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

Abstract

An asymmetric half-bridge flyback switching power supply, its control chip, and control method are provided. The asymmetric half-bridge flyback switching power supply includes a first power switch, a second power switch, a resonant capacitor, 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 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 inductance of the transformer; 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 across the auxiliary inductance of the transformer. When the first power switch is in the off state, the duration of discharge of the resonant capacitor through the second power switch to the primary inductance of the transformer is proportional to a voltage value that is the charging voltage of the primary inductance of the transformer when the first power switch is in the on state.

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] 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, a resonant capacitor, 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 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 inductance of the transformer; 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 inductance of the transformer. When the first power switch is in the off state, the duration of discharge of the resonant capacitor through the second power switch to the primary inductance of the transformer is proportional to a voltage value that is the charging voltage of the primary inductance of the transformer when the first power switch is in the on state.

[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, a resonant capacitor, and a transformer. 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 inductance of the transformer; 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 inductance of the transformer. When the first power switch is in the off state, the duration of discharge of the resonant capacitor through the second power switch to the primary inductance of the transformer is proportional to a voltage value, which is the charging voltage of the primary inductance of the transformer when the first power switch is in the on state. Attached Figure Description

[0005] The invention can be better understood from the following description of specific embodiments of the invention in conjunction with the accompanying drawings, wherein:

[0006] 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.

[0007] Figure 2 It shows Figure 1 The diagram shows the waveforms of multiple signals in an asymmetric half-bridge flyback switching power supply.

[0008] 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.

[0009] Figure 4 It shows the use of Figure 3 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.

[0010] Figure 5 It shows the use of Figure 3 The diagram shows the waveforms of multiple signals when the asymmetric half-bridge flyback switching power supply 100 of the control chip 102 is operating in discontinuous mode.

[0011] Figure 6 It shows Figure 3 The circuit schematic shown is an example implementation of the zero-voltage turn-on control unit. Detailed Implementation

[0012] 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 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.

[0013] 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, the first and second power switches Q1 and Q2 are both metal-oxide-semiconductor field-effect transistors (MOSFETs). Zero-voltage conduction of the first and second power switches Q1 and Q2 can be achieved through the resonance of the resonant capacitor Cr and the primary inductance Lp of the transformer T.

[0014] Figure 2 It shows Figure 1 The diagram shows the waveforms of multiple signals in the asymmetric half-bridge flyback switching power supply 100, where: Gate_up represents the upper transistor control signal used to control the on / off state of the first power switch Q1, Gate_down represents the lower transistor control signal used to control the on / off state of the second power switch Q2, and I... Lp I represents the current flowing through the primary inductance Lp of transformer T (referred to as the transformer primary current). Do The current flowing through the secondary inductance Ls of transformer T (referred to as transformer secondary current) is represented by HB voltage, which represents the voltage at the midpoint HB between the first and second power switches Q1 and Q2.

[0015] Combination Figure 1 and Figure 2 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 inductance Lp of the transformer T through the resonant capacitor Cr, and the primary current I of the transformer increases. Lp 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 inductor Lp of the transformer T by the input voltage Vin is broken. Since the current in the inductor cannot change abruptly, the primary current I of the transformer increases. Lp Discharging the parasitic capacitance of the second power switch Q2 causes 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 inductance Lp of the transformer T resonate, and the primary current I of the transformer... Lp After dropping to 0A, the negative current increases, and simultaneously, the secondary inductance Ls of transformer T demagnetizes; at time t3, the demagnetization of the secondary inductance Ls of transformer T ends, and the secondary current I of the transformer... Do Returning to 0A, the transformer primary current I Lp It also resonates to 0A, after which the resonant capacitor Cr discharges through the second power switch Q2 to the primary inductance Lp of the transformer T, and the primary current I of the transformer... Lp The negative value increases; at time t4, 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 inductance Lp of the transformer T is broken. Since the current in the inductor cannot change abruptly, the primary current I of the transformer... Lp Discharging the parasitic capacitance of the first power switch Q1 causes the HB voltage to rise. 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, thus achieving zero-voltage turn-on of the first power switch Q1.

[0016] Due to the primary current I of the transformer Lp At time t1, the current is at its positive peak, and the resonant energy is large enough. Therefore, the HB voltage will definitely resonate to 0V at time t2, thus achieving zero-voltage conduction of the second power switch Q2. After the second power switch Q2 changes from the on state to the off state, whether the HB voltage can resonate to the input voltage Vin, thereby achieving zero-voltage conduction of the first power switch Q1, depends on the transformer primary current I at time t4 when the second power switch Q2 changes from the on state to the off state. Lp The negative current amplitude. The duration T of the discharge T of the resonant capacitor Cr through the second power switch Q2 to the primary inductance Lp of the transformer T. ZVS The primary current I of the transformer is determined Lp The magnitude of the negative current determines the magnitude of the resonant energy after the second power switch Q2 changes from the on state to the off state, and ultimately determines the HB voltage of the first power switch Q1 before it changes from the off state to the on state. Only when the HB voltage reaches the input voltage Vin can the first power switch Q1 achieve zero-voltage turn-on.

[0017] However, as the input voltage Vin changes, the time required for the HB voltage to return to its 0V resonance value from the input voltage Vin also varies. If the time T required for the resonant capacitor Cr to discharge through the second power switch Q2 to the primary inductance Lp of the transformer T is... ZVS If the voltage is fixed, it is impossible to achieve zero-voltage conduction of the first power switch Q1 under different input voltages Vin. Specifically, if T ZVS If the time is too short, the voltage difference between the drain and source of the first power switch Q1 is still very high when it changes from the off state to the on state, and the switching loss is still very large; if T ZVS If the length is too long, the primary current I of the transformer will increase. Lp The negative current amplitude is too large, and the required transformer primary current I under the same load conditions is... Lp The peak value of the forward current will also increase, and the transformer primary current I Lp The effective value will increase significantly, and the conduction losses of the first and second power switches Q1 and Q2 will also increase significantly. The waste of resonant energy will lead to a decrease in the overall efficiency of the power supply.

[0018] exist Figure 1 In the asymmetric half-bridge flyback switching power supply 100 shown, the turns ratio of the primary inductance Lp and the secondary inductance Ls of the transformer T is N:1, and the voltage across the resonant capacitor Cr is N times the output voltage Vo (i.e., NVo); the energy required for the HB voltage to resonate to the input voltage Vin is... Coss represents the capacitance values ​​of the parasitic capacitances of the first and second power switches Q1 and Q2; when the second power switch Q2 is in the off state, the energy stored in the primary inductance Lp of the transformer T is... If the energy stored in the primary inductance Lp of transformer T is just enough to make the HB voltage resonate with the input voltage Vin, thus achieving zero-voltage conduction of the first power switch Q1, then When the second power switch Q2 changes from the on state to the off state, the primary current of the transformer... Due to the primary current I of the transformer Lp This is generated by the discharge of the resonant capacitor Cr to the primary inductance Lp of the transformer T (the discharge time of the resonant capacitor Cr through the second power switch Q2 to the primary inductance Lp of the transformer T is T). ZVS Therefore, Lp×I Lp =Vo×T zvs , Here, the inductance of the primary inductance Lp of transformer T, the parasitic capacitance Coss of the first and second power switches Q1 and Q2, the turns ratio N:1 of the primary inductance Lp to the secondary inductance Ls of transformer T, and the output voltage Vo are fixed parameters. Therefore, it is necessary to ensure that T ZVS Zero-voltage conduction of the first and second power switches Q1 and Q2 can only be achieved when the voltage is proportional to Vin-NVo.

[0019] 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. This chip can automatically adjust the discharge time T of the resonant capacitor Cr through the second power switch Q2 on the primary inductance Lp of the transformer T according to the magnitude of the input voltage Vin. ZVS This adjusts the magnitude of the resonant energy after the second power switch Q2 changes from the on state to the off state, thereby achieving zero-voltage conduction of the first power switch Q1.

[0020] Figure 3 A circuit schematic diagram of a control chip 102 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 3 ,describe Figure 3 The control chip 102 shown is used in Figure 1 The example shown is the asymmetric half-bridge flyback switching power supply 100.

[0021] like Figure 1 and Figure 3As shown, in some embodiments, the control chip 102 can be configured to: generate an upper-side control signal Gate_up for controlling the on and 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 inductor Lp of the transformer T; and generate a lower-side control signal Gate_down for controlling the on and 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 inductor Lax of the transformer T.

[0022] like Figure 1 and Figure 3 As shown, in some embodiments, the output voltage Vo is divided by a resistor and then processed by a TL431 and an optocoupler to generate an output feedback signal FB. The voltage generated by the output feedback signal FB after being stepped down by a diode and divided by a resistor, together with the current sensing signal Vcs, is sent to comparator 102-1 to generate an upper-side turn-off control signal CV_off that determines the turn-off time when the first power switch Q1 changes from the on state to the off state. That is, the control chip 102 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.

[0023] like Figure 1 and Figure 3 As shown, in some embodiments, the control chip 102 includes a dead time control unit 102-2. The dead time control unit 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 upper-side turn-on control signal ZVS_up_on 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.

[0024] like Figure 1 and Figure 3 As shown, in some embodiments, the control chip 102 includes a first logic control unit 102-3, 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 ZVS_up_on.

[0025] like Figure 1 and Figure 3As shown, in some embodiments, the control chip 102 includes a frequency control unit 102-4, a demagnetization detection unit 102-5, and a zero-voltage turn-on control unit 102-6. The frequency control unit 102-4 generates an upper clamping frequency signal maxfre_off based on the output feedback signal FB to control the operating frequency of the asymmetric half-bridge flyback switching power supply 100. The demagnetization detection unit 102-5 generates a demagnetization detection signal DEM_off based on the voltage sensing signal INV to characterize the demagnetization of the primary inductance Lp of the transformer T. The zero-voltage turn-on control unit 102-6 generates a lower transistor turn-off control signal ZVS_off based on the upper clamping frequency signal maxfre_off, the demagnetization 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.

[0026] like Figure 1 and Figure 3 As shown, in some embodiments, the dead time control unit 102-2 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 lower transistor turn-on control signal ZVS_down_on to control 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.

[0027] like Figure 1 and Figure 3 As shown, in some embodiments, the control chip 102 further includes a second logic control unit 102-7, which generates a lower transistor control signal Gate_down based on the lower transistor turn-on control signal ZVS_down_on and the lower transistor turn-off control signal ZVS_off.

[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 inductance Lp of the transformer T through the resonant capacitor Cr, and the primary current I of the transformer... Lp As the voltage rises, the current sensing signal Vcs increases. When the voltage of the current sensing signal Vcs is higher than the voltage generated by the output feedback signal FB after being stepped down and divided, the upper transistor turn-off control signal CV_off changes from low to high, 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... LpDischarge the parasitic capacitance of the second power switch Q2, and the HB voltage drops to 0V. The body diode of the second power switch Q2 turns on. After the first power switch Q1 is in the on state for a period of time that reaches the preset dead time, the dead time control unit 102-2 generates the lower diode turn-on control signal ZVS_up_on, and the second power switch Q2 achieves zero voltage turn-on.

[0029] like Figure 1 and Figure 3 As shown, the voltage sensing signal INV is sent to the demagnetization detection unit 102-5 to generate the demagnetization detection signal DEM_off; the output feedback signal FB, after being stepped down by a diode and divided by a resistor, generates a voltage that is sent to the frequency control unit 102-4 to generate the upper clamping signal maxfre_off, which limits the operating frequency of the asymmetric half-bridge flyback switching power supply 100. The upper clamping signal maxfre_off can reduce the operating frequency when the load decreases. The demagnetization detection signal DEM_off, the upper clamping signal maxfre_off, and the voltage sensing signal INV are sent to the zero-voltage turn-on control unit 102-5, where they are processed by timing to generate the lower transistor turn-off control signal ZVS_off. That is, the demagnetization detection signal DEM_off, the upper clamping signal maxfre_off, and the voltage sensing signal INV together determine the turn-off time when the second power switch Q2 changes from the on state to the off state. After the second power switch Q2 changes from the on state to the off state, the transformer primary current I Lp Discharge the parasitic capacitance of the first power switch Q1, the HB voltage rises to the input voltage Vin, the body diode of the first power switch Q1 turns on, and the dead time control unit 102-2 generates the upper transistor turn-on control signal ZVS_up_on after the duration of the second power switch Q2 being in the off state reaches the preset dead time, so that the first power switch Q1 achieves zero voltage turn-on.

[0030] Here, the different timing of the demagnetization detection signal DEM_off and the clamping frequency signal maxfre_off determines the different operating states of the asymmetric half-bridge flyback switching power supply 100. When the clamping frequency signal maxfre_off changes from low to 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 changes from low to high level earlier than the clamping frequency signal maxfre_off, the asymmetric half-bridge flyback switching power supply 100 operates in discontinuous mode.

[0031] Figure 4 It shows the use of Figure 3 The diagram shows the waveforms of multiple signals when the asymmetric half-bridge flyback switching power supply 100 of the control chip 102 operates in critical continuous mode. (See diagram for example.) Figure 4As shown, at time t0, the first power switch Q1 changes from the off state to the on state, and the input voltage Vin charges the primary inductance Lp of the transformer T through the resonant capacitor Cr, and the primary current I of the transformer increases. Lp As the current rises, the current sampling signal Vcs increases. At time t1, the voltage of the current sensing signal Vcs is higher than the voltage generated after the output feedback signal FB is stepped down by the diode and divided by the resistor. 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 T1 is broken. Since the current in the inductor cannot change abruptly, the primary current I of the transformer... Lp Discharging the parasitic capacitance of the second power switch Q2 causes the HB voltage to drop. At time t2, the HB voltage drops to 0V, the body diode of the second power switch Q2 conducts, and the second power switch Q2 achieves zero-voltage turn-on. Afterwards, the resonant capacitor Cr and the primary inductance Lp of the transformer T resonate, and the primary current I of the transformer... Lp After dropping to 0A, the negative current increases, and simultaneously, the secondary inductance Ls of transformer T demagnetizes; at time t3, the demagnetization of the secondary inductance Ls of transformer T ends, and the secondary current I of the transformer... Do Returning to 0A, the demagnetization detection unit 102-5 detects the end of demagnetization of the primary inductor Lp of transformer T by the falling slope of the voltage sensing signal INV. The demagnetization detection signal DEM_off changes from low to high. If the upper clamping frequency signal Maxfre_off is high at this time, the second power switch Q2 remains on, and the resonant capacitor Cr discharges through the second power switch Q2 to the primary inductor Lp of transformer T. The transformer primary current I... Lp The negative amplitude increases until it is large enough; at time t4, the lower transistor turn-off control signal ZVS_off generated by the zero-voltage turn-on control unit 102-6 changes from low to high, 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 inductance Lp of the transformer T is broken, and since the current in the inductor cannot change abruptly, the primary current I of the transformer... Lp The parasitic capacitance of the first power switch Q1 is discharged, causing the HB voltage to rise. At time t5, the HB voltage rises to the input voltage Vin, and the body diode of the first power switch Q1 conducts, achieving zero-voltage turn-on for the first power switch Q1. Here, the time interval from time t3, when the demagnetization of the primary winding Lp of transformer T ends, to time t4, when the second power switch Q2 changes from the on state to the off state, is T. ZVS .

[0032] Figure 5 It shows the use of Figure 3 The diagram shows the waveforms of multiple signals when the asymmetric half-bridge flyback switching power supply 100 of the control chip 102 operates in discontinuous mode. (See diagram for example.) Figure 5As shown, at time t0, the first power switch Q1 changes from the off state to the on state, and the input voltage Vin charges the primary inductance Lp of the transformer T through the resonant capacitor Cr, and the primary current I of the transformer increases. Lp As the current rises, the current sensing signal Vcs increases. At time t1, the voltage of the current sensing signal Vcs is higher than the voltage generated after the output feedback signal FB is reduced by a diode and divided by a resistor. 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 broken. Since the current in the inductor cannot change abruptly, the primary current I of the transformer... Lp Discharging the parasitic capacitance of the second power switch Q2 causes the HB voltage to drop. At time t2, the HB voltage drops to 0V, the body diode of the second power switch Q2 conducts, and the second power switch Q2 achieves zero-voltage turn-on. Afterwards, the resonant capacitor Cr and the primary inductance Lp of the transformer T resonate, and the primary current I of the transformer... Lp After dropping to 0A, the negative current increases, and simultaneously, the secondary inductance Ls of transformer T demagnetizes; at time t3, the demagnetization of the secondary inductance Ls of transformer T ends, and the secondary current I of the transformer... Do Returning to 0A, the demagnetization detection unit 102-5 detects the end of demagnetization of the primary inductance Lp of transformer T by the falling slope of the voltage sensing signal INV. The demagnetization detection signal DEM_off changes from low to high. If the upper clamping frequency signal Maxfre_off is low at this time, the second power switch Q2 directly changes from the on state to the off state. At time t4, the upper clamping frequency signal Maxfre_off changes from low to high, and the second power switch Q2 changes from the off state to the on state again. The resonant capacitor Cr discharges through the second power switch Q2 to the primary inductance Lp of transformer T, and the transformer primary current I... Lp The negative amplitude increases until it is large enough; at time t5, the lower transistor turn-off control signal ZVS_off generated by the zero-voltage turn-on control unit 102-6 changes from low to high, 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 inductance Lp of the transformer T is broken, and since the current in the inductor cannot change abruptly, the primary current I of the transformer... Lp The parasitic capacitance of the first power switch Q1 is discharged, causing the HB voltage to rise. At time t6, the HB voltage rises to the input voltage Vin, and the body diode of the first power switch Q1 conducts, achieving zero-voltage turn-on for the first power switch Q1. Here, the time interval from time t4 (when the upper clamping signal Maxfre_off changes from low to high) to time t5 (when the second power switch Q2 changes from off to on again) is T. ZVS .

[0033] Figure 6 It shows Figure 3 The circuit schematic of an example implementation of the zero-voltage turn-on control unit 102-6 is shown. Figure 6 As shown, the zero-voltage turn-on control unit 102-6 is used to control the duration T of the discharge time T of the resonant capacitor Cr to the primary inductor Lp of the transformer T through the second power switch Q2. ZVS This achieves zero-voltage turn-on of the first power switch Q1. Specifically, when the first power switch Q1 changes from the off state to the on state, the charging voltage of the primary inductor Lp of the transformer T is Vin-NVo, and the voltage divider terminal INV of the auxiliary inductor Lax of the transformer T will have a negative voltage proportional to Vin-NVo (i.e., the voltage sensing signal INV is a negative voltage and proportional to Vin-NVo); the clamping module clamps the voltage of the voltage sensing signal INV to near 0V, so that the clamping current generated when the first power switch Q1 changes from the off state to the on state will be proportional to Vin-NVo; the current source CCCS samples the clamping current, and the resulting sampling current generates a voltage V across the resistor R. R When the first power switch Q1 is in the on state, the voltage V across the resistor R is... R Sampling yields a sampling voltage Vc proportional to Vin-NVo. With both the upper clamping signal maxfre and the demagnetization detection signal DEM_off high, capacitor C is charged using a fixed current source. When the charging voltage across capacitor C exceeds the sampling voltage Vc, a lower transistor turn-off control signal ZVS_off is generated. Thus, T, proportional to Vin-NVo, can be obtained. ZVS T can be adjusted by changing the resistance between the auxiliary inductor Lax and the voltage divider terminal INV. ZVS The ratio of Vin-NVo enables the first and second power switches Q1 and Q2 to turn on at zero voltage or low voltage under different input voltages.

[0034] 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 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, a resonant capacitor, and a transformer. 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 inductance of the transformer, 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 inductor of the transformer, a lower-side control signal is generated to control the on and off of the second power switch, wherein... When the first power switch is in the off state, the duration of the discharge of the resonant capacitor to the primary inductance of the transformer through the second power switch is proportional to the following voltage value, which is the charging voltage of the primary inductance of the transformer when the first power switch is in the on state.

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: Based on the output feedback signal, an upper clamping signal is generated to control the operating frequency of the asymmetric half-bridge flyback switching power supply. Based on the voltage sensing signal, a demagnetization detection signal is generated to characterize the demagnetization of the primary inductance of the transformer; and Based on the upper clamping frequency 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.

5. The control chip according to claim 4, 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 and the lower tube turn-off control signal.

6. The control chip according to claim 4, further configured as follows: A lower clamping voltage is generated by clamping the voltage sensing signal. A sampling voltage is generated by sampling the clamping current produced by the lower clamping voltage; A charging voltage is generated by controlling a fixed current source to charge the capacitor based on the demagnetization detection signal and the upper clamping frequency signal; and The lower transistor turn-off control signal is generated by comparing the sampled voltage and the charging voltage.

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

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

9. The control chip according to claim 4, wherein, When the demagnetization of the primary inductance of the transformer ends, the demagnetization detection signal changes from low level to high level.

10. The control chip according to claim 6, wherein, When both the upper clamping signal and the demagnetization detection signal are high, the fixed current source charges the capacitor.

11. 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, a resonant capacitor, and a transformer. 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 inductance of the transformer, an upper-side control signal for controlling the on and off of the first power switch is generated; and Based on the output feedback signal and the voltage sensing signal characterizing the voltage on the auxiliary inductor of the transformer, a lower-side control signal is generated to control the on and off of the second power switch, wherein... When the first power switch is in the off state, the duration of the discharge of the resonant capacitor to the primary inductance of the transformer through the second power switch is proportional to the following voltage value, which is the charging voltage of the primary inductance of the transformer when the first power switch is in the on state.

12. The control method according to claim 11, 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.

13. The control method according to claim 12, 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.

14. The control method according to claim 11, wherein, The process of generating the lower tube control signal includes: Based on the output feedback signal, an upper clamping signal is generated to control the operating frequency of the asymmetric half-bridge flyback switching power supply. Based on the voltage sensing signal, a demagnetization detection signal is generated to characterize the demagnetization of the primary inductance of the transformer; and Based on the upper clamping frequency 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.

15. The control method according to claim 14, 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 and the lower tube turn-off control signal.

16. The control method according to claim 14, wherein, The process of generating the lower tube turn-off control signal includes: A lower clamping voltage is generated by clamping the voltage sensing signal. A sampling voltage is generated by sampling the clamping current produced by the lower clamping voltage; A charging voltage is generated by controlling a fixed current source to charge the capacitor based on the demagnetization detection signal and the upper clamping frequency signal; and The lower transistor turn-off control signal is generated by comparing the sampled voltage and the charging voltage.

17. The control method according to claim 14, wherein, When the upper clamping frequency signal changes from low level to high level earlier than the demagnetization detection signal, the asymmetric half-bridge flyback switching power supply operates in critical continuous mode.

18. The control method according to claim 14, wherein, When the demagnetization detection signal changes from low to high level earlier than the clamping signal, the asymmetric half-bridge flyback switching power supply operates in discontinuous mode.

19. The control method according to claim 14, wherein, When the demagnetization of the primary inductance of the transformer ends, the demagnetization detection signal changes from low level to high level.

20. The control method according to claim 16, wherein, When both the upper clamping signal and the demagnetization detection signal are high, the fixed current source charges the capacitor.

21. An asymmetric half-bridge flyback switching power supply, comprising the control chip according to any one of claims 1 to 10.

Images