Quasi-resonant switching power supply, its control chip and control method

Abstract

A quasi-resonant switching power supply, its control chip, and control method are provided. The quasi-resonant switching power supply includes a transformer and a power switch. The control chip is configured to: generate a valley pulse signal characterizing the valley of the drain resonant voltage waveform of the power switch based on the voltage on the auxiliary winding of the transformer; and generate a turn-on frequency control signal for controlling the power switch to change from an off state to an on state based on the valley pulse signal, the output feedback voltage characterizing the system output load of the quasi-resonant switching power supply, the input characterizing voltage characterizing the AC input voltage of the quasi-resonant switching power supply, and the gate drive signal for driving the power switch to turn on and off.

Description

Technical Field

[0001] This invention relates to the field of circuits, and more specifically to a quasi-resonant 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 a quasi-resonant switching power supply includes a transformer and a power switch. The control chip is configured to: generate a valley pulse signal characterizing the valley of the drain resonant voltage waveform of the power switch based on the voltage on the auxiliary winding of the transformer; and generate a turn-on frequency control signal for controlling the power switch to change from an off state to an on state based on the valley pulse signal, the output feedback voltage characterizing the system output load of the quasi-resonant switching power supply, the input characterization voltage characterizing the AC input voltage of the quasi-resonant switching power supply, and the gate drive signal for driving the power switch to turn on and off.

[0004] According to an embodiment of the present invention, a control method for a quasi-resonant switching power supply includes a transformer and a power switch. The control method includes: generating a valley pulse signal characterizing the valley of the drain resonant voltage waveform of the power switch based on the voltage on the auxiliary winding of the transformer; and generating a turn-on frequency control signal for controlling the power switch to change from an off state to an on state based on the valley pulse signal, an output feedback voltage characterizing the system output load of the quasi-resonant switching power supply, an input characterization voltage characterizing the AC input voltage of the quasi-resonant switching power supply, and a gate drive signal for driving the power switch to turn on and off. 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 The system schematic of a traditional quasi-resonant flyback switching power supply is shown.

[0007] Figure 2 It shows Figure 1 The diagram shows the waveforms of the drain-source voltage and gate drive signal of the power switch, as well as the current flowing through the power switch.

[0008] Figure 3A schematic diagram of the system structure of a conventional quasi-resonant flyback switching power supply with valley-locking function is shown.

[0009] Figure 4 It shows Figure 3 The diagram shows the relationship between the system frequency curve and the system output power of a quasi-resonant flyback switching power supply.

[0010] Figure 5 A schematic diagram of the system structure of a quasi-resonant flyback switching power supply according to an embodiment of the present invention is shown.

[0011] Figure 6 It shows Figure 5 The diagram shown is a schematic block diagram of the multi-mode frequency control module.

[0012] Figure 7 It shows Figure 6 The diagram shows a schematic flowchart of the control process implemented by the frequency mode integration and control unit.

[0013] Figure 8 It shows Figure 5 The diagram shows the relationship between the system frequency curve and the system output power of a quasi-resonant flyback switching power supply in low-voltage input mode.

[0014] Figure 9 It shows Figure 5 The diagram shows the relationship between the system frequency curve and the system output power of a quasi-resonant flyback switching power supply in high-voltage input mode.

[0015] Figure 10 and Figure 11 They are shown respectively Figure 5 The diagram shows the relationship between the system frequency curves of the quasi-resonant flyback switching power supply in low-voltage input mode and high-voltage input mode and the internal feedback voltage characterizing the output load. Detailed Implementation

[0016] 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.

[0017] With the increasing demand for small-size, high-frequency, and high-power-density switching power supplies, high-frequency (e.g., system frequencies exceeding 100kHz), quasi-resonant (QR), and flyback switching power supplies are being used more and more widely.

[0018] Figure 1 The system schematic of a conventional quasi-resonant flyback switching power supply 100 is shown. Figure 1 In the quasi-resonant flyback switching power supply 100 shown, the primary inductance Lp of transformer T has a parasitic leakage inductance Lleak; there is a parasitic capacitance Cp between the two ends of power switch S1; the parasitic capacitance Cp of power switch S1 and the primary inductance Lp of transformer T form an LC resonant cavity; when power switch S1 is in the off state, the quasi-resonant controller 102 detects the demagnetization of the primary inductance Lp of transformer T by detecting the voltage on the auxiliary inductance Lax of transformer T; after the primary inductance Lp of transformer T is demagnetized, it enters a free resonance state with the parasitic capacitance Cp of power switch S1; if power switch S1 changes from the off state to the on state at the bottom of its drain resonant voltage waveform, the switching loss and electromagnetic radiation interference of the system can be greatly reduced.

[0019] However, the system frequency of a traditional quasi-resonant flyback switching power supply 100 may fall outside the predetermined frequency range after the frequency is superimposed with dithering. This may cause the turn-on time of the power switch S1 to repeatedly jump at low frequencies irregularly between two or more adjacent valleys of its drain resonant voltage waveform. The envelope frequency of this repeated jumping is generally below 20KHz due to the control of the dithering envelope frequency, and will fall within the audio range, which will greatly deteriorate the system noise index. Figure 2 It shows Figure 1 The diagram shows the waveforms of the drain-source voltage Vds of the power switch S1 (since the source of the power switch S1 is grounded, the drain-source voltage Vds of the power switch S1 is equal to the drain voltage of the power switch S1), the gate drive signal gate, and the current Ip flowing through the power switch S1.

[0020] To address the noise issue caused by the low envelope frequency jump at the turn-on moment of the power switch S1 in the traditional quasi-resonant flyback switching power supply 100, a quasi-resonant flyback switching power supply with valley-locking function is proposed.

[0021] Figure 3 A schematic diagram of the system architecture of a conventional quasi-resonant flyback switching power supply 300 with valley-locking function is shown. Figure 3In the quasi-resonant flyback switching power supply 300 shown, when the power switch S1 is in the on state, the system input voltage Vin obtained by rectifying and filtering the AC input voltage Vac (not shown in the figure) charges the primary inductor Lp of the transformer T; the freewheeling diode D1 on the secondary side of the transformer T is turned off; the output capacitor C1 supplies power to the system output load; the error amplification and isolation feedback module 304 provides the output feedback voltage VFB, which characterizes the system output load, to the quasi-resonant controller 302; in the quasi-resonant controller 302, the pulse width modulation (PWM) comparator compares the divided voltage FB_in of the output feedback voltage VFB (hereinafter referred to as the internal feedback voltage FB_in) with the current sensing voltage Vcs, which characterizes the current flowing through the power switch S1, to generate a turn-off control signal for controlling the power switch S1 to change from the on state to the off state. Here, the turn-off control signal can control the frequency and duty cycle of the gate drive signal gate, thereby maintaining the system output voltage Vout constant.

[0022] Furthermore, in Figure 3 In the quasi-resonant flyback switching power supply 300 shown, when the power switch S1 is in the off state, the primary inductance Lp of the transformer T is demagnetized; the freewheeling diode D1 on the secondary side of the transformer T is turned on; the secondary inductance Ls of the transformer T charges the output capacitor C1 and supplies power to the system output load; after the primary inductance Lp of the transformer T is demagnetized, the primary inductance Lp of the transformer T and the parasitic capacitance Cp of the power switch S1 enter a free resonance state; in the quasi-resonant controller 302, the demagnetization detection module generates a valley pulse signal characterizing the valley of the drain resonant voltage waveform of the power switch S1 based on the voltage on the auxiliary inductor Lax of the transformer T; the valley locking module generates a turn-on frequency control signal to control the power switch S1 to change from the off state to the on state at a specific valley of its drain resonant voltage waveform based on the valley pulse signal, the internal feedback voltage FB_in, and the gate drive signal gate.

[0023] Figure 4 It shows Figure 3 The diagram shows the relationship between the system frequency curve Freq and the system output power Pout of the quasi-resonant flyback switching power supply 300. It should be noted that the numbers 1, 2, 3, ... n in the diagram represent the 1st valley lock-in state, the 2nd valley lock-in state, the 3rd valley lock-in state, ... the nth valley lock-in state, and not merely the order in which the valleys of the drain resonant voltage waveform of the power switch S1 appear.

[0024] from Figure 4It can be seen that when the system output load decreases, the quasi-resonant controller 302 controls the power switch S1 to change from the off state to the on state at a later trough of its drain resonant voltage waveform, thereby reducing the system frequency of the quasi-resonant flyback switching power supply 300 and improving its operating efficiency. When the system output load increases, the quasi-resonant controller 302 controls the power switch S1 to change from the off state to the on state at an earlier trough of its drain resonant voltage waveform, thereby increasing the system frequency of the quasi-resonant flyback switching power supply 300 and improving its operating efficiency. Because quasi-resonant switching power supplies typically have a maximum system frequency Fmax, when the system output power Pout of the quasi-resonant flyback switching power supply 300 exceeds P1, the quasi-resonant controller 301 controls the power switch S1 to change from the off state to the on state at the first trough of its drain resonant voltage waveform.

[0025] Specifically, Figure 3 The expression for the system output power of the quasi-resonant flyback switching power supply 300 shown is as follows:

[0026] Where η represents the conversion efficiency between the system input power and the system output power of the quasi-resonant flyback switching power supply 300, Lp represents the inductance of the primary inductance Lp of the transformer T, Ipk represents the peak current flowing through the power switch S1, and Fsw represents the system frequency of the quasi-resonant flyback switching power supply 300.

[0027] exist Figure 3 In the quasi-resonant flyback switching power supply 300 shown, as the system output power Pout further increases, the peak current Ipk flowing through the power switch S1 increases, the time that the power switch S1 is in the on state increases, and the demagnetizing time of the primary inductance Lp of the transformer T also increases. This causes the system frequency to decrease when the power switch S1 changes from the off state to the on state at the first valley of its drain resonant voltage waveform. Because the quasi-resonant flyback switching power supply 300 does not have minimum system frequency control under heavy load and continuous conduction mode (CCM), the heavier the output load, the lower the system frequency when the power switch S1 is controlled to change from the off state to the on state at the first valley of its drain resonant voltage waveform. In particular, when the quasi-resonant flyback switching power supply 300 operates under heavy load conditions and the system input voltage Vin is at the valley voltage, the system frequency will drop to its minimum value, and the peak current Ipk flowing through the power switch S1 will reach its maximum value, which can easily cause transformer T to saturate, greatly increasing the design difficulty of transformer T. This problem is even more pronounced in quasi-resonant switching power supplies with small size, high frequency, and high power density.

[0028] In view of the above problems, a control chip and control method for a quasi-resonant switching power supply according to embodiments of the present invention are proposed to avoid the transformer operating in saturation state when the quasi-resonant switching power supply is in low-voltage input mode and under heavy output load, and the power switch is controlled to change from the off state to the on state at the first valley of its drain resonant voltage waveform. This can significantly reduce the design difficulty of the transformer.

[0029] The following description, with reference to the accompanying drawings, uses a multi-mode quasi-resonant controller for a quasi-resonant flyback switching power supply as an example to illustrate the control chip and control method for a quasi-resonant switching power supply according to an embodiment of the present invention.

[0030] Figure 5 A schematic diagram of the system structure of a quasi-resonant flyback switching power supply 500 according to an embodiment of the present invention is shown. Figure 5 As shown, the quasi-resonant flyback switching power supply 500 includes a transformer T, a power switch S1, a multi-mode quasi-resonant controller 502, and an error amplification and isolation feedback module 504. The error amplification and isolation feedback module 504 is configured to provide the output feedback voltage VFB, representing the system output load of the quasi-resonant flyback switching power supply 500, to the multi-mode quasi-resonant controller 502. The multi-mode quasi-resonant controller 502 is configured to generate a valley pulse signal Valley, representing the valley of the drain resonant voltage waveform of the power switch S1, based on the voltage on the auxiliary winding Lax of the transformer T. Furthermore, based on the valley pulse signal Valley, the output feedback voltage VFB, the input characterization voltage Vac_dec (not shown in the figure), representing the AC input voltage Vac (not shown in the figure) of the quasi-resonant flyback switching power supply 500, and the gate drive signal gate, used to drive the power switch S1 to turn on and off, it generates a turn-on frequency control signal Clk_out to control the power switch S1 from the off state to the on state.

[0031] like Figure 5 As shown, in some embodiments, the multi-mode quasi-resonant controller 502 is further configured to generate a turn-off control signal pwm_out for controlling the power switch S1 to change from an on state to an off state based on the output feedback voltage VFB and the current sensing voltage Vcs characterizing the current flowing through the power switch S1. Here, the turn-off control signal Pwm_out can control the frequency and duty cycle of the gate drive signal gate, thereby maintaining a constant system output voltage Vout.

[0032] exist Figure 5In the quasi-resonant flyback switching power supply 500 shown, when the power switch S1 is in the on state, the system input voltage Vin obtained by rectifying and filtering the AC input voltage Vac charges the primary inductor Lp of the transformer T; the freewheeling diode D1 on the secondary side of the transformer T is turned off; the output capacitor C1 supplies power to the system output load; the error amplification and isolation feedback module 504 provides the output feedback voltage VFB, which characterizes the system output load and is generated according to the change of the system output voltage Vout, to the multi-mode quasi-resonant controller 502; in the multi-mode quasi-resonant controller 502, the PWM comparator generates the turn-off control signal Pwm_out by comparing the voltage division FB_in of the output feedback voltage VFB (hereinafter referred to as the internal feedback voltage FB_in) with the current sensing voltage Vcs, which characterizes the current flowing through the power switch S1.

[0033] exist Figure 5 In the quasi-resonant flyback switching power supply 500 shown, when the power switch S1 is in the off state, the primary inductance Lp of the transformer T is demagnetized; the freewheeling diode D1 on the secondary side of the transformer T is turned on; the secondary inductance Ls of the transformer T charges the output capacitor C1 and supplies power to the system output load; after the primary inductance Lp of the transformer T is demagnetized, the primary inductance Lp of the transformer T and the parasitic capacitance Cp of the power switch S1 enter a free resonance state; in the multi-mode quasi-resonant controller 502, the demagnetization detection module generates a valley pulse signal Valley, which characterizes the valley of the drain resonant voltage waveform of the power switch S1, based on the voltage on the auxiliary inductor Lax of the transformer T; the multi-mode frequency control module generates a turn-on frequency control signal Clk_out based on the valley pulse signal Valley, the internal feedback voltage FB_in, the gate drive signal gate, and the input characterization voltage Vac_dec.

[0034] Figure 6 It shows Figure 5 The diagram shows a schematic block diagram of the multi-mode frequency control module. Figure 6 As shown, in some embodiments, Figure 5The multi-mode frequency control module shown includes an AC voltage detection unit 602, a valley-locking control unit 604, a minimum operating frequency control unit 606, and a frequency mode synthesis and control unit 608. The AC voltage detection unit 602 is configured to generate an input mode characterization signal AC-in based on the input characterization voltage Vac_dec and a preset threshold, which characterizes whether the quasi-resonant flyback switching power supply 500 is in high-voltage input mode or low-voltage input mode. The valley-locking control unit 604 is configured to base its signal on the valley pulse signal Valley, the output feedback voltage VFB, and the gate drive signal gate. A valley selection and latching signal is generated to control the power switch S1 to change from the off state to the on state at a specific valley of its drain resonant voltage waveform; the minimum operating frequency control unit 606 is configured to generate a minimum frequency control signal based on the output feedback voltage VFB and the input mode characterization signal AC-in to control the quasi-resonant flyback switching power supply 500 to operate in continuous conduction mode; the frequency mode synthesis and control unit 608 is configured to generate a conduction frequency control signal Clk_out based on the valley selection and latching signal, the input mode characterization signal AC-in, and the minimum frequency control signal.

[0035] In some embodiments, the AC voltage detection unit 602 can obtain the input characterization voltage Vac_dec by directly detecting the AC input voltage Vac or the system input voltage Vin, or by indirectly detecting the system input voltage Vin. It compares the input characterization voltage Vac_dec with an internally set threshold to determine whether the current input is high voltage or low voltage. It then provides the input mode characterization signal AC_in, indicating whether the quasi-resonant flyback switching power supply 500 is in high voltage or low voltage input mode, to the minimum operating frequency control unit 606 and the frequency mode synthesis and control unit 608. For example, the AC voltage detection unit 602 can compare the input characterization voltage Vac_dec with a first preset threshold, and determine that the quasi-resonant flyback switching power supply 500 is in high voltage input mode when the input characterization voltage Vac_dec is greater than the first preset threshold; and compare the input characterization voltage Vac_dec with a second preset threshold, and determine that the quasi-resonant flyback switching power supply 500 is in low voltage input mode when the input characterization voltage Vac_dec is less than the second preset threshold, wherein the first preset threshold is greater than the second preset threshold.

[0036] In some embodiments, the minimum operating frequency control unit 604 can generate a minimum frequency control signal for controlling the quasi-resonant flyback switching power supply 500 to operate in continuous conduction mode based on the internal feedback voltage FB_in and the input mode characterization signal AC_in. The valley-locking control unit 606 can generate a valley selection and locking signal for controlling the power switch S1 to change from an off state to a conduction state at a specific valley of its drain resonant voltage waveform based on the valley pulse signal Valley, the internal feedback voltage FB_in, and the gate drive signal gate. The frequency mode synthesis and control unit 608 can synthesize and generate a conduction frequency control signal Clk_out based on the input mode characterization signal AC-in, the valley selection and locking signal, and the minimum frequency control signal.

[0037] Figure 7 It shows Figure 6 The diagram shows a schematic flowchart illustrating the control process implemented by the frequency mode synthesis and control unit. Figure 7 As shown, the frequency mode integration and control unit 608, based on the input mode characterization signal generated by the AC voltage detection unit 602, the minimum frequency control signal generated by the minimum operating frequency control unit 604, and the valley selection and locking signal generated by the valley lockout control unit 606, integrates and generates a conduction frequency control signal Clk_out to control the power switch S1 from the off state to the on state. Specifically, when the quasi-resonant flyback switching power supply 500 is in low-voltage input mode, the frequency mode integration and control unit 608 generates a frequency control curve with a quasi-resonant valley lockout superimposed continuous conduction minimum frequency maximum value of Fmin_H; when the quasi-resonant flyback switching power supply 500 is in high-voltage input mode, the frequency mode integration and control unit 608 generates a frequency control curve with a quasi-resonant valley lockout superimposed continuous conduction minimum frequency maximum value of Fmin_L (greater than the minimum system frequency Fburst), where the frequency value represented by Fmin_H is greater than the frequency value represented by Fmin_L. This allows the quasi-resonant flyback switching power supply 500 to achieve frequency division in both high and low input modes under continuous conduction mode, thus avoiding the transformer operating in saturation due to active frequency reduction when the power switch S1 changes from off to on state at the first valley of its drain resonant voltage waveform under low input voltage and heavy output load conditions. This reduces the design difficulty of the transformer and ensures that the quasi-resonant flyback switching power supply 500 operates in the quasi-resonant valley conduction mode under high input and heavy output load conditions, thereby not reducing the system efficiency under high input mode.

[0038] Figure 8 It shows Figure 5The diagram shows the relationship between the system frequency curve Freq and the system output power Pout of the quasi-resonant flyback switching power supply 500 in low-voltage input mode. It should be noted that the numbers 1, 2, 3, ... n in the diagram represent the 1st valley lock-in state, the 2nd valley lock-in state, the 3rd valley lock-in state, ... the nth valley lock-in state, and not merely the order in which the valleys of the drain resonant voltage waveform of power switch S1 appear.

[0039] Combination Figure 4 and Figure 8 It can be seen that, compared to Figure 4 The diagram shown illustrates the relationship between the system frequency curve and the system output power. Figure 8 A minimum system frequency control curve for continuous conduction mode has been added. For example... Figure 8 As shown, when the quasi-resonant flyback switching power supply 500 is in low-voltage input mode, when the system is operating in quasi-resonant mode and the system output power is higher than the first preset power (e.g., P2) or when it is operating in continuous conduction mode, the minimum system frequency is the first fixed frequency (e.g., FCCM_H).

[0040] When the quasi-resonant flyback switching power supply 500 is in low-voltage input mode, the system frequency decreases rapidly with increasing system output power when the power switch S1 changes from the off state to the on state at the first valley of its drain resonant voltage waveform. Therefore, the system is more likely to enter a continuous conduction fixed-frequency mode (e.g., at power point P3). The FCCM_H frequency can be maintained at a suitable higher frequency value by setting internally or adjusting externally, avoiding active frequency reduction that would cause the transformer to operate in saturation when the system is operating under low input voltage and heavy output load, as the power switch S1 is locked at the first valley of its drain resonant voltage waveform. This reduces the design complexity of the transformer. Furthermore, when the system output power is lower than P3, the system operates in a quasi-resonant valley-locked conduction mode. As the system output power decreases, the multi-mode quasi-resonant controller 502 reduces the frequency by controlling the power switch S1 to change from the off state to the on state at a later valley of its drain resonant voltage waveform, thereby improving efficiency in the light-load section.

[0041] Figure 9 It shows Figure 5 The diagram shows the relationship between the system frequency curve Freq and the system output power Pout of the quasi-resonant flyback switching power supply 500 in high-voltage input mode. It should be noted that the numbers 1, 2, 3, ... n in the diagram represent the 1st valley lock-in state, the 2nd valley lock-in state, the 3rd valley lock-in state, ... the nth valley lock-in state, and not merely the order in which the valleys of the drain resonant voltage waveform of power switch S1 appear.

[0042] Combination Figure 4 and Figure 9 It can be seen that, compared to Figure 4 The diagram shown illustrates the relationship between the system frequency curve and the system output power. Figure 9 A minimum system frequency control curve for continuous conduction mode has been added. For example... Figure 9 As shown, when the quasi-resonant flyback switching power supply 500 is in high-voltage input mode, when the system is operating in quasi-resonant mode and the system output power is higher than the second preset power (e.g., P5) or when the system is operating in continuous conduction mode, the minimum system frequency is the second fixed frequency (e.g., FCCM_L), where FCCM_L can be set to be less than FCCM_H.

[0043] When the quasi-resonant flyback switching power supply 500 is in high-voltage input mode, as the power switch S1 transitions from the off state to the on state at the first valley of its drain resonant voltage waveform, the system frequency decreases very slowly with increasing system output power. Therefore, the power point P6 at which the system enters continuous conduction mode is much larger than the power point P3. This ensures that even under high-voltage input and heavy output load, the system operates in quasi-resonant valley conduction mode, without reducing system efficiency under high-voltage input mode.

[0044] Figure 10 and Figure 11 They are shown respectively Figure 5 The diagram shows the relationship between the system frequency curves of the quasi-resonant flyback switching power supply 500 in low-voltage input mode and high-voltage input mode and the internal feedback voltage FB_in characterizing the output load. It should be noted that the numbers 1, 2, 3, ... n in the diagram represent the 1st valley lock-in state, the 2nd valley lock-in state, the 3rd valley lock-in state, ... the nth valley lock-in state, respectively, and do not simply represent the order in which the valleys of the drain resonant voltage waveform of the power switch S1 appear.

[0045] It should be noted that the multi-mode quasi-resonant controller 502 described in conjunction with the quasi-resonant flyback switching power supply is applicable not only to quasi-resonant switching power supplies with flyback architecture, but also to quasi-resonant switching power supplies with BUCK and BOOST architectures.

[0046] In summary, the multi-mode quasi-resonant controller 502, described in conjunction with a quasi-resonant flyback switching power supply, achieves multi-mode frequency control that allows for the coexistence of high-frequency quasi-resonant valley-locking and minimum system frequency control in continuous conduction mode. While ensuring that the system operates in quasi-resonant conduction mode under high AC input and heavy output load, it avoids the transformer operating in saturation due to active frequency reduction when the power switch S1 is locked at the first valley of its drain resonant voltage waveform from the off state to the on state under low AC input voltage and heavy output load. This significantly reduces the design difficulty of the transformer.

[0047] Here, it should be understood that the power switch S1 can be implemented as, for example, a metal-oxide-semiconductor field-effect transistor (MOSFET), a bipolar junction NPN transistor (BJT-NPN), an insulated gate bipolar transistor (IGBT), and a gallium nitride (GaN) transistor.

[0048] 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 a quasi-resonant switching power supply, wherein, The quasi-resonant switching power supply includes a transformer and a power switch, and the control chip is configured as follows: Based on the voltage on the auxiliary winding of the transformer, a valley pulse signal is generated that characterizes the valley of the drain resonant voltage waveform of the power switch. Based on the valley pulse signal, the output feedback voltage characterizing the system output load of the quasi-resonant switching power supply, and the gate drive signal used to drive the power switch to turn on and off, a valley selection and locking signal is generated to control the power switch to change from the off state to the on state at a specific valley of its drain resonant voltage waveform. Based on the input characterization voltage that characterizes the AC input voltage of the quasi-resonant switching power supply and a preset threshold, an input mode characterization signal is generated to characterize whether the quasi-resonant switching power supply is in high-voltage input mode or low-voltage input mode. Based on the output feedback voltage and the input mode characterization signal, a minimum frequency control signal is generated for controlling the quasi-resonant switching power supply to operate in continuous conduction mode at the minimum system frequency. as well as Based on the valley selection and locking signal, the input mode characterization signal, and the minimum frequency control signal, a conduction frequency control signal is generated to control the power switch to change from the off state to the on state.

2. The control chip according to claim 1, wherein: When the input characterization voltage is greater than the first preset threshold, the input mode characterization signal indicates that the quasi-resonant switching power supply is in high-voltage input mode; When the input characterization voltage is less than the second preset threshold, the input mode characterization signal indicates that the quasi-resonant switching power supply is in low-voltage input mode.

3. The control chip according to claim 1, further configured as follows: Based on the output feedback voltage and the current sensing voltage characterizing the current flowing through the power switch, a turn-off control signal is generated to control the power switch to change from the on state to the off state.

4. The control chip according to claim 1, wherein: When the quasi-resonant switching power supply is in low-voltage input mode, when the quasi-resonant switching power supply is operating in quasi-resonant mode and the system output power is higher than the first preset power, or when the quasi-resonant switching power supply is operating in continuous conduction mode, the minimum frequency of the gate drive signal is the first fixed frequency.

5. The control chip according to claim 4, wherein: When the quasi-resonant switching power supply is in high-voltage input mode, when the quasi-resonant switching power supply is operating in quasi-resonant mode and the system output power is higher than the second preset power, or when the quasi-resonant switching power supply is operating in continuous conduction mode, the lowest frequency of the gate drive signal is the second fixed frequency, which is less than the first fixed frequency.

6. A control method for a quasi-resonant switching power supply, wherein, The quasi-resonant switching power supply includes a transformer and a power switch, and the control method includes: Based on the voltage on the auxiliary winding of the transformer, a valley pulse signal is generated that characterizes the valley of the drain resonant voltage waveform of the power switch. Based on the valley pulse signal, the output feedback voltage characterizing the system output load of the quasi-resonant switching power supply, and the gate drive signal used to drive the power switch to turn on and off, a valley selection and locking signal is generated to control the power switch to change from the off state to the on state at a specific valley of its drain resonant voltage waveform. Based on the input characterization voltage that characterizes the AC input voltage of the quasi-resonant switching power supply and a preset threshold, an input mode characterization signal is generated to characterize whether the quasi-resonant switching power supply is in high-voltage input mode or low-voltage input mode. Based on the output feedback voltage and the input mode characterization signal, a minimum frequency control signal is generated for controlling the quasi-resonant switching power supply to operate in continuous conduction mode at the lowest system frequency; and Based on the valley selection and locking signal, the input mode characterization signal, and the minimum frequency control signal, a conduction frequency control signal is generated to control the power switch to change from the off state to the on state.

7. The control method according to claim 6, wherein: When the input characterization voltage is greater than the first preset threshold, the input mode characterization signal indicates that the quasi-resonant switching power supply is in high-voltage input mode; When the input characterization voltage is less than the second preset threshold, the input mode characterization signal indicates that the quasi-resonant switching power supply is in low-voltage input mode.

8. The control method according to claim 6, further configured as follows: Based on the output feedback voltage and the current sensing voltage characterizing the current flowing through the power switch, a turn-off control signal is generated to control the power switch to change from the on state to the off state.

9. The control method according to claim 6, wherein: When the quasi-resonant switching power supply is in low-voltage input mode, when the quasi-resonant switching power supply is operating in quasi-resonant mode and the system output power is higher than the first preset power, or when the quasi-resonant switching power supply is operating in continuous conduction mode, the minimum system frequency of the quasi-resonant switching power supply is the first fixed frequency.

10. The control method according to claim 9, wherein: When the quasi-resonant switching power supply is in high-voltage input mode, when the quasi-resonant switching power supply is operating in quasi-resonant mode and the system output power is higher than the second preset power, or when the quasi-resonant switching power supply is operating in continuous conduction mode, the minimum system frequency of the quasi-resonant switching power supply is the second fixed frequency, which is less than the first fixed frequency.

11. A quasi-resonant switching power supply, comprising a control chip according to any one of claims 1 to 5.

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