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, a resonant capacitor, and a transformer, the primary excitation inductance of the transformer comprising a primary inductance and a primary leakage inductance. 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 an output feedback signal representing the output voltage of the asymmetric half-bridge flyback switching power supply and a current sensing signal representing the current flowing through the primary inductance; and generate a lower tube control signal for controlling the turn-on and turn-off of the second power switch based on the output feedback signal and a voltage sensing signal representing the voltage on the auxiliary winding of the transformer. The control chip is configured to identify the time when the primary excitation inductance of the transformer demagnetizes based on the output feedback signal and the voltage sensing signal, and generate the lower tube control signal based on the time.

Description

Technical Field

[0001] This invention relates to the field of circuits, and more specifically to an asymmetric half-bridge flyback switching power supply, its control chip, and control method. Background Technology

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

[0003] One aspect of this disclosure provides a control chip for an asymmetric half-bridge flyback switching power supply. The asymmetric half-bridge flyback switching power supply includes a first power switch, a second power switch, a resonant capacitor, and a transformer, wherein the primary-side magnetizing inductance of the transformer includes a primary-side inductance and a primary-side leakage inductance. 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 an output feedback signal characterizing the output voltage of the asymmetric half-bridge flyback switching power supply and a current sensing signal characterizing the current flowing through the primary-side inductance; and generate a lower-side control signal for controlling the on / off state of the second power switch based on the output feedback signal and a voltage sensing signal characterizing the voltage on the auxiliary winding of the transformer. The control chip is configured to identify the moment when the demagnetization of the primary-side magnetizing inductance of the transformer ends based on the output feedback signal and the voltage sensing signal, and to generate the lower-side control signal based on that moment.

[0004] Another aspect of this disclosure provides a control method for an asymmetric half-bridge flyback switching power supply. The asymmetric half-bridge flyback switching power supply includes a first power switch, a second power switch, a resonant capacitor, and a transformer, wherein the primary-side magnetizing inductance of the transformer includes a primary-side inductance and a primary-side leakage inductance. The control method includes generating an upper-side control signal for controlling the on / off state of the first power switch based on an output feedback signal characterizing the output voltage of the asymmetric half-bridge flyback switching power supply and a current sensing signal characterizing the current flowing through the primary-side inductance; and generating a lower-side control signal for controlling the on / off state of the second power switch based on the output feedback signal and a voltage sensing signal characterizing the voltage on the auxiliary winding of the transformer. The control chip is configured to identify the moment when the demagnetization of the primary-side magnetizing inductance of the transformer ends based on the output feedback signal and the voltage sensing signal, and to generate the lower-side control signal based on that moment.

[0005] Another aspect of this disclosure provides an asymmetric half-bridge flyback switching power supply using the above-described control chip or control method. Attached Figure Description

[0006] The invention can be better understood from the following description of specific embodiments in conjunction with the accompanying drawings. The drawings are not to scale, and well-known structures or parts may be omitted.

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

[0008] Figure 2 It shows Figure 1 The diagram shows the waveforms of multiple signals of an asymmetric half-bridge flyback switching power supply in critical continuous mode (CRM).

[0009] Figure 3 It shows Figure 1 The diagram shows the waveforms of multiple signals in discontinuous current mode (DCM) of an asymmetric half-bridge flyback switching power supply.

[0010] Figure 4 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.

[0011] Figure 5 It shows the use of Figure 4 The diagram shows the waveforms of multiple signals when the asymmetric half-bridge flyback switching power supply of the control chip is operating in critical continuous mode.

[0012] Figure 6 It shows the use of Figure 4 The diagram shows the waveforms of multiple signals when the asymmetric half-bridge flyback switching power supply of the control chip operates in discontinuous current mode.

[0013] Figure 7 It shows Figure 4 The circuit schematic is shown as an example implementation of the demagnetization detection unit in the control chip.

[0014] Figure 8 It shows Figure 4 The circuit schematic is shown as another example of the demagnetization detection unit in the control chip. Detailed Implementation

[0015] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific configurations and algorithms presented below, but covers any modifications, substitutions, and improvements to elements, components, and algorithms without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description in order to avoid unnecessarily obscuring the invention.

[0016] Figure 1 A schematic diagram of the topology of an asymmetric half-bridge flyback switching power supply 100 according to an embodiment of the present invention is shown. Figure 1 As shown, in the asymmetric half-bridge flyback switching power supply 100, both the first power switch Q1 and the second power switch Q2 are metal-oxide-semiconductor field-effect transistors (MOSFETs). Zero-voltage conduction of the first power switch Q1 and the second power switch Q2 can be achieved through the resonance of the resonant capacitor Cr and the primary inductance Lp and primary leakage inductance Lr of the transformer T. In this application, the sum of the primary inductance Lp and primary leakage inductance Lr of the transformer T is referred to as the primary magnetizing inductance Lm of the transformer T, and the secondary inductance of the transformer T is denoted by Ls.

[0017] Figure 2 It shows Figure 1 The diagram shows the waveforms of multiple signals operating in critical continuous mode (CRM) of the asymmetric half-bridge flyback switching power supply 100. Figure 2 In the diagram, Gate_up represents the upper transistor control signal used to control the on / off state of the first power switch Q1, and Gate_down represents the lower transistor control signal used to control the on / off state of the second power switch Q2. Lr I represents the primary resonant current (or simply primary resonant current) of transformer T. Lm I represents the primary magnetizing current (or simply primary magnetizing current) of transformer T. Do V represents the current flowing through the secondary inductance Ls of transformer T (referred to as secondary current). HB This represents the voltage at the midpoint HB between the first power switch Q1 and the second power switch Q2 (abbreviated as HB voltage).

[0018] Combination Figure 1 and Figure 2As shown, at time t0, the first power switch Q1 changes from the off state to the on state. The input voltage (i.e., DC input voltage) Vin of the asymmetrical half-bridge flyback switching power supply 100 charges the primary magnetizing inductance Lm (including the primary inductance Lp and the primary leakage inductance Lr) of the transformer T through the resonant capacitor Cr. The primary resonant current I Lr The positive increase occurs; at time t1, the first power switch Q1 changes from the on state to the off state, and the circuit for charging the primary excitation inductor Lm of the transformer T by the input voltage Vin is broken. Since the current in the inductor cannot change abruptly, the primary resonant current I... Lr The parasitic capacitance of the second power switch Q2 is discharged, and the parasitic capacitance of the first power switch Q1 is charged, causing the HB voltage to drop. 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, achieving zero-voltage conduction of the second power switch Q2. Afterwards, the resonant capacitor Cr and the primary leakage inductance Lr of the transformer T resonate, and the primary resonant current I of the transformer... Lr After dropping to 0A, the negative current increases, and at the same time, the secondary inductance Ls of transformer T demagnetizes, and the primary excitation current I... Lm The primary excitation current I decreases linearly; at time t3, the primary excitation current I... Lm Reduced to 0A, primary resonant current I Lr The current remains negative, therefore resonance continues; at time t4, the primary resonant current I... Lr Resonance to the primary excitation current I Lm The same size, the demagnetization of the transformer secondary side is complete, I Do Returning to 0A, the resonant capacitor Cr then discharges through the second power switch Q2 to the primary magnetizing inductance Lm of the transformer T, and the primary resonant current I... Lr The negative value increases; at time t5, the second power switch Q2 changes from the on state to the off state, and the discharge circuit of the resonant capacitor Cr to the primary excitation inductance Lm of the transformer T is broken. Since the current in the inductor cannot change abruptly, the primary resonant current I of the transformer... Lr Discharging the parasitic capacitance of the first power switch Q1 and charging the parasitic capacitance of the second power switch Q2 causes the HB voltage to rise (if the negative primary resonant current I...). Lr If the voltage is large enough, the HB voltage will rise until it reaches the input voltage Vin. At time t6, 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, so the first power switch Q1 achieves zero-voltage conduction.

[0019] Figure 3 It shows Figure 1 The diagram shows the waveforms of multiple signals operating in discontinuous current mode (DCM) of the asymmetric half-bridge flyback switching power supply 100. Figure 3In the diagram, Gate_up represents the upper transistor control signal used to control the on / off state of the first power switch Q1, and Gate_down represents the lower transistor control signal used to control the on / off state of the second power switch Q2. Lr I represents the primary resonant current (or simply primary resonant current) of transformer T. Lm I represents the primary magnetizing current (or simply primary magnetizing current) of transformer T. Do V represents the current flowing through the secondary inductance Ls of transformer T (referred to as secondary current). HB This represents the voltage at the midpoint HB between the first power switch Q1 and the second power switch Q2 (abbreviated as HB voltage).

[0020] Combination Figure 1 and Figure 3 As shown, at time t0, the first power switch Q1 changes from the off state to the on state. The input voltage (i.e., DC input voltage) Vin of the asymmetrical half-bridge flyback switching power supply 100 charges the primary magnetizing inductance Lm (including the primary inductance Lp and the primary leakage inductance Lr) of the transformer T through the resonant capacitor Cr. The primary resonant current I Lr The positive current increases; at time t1, the first power switch Q1 changes from the on state to the off state, and the circuit for charging the primary excitation inductor Lm of the transformer T by the input voltage Vin is broken. Since the current in the inductor cannot change abruptly, the positive primary resonant current I... Lr The parasitic capacitance of the second power switch Q2 is discharged, and the parasitic capacitance of the first power switch Q1 is charged, causing the HB voltage to drop. 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, achieving zero-voltage conduction of the second power switch Q2. Afterwards, the resonant capacitor Cr and the primary leakage inductance Lr of the transformer T resonate, and the primary resonant current I... Lr After dropping to 0A, the negative current increases, and at the same time, the secondary inductance Ls of transformer T demagnetizes, and the primary excitation current I... Lm The primary excitation current I decreases linearly; at time t3, the primary excitation current I... Lm Reduced to 0A, primary resonant current I Lr The current remains negative, therefore resonance continues; at time t4, the second power switch Q2 changes from the on state to the off state, and the resonant circuit of the transformer T's resonant capacitor Cr and primary leakage inductance Lr is broken, but the primary resonant current I... Lr Since the current is still negative, the body diode of the first power switch Q1 returns energy to the input voltage Vin. Then, the parasitic capacitances of the first power switch Q1 and the second power switch Q2 resonate with the primary magnetizing inductance Lm. At time t5, the second power switch Q2 changes from the off state to the on state again, and the resonant capacitor Cr discharges through the second power switch Q2 onto the primary magnetizing inductance Lm of the transformer T, causing the primary resonant current I...Lr The negative current increases; at time t6, the second power switch Q2 changes from the on state to the off state again, the discharge circuit of the resonant capacitor Cr to the primary excitation inductance Lm of the transformer T is broken, and the parasitic capacitances of the primary excitation inductance Lm of the transformer T and the first power switch Q1 and the second power switch Q2 resonate. Since the current in the primary excitation inductance Lm cannot change abruptly, the negative primary resonant current I... Lr Discharging the parasitic capacitance of the first power switch Q1 and charging the parasitic capacitance of the second power switch Q2 causes the HB voltage to rise (if the negative primary resonant current I...). Lr If the voltage is large enough, the HB voltage will rise until it reaches the input voltage Vin. At time t7, 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, so that the first power switch Q1 achieves zero-voltage conduction.

[0021] In such Figure 2 In the critical continuous mode shown, during the time period from t5 to t6, after the second power switch Q2 is turned off and before the first power switch Q1 is turned on, the negative primary resonant current I... Lr The magnitude of the negative current required for the first power switch Q1 to turn on at zero voltage is determined by the magnitude of the negative current, which is determined by the magnitude of the parasitic capacitance of the first power switch Q1 and the second power switch Q2. In critical continuous mode, as the load output current Io decreases, the positive peak current Ip also decreases, and the conduction time of the first power switch Q1 decreases accordingly. The operating frequency of the switching power supply 100 increases. However, under light load conditions, the increased frequency leads to decreased efficiency, so it is necessary to enter... Figure 3 The current discontinuous mode is shown. In the current discontinuous mode, during the time period from t6 to t7, after the second power switch Q2 is turned off for the second time and before the first power switch Q1 is turned on, the negative primary resonant current I... Lr The magnitude of this negative current is determined by the magnitude of the negative current required for the first power switch Q1 to conduct at zero voltage, which is determined by the magnitude of the parasitic capacitances of the first power switch Q1 and the second power switch Q2. This negative current is usually small. Meanwhile, the negative primary-side resonant current I after the first power switch Q1 is first turned off (i.e., at time t1) is... Lr The magnitude of the amplitude In is determined by the conduction time of the second power switch Q2. The longer the conduction time of the second power switch Q2, the greater the negative primary resonant current I when the second power switch Q2 is turned off. Lr The larger the amplitude In, the larger the positive peak current Ip required for a constant output, and the higher the operating frequency of the switching power supply 100. Therefore, the conduction time of the second power switch Q2 in discontinuous current mode determines the frequency reduction speed of the switching power supply 100. However, the conduction time of the second power switch Q2 cannot be too short, otherwise the primary side magnetizing current I... LmEven after the second power switch Q2 is turned off, the positive primary excitation current I is less than 0A. Lm The demagnetization continues through the body diode of the second power switch Q2. The large forward voltage drop of the body diode significantly impacts efficiency. Therefore, for discontinuous current mode (see...), Figure 3 The second power switch Q2 has a primary-side excitation current I. Lm Turning off at the moment of demagnetization to 0A yields the best efficiency, while for critical continuous mode (see...) Figure 2 ), which requires the primary excitation current I Lm Starting from the moment of demagnetization to 0A, the primary resonant current I... Lr The time it takes for the negative voltage to increase sufficiently to turn on the first power switch Q1 with zero voltage is timed. During the conduction of the second power switch Q2, the current sensing resistor Rcs in the asymmetric half-bridge flyback switching power supply 100 (see...) Figure 1 What was detected was only the resonant current I in the leakage inductance. Lr The primary excitation current I Lm The current can only be detected on the current sensing resistor Rcs after the second power switch Q2 is turned off, so the resonant current I on the current sensing resistor Rcs cannot be directly obtained. Lr The turn-off time of the second power switch Q2 is determined by detecting the end of demagnetization of the excitation inductor Lm.

[0022] At least in view of the above problems, a control chip and control method for an asymmetric half-bridge flyback switching power supply 100 according to an embodiment of the present invention are proposed. The control chip and control method can calculate the moment when the primary side excitation current demagnetizes to 0A during the conduction period of the second power switch Q2 under different input voltages, different output voltages or different load currents, thereby controlling the turn-off moment of the second power switch Q2. This allows the circuit system using the switching power supply 100 to smoothly reduce the frequency after entering a light load, thereby optimizing the light load efficiency.

[0023] Figure 4 A circuit schematic diagram of a control chip 400 for an asymmetric half-bridge flyback switching power supply according to an embodiment of the present invention is shown. The following is in conjunction with... Figure 1 and Figure 4 ,describe Figure 4 The control chip 400 shown is used in Figure 1 The example shown is the asymmetric half-bridge flyback switching power supply 100.

[0024] like Figure 1 and Figure 4As shown, in some embodiments, the control chip 400 can be configured to: generate an upper-side control signal Gate_up for controlling the on / off of the first power switch Q1 based on an output feedback signal FB characterizing the output voltage Vo of the asymmetric half-bridge flyback switching power supply 100 and a current sensing signal Vcs characterizing the current flowing through the primary inductance Lp of the transformer T; and generate a lower-side control signal Gate_down for controlling the on / off of the second power switch Q2 based on the output feedback signal FB and a voltage sensing signal INV characterizing the voltage on the auxiliary winding of the transformer T. Specifically, for example, the control chip 400 can be configured to at least identify the moment when the demagnetization of the primary magnetizing inductance Lm of the transformer of the asymmetric half-bridge flyback switching power supply 100 ends, i.e., the primary magnetizing current I, based on the output feedback signal FB and the voltage sensing signal INV. Lm The time when the current decreases to 0A is used to generate the gate control signal Gate_down based on that time.

[0025] Optionally, the control chip 400 is configured to identify the moment when the primary magnetizing inductance Lm of the transformer of the asymmetric half-bridge flyback switching power supply 100 ends demagnetization based on the output feedback signal FB, the voltage sensing signal INV, and the external adjustment signal ADJ.

[0026] like Figure 1 and Figure 4 As shown, in some embodiments, the output voltage Vo is divided by resistors and then processed by a Zener diode TL431 and an optocoupler to generate an output feedback signal FB; the output feedback signal FB is then stepped down by a diode and divided by resistors to generate a voltage V. FB_2 The current sensing signal Vcs is fed into comparator 401 of control chip 400. Comparator 401 compares Vcs with the current sensing signal Vcs. FB_2 The magnitude of Vcs determines the turn-off moment when the first power switch Q1 changes from the on state to the off state, which is the upper-side turn-off control signal CV_off. In other words, the control chip 400 is further configured to generate the upper-side turn-off control signal CV_off for controlling the first power switch Q1 to change from the on state to the off state based on the output feedback signal FB and the current sensing signal Vcs.

[0027] like Figure 1 and Figure 4 As shown, in some embodiments, the control chip 400 includes a dead time control unit 402, which starts timing the duration of the second power switch Q2 being in the off state when the second power switch Q2 changes from the on state to the off state, and generates an up-on control signal for controlling the first power switch Q1 to change from the off state to the on state when the duration of the second power switch Q2 being in the off state reaches a preset dead time.

[0028] like Figure 1 and Figure 4 As shown, in some embodiments, the control chip 400 includes a first logic control unit (Logic1) 403, which generates an upper-side control signal Gate_up based on the upper-side turn-off control signal CV_off and the upper-side turn-on control signal up_on.

[0029] like Figure 1 and Figure 4 As shown, in some embodiments, the control chip 400 includes a frequency control unit 404, a demagnetization (DEM) detection unit 405, and a zero-voltage conduction (ZVS) control unit 406, wherein the frequency control unit 404 is based on an output feedback signal FB (such as V). FB_2 The system generates a frequency control signal DCM_on to control the operating frequency of the asymmetric half-bridge flyback switching power supply 100. For example, when the load is heavy, the asymmetric half-bridge flyback switching power supply 100 operates in critical continuous mode, while when the load decreases, the frequency control signal DCM_on can reduce the operating frequency of the asymmetric half-bridge flyback switching power supply 100 to operate in discontinuous current mode. The demagnetization detection unit 405 is based at least on the voltage sensing signal INV and the output feedback signal FB (such as V). FB_2 The demagnetizing detection signal DEM_off is generated to characterize the demagnetization of the primary magnetizing inductance Lm of transformer T. The zero-voltage turn-on control unit 406 generates a lower transistor turn-off control signal ZVS_off based on the frequency control signal DCM_on, the demagnetizing detection signal DEM_off, and the voltage sensing signal INV, to control the second power switch Q2 to change from the on state to the off state. Optionally, in some other embodiments, the demagnetizing detection unit 405 may be configured to generate a lower transistor turn-off control signal ZVS_off based on the voltage sensing signal INV and the output feedback signal FB (e.g., V). FB_2 The external adjustment signal ADJ is used to generate the demagnetization detection signal DEM_off.

[0030] In the embodiments of this application, the control chip 400 can identify the moment when the demagnetization of the primary excitation inductance Lm of the transformer of the asymmetric half-bridge flyback switching power supply 100 ends based on the demagnetization detection signal DEM_off. As an example only, the following will be combined with... Figure 7 and Figure 8 This section describes in detail how to identify the moment when the demagnetization of the primary excitation inductance Lm of the transformer in an asymmetric half-bridge flyback switching power supply 100 ends based on the demagnetization detection signal DEM_off.

[0031] like Figure 1 and Figure 4As shown, in some embodiments, the dead time control unit 402 also starts timing the duration of the first power switch Q1 being in the off state when the first power switch Q1 changes from the on state to the off state, and generates a down_on control signal for controlling the second power switch Q2 to change from the off state to the on state when the duration of the first power switch Q1 being in the off state reaches a preset dead time.

[0032] like Figure 1 and Figure 4 As shown, in some embodiments, the control chip 400 further includes a second logic control unit 407, which generates a lower transistor control signal Gate_down based on the lower transistor turn-off control signal ZVS_off, the demagnetization detection signal DEM_off, the frequency control signal DCM_on, and the lower transistor turn-on control signal down_on.

[0033] Specifically, the second logic control unit 407 can determine different operating states of the asymmetric half-bridge flyback switching power supply 100 based on the frequency control signal DCM_on. For example, when the frequency control signal DCM_on is continuously high or becomes high before the instantaneous pulse of the demagnetization detection signal DEM_off, the asymmetric half-bridge flyback switching power supply 100 operates in critical continuous mode; when the frequency control signal DCM_on is low when the instantaneous pulse of the demagnetization detection signal DEM_off occurs, the asymmetric half-bridge flyback switching power supply 100 operates in discontinuous current mode. The second logic control unit 407 can determine the turn-off time that causes the second power switch Q2 to change from the on state to the off state based on the lower transistor turn-off control signal ZVS_off and the demagnetization detection signal DEM_off, and generate the lower transistor control signal Gate_down in combination with the operating mode of the asymmetric half-bridge flyback switching power supply 100 determined by the frequency control signal DCM_on.

[0034] Specifically, for example, the second logic control unit 407 can determine that the asymmetric half-bridge flyback switching power supply 100 is operating in critical continuous mode when the frequency control signal DCM_on is continuously high or becomes high before the demagnetization detection signal DEM_off appears with a transient pulse, and when the demagnetization detection signal DEM_off appears with a transient pulse, it keeps the lower transistor turn-off control signal ZVS_off at a low level until the reverse resonant current I flowing through the primary leakage inductance Lr of the transformer T. LrWhen sufficient voltage is applied to achieve zero-voltage conduction of the first power switch Q1, a momentary pulse is generated in the lower transistor turn-off control signal ZVS_off to turn off the second power switch Q2; and when the frequency control signal DCM_on is low when the demagnetization detection signal DEM_off generates a momentary pulse, it is determined that the asymmetric half-bridge flyback switching power supply 100 operates in discontinuous current mode and the second power switch Q2 is changed from the on state to the off state. When the frequency control signal DCM_on generates a momentary pulse, the second power switch Q2 is changed from the off state to the on state, and the reverse resonant current I flowing through the primary leakage inductance Lr of the transformer T... Lr When the first power switch Q1 is turned on at zero voltage, a momentary pulse is generated in the lower transistor turn-off control signal ZVS_off to turn off the second power switch.

[0035] Figure 1 The asymmetric half-bridge flyback switching power supply 100 shown is in Figure 4 Under the control of the control chip 400 shown, when the first power switch Q1 enters the on state from the off state, the input voltage (i.e., the DC input voltage) Vin charges the primary magnetizing inductance Lm (including the primary inductance Lp and the primary leakage inductance Lr) of the transformer T through the resonant capacitor Cr, and the primary resonant current I... Lr As the current increases, the current sensing signal Vcs increases. When the current sensing signal Vcs is higher than the voltage V after the output feedback signal FB is divided... FB_2 At this time, comparator 401 generates a high-level transistor turn-off control signal CV_off (e.g., high level) to indicate that the first power switch Q1 changes from the on state to the off state. After the first power switch Q1 is turned off, since the current in the inductor cannot change abruptly, the positive primary-side resonant current I... Lr The parasitic capacitance of the second power switch Q2 is discharged while the parasitic capacitance of the first power switch Q1 is charged, causing the HB voltage to drop to 0V. This causes the body diode of the second power switch Q2 to change from the off state to the on state. At this time, the dead-time control unit 402 starts timing the duration of the first power switch Q1 being in the off state from the time it changes from the on state to the off state. When the duration of the first power switch Q1 being in the off state reaches the preset dead time, it generates a down_on control signal to control the second power switch Q2 to change from the off state to the on state, achieving zero-voltage turn-on of the second power switch Q2.

[0036] As described above, the frequency control unit 404 bases its output feedback signal FB on the voltage V obtained after voltage division. FB_2 The frequency control signal DCM_on is generated; the demagnetization detection unit 405 generates the voltage V after the voltage sensing signal INV and the output feedback signal FB are divided. FB_2(Optionally, based on the external adjustment signal ADJ), a demagnetization detection signal DEM_off is generated; the zero-voltage turn-on control unit 406 generates a lower transistor turn-off control signal ZVS_off for controlling the second power switch Q2 to change from the on state to the off state based on the frequency control signal DCM_on, the demagnetization detection signal DEM_off, and the voltage sensing signal INV. After the second power switch Q2 is turned off, since the current in the inductor cannot change abruptly, the negative primary resonant current I... Lr The parasitic capacitance of the first power switch Q1 is discharged, and the parasitic capacitance of the second power switch Q2 is charged, causing the HB voltage to rise to Vin. This causes the body diode of the first power switch Q1 to change from the off state to the on state. The dead-time control unit 402 starts timing the duration of the second power switch Q2 being in the off state when it changes from the on state to the off state. When the duration of the second power switch Q2 being in the off state reaches a preset dead time, it generates an up_on control signal to control the first power switch Q1 to change from the off state to the on state, achieving zero-voltage turn-on of the first power switch Q1.

[0037] Figure 5 It shows the use of Figure 4 The diagram shows the waveforms of multiple signals when the asymmetric half-bridge flyback switching power supply 100 of the control chip 400 operates in critical continuous mode. Figure 5 As shown, at time t0, the first power switch Q1 changes from the off state to the on state. The input voltage (i.e., DC input voltage) Vin of the asymmetrical half-bridge flyback switching power supply 100 charges the primary magnetizing inductance Lm (including the primary inductance Lp and the primary leakage inductance Lr) of the transformer T through the resonant capacitor Cr. The primary resonant current I Lr As the positive current increases, the current sensing signal Vcs increases; at time t1, the current sensing signal Vcs is higher than the voltage V of the output feedback signal FB after voltage division. FB_2 When the first power switch Q1 changes from the on state to the off state, the circuit for charging the primary magnetizing inductor Lm of transformer T by the input voltage Vin is broken. Since the current in the inductor cannot change abruptly, the positive primary resonant current I... LrThe parasitic capacitance of the second power switch Q2 is discharged, and the parasitic capacitance of the first power switch Q1 is charged. The voltage at the midpoint HB between the first power switch Q1 and the second power switch Q2 (hereinafter referred to as HB voltage) decreases. When the HB voltage drops to 0V, the body diode of the second power switch Q2 changes from the off state to the on state. The dead time control unit 402 starts timing the duration of the first power switch Q1 being in the off state from time t1. When the duration of the first power switch Q1 being in the off state reaches the preset dead time, at time t2, a down_on control signal (e.g., high level) is generated to turn the second power switch Q2 from the off state to the on state, realizing zero-voltage turn-on of the second power switch Q2. Afterwards, the resonant capacitor Cr and the primary leakage inductance Lr of the transformer T resonate, and the primary resonant current I of the transformer... Lr After dropping to 0A, the negative current increases, and at the same time, the secondary inductance Ls of transformer T demagnetizes, and the primary excitation current I... Lm Decrease; at time t3, the primary excitation current I Lm When the current is reduced to 0A, a momentary pulse appears in the demagnetization detection signal DEM_off. If the frequency control signal DCM_on remains high or becomes high before the momentary pulse appears in the demagnetization detection signal DEM_off (i.e., the asymmetric half-bridge flyback switching power supply 100 is operating in critical continuous mode), the second power switch Q2 remains on. The resonant capacitor Cr discharges through the second power switch Q2 to the primary magnetizing inductance Lm of the transformer T, and the primary resonant current I... Lr The negative value increases until the primary resonant current I... Lr The negative amplitude is sufficient to achieve zero-voltage turn-on of the first power switch Q1; at time t4, the down-switch turn-off control signal ZVS_off produces a transient pulse, and the second power switch Q2 changes from the on state to the off state. The discharge circuit of the resonant capacitor Cr to the primary excitation inductance Lm of the transformer T is broken. Since the current in the inductor cannot change abruptly, the negative primary resonant current I... Lr Discharging the parasitic capacitance of the first power switch Q1 and charging the parasitic capacitance of the second power switch Q2 causes the HB voltage to rise (if the negative primary resonant current I...). Lr If the voltage is large enough, the HB voltage will rise until the input voltage Vin. After the HB voltage rises to the input voltage Vin, the body diode of the first power switch Q1 changes from the off state to the on state. The dead time control unit 402 starts timing the duration of the second power switch Q2 being in the off state from time t4. When the duration of the second power switch Q2 being in the off state reaches the preset dead time, at time t5, the upper transistor turn-on control signal up_on (e.g., high level) is generated to make the first power switch Q1 change from the off state to the on state, realizing the zero-voltage turn-on of the first power switch Q1.

[0038] exist Figure 5 In the diagram, the duration T of the on-time of the first power switch Q1 (from time t0 to time t1) is... on The magnitude of the output feedback signal FB determines the time from t2 when the second power switch Q2 turns on to the primary excitation current I. Lm The duration T from the peak current Ip to 0A at time t3 dem The demagnetization time is controlled by the demagnetization detection unit 405; the demagnetization detection unit 405 determines the time from the end of demagnetization (t3) to the primary resonant current I. Lr The duration T of the negative voltage increasing to a level sufficient to turn on the first power switch Q1 with zero voltage (at which point the second power switch Q2 changes from the on state to the off state). ZVS The HB voltage is controlled by the zero-voltage turn-on control unit 406 when the first power switch Q1 becomes the turn-on state, as determined by the voltage sensing signal INV.

[0039] Figure 6 It shows the use of Figure 4 The diagram shows the waveforms of multiple signals when the asymmetric half-bridge flyback switching power supply 100 of the control chip 400 operates in discontinuous current mode. Figure 6 As shown, at time t0, the first power switch Q1 changes from the off state to the on state. The input voltage (i.e., DC input voltage) Vin of the asymmetrical half-bridge flyback switching power supply 100 charges the primary magnetizing inductance Lm (including the primary inductance Lp and the primary leakage inductance Lr) of the transformer T through the resonant capacitor Cr. The primary resonant current I Lr As the positive current increases, the current sensing signal Vcs increases; at time t1, the current sensing signal Vcs is higher than the voltage V of the output feedback signal FB after voltage division. FB_2 When the first power switch Q1 changes from the on state to the off state, the circuit for charging the primary magnetizing inductor Lm of transformer T by the input voltage Vin is broken. Since the current in the inductor cannot change abruptly, the positive primary resonant current I... Lr The parasitic capacitance of the second power switch Q2 is discharged, and the parasitic capacitance of the first power switch Q1 is charged, causing the HB voltage to drop. When the HB voltage drops to 0V, the body diode of the second power switch Q2 changes from the off state to the on state. The dead time control unit 402 starts timing the duration of the first power switch Q1 being in the off state from time t1, and when the duration of the first power switch Q1 being in the off state reaches the preset dead time, at time t2, a down_on control signal (e.g., high level) is generated to turn the second power switch Q2 from the off state to the on state, realizing zero-voltage turn-on of the second power switch Q2. Afterwards, the resonant capacitor Cr and the primary leakage inductance Lr of the transformer T resonate, and the primary resonant current I of the transformer... LrAfter dropping to 0A, the negative current increases, and at the same time, the secondary inductance Ls of transformer T demagnetizes, and the primary excitation current I... Lm Decrease; at time t3, the primary excitation current I Lm When the current is reduced to 0A, a momentary pulse appears in the demagnetization detection signal DEM_off. If the frequency control signal DCM_on is low at this time (i.e., the asymmetric half-bridge flyback switching power supply 100 is operating in discontinuous current mode), the second power switch Q2 is directly turned off. At time t4, the frequency control unit 404, based on the output feedback signal FB, makes the output frequency control signal DCM_on high, causing the second power switch Q2 to turn on again. The resonant capacitor Cr discharges through the second power switch Q2 to the primary magnetizing inductance Lm of the transformer T, and the primary resonant current I... Lr The negative value increases until the primary resonant current I... Lr The negative amplitude is sufficient to achieve zero-voltage turn-on of the first power switch Q1; at time t5, the down-switch turn-off control signal ZVS_off shows a momentary pulse, and the second power switch Q2 changes from the on state to the off state again. The circuit of discharge from the resonant capacitor Cr to the primary excitation inductance Lm of the transformer T is broken. Since the current in the inductor cannot change abruptly, the negative primary resonant current I... Lr Discharging the parasitic capacitance of the first power switch Q1 and charging the parasitic capacitance of the second power switch Q2 causes the HB voltage to rise (if the negative primary resonant current I...). Lr If the voltage is large enough, the HB voltage will rise until the input voltage Vin. After the HB voltage rises to the input voltage Vin, the body diode of the first power switch Q1 changes from the off state to the on state. The dead time control unit 402 starts timing the duration of the second power switch Q2 being in the off state from time t5. When the duration of the second power switch Q2 being in the off state reaches the preset dead time, at time t6, the upper transistor turn-on control signal up_on (e.g., high level) is generated to make the first power switch Q1 change from the off state to the on state, realizing the zero-voltage turn-on of the first power switch Q1.

[0040] exist Figure 6 In the diagram, the duration T of the on-time of the first power switch Q1 (from time t0 to time t1) is... on The magnitude of the output feedback signal FB determines the time from t2 when the second power switch Q2 turns on to the primary excitation current I. Lm The duration T from the demagnetization of the peak current Ip to 0A at time t3 (when the second power switch Q2 changes from the on state to the off state) dem The demagnetization time is controlled by the demagnetization detection unit 405; the frequency control signal DCM_on becomes high, causing the second power switch Q2 to turn on again at time t4, until the primary resonant current I... LrThe time T between the negative increase to a point t5, which is sufficient to turn on the first power switch Q1 with zero voltage (at which point the second power switch Q2 changes from the on state to the off state), and the time T between these two points is sufficient to increase the negative voltage to a point t5, which is sufficient to turn on the first power switch Q1 with zero voltage (at which point the second power switch Q2 changes from the on state to the off state). ZVS The HB voltage is controlled by the zero-voltage turn-on control unit 406 when the first power switch Q1 becomes the turn-on state, as determined by the voltage sensing signal INV.

[0041] Combination Figure 1 , Figures 4-6 It can be concluded that during the conduction of the second power switch Q2, the current sensing resistor Rcs only detects the resonant current I in the primary leakage inductance Lr. Lr However, the excitation current I cannot be directly detected. Lm Therefore, it is impossible to directly determine time t3 by detecting the excitation current changing to 0A based on the current sensing signal Vcs. The peak current Ip at the moment when the first power switch Q1 turns off is determined by the voltage V after the output feedback signal FB is divided. FB_2 Decision: Ip = V FB_2 / Rcs, based on the voltage sensing signal INV, can determine the demagnetization voltage, and thus the demagnetization time can be calculated.

[0042] Regardless of whether the asymmetric half-bridge flyback switching power supply 100 operates in critical continuous mode or discontinuous current mode, the demagnetizing voltage of the primary excitation inductor Lm during the demagnetizing period when the second power switch Q2 is turned on is N·Vo, where N=N P :N s N P N represents the number of turns in the primary winding of transformer T. s This represents the number of turns in the secondary winding of transformer T, and Vo represents the output voltage of the asymmetrical half-bridge flyback switching power supply 100. Therefore, the magnetizing current I... Lm The time T required for demagnetization from peak current Ip to 0A dem Size:

[0043] T dem = Lp×Ip / (N·Vo)=Lp×V FB_2 / (Rcs ×N·Vo) (1).

[0044] Figure 7 It shows Figure 4 The circuit diagram shown illustrates an example implementation of the demagnetization detection unit 405 in the control chip 400. In this example implementation, the demagnetization detection unit 405 is based on the voltage sensing signal INV and the voltage V obtained by voltage division of the output feedback signal FB. FB_2 In addition to the external adjustment signal ADJ, a demagnetization detection signal DEM_off is generated to characterize the demagnetization of the primary magnetizing inductance Lm of transformer T.

[0045] Specifically, the demagnetization detection unit 405 can be configured to sample the voltage sensing signal during the demagnetization period of the primary excitation inductor Lm to obtain a sampled voltage V1 proportional to the demagnetization voltage N·Vo, and generate a controlled signal V based on the sampled voltage V1 and the external adjustment signal ADJ. C1 By comparing the controlled signal V C1 The voltage V after the output feedback signal FB is divided FB_2 The magnitude of the signal determines whether a momentary pulse should appear in the demagnetization detection signal DEM_off. Furthermore, by setting an external adjustment signal ADJ, the demagnetization detection signal DEM_off is made to appear precisely at the moment the demagnetization of the primary magnetizing inductance Lm of transformer T ends. This allows the timing of the end of demagnetization of the primary magnetizing inductance Lm of transformer T to be identified through the demagnetization detection signal DEM_off. Figure 5 or Figure 6 The time t3 is shown in the figure.

[0046] Figure 7 The diagram illustrates a specific implementation of the demagnetization detection unit 405 under the aforementioned configuration. For example... Figure 7 As shown, the demagnetization detection unit 405 may include a sampling module 405-1, a voltage-controlled current source 405-2, a comparison module 405-3, and switches S0 / S1 and capacitor C2, which are connected as shown in the figure.

[0047] The sampling module 405-1 operates during the demagnetization period T after the second power switch Q2 is turned on. dem The voltage V1 is obtained by sampling the voltage sensing signal INV:

[0048]

[0049] Where, N P N represents the number of turns in the primary winding of transformer T. s N represents the number of turns in the secondary winding of transformer T, where N = N P :N s The ratio of the number of turns in the primary winding to the number of turns in the secondary winding of transformer T is given. Naux represents the number of turns in the auxiliary winding of transformer T in the asymmetric half-bridge flyback switching power supply 100. R1 and R2 are the resistance values ​​of the voltage divider resistors in the voltage divider structure of the auxiliary winding of transformer T in the asymmetric half-bridge flyback switching power supply 100. Vo represents the output voltage of the asymmetric half-bridge flyback switching power supply 100. NVo represents the demagnetizing voltage of the primary excitation inductance Lm during the demagnetizing period when the second power switch Q2 is turned on.

[0050] Voltage V1 and external adjustment signal ADJ are fed into voltage-controlled current source 405-2 to generate current I1, I1 = k1·V1, where the coefficient k1 is controlled by external adjustment signal ADJ. The demagnetization period (i.e., T) when the second power switch Q2 is turned on... dem When switch S0 is turned on, current I1 charges capacitor C1 to obtain voltage V. C1 Voltage V C1 The voltage V after the output feedback signal FB is divided FB_2 It is sent to comparison module 405-3 for comparison. When voltage V... C1 Higher than voltage V FB_2 At that time, the DEM_off signal changes from low level to high level.

[0051] Therefore, the demagnetization period T when the second power switch Q2 is turned on can be calculated. dem for:

[0052]

[0053] Where C1 represents the capacitance value of capacitor C1.

[0054] After the DEM_off signal goes high, it immediately turns off switch S0 and turns on switch S1, transferring voltage V. C1 Discharge to 0V to prepare for the next demagnetization and charging, then switch S1 is turned off. As a result, the DEM_off signal appears as a transient pulse.

[0055] Primary excitation current I Lm T required to demagnetize from peak current Ip to 0A dem Duration:

[0056] T dem = Lp×V FB 2 / (Rcs ×NVo) (4).

[0057] Therefore, to make equations (3) and (4) equal, it is only necessary to ensure that Right now This satisfies the requirement that the primary excitation current I is exactly at the moment the DEM_off signal produces a transient pulse. Lm Demagnetize to 0A.

[0058] The capacitance value of capacitor C1 is a pre-set fixed parameter. The primary inductance Lp, the number of turns Np of the primary winding, the number of turns Naux of the auxiliary winding, the voltage-dividing resistors R1 and R2 of the auxiliary winding, and the current sensing resistor Rcs are all determined by system parameters. Therefore, it is only necessary to set the external adjustment signal ADJ to satisfy the equation. Alternatively, in some embodiments, the magnitude of k1 can be determined by internally calculating the inductor charging slope during the conduction of the first power switch Q1. Therefore, the external adjustment signal ADJ can be set so that the demagnetization detection signal appears as a momentary pulse precisely at the moment when the demagnetization of the primary excitation inductor of the transformer ends.

[0059] Figure 8 It shows Figure 4 The circuit schematic shows another example implementation of the demagnetization detection unit 405 in the control chip 400. In this example implementation, the demagnetization detection unit 405 relies solely on the voltage sensing signal INV and the voltage V obtained by voltage division of the output feedback signal FB. FB_2 This enables the generation of a demagnetization detection signal, DEM_off, to characterize the demagnetization of the primary magnetizing inductance Lm of transformer T.

[0060] Specifically, the demagnetization detection unit 405 can be configured to sample the voltage sensing signal INV during the first power switch Q1's conduction period to obtain a first sampling voltage V2 proportional to (Vin-N·Vo), and when the first power switch Q1 changes from the on state to the off state, based on the first sampling voltage V2 and the voltage V after voltage division of the output feedback signal FB, it can detect the voltage V2. FB_2 The proportional control signal is calculated. During the demagnetization period of the primary excitation inductor Lm, the voltage sensing signal INV is sampled to obtain a second sampling voltage V3 that is proportional to the demagnetization voltage N·Vo. Based on the proportional control signal and the second sampling voltage V3, the controlled signal V is obtained. C3 By comparing the controlled signal V C3 The output feedback signal FB is divided into voltages V. FB_2 The magnitude of the signal determines whether a momentary pulse should appear in the demagnetization detection signal DEM_off. Furthermore, by setting a proportional control signal, the demagnetization detection signal DEM_off is made to appear precisely at the moment the demagnetization of the primary magnetizing inductance Lm of transformer T ends. This allows the timing of the end of demagnetization of the primary magnetizing inductance Lm of transformer T to be identified through the demagnetization detection signal DEM_off. Figure 5 or Figure 6 The time t3 is shown in the figure.

[0061] Figure 8 The diagram illustrates a specific implementation of the demagnetization detection unit 405 under the aforementioned configuration. For example... Figure 8As shown, the demagnetization detection unit 405 may include a sampling module 405-1', a first voltage-controlled current source 405-2', a second voltage-controlled current source 405-3', a calculation module 405-4', a comparison module 405-5', and switches S2 / S3 / S4 / S5 and capacitors C2 / C3, which are connected as shown in the figure.

[0062] The sampling module 405-1' samples the voltage sensing signal INV to obtain voltages V2 and V3, where voltage V2 is a voltage sampled during the conduction of the first power switch Q1 that is proportional to the magnetizing voltage (Vin-N·Vo).

[0063]

[0064] V3 is a voltage sampled during the demagnetizing period after the second power switch Q2 is turned on, which is proportional to the demagnetizing voltage N·Vo.

[0065]

[0066] Where Np represents the number of turns in the primary winding of the transformer T in the asymmetrical half-bridge flyback switching power supply 100, Naux represents the number of turns in the auxiliary winding of the transformer T in the asymmetrical half-bridge flyback switching power supply 100, R1 and R2 are the resistance values ​​of the voltage divider resistors in the voltage divider structure of the auxiliary winding of the transformer T in the asymmetrical half-bridge flyback switching power supply 100, (Vin-N·Vo) represents the magnetizing voltage during the conduction of the first power switch Q1, Vin represents the input voltage of the asymmetrical half-bridge flyback switching power supply 100, Vo represents the output voltage of the asymmetrical half-bridge flyback switching power supply 100, and N = N P :N s N P N represents the number of turns in the primary winding of transformer T. s This indicates the number of turns in the secondary winding of transformer T.

[0067] The first voltage-controlled current source 405-2' generates current I2 based on voltage V2: I2 = k2·V2, where the coefficient k2 is a preset fixed value. During the conduction period Ton of the first power switch Q1, switch S2 is turned on, and current I2 charges capacitor C2 to obtain voltage V. C2 At the same time that the first power switch Q1 turns off, switch S2 is also turned off, ending the charging of capacitor C2. When the charging of capacitor C2 is complete, During the demagnetizing period after the second power switch Q2 is turned on, the voltage V C2 The time interval remains unchanged. The conduction period of the first power switch Q1 is calculated using the formula for the volt-second charge of the primary inductance of the transformer. Substituting equation (8) into equation (7) yields the following result:

[0068] Module 405-4' is based on voltage V C2 The voltage V after the output feedback signal FB is divided FB_2 The proportional control signal k3×(V) is obtained. FB_2 / V C2 ).

[0069] The second voltage-controlled current source 405-3' is based on voltage V3 and proportional control signal k3×(V FB_2 / V C2 The generated current I3 is: I3 = k3 × (V) FB_2 / V C2 )×V3. During the demagnetization period T after the second power switch Q2 is turned on. dem Internally, switch S4 is turned on, and current I3 charges capacitor C3 to obtain voltage V. C3 Voltage V C3 The voltage V after the output feedback signal FB is divided FB_2 It is sent to comparison module 405-5' for comparison. When voltage V... C3 Higher than voltage V FB_2 At this time, the DEM_off signal changes from low to high. Therefore, the demagnetization period T when the second power switch Q2 is turned on can be calculated. dem for:

[0070]

[0071] Primary excitation current I Lm T required to demagnetize from peak current Ip to 0A dem Duration:

[0072]

[0073] Therefore, to make equations (10) and (11) equal, it is only necessary to ensure the internal parameters. This ensures the primary excitation current I Lm When demagnetizing to 0A, the DEM_off signal changes from low to high. Immediately after the DEM_off signal goes high, switches S3 and S5 are turned on, transferring voltage V... C2 and voltage V C3 Discharge to 0V to prepare for the next demagnetization calculation, then turn off switches S3 and S5. As a result, the DEM_off signal appears as a transient pulse.

[0074] This invention can be implemented in other specific forms without departing from its spirit and essential characteristics. For example, the algorithm described in a particular embodiment can be modified without departing from the basic spirit of the invention. Therefore, the present embodiments are to be regarded as exemplary rather than limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and all changes falling within the meaning and scope of the claims and their equivalents are thus included within the scope of the invention.

Claims

1. A control chip for 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, a resonant capacitor, and a transformer. The primary-side magnetizing inductance of the transformer includes a primary-side inductance and a primary-side leakage inductance. The control chip is configured as follows: Based on the output feedback signal characterizing the output voltage of the asymmetric half-bridge flyback switching power supply and the current sensing signal characterizing the current flowing through the primary inductor, an upper-side control signal for controlling the on and off of the first power switch is generated. as well as Based on the output feedback signal and the voltage sensing signal characterizing the voltage on the auxiliary winding of the transformer, a lower-switch control signal is generated to control the on and off of the second power switch. The control chip is configured to identify the moment when the demagnetization of the primary-side magnetizing inductor of the transformer ends based on the output feedback signal and the voltage sensing signal, and to generate the lower control signal based on that moment. The control chip is further configured as follows: Based on the output feedback signal, a frequency control signal is generated to control the operating frequency of the asymmetric half-bridge flyback switching power supply. Based on the output feedback signal and the voltage sensing signal, a demagnetization detection signal is generated to characterize the demagnetization status of the primary magnetizing inductance of the transformer. as well as Based on the frequency control signal, the demagnetization detection signal, and the voltage sensing signal, a lower transistor turn-off control signal is generated to control the second power switch to change from the on state to the off state. Furthermore, the control chip is further configured as follows: When the frequency control signal remains high or becomes high before the demagnetization detection signal experiences a transient pulse, the asymmetric half-bridge flyback switching power supply is determined to be operating in critical continuous mode; and After the demagnetization detection signal generates a momentary pulse, the lower transistor turn-off control signal is kept at a low level until the reverse resonant current flowing through the primary leakage inductance of the transformer is sufficient to achieve zero-voltage conduction of the first power switch. Then, the lower transistor turn-off control signal generates a momentary pulse to turn off the second power switch.

2. The control chip according to claim 1, further configured as follows: Based on the output feedback signal and the current sensing signal, an upper-side turn-off control signal is generated to control the first power switch to change from the on state to the off state.

3. The control chip according to claim 2, further configured as follows: When the second power switch changes from the on state to the off state, the duration of the second power switch being in the off state is timed. When the duration of the second power switch being in the off state reaches a preset dead time, an upper-side conduction control signal is generated to control the first power switch to change from the off state to the on state; and The upper tube control signal is generated based on the upper tube turn-on control signal and the upper tube turn-off control signal.

4. The control chip according to claim 1, further configured as follows: When the first power switch changes from the on state to the off state, the timer for the duration of the first power switch being in the off state begins. When the duration of the first power switch being in the off state reaches a preset dead time, a lower transistor turn-on control signal is generated to control the second power switch to change from the off state to the on state; and The lower tube control signal is generated based on the lower tube turn-on control signal, the lower tube turn-off control signal, the frequency control signal, and the demagnetization detection signal.

5. The control chip according to claim 1, further configured as follows: During the conduction of the first power switch, the voltage sensing signal is sampled to obtain a first sampling voltage that is proportional to the magnetization voltage; When the first power switch changes from the on state to the off state, a proportional control signal is calculated based on the first sampled voltage and the output feedback signal. During the demagnetization of the primary magnetizing inductor, the voltage sensing signal is sampled to obtain a second sampling voltage that is proportional to the demagnetization voltage; A first controlled signal is obtained based on the proportional control signal and the second sampled voltage; Whether to cause a transient pulse in the demagnetization detection signal is determined by comparing the magnitudes of the first controlled signal and the output feedback signal. as well as The proportional control signal is set so that the demagnetization detection signal produces an instantaneous pulse precisely at the moment when the demagnetization of the primary excitation inductor of the transformer ends.

6. The control chip according to claim 1, further configured as follows: In addition to the output feedback signal and the voltage sensing signal, the demagnetization detection signal is also generated based on an external adjustment signal.

7. The control chip according to claim 6, further configured as follows: During the demagnetization of the primary magnetizing inductor, the voltage sensing signal is sampled to obtain a third sampling voltage that is proportional to the demagnetization voltage; A second controlled signal is generated based on the third sampling voltage and the external adjustment signal; Whether to cause a transient pulse in the demagnetization detection signal is determined by comparing the magnitudes of the second controlled signal and the output feedback signal; as well as The external adjustment signal is set so that the demagnetization detection signal produces an instantaneous pulse precisely at the moment when the demagnetization of the primary excitation inductor of the transformer ends.

8. The control chip according to claim 1, further configured as follows: If the frequency control signal is low when the demagnetization detection signal has a transient pulse, then the asymmetric half-bridge flyback switching power supply is determined to be operating in discontinuous current mode, and the second power switch is changed from the on state to the off state. When a momentary pulse appears in the frequency control signal, the second power switch is changed from the off state to the on state; and When the reverse resonant current flowing through the primary leakage inductance of the transformer is sufficient to achieve zero-voltage conduction of the first power switch, a momentary pulse is generated in the lower transistor turn-off control signal to turn off the second power switch.

9. A control method for an asymmetrical half-bridge flyback switching power supply, wherein, The asymmetric half-bridge flyback switching power supply includes a first power switch, a second power switch, a resonant capacitor, and a transformer. The primary-side magnetizing inductance of the transformer includes a primary-side inductance and a primary-side leakage inductance. The control method includes: Based on the output feedback signal characterizing the output voltage of the asymmetric half-bridge flyback switching power supply and the current sensing signal characterizing the current flowing through the primary inductor, an upper-side control signal is generated to control the on / off state of the first power switch; and Based on the output feedback signal and the voltage sensing signal characterizing the voltage on the auxiliary winding of the transformer, a lower-switch control signal is generated to control the on and off of the second power switch. Specifically, generating the down-switch control signal includes identifying the moment when the demagnetization of the primary-side magnetizing inductor of the transformer ends based on the output feedback signal and the voltage sensing signal, and generating the down-switch control signal based on that moment. The process of generating the lower tube control signal includes: Based on the output feedback signal, a frequency control signal is generated to control the operating frequency of the asymmetric half-bridge flyback switching power supply. Based on the output feedback signal and the voltage sensing signal, a demagnetization detection signal is generated to characterize the demagnetization status of the primary magnetizing inductance of the transformer; and Based on the frequency control signal, the demagnetization detection signal, and the voltage sensing signal, a lower transistor turn-off control signal is generated to control the second power switch to change from the on state to the off state. The process of generating the lower tube control signal also includes: When the frequency control signal remains high or becomes high before the demagnetization detection signal experiences a transient pulse, the asymmetric half-bridge flyback switching power supply is determined to be operating in critical continuous mode; and After the demagnetization detection signal generates a momentary pulse, the lower transistor turn-off control signal is kept at a low level until the reverse resonant current flowing through the primary leakage inductance of the transformer is sufficient to achieve zero-voltage conduction of the first power switch. Then, the lower transistor turn-off control signal generates a momentary pulse to turn off the second power switch.

10. The control method according to claim 9, wherein The process of generating the upper tube control signal includes: Based on the output feedback signal and the current sensing signal, an upper-side turn-off control signal is generated to control the first power switch to change from the on state to the off state.

11. The control method according to claim 10, wherein the process of generating the upper tube control signal further includes: When the second power switch changes from the on state to the off state, the duration of the second power switch being in the off state is timed. When the duration of the second power switch being in the off state reaches the preset dead time, an upper tube conduction control signal is generated to control the first power switch to change from the off state to the on state. as well as The upper tube control signal is generated based on the upper tube turn-on control signal and the upper tube turn-off control signal.

12. The control method according to claim 9, wherein The process of generating the lower tube control signal also includes: When the first power switch changes from the on state to the off state, the timer for the duration of the first power switch being in the off state begins. When the duration of the first power switch being in the off state reaches a preset dead time, a lower transistor turn-on control signal is generated to control the second power switch to change from the off state to the on state; and The lower tube control signal is generated based on the lower tube turn-on control signal, the lower tube turn-off control signal, the frequency control signal, and the demagnetization detection signal.

13. The control method according to claim 9, wherein Generating the demagnetization detection signal includes: During the conduction of the first power switch, the voltage sensing signal is sampled to obtain a first sampling voltage that is proportional to the magnetization voltage; When the first power switch changes from the on state to the off state, a proportional control signal is calculated based on the first sampled voltage and the output feedback signal. During the demagnetization of the primary magnetizing inductor, the voltage sensing signal is sampled to obtain a second sampling voltage that is proportional to the demagnetization voltage; A first controlled signal is obtained based on the proportional control signal and the second sampled voltage; Whether to cause a transient pulse in the demagnetization detection signal is determined by comparing the magnitudes of the first controlled signal and the output feedback signal; and The proportional control signal is set so that the demagnetization detection signal produces an instantaneous pulse precisely at the moment when the demagnetization of the primary excitation inductor of the transformer ends.

14. The control method according to claim 9, wherein Generating the demagnetization detection signal based on the output feedback signal and the voltage sensing signal includes: The demagnetization detection signal is generated based on the output feedback signal, the voltage sensing signal, and the external adjustment signal.

15. The control method according to claim 14, wherein Generating the demagnetization detection signal includes: During the demagnetization of the primary magnetizing inductor, the voltage sensing signal is sampled to obtain a third sampling voltage that is proportional to the demagnetization voltage; A second controlled signal is generated based on the third sampling voltage and the external adjustment signal; Whether to cause a transient pulse in the demagnetization detection signal is determined by comparing the magnitudes of the second controlled signal and the output feedback signal; and The external adjustment signal is set so that the demagnetization detection signal produces an instantaneous pulse precisely at the moment when the demagnetization of the primary excitation inductor of the transformer ends.

16. The control method according to claim 9, further comprising: If the frequency control signal is low when the demagnetization detection signal has a transient pulse, then the asymmetric half-bridge flyback switching power supply is determined to be operating in discontinuous current mode, and the second power switch is changed from the on state to the off state. When the frequency control signal produces a momentary pulse, the second power switch is changed from the off state to the on state; and When the reverse resonant current flowing through the primary leakage inductance of the transformer is sufficient to achieve zero-voltage conduction of the first power switch, a momentary pulse is generated in the lower transistor turn-off control signal to turn off the second power switch.

17. An asymmetric half-bridge flyback switching power supply, comprising the control chip according to any one of claims 1 to 8.

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