Asymmetrical half-bridge flyback switching power supply, control chip and control method thereof

Abstract

Provided are an asymmetric half-bridge flyback switching power supply, a control chip thereof, and a control method. The asymmetric half-bridge flyback switching power supply comprises a first power switch, a second power switch, and a transformer. The control chip is configured to generate an upper tube control signal for controlling the turn-on and turn-off of the first power switch based on a current sensing signal representing a current flowing through a primary inductor of the transformer, and generate a lower tube control signal for controlling the turn-on and turn-off of the second power switch based on the current sensing signal and a demagnetization sensing signal representing a demagnetization condition of the primary inductor of the transformer.

Description

Technical Field

[0001] The present invention relates to the field of integrated circuits, and more particularly to an asymmetric half-bridge flyback switching power supply, a control chip thereof, and a control method thereof. Background Art

[0002] A switching power supply, also known as an alternating current power supply or switching converter, is a type of power supply. Its function is to convert a voltage level to the voltage or current required by the user through various topologies (e.g., flyback, buck, or boost). Summary of the Invention

[0003] According to an embodiment of the present invention, a control chip for an asymmetric half-bridge flyback switching power supply includes a first power switch, a second power switch, and a transformer. The control chip is configured to: generate an upper-side control signal for controlling the on / off state of the first power switch based on a current sensing signal representing a current flowing through a primary inductor of the transformer; and generate a lower-side control signal for controlling the on / off state of the second power switch based on the current sensing signal and a demagnetization sensing signal representing a demagnetization condition of the primary inductor of the transformer.

[0004] According to an embodiment of the present invention, a control method for an asymmetric half-bridge flyback switching power supply includes a first power switch, a second power switch, and a transformer. The control method includes: generating an upper switch control signal for controlling the on / off state of the first power switch based on a current sensing signal representing a current flowing through a primary inductor of the transformer; and generating a lower switch control signal for controlling the on / off state of the second power switch based on the current sensing signal and a demagnetization sensing signal representing a demagnetization condition of the primary inductor of the transformer.

[0005] According to the control chip and control method for an asymmetric half-bridge flyback switching power supply according to the embodiments of the present invention, constant current control of the asymmetric half-bridge flyback switching power supply can be achieved, so that the asymmetric half-bridge flyback switching power supply can be applied to applications requiring constant current control. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present invention can be better understood from the following description of specific embodiments of the present invention in conjunction with the accompanying drawings, in which:

[0007] Figure 1 A schematic diagram of a topology structure of an asymmetric half-bridge flyback switching power supply according to an embodiment of the present invention is shown.

[0008] Figure 2 Shown Figure 1The working waveforms of multiple signals in the asymmetrical half-bridge flyback switching power supply are shown.

[0009] Figure 3 A circuit schematic diagram of a control chip for an asymmetric half-bridge flyback switching power supply according to an embodiment of the present invention is shown.

[0010] Figure 4 Shown Figure 1 The asymmetrical half-bridge flyback switching power supply shown uses Figure 3 The control chip shown is a working waveform diagram of multiple signals when working in critical continuous mode.

[0011] Figure 5 Shown Figure 1 The asymmetrical half-bridge flyback switching power supply shown uses Figure 3 The control chip shown is a working waveform diagram of multiple signals when working in discontinuous mode.

[0012] Figure 6 Shown Figure 1 The asymmetrical half-bridge flyback switching power supply shown uses Figure 3 The control chip shown is a working waveform diagram of multiple signals related to current sampling when working in critical continuous mode.

[0013] Figure 7 Shown Figure 1 The asymmetrical half-bridge flyback switching power supply shown uses Figure 3 The control chip shown is a working waveform diagram of multiple signals related to current sampling when working in discontinuous mode. DETAILED DESCRIPTION

[0014] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is by no means limited to any specific configuration and algorithm proposed below, but covers any modification, replacement, and improvement of elements, components, and algorithms without departing from the spirit of the present invention. In the accompanying drawings and the following description, known structures and techniques are not shown to avoid causing unnecessary ambiguity to the present invention.

[0015] Figure 1 FIG. 1 shows a schematic diagram of a topological structure of an asymmetric half-bridge flyback switching power supply 100 according to an embodiment of the present invention. Figure 1As shown, in the asymmetric half-bridge flyback switching power supply 100, the first and second power switches Q1 and Q2 are both metal oxide semiconductor field effect transistors (MOSFETs), and the zero voltage turn-on of the first and second power switches Q1 and Q2 can be achieved through the resonance of the resonant capacitor Cr and the primary inductor Lp of the transformer T.

[0016] Figure 2 Shown Figure 1 FIG1 is a working waveform diagram of multiple signals in the asymmetric half-bridge flyback switching power supply 100, wherein gate_up represents the upper tube control signal for controlling the on and off of the first power switch Q1, gate_down represents the lower tube control signal for controlling the on and off of the second power switch Q2, and I Lp Represents the current flowing through the primary inductance Lp of the transformer T (referred to as the transformer primary current), I Do represents the current flowing through the secondary inductor Ls of the transformer T (abbreviated as transformer secondary current), and the HB voltage represents the voltage at the middle point HB between the first and second power switches Q1 and Q2.

[0017] Combine Figure 1 and Figure 2 As shown, at time t0, the first power switch Q1 changes from the off state to the on state, and the input voltage (i.e., DC input voltage) Vin of the asymmetric half-bridge flyback switching power supply 100 charges the primary inductor Lp of the transformer T through the resonant capacitor Cr, and the primary current I Lp At time t1, the first power switch Q1 changes from the on state to the off state, and the circuit for the input voltage Vin to charge the primary inductor Lp of the transformer T is disconnected. Since the current in the inductor cannot change suddenly, the primary current I Lp The parasitic capacitance of the second power switch Q2 is discharged, and the HB voltage drops. At time t2, the HB voltage drops to 0V, and the body diode of the second power switch Q2 changes from the off state to the on state. The second power switch Q2 achieves zero voltage conduction. After that, the resonant capacitor Cr resonates with the primary inductance Lp of the transformer T, and the primary current I Lp After dropping to 0A, it increases in a negative direction, and at the same time, the secondary inductance Ls of the transformer T demagnetizes; at time t3, the secondary inductance Ls of the transformer T is demagnetized, and the secondary current I Do Back to 0A, the transformer primary current I Lp It also resonates to 0A, and then the resonant capacitor Cr discharges the primary inductance Lp of the transformer T through the second power switch Q2, and the primary current I Lpnegatively increases; at time t4, the second power switch Q2 changes from the on state to the off state, and the circuit for the resonant capacitor Cr to discharge the primary inductor Lp of the transformer T is disconnected. Since the current in the inductor cannot change suddenly, the primary current I Lp The parasitic capacitance of the first power switch Q1 is discharged, and the HB voltage rises. At time t5, the HB voltage rises to the input voltage Vin, and the body diode of the first power switch Q1 changes from the off state to the on state, and the first power switch Q1 achieves zero voltage turn-on.

[0018] at present, Figure 1 The topology shown is only used in power adapters with constant voltage control and is not applicable to applications requiring constant current control, such as LED lighting. The present invention proposes a control chip and control method for an asymmetric half-bridge flyback switching power supply 100, which can achieve constant current control for the asymmetric half-bridge flyback switching power supply 100.

[0019] Figure 3 The circuit principle diagram of the control chip 102 for the asymmetric half-bridge flyback switching power supply 100 according to an embodiment of the present invention is shown. Figure 1 and Figure 3 , describing the working principle of the control chip 102 when applied to the asymmetric half-bridge flyback switching power supply 100.

[0020] like Figure 1 and Figure 3 As shown, in some embodiments, the control chip 102 can be configured to: based on the current I representing the primary inductance Lp flowing through the transformer T Lp The upper tube control signal gate_up for controlling the on and off of the first power switch Q1 is generated based on the current sensing signal Vcs; and the lower tube control signal gate_down for controlling the on and off of the second power switch Q2 is generated based on the current sensing signal Vcs and the demagnetization sensing signal INV representing the demagnetization condition of the primary inductor Lp of the transformer T (for example, a divided voltage obtained by dividing the voltage on the auxiliary inductor Laux of the transformer T).

[0021] like Figure 1 and Figure 3As shown, in some embodiments, the control chip 102 can be further configured to: generate an output current feedback signal representing the output current of the asymmetric half-bridge flyback switching power supply 100 based on the current sensing signal Vcs; generate an output current compensation signal comp for controlling the compensation of the output current of the asymmetric half-bridge flyback switching power supply 100 based on the output current feedback signal; and generate an upper tube shutdown control signal CC_off for controlling the first power switch Q1 to change from the on state to the off state based on the output current compensation signal comp and the current sensing signal Vcs.

[0022] like Figure 1 and Figure 3 As shown, in some embodiments, the control chip 102 can be further configured to: generate a positive voltage amplitude Vp by sampling the current sensing signal Vcs at the upper tube turn-off moment when the first power switch Q1 changes from the on state to the off state; generate a negative voltage amplitude Vn by sampling the current sensing signal Vcs at the lower tube turn-off moment when the second power switch Q2 changes from the on state to the off state; and generate an output current feedback signal by subtracting the positive voltage amplitude Vp from the negative voltage amplitude Vn.

[0023] like Figure 1 and Figure 3 As shown, in some embodiments, the control chip 102 can be further configured to: when the second power switch Q2 changes from the on state to the off state, start timing the duration of the second power switch Q2 in the off state; and when the duration of the second power switch Q2 in the off state reaches a preset dead time, generate an upper tube conduction control signal ZVS_up_on for controlling the first power switch Q1 to change from the off state to the on state.

[0024] For example, Figure 1 and Figure 3As shown, in the control chip 102, the sampling module 102-1 generates a positive amplitude voltage Vp and a negative amplitude voltage Vn by sampling the current sensing signal Vcs when the first and second power switches Q1 and Q2 change from the on state to the off state; the subtraction module 102-2 generates a difference voltage Vs by subtracting the positive amplitude voltage Vp from the negative amplitude voltage Vn; the control signals of the switches S1 and S2 are mutually inverse signals; when the switch S1 is in the on state and the switch S2 is in the off state, the difference voltage Vs is sent to the inverting input terminal of the operational amplifier 102-3 as the output current feedback signal; when the switch S1 is in the off state and the switch S2 is in the on state, the inverting input terminal of the operational amplifier 102-3 is grounded, and the output current feedback signal is zero; the positive input terminal of the operational amplifier 102-3 is connected to the reference voltage V ref; the operational amplifier 102-3 generates an output current compensation signal comp on the capacitor C by integrating the output current generated by differentiating the reference voltage Vref and the output current feedback signal; the comparator 102-4 generates an upper tube shutdown control signal CC_off for controlling the first power switch Q1 to change from the on state to the off state by comparing the voltage generated by the output current compensation signal comp after the diode step-down and resistor voltage division with the current sensing signal Vcs; the dead time control module 102-5 generates an upper tube conduction control signal ZVS_up_on when a preset dead time has passed after the second power switch Q2 is turned off; the first logic module 102-6 generates an upper tube control signal gate_up based on the upper tube shutdown control signal CC_off and the upper tube conduction control signal ZVS_up_on.

[0025] like Figure 1 and Figure 3 As shown, in some embodiments, the control chip 102 can be further configured to: generate an upper clamping signal maxfre_off for controlling the operating frequency of the asymmetric half-bridge flyback switching power supply 100 based on the output current compensation signal comp; generate a demagnetization detection signal DEM_off indicating whether the demagnetization of the primary inductor Lp of the transformer T is completed based on the demagnetization sensing signal INV; generate a zero voltage turn-on control signal ZVS_off for controlling the zero voltage turn-on of the second power switch Q2 based on the upper clamping signal maxfre_off and the demagnetization detection signal DEM_off; and generate a lower switch turn-off control signal for controlling the second power switch Q2 to change from the on state to the off state based on the upper clamping signal maxfre_off, the demagnetization detection signal DEM_off, and the zero voltage turn-on control signal ZVS_off (i.e., the demagnetization detection signal DEM_off, the upper clamping signal maxfre_off, and the zero voltage turn-on control signal ZVS_off jointly determine the turn-off moment of the second power switch Q2).

[0026] like Figure 1 and Figure 3 As shown, in some embodiments, the control chip 102 can be further configured to: when the first power switch Q1 changes from the on state to the off state, start timing the duration of the first power switch Q1 being in the off state; and when the duration of the first power switch Q1 being in the off state reaches a preset dead time, generate a down-tube conduction control signal ZVS_down_on for controlling the second power switch Q2 to change from the off state to the on state.

[0027] For example, Figure 1 and Figure 3 As shown, in the control chip 102, the dead time control module 102-5 generates a lower switch conduction control signal ZVS_down_on when a preset dead time has passed after the first power switch Q1 is turned off; the demagnetization detection module 102-7 generates a demagnetization detection signal DEM_off based on the demagnetization sensing signal INV; the frequency control module 102-8 generates an upper frequency clamping signal maxfre_off and an upper frequency clamping signal maxf_off for limiting the operating frequency of the asymmetric half-bridge flyback switching power supply 100 based on a signal generated by the output current compensation signal comp after diode step-down and resistor voltage division. re_off can reduce the operating frequency when the load decreases; the delay module 102-8 generates a zero voltage turn-on control signal ZVS_off based on the demagnetization detection signal DEM_off and the upper clamping frequency signal maxfre_off; the second logic module 102-10 generates a lower tube shutdown control signal based on the demagnetization detection signal DEM_off, the upper clamping frequency signal maxfre_off, and the zero voltage turn-on control signal ZVS_off, and generates a lower tube control signal gate_down based on the lower tube shutdown control signal and the lower tube conduction control signal ZVS_down_on.

[0028] like Figure 1 and Figure 3 As shown, after the first power switch Q1 changes from the off state to the on state, the input voltage Vin charges the primary inductor Lp of the transformer T through the resonant capacitor Cr, and the primary current I Lp The positive direction increases, and the current sensing signal Vcs increases; when the current sensing signal Vcs is greater than the voltage generated by the output current compensation signal comp after the diode step-down and the resistor voltage division, the upper tube shutdown control signal CC_off changes from a low level to a high level, and the first power switch Q1 changes from the on state to the off state; after the first power switch Q1 changes from the on state to the off state, the transformer primary current I LpThe parasitic capacitance of the second power switch Q2 is discharged, the HB voltage drops to 0V, the body diode of the second power switch Q2 is turned on, and the second power switch Q2 achieves zero voltage turn-on; after the second power switch Q2 changes from the on state to the off state, the primary current I Lp The parasitic capacitance of the first power switch Q1 is discharged, the HB voltage rises to the input voltage Vin, the body diode of the first power switch Q1 is turned on, and the first power switch Q1 is turned on at zero voltage.

[0029] In the asymmetrical half-bridge flyback switching power supply 100 Figure 3 In the case of the control chip 102 shown, the different timings of the demagnetization detection signal DEM_off and the upper frequency clamp signal maxfre_off determine different operating states of the asymmetric half-bridge flyback switching power supply 100. When the upper frequency clamp signal maxfre_off transitions from a low level to a high level earlier than the demagnetization detection signal DEM_off, the asymmetric half-bridge flyback switching power supply 100 operates in critical continuous mode. When the demagnetization detection signal DEM_off transitions from a low level to a high level earlier than the upper frequency clamp signal maxfre_off, the asymmetric half-bridge flyback switching power supply 100 operates in discontinuous mode.

[0030] Figure 4 Shown Figure 1 The asymmetrical half-bridge flyback switching power supply 100 shown in FIG. Figure 3 The control chip 102 shown in FIG. 1 is a working waveform diagram of multiple signals when the control chip 102 works in the critical continuous mode. Figure 4 As shown, when the demagnetization detection module 102-7 detects that the primary inductance Lp of the transformer T has finished demagnetizing through the falling slope of the demagnetization sensing signal INV, the demagnetization detection signal DEM_off changes from a low level to a high level. If the upper clamping frequency signal Maxfre_off is at a high level at this time, the delay module 102-9 delays the demagnetization detection signal DEM_off by a fixed time T. ZVS Then, a high-level zero voltage turn-on control signal ZVS_off is generated, so that the second power switch Q2 changes from the on state to the off state.

[0031] Figure 5 Shown Figure 1 The asymmetrical half-bridge flyback switching power supply 100 shown in FIG. Figure 3 The control chip 102 shown in FIG. 1 is a working waveform diagram of multiple signals when the control chip 102 works in the discontinuous mode. Figure 5As shown, when the demagnetization detection module 102-7 detects that the primary inductance Lp of the transformer T has finished demagnetizing based on the falling slope of the demagnetization sensing signal INV, the demagnetization detection signal DEM_off changes from a low level to a high level. If the upper clamping frequency signal Maxfre_off is still at a low level at this time, the second power switch Q2 is directly controlled to change from an on state to an off state. When the upper clamping frequency signal Maxfre_off changes from a low level to a high level, the second power switch Q2 is again controlled to change from an off state to an on state. The delay module 102-9 delays the high-level upper clamping frequency signal Maxfre_off by a fixed time T. ZVS Then, a high-level zero voltage turn-on control signal ZVS_off is generated, so that the second power switch Q2 changes from the on state to the off state.

[0032] Figure 6 and Figure 7 Shown respectively Figure 1 The asymmetrical half-bridge flyback switching power supply 100 shown in FIG. Figure 3 The control chip 102 shown in the figure is working in the critical continuous mode and the discontinuous mode and the working waveform of multiple signals related to current sampling, wherein: S1 represents the control signal for controlling the conduction and shutoff of the switch S1; S2 represents the control signal for controlling the conduction and shutoff of the switch S2. Figure 6 and Figure 7 It can be seen that when the asymmetric half-bridge flyback switching power supply 100 is in different operating modes, the sampling module 102 - 1 samples the current sensing signal Vcs at different sampling times.

[0033] like Figure 6 As shown, when the asymmetric half-bridge flyback switching power supply 100 operates in the critical continuous mode: at the upper tube turn-off time tp1 when the first power switch Q1 changes from the on state to the off state, the sampling module 102-1 samples the current sensing signal Vcs to obtain the positive voltage amplitude Vp; at the lower tube turn-off time tn1 when the second power switch Q2 changes from the on state to the off state, the sampling module 102-1 samples the current sensing signal Vcs to obtain the negative voltage amplitude Vn; the subtraction module 102-2 obtains the difference voltage Vs by subtracting the positive voltage amplitude Vp from the negative voltage amplitude Vn; due to the primary current I Lp The discontinuous mode is not entered, the switch S1 is always in the on state and the switch S2 is always in the off state, and the difference voltage Vs is sent to the inverting input terminal of the operational amplifier 102 - 3 as the output current feedback signal.

[0034] like Figure 7As shown, when the asymmetric half-bridge flyback switching power supply 100 operates in the discontinuous mode: at the upper tube turn-off time tp2 when the first power switch Q1 changes from the on state to the off state, the sampling module 102-1 samples the current sensing signal Vcs to obtain the positive voltage amplitude Vp; at the lower tube turn-off time tn2 when the primary inductor Lp of the transformer T is demagnetized and the second power switch Q2 changes from the on state to the off state, the sampling module 102-1 samples the current sensing signal Vcs to obtain the first negative voltage amplitude Vn1; in the same switching cycle, when the second power switch Q2 is in the on state for T ZVS At the turn-off time tn3 when the lower tube changes from the on state to the off state again after a certain time, the sampling module 102-1 samples the current sensing signal Vcs to obtain the second negative voltage amplitude Vn2; the larger of the first and second negative voltage amplitudes Vn1 and Vn2 is the negative voltage amplitude Vn; the subtraction module 102-2 obtains the difference voltage Vs by subtracting the positive voltage amplitude Vp from the negative voltage amplitude Vn; due to the transformer primary current I Lp Working in the discontinuous state, the second power switch Q2 is in the off state for a duration T DCM During this period, the switch S2 is in the on state, the inverting input terminal of the operational amplifier 102-3 is grounded, and the output current feedback signal is zero. DCM During the time, the switch S1 is in the on state, and the inverting input terminal of the operational amplifier 102 - 3 is connected to the difference voltage Vs. That is, the difference voltage Vs is sent to the inverting input terminal of the operational amplifier 102 - 3 as the output current feedback signal.

[0035] In summary, Figure 3 The control chip 102 shown can be used to control various asymmetric half-bridge flyback switching power supplies that require constant current, achieving zero voltage conduction of the two power switches and maximizing system efficiency. Figure 1 The asymmetrical half-bridge flyback switching power supply 100 and Figure 3 The control chip 102 shown can be applied to the field of LED lighting to reduce the size of the lighting power supply.

[0036] The present invention may be implemented in other specific forms without departing from its spirit and essential characteristics. For example, the algorithms described in the specific embodiments may be modified without departing from the basic spirit of the present invention. Therefore, the present embodiments are to be considered in all respects as illustrative and not restrictive, the scope of the invention is defined by the appended claims rather than the foregoing description, and all modifications coming within the meaning and scope of equivalents of the claims are intended to be included within the scope of the present invention.

Claims

1. A control chip for an asymmetric half-bridge flyback switching power supply, wherein: The asymmetric half-bridge flyback switching power supply includes a first power switch, a second power switch, and a transformer, and the control chip is configured as follows: The first power switch is controlled to be turned on and off by the following process: generating an output current feedback signal representing an output current of the asymmetric half-bridge flyback switching power supply based on a current sensing signal representing a current flowing through a primary inductance of the transformer; generating an output current compensation signal for controlling compensation of an output current of the asymmetric half-bridge flyback switching power supply based on the output current feedback signal; Based on the output current compensation signal and the current sensing signal, generating an upper tube shutoff control signal for controlling the first power switch to change from an on state to an off state; When the second power switch changes from the on state to the off state, starting to count the duration of the second power switch being in the off state; and When the duration of the second power switch being in the off state reaches a preset dead time, generating an upper tube conduction control signal for controlling the first power switch to change from the off state to the on state; as well as The second power switch is controlled to be turned on and off by the following process: generating an upper frequency clamping signal for controlling the operating frequency of the asymmetric half-bridge flyback switching power supply based on the output current compensation signal; generating a demagnetization detection signal indicating whether demagnetization of the primary inductance of the transformer has been completed based on a demagnetization sensing signal indicating a demagnetization condition of the primary inductance of the transformer; generating a zero voltage turn-on control signal for controlling zero voltage turn-on of the second power switch based on the upper clamping signal and the demagnetization detection signal; Generate a lower switch off control signal for controlling the second power switch to change from an on state to an off state based on the upper clamping signal, the demagnetization detection signal, and the zero voltage turn-on control signal; When the first power switch changes from the on state to the off state, starting to time the duration of the first power switch being in the off state; as well as When the duration of the first power switch being in the off state reaches a preset dead time, a lower switch conduction control signal is generated for controlling the second power switch to change from the off state to the on state.

2. The control chip according to claim 1, further configured to: Generate a forward voltage amplitude by sampling the current sensing signal at the turn-off moment of the upper tube when the first power switch changes from the on state to the off state; Generate a negative voltage amplitude by sampling the current sensing signal at the lower tube turn-off moment when the second power switch changes from the on state to the off state; and The output current feedback signal is generated by subtracting the positive voltage amplitude from the negative voltage amplitude.

3. The control chip according to claim 1, wherein: When the upper frequency clamping signal changes from a low level to a high level earlier than the demagnetization detection signal, the asymmetric half-bridge flyback switching power supply operates in a critical continuous mode.

4. The control chip according to claim 1, wherein: When the demagnetization detection signal changes from a low level to a high level earlier than the upper frequency clamping signal, the asymmetric half-bridge flyback switching power supply operates in a discontinuous mode.

5. The control chip according to claim 3, further configured to: When the upper frequency clamping signal is at a high level, the zero voltage turn-on control signal is generated by delaying the demagnetization detection signal.

6. The control chip according to claim 4, further configured to: When the demagnetization detection signal is at a low level, the zero voltage turn-on control signal is generated by delaying the upper frequency clamping signal.

7. A control method for an asymmetric half-bridge flyback switching power supply, wherein: The asymmetric half-bridge flyback switching power supply includes a first power switch, a second power switch, and a transformer, and the control method includes: The first power switch is controlled to be turned on and off by the following process: generating an output current feedback signal representing an output current of the asymmetric half-bridge flyback switching power supply based on a current sensing signal representing a current flowing through a primary inductance of the transformer; generating an output current compensation signal for controlling compensation of an output current of the asymmetric half-bridge flyback switching power supply based on the output current feedback signal; Based on the output current compensation signal and the current sensing signal, generating an upper tube shutoff control signal for controlling the first power switch to change from an on state to an off state; When the second power switch changes from the on state to the off state, starting to count the duration of the second power switch being in the off state; and When the duration of the second power switch being in the off state reaches a preset dead time, generating an upper tube conduction control signal for controlling the first power switch to change from the off state to the on state; and The second power switch is controlled to be turned on and off by the following process: generating an upper frequency clamping signal for controlling the operating frequency of the asymmetric half-bridge flyback switching power supply based on the output current compensation signal; generating a demagnetization detection signal indicating whether demagnetization of the primary inductance of the transformer has been completed based on a demagnetization sensing signal indicating a demagnetization condition of the primary inductance of the transformer; generating a zero voltage turn-on control signal for controlling zero voltage turn-on of the second power switch based on the upper clamping signal and the demagnetization detection signal; Generate a lower switch off control signal for controlling the second power switch to change from an on state to an off state based on the upper clamping signal, the demagnetization detection signal, and the zero voltage turn-on control signal; When the first power switch changes from the on state to the off state, starting to count the duration of the first power switch being in the off state; and When the duration of the first power switch being in the off state reaches a preset dead time, a lower switch conduction control signal is generated for controlling the second power switch to change from the off state to the on state.

8. The control method according to claim 7, wherein: The process of generating the output current feedback signal includes: Generate a forward voltage amplitude by sampling the current sensing signal at the turn-off moment of the upper tube when the first power switch changes from the on state to the off state; Generate a negative voltage amplitude by sampling the current sensing signal at the lower tube turn-off moment when the second power switch changes from the on state to the off state; and The output current feedback signal is generated by subtracting the positive voltage amplitude from the negative voltage amplitude.

9. The control method according to claim 7, wherein: When the upper frequency clamping signal changes from a low level to a high level earlier than the demagnetization detection signal, the asymmetric half-bridge flyback switching power supply operates in a critical continuous mode.

10. The control method according to claim 7, wherein: When the demagnetization detection signal changes from a low level to a high level earlier than the upper frequency clamping signal, the asymmetric half-bridge flyback switching power supply operates in a discontinuous mode.

11. The control method according to claim 9, wherein: The process of generating the zero voltage turn-on control signal includes: When the upper frequency clamping signal is at a high level, the zero voltage turn-on control signal is generated by delaying the demagnetization detection signal.

12. The control method according to claim 10, wherein: The process of generating the zero voltage turn-on control signal includes: When the demagnetization detection signal is at a low level, the zero voltage turn-on control signal is generated by delaying the upper frequency clamping signal.

13. An asymmetric half-bridge flyback switching power supply, comprising the control chip according to any one of claims 1 to 6.

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