TWI842011B - Quasi-resonant switching power supply and control chip and control method thereof - Google Patents

Abstract

A quasi-resonant switching power supply and a control chip and a control method thereof are provided. The quasi-resonant switching power supply includes a transformer and a power switch, and the control chip is configured to: generate a valley pulse signal representing 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 conduction frequency control signal for controlling the power switch to change from the off state to the on state based on the valley pulse signal, the output feedback voltage representing the system output load of the quasi-resonant switching power supply, the input characteristic voltage representing 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

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

The present invention relates to the field of circuits, and more specifically to a quasi-resonant switching power supply, a control chip and a control method thereof.

A switching power supply, also known as an alternating current power supply or a switching converter, is a type of power supply. The function of a switching power supply is to convert a voltage level into the voltage or current required by the user through different forms of architecture (for example, fly-back architecture, buck architecture, or boost architecture, etc.).

According to a control chip for a quasi-resonant switching power supply according to an embodiment of the present invention, the quasi-resonant switching power supply includes a transformer and a power switch, and the control chip is configured to: generate a valley pulse signal representing 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 conduction frequency control signal for controlling the power switch to change from the off state to the on state based on the valley pulse signal, the output feedback voltage representing the system output load of the quasi-resonant switching power supply, the input characteristic voltage representing 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.

According to a control method for a quasi-resonant switching power supply according to an embodiment of the present invention, 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, generating a valley pulse signal representing the valley of the drain resonant voltage waveform of the power switch; and based on the valley pulse signal, the output feedback voltage representing the system output load of the quasi-resonant switching power supply, the input characteristic voltage representing 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, generating a conduction frequency control signal for controlling the power switch to change from the off state to the on state.

100,300,500: Quasi-resonant flyback converter power supply

102,301,302: Quasi-resonant controller

304,504: Error amplification and isolation feedback module

502:Multi-mode quasi-resonant controller

602: AC voltage detection unit

604: Valley lock control unit

606: Minimum operating frequency control unit

608: Frequency mode integration and control unit

AC-in: Input mode characteristic signal

C1: output capacitor

Clk_out: conduction frequency control signal

Cp: parasitic capacitance

CS: Current sampling terminal

D1: Follow-up diode

D2: Feedback voltage internal divider diode

dem: demagnetization signal detection terminal

FB: Feedback voltage detection terminal

FB_in: internal feedback voltage

Fburst: minimum system frequency

FCCM_H, FCCM_L, Fmin_H, Fmin_L: frequency value

Fmax: Maximum system frequency

Freq: System frequency curve

gate: gate drive signal

Ip: current

Ipk: Peak current

Laux: Auxiliary inductor

Lleak: parasitic leakage inductance

Lp: primary inductance

Ls: Secondary inductance

P1, P2, P3, P5, P6: power points

Pout: system output power

Pwm_out: turn off control signal

Q: Trigger positive phase output terminal

Qb: Trigger inverting output terminal

R: Trigger reset input terminal

R1: bias resistor on the internal voltage divider of the feedback voltage

R2: Bias resistor for the internal voltage divider of the feedback voltage

Rsense: Current sampling resistor

S: Trigger set input terminal

S1: Power switch

T: Transformer

Vac: AC input voltage

Vac_dec: Input characteristic voltage

Valley: valley pulse signal

Vcs: Current flow measurement voltage

VD2: Feedback voltage internal voltage divider diode forward conduction voltage drop

Vds: drain-source voltage

VFB: Output feedback voltage

Vin: System input voltage

Vout: system output voltage

1st: 1st valley locked state

No. 2: The second valley lock state

No. 3: The third valley lock state

nth: nth valley locked state

The present invention can be better understood from the following description of the specific implementation of the present invention in conjunction with the drawings, wherein:

Figure 1 shows the system schematic of a conventional quasi-resonant flyback converter power supply.

FIG2 shows the waveform of the drain-source voltage and gate drive signal of the power switch shown in FIG1 , as well as the current flowing through the power switch.

Figure 3 shows a schematic diagram of the system structure of a traditional quasi-resonant flyback converter power supply with valley locking function.

FIG4 is a schematic diagram showing the relationship between the system frequency curve and the system output power of the quasi-resonant flyback converter power supply shown in FIG3.

FIG5 shows a schematic diagram of the system structure of a quasi-resonant flyback converter power supply according to an embodiment of the present invention.

FIG6 shows a schematic block diagram of the multi-mode frequency control module shown in FIG5.

FIG7 shows a schematic flow chart of the control process implemented by the frequency mode integration and control unit shown in FIG6.

FIG8 is a schematic diagram showing the relationship between the system frequency curve and the system output power of the quasi-resonant flyback converter power supply shown in FIG5 in the low voltage input mode.

FIG9 is a schematic diagram showing the relationship between the system frequency curve and the system output power of the quasi-resonant flyback converter power supply shown in FIG5 in the high voltage input mode.

Figures 10 and 11 are schematic diagrams showing the relationship between the system frequency curve of the quasi-resonant flyback converter power supply shown in Figure 5 in low voltage input mode and high voltage input mode and the internal feedback voltage representing the output load.

The features and exemplary embodiments of various aspects of the present invention are described in detail below. In the detailed description below, many specific details are set forth in order to provide a comprehensive understanding of the present invention. However, it is obvious to a person skilled in the art that the present invention can be implemented without some of these specific details. The following description of the embodiments is only for the purpose of providing a better understanding of the present invention by illustrating examples of the present invention. The present invention is in no way limited to any specific configuration and algorithm set forth below, but covers any modification, substitution and improvement of elements, components and algorithms without departing from the spirit of the present invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessary ambiguity of the present invention.

As the demand for small-size, high-frequency, and high-power-density switching power supplies increases, high-frequency (e.g., system frequency exceeds 100KHz), quasi-resonant (QR), flyback converter power supplies are increasingly being used.

FIG1 shows a system schematic diagram of a conventional quasi-resonant flyback converter power supply 100. In the quasi-resonant flyback converter power supply 100 shown in FIG1 , the primary inductor Lp of the transformer T has a parasitic leakage inductance Lleak; there is a parasitic capacitor Cp between the two ends of the power switch S1; the parasitic capacitor Cp of the power switch S1 and the primary inductor Lp of the transformer T form an LC resonant cavity; when the power switch S1 is in the off state, the quasi-resonant controller 102 detects the transformer T The voltage on the auxiliary inductor Laux is used to detect the demagnetization of the primary inductor Lp of the transformer T; after the demagnetization, the primary inductor Lp of the transformer T enters a free resonance state with the parasitic capacitance Cp of the power switch S1; if the 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.

However, the system frequency of the conventional quasi-resonant flyback converter power supply 100 may fall outside the predetermined frequency range after superimposed frequency jittering, which may cause the turn-on time of the power switch S1 to randomly and repeatedly jump at low frequencies between two or even more adjacent valleys of its drain resonant voltage waveform. The envelope frequency of such repeated jumps is generally lower than 20KHz because it is controlled by the frequency jittering envelope frequency, and will fall within the audio range, greatly deteriorating the system noise index. FIG2 shows the waveform of the drain-source voltage Vds of the power switch S1 shown in FIG1 (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.

In order to solve the problem of distorted sound caused by the low envelope frequency jump at the turn-on moment of the power switch S1 in the traditional quasi-resonant flyback converter power supply 100, a quasi-resonant flyback converter power supply with a valley locking function is proposed.

FIG. 3 shows a schematic diagram of the system structure of a conventional quasi-resonant flyback converter power supply 300 with a valley locking function. In the quasi-resonant flyback converter power supply 300 shown in FIG3 , when the power switch S1 is in the on state, the system input voltage Vin obtained by rectifying and filtering the alternating current (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 representing the system output load to the quasi-resonant controller 302; in the quasi-resonant controller 302, the pulse width modulation (Pulse Width The PWM (PWM) comparator compares the divided voltage FB_in (hereinafter referred to as the internal feedback voltage FB_in) of the output feedback voltage VFB with the current sensing voltage Vcs representing the current flowing through the power switch S1, and generates a shutdown control signal for controlling the power switch S1 from the on state to the off state. Here, the shutdown control signal can control the frequency and duty cycle of the gate drive signal gate, thereby keeping the system output voltage Vout constant.

Furthermore, in the quasi-resonant flyback converter power supply 300 shown in FIG3 , when the power switch S1 is in the off state, the primary inductor Lp of the transformer T is demagnetized; the freewheeling diode D1 on the secondary side of the transformer T is turned on; the secondary inductor Ls of the transformer T charges the output capacitor C1 and supplies power to the system output load; after the demagnetization of the primary inductor Lp of the transformer T is completed, the primary inductor Lp of the transformer T and the parasitic capacitor Cp of the power switch S1 enter a free resonance state. state; in the quasi-resonant controller 302, the demagnetization detection module generates a valley pulse signal representing the valley of the drain resonant voltage waveform of the power switch S1 based on the voltage on the auxiliary inductor Laux of the transformer T, and the valley lock module generates a conduction frequency control signal for controlling 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.

FIG4 shows a schematic diagram of the relationship between the system frequency curve Freq and the system output power Pout of the quasi-resonant flyback converter power supply 300 shown in FIG3. It should be noted here that the 1st, 2nd, 3rd, ... nth shown in the figure represent the 1st valley lock state, the 2nd valley lock state, the 3rd valley lock state, ... the nth valley lock state, respectively, and do not only represent the order in which the valleys of the drain resonant voltage waveform of the power switch S1 appear.

As can be seen from FIG4 , when the system output load decreases, the quasi-resonant controller 302 reduces the system frequency of the quasi-resonant flyback converter power supply 300 by controlling the power switch S1 to change from the off state to the on state at a valley bottom that appears later in the drain resonant voltage waveform, thereby improving the working efficiency of the quasi-resonant flyback converter power supply 300; when the system output load increases, the quasi-resonant controller 302 increases the system frequency of the quasi-resonant flyback converter power supply 300 by controlling the power switch S1 to change from the off state to the on state at a valley bottom that appears earlier in the drain resonant voltage waveform, thereby improving the working efficiency of the quasi-resonant flyback converter power supply 300. Because the quasi-resonant switching power supply usually has the highest system frequency Fmax, when the system output power Pout of the quasi-resonant flyback converter 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 valley of its drain resonant voltage waveform.

Specifically, the system output power Pout of the quasi-resonant flyback converter power supply 300 shown in FIG3 is calculated as:

Among them, η represents the conversion efficiency between the system input power and the system output power of the quasi-resonant flyback converter power supply 300, Lp represents the inductance of the primary inductor 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 converter power supply 300.

In the quasi-resonant flyback converter power supply 300 shown in FIG. 3 , 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 demagnetization time of the primary inductor Lp of the transformer T also increases, resulting in a decrease in the system frequency 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 converter power supply 300 does not have a heavy load and continuous conduction mode (Continuous Conduction Mode), the system frequency of the power switch S1 is reduced. The system frequency is controlled at the lowest system frequency under the quasi-resonant flyback mode (CCM), so 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, the heavier the output load, the lower the system frequency will drop. In particular, when the quasi-resonant flyback converter 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 the lowest value, and the peak current Ipk flowing through the power switch S1 will reach the maximum value, which is easy to cause the transformer T to be saturated, greatly increasing the difficulty of designing the transformer T. This problem is more prominent in quasi-resonant switching power supplies with small size, high frequency, and high power density.

In view of the above problems, a control chip and control method for a quasi-resonant switching power supply according to an embodiment of the present invention are proposed to avoid the transformer operating in a saturated state due to active frequency reduction when the power switch is controlled to change from an off state to an on state at the first valley of its drain resonant voltage waveform when the quasi-resonant switching power supply is in a low voltage input mode and the output is overloaded, which can significantly reduce the difficulty of transformer design.

The following is a description of the control chip and control method for a quasi-resonant switching power supply according to an embodiment of the present invention, with reference to the diagram, taking a multi-mode quasi-resonant controller for a quasi-resonant flyback converter power supply as an example.

FIG5 shows a schematic diagram of the system structure of a quasi-resonant flyback converter power supply 500 according to an embodiment of the present invention. As shown in FIG5 , the quasi-resonant flyback converter power supply 500 includes a transformer T, a power switch S1, a multi-mode quasi-resonant controller 502, and an error amplification and isolation module 504, wherein: 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 converter power supply 500 to the multi-mode quasi-resonant controller 502; the multi-mode quasi-resonant controller 502 is configured to generate a drain resonant voltage VFB representing the power switch S1 based on the voltage on the auxiliary inductor Laux of the transformer T. The bottom pulse signal Valley of the bottom of the voltage waveform is generated, and based on the bottom pulse signal Valley, the output feedback voltage VFB representing the system output load, the input characteristic voltage Vac_dec (not shown in the figure) representing the AC input voltage Vac (not shown in the figure) of the quasi-resonant flyback converter power supply 500, and the gate drive signal gate for driving the power switch S1 to turn on and off, a conduction frequency control signal Clk_out for controlling the power switch S1 to change from the off state to the on state is generated.

As shown in FIG5 , in some embodiments, the multi-mode quasi-resonant controller 502 is further configured to generate a shutdown control signal Pwm_out for controlling the power switch S1 to change from the on state to the off state based on the output feedback voltage VFB and the current flow sensing voltage Vcs representing the current flowing through the power switch S1. Here, the shutdown control signal Pwm_out can control the frequency and duty cycle of the gate drive signal gate, thereby maintaining the system output voltage Vout constant.

In the quasi-resonant flyback converter power supply 500 shown in FIG5 , 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 will be based on the system output voltage Vout The output feedback voltage VFB representing the system output load generated by the change of is provided to the multi-mode quasi-resonant controller 502; in the multi-mode quasi-resonant controller 502, the PWM comparator generates a shutdown control signal Pwm_out by comparing the divided voltage FB_in of the output feedback voltage VFB (hereinafter referred to as the internal feedback voltage FB_in) with the current flow detection voltage Vcs representing the current flowing through the power switch S1.

In the quasi-resonant flyback converter power supply 500 shown in FIG5 , when the power switch S1 is in the off state, the primary inductor Lp of the transformer T is demagnetized; the freewheeling diode D1 on the secondary side of the transformer T is turned on; the secondary inductor Ls of the transformer T charges the output capacitor C1 and supplies power to the system output load; after the demagnetization of the primary inductor Lp of the transformer T is completed, the primary inductor Lp of the transformer T and the parasitic capacitor Cp of the power switch S1 enter a free resonant state; in the multi- In the mode quasi-resonant controller 502, the demagnetization detection module generates 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 inductor Laux of the transformer T, and the multi-mode frequency control module generates a conduction 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 characteristic voltage Vac_dec.

FIG6 shows a schematic block diagram of the multi-mode frequency control module shown in FIG5 . As shown in FIG6 , in some embodiments, the multi-mode frequency control module shown in FIG5 includes an AC voltage detection unit 602, a valley lock control unit 604, a minimum operating frequency control unit 606, and a frequency mode integration and control unit 608, wherein the AC voltage detection unit 602 is configured to generate an input mode characteristic signal AC-in for characterizing whether the quasi-resonant flyback converter power supply 500 is in a high voltage input mode or a low voltage input mode based on an input characteristic voltage Vac_dec and a preset threshold value; the valley lock control unit 604 is configured to generate an input mode characteristic signal AC-in for characterizing whether the quasi-resonant flyback converter power supply 500 is in a high voltage input mode or a low voltage input mode based on a valley pulse signal Valley, an output feedback voltage VFB, and a gate driver. The gate driving signal generates a valley selection and locking signal for controlling the power switch S1 to change from the off state to the on state at a specific valley of the drain resonant voltage waveform; the minimum operating frequency control unit 606 is configured to generate a minimum frequency control signal for controlling the minimum system frequency of the quasi-resonant flyback converter power supply 500 to operate in the continuous conduction mode based on the output feedback voltage VFB and the input mode characteristic signal AC-in; the frequency mode integration and control unit 608 is configured to generate a conduction frequency control signal Clk_out based on the valley selection and locking signal, the input mode characteristic signal AC-in, and the minimum frequency control signal.

In some embodiments, the AC voltage detection unit 602 can obtain the input characteristic 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, compare the input characteristic voltage Vac_dec with the internally set threshold to determine whether the current input is a high voltage input or a low voltage input, and provide the input mode characteristic signal AC_in indicating whether the quasi-resonant flyback converter power supply 500 is in a high voltage input mode or a low voltage input mode to the minimum operating frequency control unit 606 and the frequency mode integration and control unit 608. For example, the AC voltage detection unit 602 can compare the input characteristic voltage Vac_dec with a first preset threshold value, and determine that the quasi-resonant flyback converter power supply 500 is in a high voltage input mode when the input characteristic voltage Vac_dec is greater than the first preset threshold value; and compare the input characteristic voltage Vac_dec with a second preset threshold value, and determine that the quasi-resonant flyback converter power supply 500 is in a low voltage input mode when the input characteristic voltage Vac_dec is less than the second preset threshold value, wherein the first preset threshold value is greater than the second preset threshold value.

In some embodiments, the minimum operating frequency control unit 606 can generate a minimum frequency control signal for controlling the minimum system frequency of the quasi-resonant flyback converter power supply 500 to operate in the continuous conduction mode according to the internal feedback voltage FB_in and the input mode characteristic signal AC_in. The valley lock control unit 604 can generate a valley selection and lock signal for controlling the power switch S1 to change from the off state to the on state at a specific valley of its drain resonant voltage waveform according to the valley pulse signal Valley, the internal feedback voltage FB_in, and the gate drive signal gate. The frequency mode integration and control unit 608 can generate the conduction frequency control signal Clk_out by comprehensive processing according to the input mode characteristic signal AC-in, the valley selection and locking signal, and the minimum frequency control signal.

Fig. 7 shows a schematic flow chart of the control process implemented by the frequency mode integration and control unit shown in Fig. 6. As shown in Fig. 7, the frequency mode integration and control unit 608 generates a conduction frequency control signal Clk_out by comprehensive processing according to the input mode characteristic signal generated by the AC voltage detection unit 602, the minimum frequency control signal generated by the minimum operating frequency control unit 606, and the valley selection and locking signal generated by the valley locking control unit 604 to control the power switch S1 from the off state to the on state. Specifically, when the quasi-resonant flyback converter power supply 500 is in the low voltage input mode, the frequency mode integration and control unit 608 generates a frequency control curve with a quasi-resonant valley bottom locking and a maximum value of the continuous conduction minimum frequency of Fmin_H; when the quasi-resonant flyback converter power supply 500 is in the high voltage input mode, the frequency mode integration and control unit 608 generates a frequency control curve with a quasi-resonant valley bottom locking and a maximum value of the continuous conduction minimum frequency of Fmin_L (greater than the minimum system frequency Fburst), wherein the frequency value represented by Fmin_H is greater than the frequency value represented by Fmin_L. In this way, the minimum system frequency of the quasi-resonant flyback converter power supply 500 in the continuous conduction mode can be divided in the high input mode and the low input mode, which can avoid the quasi-resonant flyback converter power supply 500 under the conditions of low input voltage and heavy output load, when the power switch S1 is locked at the first valley of its drain resonant voltage waveform and changes from the off state to the on state, and the transformer works in the saturated state due to active frequency reduction, thereby reducing the difficulty of transformer design, and ensuring that the quasi-resonant flyback converter power supply 500 works in the quasi-resonant valley conduction mode under the conditions of high voltage input and heavy output load, thereby not reducing the system working efficiency in the high voltage input mode.

FIG8 shows a schematic diagram of the relationship between the system frequency curve Freq and the system output power Pout of the quasi-resonant flyback converter power supply 500 shown in FIG5 in the low voltage input mode. It should be noted here that the 1st, 2nd, 3rd, ... nth shown in the figure represent the 1st valley lock state, the 2nd valley lock state, the 3rd valley lock state ... the nth valley lock state, respectively, and do not only represent the order in which the valleys of the drain resonant voltage waveform of the power switch S1 appear.

Combining FIG4 and FIG8, it can be seen that compared with the schematic diagram of the relationship between the system frequency curve and the system output power shown in FIG4, FIG8 adds the minimum system frequency control curve in the continuous conduction mode. As shown in FIG8, when the quasi-resonant flyback converter power supply 500 is in the low voltage input mode, when the system operates in the quasi-resonant mode and the system output power is higher than the first preset power (for example, P2) or when the system operates in the continuous conduction mode, the minimum system frequency is the first fixed frequency (for example, FCCM_H).

When the quasi-resonant flyback converter power supply 500 is in the low voltage input mode, when the power switch S1 changes from the off state to the on state at the first valley of its drain resonant voltage waveform, the system frequency decreases rapidly as the system output power increases, so the system is more likely to enter the continuous conduction constant frequency mode (for example, at the P3 power point). The FCCM_H frequency can be maintained at an appropriate high frequency value by setting it internally in the circuit or by externally adjusting and controlling it, so as to avoid the active frequency reduction when the power switch S1 is locked at the first valley of its drain resonant voltage waveform and changes from the off state to the on state when the system is working at low input voltage and heavy output load, causing the transformer to work in a saturated state, thereby reducing the difficulty of transformer design. Moreover, when the system output power is lower than P3, the system operates in the quasi-resonant locked valley conduction mode. As the system output power decreases, the multi-mode quasi-resonant controller 502 controls the power switch S1 to change from the off state to the on state at the later valley of its drain resonant voltage waveform to achieve frequency reduction, so as to improve the working efficiency in the light load section.

FIG9 shows a schematic diagram of the relationship between the system frequency curve Freq and the system output power Pout of the quasi-resonant flyback converter power supply 500 shown in FIG5 in the high voltage input mode. It should be noted here that the 1st, 2nd, 3rd, ... nth shown in the figure represent the 1st valley lock state, the 2nd valley lock state, the 3rd valley lock state, ... nth valley lock state, respectively, and do not only represent the order in which the valleys of the drain resonant voltage waveform of the power switch S1 appear.

Combining FIG4 and FIG9, it can be seen that, compared with the schematic diagram of the relationship between the system frequency curve and the system output power shown in FIG4, FIG9 adds the minimum system frequency control curve in the continuous conduction mode. As shown in FIG9, when the quasi-resonant flyback converter power supply 500 is in the high voltage input mode, when the system operates in the quasi-resonant mode and the system output power is higher than the second preset power (for example, P5) or when the system operates in the continuous conduction mode, the minimum system frequency is the second fixed frequency (for example, FCCM_L), wherein FCCM_L can be set to be less than FCCM_H.

When the quasi-resonant flyback converter power supply 500 is in the high voltage input mode, when the power switch S1 changes from the off state to the on state at the first valley of its drain resonant voltage waveform, the system frequency decreases very slowly as the system output power increases, so the power point P6 at which the system enters the continuous conduction mode will be much greater than the power point P3. Therefore, it can be ensured that when the input voltage is high and the output is heavy, the system works in the quasi-resonant valley conduction mode, and the system working efficiency in the high voltage input mode will not be reduced.

FIG10 and FIG11 respectively show the relationship between the system frequency curve of the quasi-resonant flyback converter power supply 500 shown in FIG5 in the low voltage input mode and the high voltage input mode and the internal feedback voltage FB_in representing the output load. Here, it should be noted that the 1st, 2nd, 3rd, ... nth in the figure can respectively represent the 1st valley bottom locked state, the 2nd valley bottom locked state, the 3rd valley bottom locked state, ... nth valley bottom locked state, and do not only represent the order in which the valley bottoms of the drain resonant voltage waveform of the power switch S1 appear.

It should be noted that the multi-mode quasi-resonant controller 502 described in combination with the quasi-resonant flyback converter power supply is not only applicable to the quasi-resonant switching power supply of the flyback structure, but also to the quasi-resonant switching power supply of the BUCK structure and the BOOST structure.

In summary, in the multi-mode quasi-resonant controller 502 described in combination with the quasi-resonant flyback converter power supply, a multi-mode frequency control is implemented in which high-frequency quasi-resonant valley locking and minimum system frequency control in the continuous conduction mode coexist. While ensuring that the system works in the quasi-resonant conduction mode when the AC input voltage is high and the output is heavy-loaded, it can avoid the active frequency reduction when the power switch S1 is locked at the first valley of its drain resonant voltage waveform and changes from the off state to the on state when the system works at a low AC input voltage and the output is heavy-loaded, causing the transformer to work in a saturated state, which can significantly reduce the difficulty of transformer design.

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 transistor-NPN (BJT-NPN), an insulated gate bipolar transistor (IGBT), and a gallium nitride (GaN) transistor, etc.

The present invention may be implemented in other specific forms without departing from its spirit and essential features. For example, the algorithm described in a specific embodiment may be modified, and the system architecture does not deviate from the basic spirit of the present invention. Therefore, the present embodiments are considered to be illustrative rather than restrictive in all aspects, the scope of the present invention is defined by the attached claims rather than the above description, and all changes that fall within the meaning and scope of equivalents of the claims are therefore included in the scope of the present invention.

500: Quasi-resonant flyback converter power supply

502:Multi-mode quasi-resonant controller

504: Error amplification and isolation feedback module

AC-in: Input mode characteristic signal

C1: output capacitor

Clk_out: conduction frequency control signal

Cp: parasitic capacitance

CS: Current sampling terminal

D1: Follow-up diode

D2: Feedback voltage internal divider diode

dem: demagnetization signal detection terminal

FB: Feedback voltage detection terminal

FB_in: internal feedback voltage

gate: gate drive signal

Laux: Auxiliary inductor

Lp: primary inductance

Ls: Secondary inductance

Pwm_out: turn off control signal

Q: Trigger positive phase output terminal

Qb: Trigger inverting output terminal

R: Trigger reset input terminal

R1: bias resistor on the internal voltage divider of the feedback voltage

R2: Bias resistor for the internal voltage divider of the feedback voltage

Rsense: Current sampling resistor

S: Trigger set input terminal

S1: Power switch

T: Transformer

Valley: valley pulse signal

Vcs: Current flow measurement voltage

VD2: Feedback voltage internal voltage divider diode forward conduction voltage drop

VFB: Output feedback voltage

Vin: System input voltage

Vout: system output voltage

Claims (11)

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 to: generate a valley pulse signal representing 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 valley pulse signal representing the valley of the drain resonant voltage waveform of the power switch based on the valley pulse signal. The output feedback voltage of the system output load of the power supply, the input characteristic voltage representing the AC input voltage of the quasi-resonant switching power supply, and the gate drive signal for driving the on and off of the power switch are used to generate a conduction frequency control signal for controlling the power switch to change from the off state to the on state; wherein: based on the valley pulse signal, the output The feedback voltage and the gate drive signal are used to generate a valley selection and locking signal for controlling the power switch to change from the off state to the on state at a specific valley of the drain resonant voltage waveform; based on the input characteristic voltage and the preset threshold value, an input mode characteristic signal is generated to characterize whether the quasi-resonant switching power supply is in a high voltage input mode or a low voltage input mode; based on the output feedback voltage and the input mode characteristic signal, a minimum frequency control signal is generated to control the minimum system frequency of the quasi-resonant switching power supply in the continuous conduction mode; and based on the valley selection and locking signal, the input mode characteristic signal, and the minimum frequency control signal, the conduction frequency control signal is generated. A control chip as described in claim 1, wherein: when the input characteristic voltage is greater than a first preset threshold, the input mode characteristic signal indicates that the quasi-resonant switching power supply is in a high voltage input mode; when the input characteristic voltage is less than a second preset threshold, the input mode characteristic signal indicates that the quasi-resonant switching power supply is in a low voltage input mode. The control chip as described in claim 1 is further configured to generate a shutdown control signal for controlling the power switch to change from an on state to an off state based on the output feedback voltage and the inductive sensing voltage representing the current flowing through the power switch. A control chip as described in claim 1, wherein: when the quasi-resonant switching power supply is in a low voltage input mode, when the quasi-resonant switching power supply operates in a quasi-resonant mode and the system output power is higher than a first preset power, or when the quasi-resonant switching power supply operates in a continuous conduction mode, the minimum frequency of the gate drive signal is a first fixed frequency. A control chip as described in claim 4, wherein: when the quasi-resonant switching power supply is in a high voltage input mode, when the quasi-resonant switching power supply operates in a quasi-resonant mode and the system output power is higher than a second preset power, or when the quasi-resonant switching power supply operates in a continuous conduction mode, the minimum frequency of the gate drive signal is a second fixed frequency, and the second fixed frequency is less than the first fixed frequency. 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: generating a valley pulse signal representing the valley bottom of a drain resonant voltage waveform of the power switch based on a voltage on an auxiliary winding of the transformer; and controlling a system input of the quasi-resonant switching power supply based on the valley pulse signal and the system input of the quasi-resonant switching power supply. The output feedback voltage of the load, the input characteristic voltage representing 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 generate a conduction frequency control signal for controlling the power switch to change from the off state to the on state; wherein: the process of generating the conduction frequency control signal includes: based on the valley pulse The invention relates to a circuit for generating a valley selection and locking signal for controlling the power switch to change from an off state to an on state at a specific valley of the drain resonant voltage waveform according to the impulse signal, the output feedback voltage, and the gate drive signal; and an input mode signal for characterizing whether the quasi-resonant switching power supply is in a high voltage input mode or a low voltage input mode based on the input characteristic voltage and the preset threshold value. Based on the output feedback voltage and the input mode characteristic signal, a minimum frequency control signal is generated for controlling the minimum system frequency of the quasi-resonant switching power supply operating in the continuous conduction mode; and based on the valley selection and locking signal, the input mode characteristic signal, and the minimum frequency control signal, the conduction frequency control signal is generated. A control method as described in claim 6, wherein: when the input characteristic voltage is greater than a first preset threshold, the input mode characteristic signal indicates that the quasi-resonant switching power supply is in a high voltage input mode; when the input characteristic voltage is less than a second preset threshold, the input mode characteristic signal indicates that the quasi-resonant switching power supply is in a low voltage input mode. The control method as described in claim 6 is further configured to generate a shutdown control signal for controlling the power switch to change from an on state to an off state based on the output feedback voltage and the inductive sensing voltage representing the current flowing through the power switch. A control method as described in claim 6, wherein: when the quasi-resonant switching power supply is in a low voltage input mode, when the quasi-resonant switching power supply operates in a quasi-resonant mode and the system output power is higher than a first preset power, or when the quasi-resonant switching power supply operates in a continuous conduction mode, the minimum system frequency of the quasi-resonant switching power supply is a first fixed frequency. A control method as described in claim 9, wherein: when the quasi-resonant switching power supply is in a high voltage input mode, when the quasi-resonant switching power supply operates in a quasi-resonant mode and the system output power is higher than a second preset power, or when the quasi-resonant switching power supply operates in a continuous conduction mode, the lowest system frequency of the quasi-resonant switching power supply is a second fixed frequency, and the second fixed frequency is less than the first fixed frequency. A quasi-resonant switching power supply, comprising a control chip as described in any one of claims 1 to 5.

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