuit and the zero-crossing time of the drain-source voltage of the main switch tube;

[0013] The first driver receives the switching control signals to drive the switching action of the main switch tube;

[0014] The second driver receives the switching control signals to drive the switching action of the auxiliary switch tube.

[0015] Preferably, the operating mode of the switch power supply comprises a first mode, a second mode and a third mode, one working cycle of the third mode comprises M second mode working cycles limited by time and a stop time.

[0016] Preferably, the auxiliary switch tube, the first inductor, the first capacitor and the primary winding of the transformer constitute a resonance circuit.

[0017] In a second aspect, a control method of a switching power supply is disclosed, the switching power supply comprising a main switch and an auxiliary switch constituting a half-bridge,

[0018] controlling the operation mode of the switching power supply in a first mode and a second mode according to an output feedback signal of the switching power supply, one working cycle of the first mode comprising one critical mode switching cycle, one working cycle of the second mode comprising N critical mode switching cycles and one discontinuous mode switching cycle,

[0019] when a working cycle of the current second mode enters a next working cycle or the current second mode enters the first mode, discharging the parasitic capacitance of the main switch by turning on the auxiliary switch once before the next working cycle or the first mode starts, to realize zero-voltage turn-on of the main switch.

[0020] Further comprising, the operation mode of the switching power supply is set according to the output feedback signal of the switching power supply, the first current curve and the first frequency curve are set according to the operation mode of the switching power supply; when the switching power supply works in a certain mode, the switching state of the main switch and the auxiliary switch is controlled according to the comparison between the inductor current sampling signal of the switching power supply and the first current curve and the comparison between the working frequency signal of the switching power supply and the first frequency curve.

[0021] Further comprising, when a working cycle of the current first mode enters a next working cycle or the current second mode enters the first mode, the specific steps of discharging the parasitic capacitance of the main switch by turning on the auxiliary switch before the next working cycle or the first mode starts include: comparing the working frequency signal of the switching power supply with the first frequency curve to control the turning on of the auxiliary switch according to the comparison result.

[0022] Further comprising, controlling the operation mode of the switching power supply in a first mode, a second mode and a third mode according to an output feedback signal of the switching power supply,

[0023] one working cycle of the third mode comprising M period time-limited second mode working cycles and a period of stop time.

[0024] In a third aspect, a switching power supply is disclosed, comprising a main switch and an auxiliary switch constituting a half-bridge, the auxiliary switch and a first inductor, a first capacitor and a primary winding in a transformer of the switching power supply constituting a resonance circuit, further comprising the control circuit as described above.

[0025] Compared with the prior art, the switch circuit structure has the following advantages: the asymmetric half-bridge switch power supply switches between the second mode and the first mode according to an output feedback signal, and when a working period of the current first mode enters a next working period or the current second mode enters the first mode, the parasitic capacitance of the main switch tube is discharged by turning on the auxiliary switch tube once before the next working period or the first mode starts, so that the main switch tube realizes zero-voltage turn-on. The switch power supply can well realize the control of zero-voltage turn-on of the asymmetric half-bridge switch power supply, and has good effect. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a circuit block diagram of the asymmetric switch power supply according to the first embodiment of the present application;

[0027] Figure 2 It is Figure 1 a specific circuit block diagram of the control circuit;

[0028] Figure 3 It is a working waveform diagram according to Figure 1 ;

[0029] Figure 4 It is another working waveform diagram according to Figure 1 ;

[0030] Figure 5 It is a first current curve schematic diagram according to the present application;

[0031] Figure 6 It is a first frequency curve schematic diagram according to the present application;

[0032] Figure 7 It is a circuit block diagram of the asymmetric switch power supply according to the second embodiment of the present application. DETAILED DESCRIPTION

[0033] The preferred embodiments of the present application are described in detail below with reference to the accompanying drawings, but the present application is not limited to only these embodiments. The present application covers any alternative, modification, equivalent method and scheme made within the spirit and scope of the present application.

[0034] In order for the public to have a thorough understanding of the present application, specific details are described in the following preferred embodiments of the present application, and the present application can also be completely understood without the description of these details by those skilled in the art.

[0035] The present application is described in more detail in the following paragraphs with reference to the accompanying drawings. It should be noted that the drawings are in a simplified form and use non-precise proportions, only to facilitate, clearly assist in the purpose of describing the embodiments of the present application.

[0036] Reference Figure 1This is a circuit block diagram of a first embodiment of the asymmetric switching power supply according to the present invention. Figure 2 for Figure 1 A detailed circuit block diagram of the control circuit is provided. In this embodiment of the invention, the switching power supply includes a main switching transistor and an auxiliary switching transistor forming a half-bridge. The auxiliary switching transistor, a first inductor, a first capacitor, and the primary winding of a transformer form a resonant circuit. The control circuit U1 includes an error amplifier circuit, a switch control circuit, a logic circuit, a first driver, and a second driver. The error amplifier circuit, the switch control circuit, and the logic circuit constitute a control unit U1. The error amplifier circuit detects the output feedback signal of the switching power supply to obtain an error compensation signal Vcomp. The error compensation signal can be obtained by amplifying the output feedback signal and a reference signal and then compensating for the error. The switch control circuit receives the error compensation signal to set a first current curve and a first frequency curve accordingly. The switch control circuit receives the inductor current sampling signal and the operating frequency signal of the switching power supply, and controls the switching states of the main switching transistor and the auxiliary switching transistor based on the comparison between the inductor current sampling signal and the first current curve, and the comparison between the operating frequency signal and the first frequency curve.

[0037] In one example, the switching control circuit includes a current curve setting circuit and a frequency curve setting circuit. The control mode of the switching power supply is set according to the error compensation signal, and the current curve setting circuit sets the first current curve according to the control mode of the switching power supply, such as... Figure 5 The curve shown represents the voltage information corresponding to the inductor current (VCS). The frequency curve setting circuit sets the first frequency curve according to the control mode of the switching power supply, such as... Figure 6 The curve; In this embodiment of the invention, the control mode of the switching power supply includes a first mode and a second mode. One operating cycle of the first mode includes one critical mode switching cycle, denoted as BCM mode. One operating cycle of the second mode includes N critical mode switching cycles and one discontinuous mode switching cycle, denoted as BUR mode. For example, when the load power is large, the switching power supply operates in the second mode; when the load power is small, the switching power supply operates in the first mode. Specifically, when the operating mode of the switching power supply is switched, the corresponding first current curve or first frequency curve will be adjusted accordingly. For example, when switching from the second mode to the first mode, the Vcs value of the first current curve decreases, and the value of the frequency curve increases; when switching from the first mode to the second mode, the Vcs value of the first current curve increases, and the value of the frequency curve decreases. Figure 5 , Figure 6 In the diagram, ① represents the curve relationship in the first mode, and ② represents the curve relationship in the second mode. The curve relationships are different in different modes.

[0038] In one example, the switch control circuit includes a first comparison circuit and a second comparison circuit. When the switch power supply operates in a certain mode, the first comparison circuit compares the inductor current sampling signal of the switch power supply with the first current curve to control the switching state of the main switch tube; the second comparison circuit compares the operating frequency signal of the switch power supply with the first frequency curve to control the switching state of the auxiliary switch tube. For example, the switching-off of the main switch tube is controlled by comparing the inductor current sampling signal of the switch power supply at a certain moment with the sampling signal corresponding to the first current curve; the switching-off of the auxiliary switch tube is controlled by comparing the operating frequency signal of the switch power supply at a certain moment with the frequency value corresponding to the first frequency curve. Figure 5 In the figure, the dashed line is the set inductor current curve, and the solid line is the actual inductor current sampling signal value. Figure 6 In the figure, the dashed line is the set frequency curve, and the solid line is the actual operating frequency value.

[0039] For example, continuing to refer to Figure 1 , the switch power supply includes a primary winding, a secondary winding and an auxiliary winding, and the control circuit further includes an input terminal receiving the voltage between any winding of the primary winding, the secondary winding and the auxiliary winding, such as Figure 1 In the figure, the voltage Vs of the auxiliary winding is taken as the input terminal voltage, and the control circuit determines the zero-crossing moment of the drain-source voltage of the main switch tube according to the voltage received by the input terminal to control the switching state of the main switch tube and the auxiliary switch tube. Here, the voltage received by the input terminal determines the zero-crossing moment of the drain-source voltage of the main switch tube by comparing the drain-source voltage of the main switch tube with the set power supply threshold value (such as the input voltage value) to control the switching-off of the auxiliary switch tube and the switching-on of the main switch tube after a predetermined time (such as half of the resonance period or one quarter of the resonance period) of the switching-off delay of the auxiliary switch tube, so as to adjust the main switch tube to be turned on at zero voltage or near zero voltage in each switching period.

[0040] In one example, the switch control circuit further includes a logic circuit, and the control circuit further includes a first driver and a second driver. The logic circuit generates the switching control signals of the main switch tube and the auxiliary switch tube according to the comparison results of the first comparison circuit and the second comparison circuit and the zero-crossing moment of the drain-source voltage of the main switch tube; the first driver receives the switching control signals to drive the switching action of the main switch tube; and the second driver receives the switching control signals to drive the switching action of the auxiliary switch tube.

[0041] Referring to Figure 3 the operating waveform diagram according to Figure 1 ; Figure 3In the formula, GON is the switch control signal of the main switch tube, GAC is the switch control signal of the auxiliary switch tube, ilm is the inductance current, Vsw is the drain-source voltage of the main switch tube, the second mode is denoted as BUR, and the first mode is denoted as BCM, the working period of the BUR is N critical conduction mode switching periods plus one discontinuous conduction mode switching period, denoted as a working period, as shown in Figure 3 FIG. 3, N is 3. In the embodiment of the present application, when the switching power supply works in the BUR mode, the working frequency signal of the switching power supply is compared with the first frequency curve when one working period enters the next working period, so as to control the turn-on of the auxiliary switch tube according to the comparison result, thereby realizing the zero-voltage conduction of the main switch tube by turning on the auxiliary switch tube once again before the start of the next working period. Alternatively, when the current second mode enters the first mode, the working frequency signal of the switching power supply is compared with the first frequency curve, so as to control the turn-on of the auxiliary switch tube according to the comparison result, thereby realizing the zero-voltage conduction of the main switch tube by turning on the auxiliary switch tube once again before the start of the next first mode, discharging the drain-source parasitic voltage of the main switch tube, and then the switching power supply enters the BCM working mode.

[0042] Through the above-mentioned control mode of the switching power supply, the switching power supply is controlled to work in the second mode and the first mode in the asymmetric half-bridge switching power supply, and the turn-on and turn-off of the auxiliary switch tube are controlled, so as to realize that the main switch tube can be turned on at zero voltage or near zero voltage, reduce the switching loss, and improve the system working efficiency.

[0043] In one example, as shown in Figure 4 , Figure 4 is another working waveform diagram according to Figure 1 When the power of the load is very low, the working mode of the switching power supply is controlled to enter the third mode, such as the Burst mode, and one working period of the third mode includes M second mode working periods defined by time and a period of stop time. Referring to Figure 4 FIG. 4, M is 2, and here the second mode working period defined by time means that the second mode working period is inconsistent with the working period in the second mode, such as the period of time being less than the working period in the second mode; the period of stop time is the preset non-working time of the switching power supply. In this way, the values of the first current curve and the first frequency curve are adjusted to be small in this process, and the low-power output can be well realized.

[0044] Figure 7 is the circuit block diagram of the second embodiment of the asymmetric switching power supply of the present application. The control circuit implementation of the present application can be applied to the switching power supply topology shown in Figure 7 FIG. 5.

[0045] The above-described embodiments do not constitute a limitation on the protection scope of the technical solutions. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described embodiments should be included in the protection scope of the technical solutions.

Claims

1. A control circuit of a switching power supply including a main switching transistor and an auxiliary switching transistor constituting a half bridge, characterized by, The application relates to a switching power supply, comprising: an error amplification circuit receiving an output feedback signal of the switching power supply to obtain an error compensation signal; a switching control circuit receiving the error compensation signal to set a first current curve and a first frequency curve according to the error compensation signal, the switching control circuit receiving an inductor current sampling signal and a working frequency signal of the switching power supply, and controlling switching states of a main switch tube and an auxiliary switch tube according to comparison of the inductor current sampling signal and the first current curve and comparison of the working frequency signal and the first frequency curve, wherein the first current curve represents an inductor current curve and the first frequency curve represents a working frequency curve of the switching power supply; the switching power supply has a first mode and a second mode, one working cycle of the first mode comprises one critical mode switching cycle, and the second mode comprises N critical mode switching cycles and one discontinuous mode switching cycle, when a current working cycle of the second mode enters a next working cycle or the current second mode enters the first mode, the switching control circuit controls the auxiliary switch tube to be turned on once to discharge a parasitic capacitor of the main switch tube to realize zero-voltage turn-on of the main switch tube by comparing the working frequency signal of the switching power supply with the first frequency curve before the next working cycle or the first mode starts.

2. The control circuit of a switching power supply according to claim 1, characterized in that, The first current curve is a preset inductor current signal variation curve with the error compensation signal. The first frequency curve is a preset system working frequency variation curve with the error compensation signal.

3. The control circuit of a switching power supply according to claim 2, characterized in that The switching control circuit comprises a current curve setting circuit and a frequency curve setting circuit, the operation mode of the switching power supply is set according to the error compensation signal, the current curve setting circuit sets the first current curve according to the operation mode of the switching power supply, the frequency curve setting circuit sets the first frequency curve according to the operation mode of the switching power supply.

4. The control circuit of a switching power supply according to claim 3, characterized in that The switching control circuit comprises a first comparison circuit and a second comparison circuit, when the switching power supply works in a certain mode, the first comparison circuit compares the inductor current sampling signal of the switching power supply with the first current curve to control the switching state of the main switch tube, and the second comparison circuit compares the working frequency signal of the switching power supply with the first frequency curve to control the switching state of the auxiliary switch tube.

5. The control circuit of a switching power supply according to claim 4, characterized in that The switching power supply comprises a primary winding, a secondary winding and an auxiliary winding, the control circuit further comprises an input end receiving a voltage between any winding of the primary winding, the secondary winding and the auxiliary winding, the control circuit determines a drain-source voltage zero-crossing time of the main switch tube according to the voltage received by the input end to control the switching states of the main switch tube and the auxiliary switch tube.

6. The control circuit of a switching power supply according to claim 5, wherein The control circuit further comprises a logic circuit, a first driver and a second driver, the logic circuit generates switching control signals of the main switch tube and the auxiliary switch tube according to comparison results of the first comparison circuit and the second comparison circuit and the drain-source voltage zero-crossing time of the main switch tube. The first driver receives the switch control signal to drive the switching action of the main switch tube; The second driver receives the switch control signal to drive the switching action of the auxiliary switch tube.

7. The control circuit of a switching power supply according to claim 3, wherein The operation mode of the switching power supply includes a first mode, a second mode and a third mode, One working cycle of the third mode includes M period time limited second mode working cycle and a period of stop time.

8. The control circuit of a switching power supply according to claim 1, characterized by The auxiliary switch tube, the first inductor, the first capacitor and the primary winding of the transformer constitute a resonant circuit.

9. A control method of a switching power supply, the switching power supply including a main switch tube and an auxiliary switch tube constituting a half bridge, characterized in that, The operation mode of the switching power supply is controlled according to the output feedback signal of the switching power supply in the first mode and the second mode, one working cycle of the first mode includes a critical mode switching cycle, and one working cycle of the second mode includes N critical mode switching cycles and an intermittent mode switching cycle, When the current second mode working cycle enters the next working cycle or the current second mode enters the first mode, the parasitic capacitance of the main switch tube is discharged by turning on the auxiliary switch tube once before the next working cycle or the first mode starts, realizing zero voltage turn-on of the main switch tube, The operation mode of the switching power supply is set according to the output feedback signal of the switching power supply, The first current curve and the first frequency curve are set according to the operation mode of the switching power supply; When the switching power supply works in a certain mode, the switching state of the main switch tube and the auxiliary switch tube is controlled according to the comparison of the inductor current sampling signal of the switching power supply and the first current curve and the comparison of the working frequency signal of the switching power supply and the first frequency curve.

10. The control method of a switching power supply according to claim 9, characterized by When the current first mode working cycle enters the next working cycle or the current second mode enters the first mode, the specific steps of turning on the auxiliary switch tube before the next working cycle or the first mode starts include comparing the working frequency signal of the switching power supply with the first frequency curve to control the turning on of the auxiliary switch tube according to the comparison result.

11. The control method of a switching power supply according to claim 9, characterized by, The operation mode of the switching power supply is controlled according to the output feedback signal of the switching power supply in the first mode, the second mode and the third mode, One working cycle of the third mode includes M period time limited second mode working cycle and a period of stop time.

12. A switching power supply comprising a main switch and an auxiliary switch constituting a half bridge, the auxiliary switch and a primary winding in a transformer and a first inductor and a first capacitor of the switching power supply constituting a resonance circuit, characterized in that, The control circuit of any one of claims 1-8 is further included.

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