TWI689162B - Quasi-resonant flyback converter power supply system - Google Patents

Abstract

A quasi-resonant flyback converter power supply system is disclosed, which includes a transformer, a power switch, and a quasi-resonant controller including a frequency-jittering module and a valley control module. Frequency dithering module adjusts the switching frequency of the power switch by adjusting the peak current flowing through the primary winding of the transformer, or by adding an advance or delay to the resonance valley of the drain voltage of the power switch to adjust the switching frequency of the power switch; The control module calculates the switching frequency of the power switch and the relationship between the frequency and the first reference frequency and the second reference frequency, and obtains the increased valley signal and the reduced valley signal after the processing, and controls according to the increased valley signal and the reduced valley signal The power switch switches from an off state to an on state at a predetermined resonance valley bottom of its drain voltage.

Description

Quasi-resonant flyback converter power supply system

The present invention relates to the field of circuits, and more particularly to a quasi-resonant flyback converter power supply system.

Figure 1 shows a schematic diagram of a conventional quasi-resonant flyback converter power supply system. FIG. 2 shows a waveform diagram of the drain voltage Vd, the gate voltage Vg, and the current Ip flowing through the primary winding of the transformer T in the system shown in FIG. 1, where Ton is the power switch The turn-on time of S1, Toff is the turn-off time of the power switch S1. As shown in FIG. 2, when the power switch S1 is in an off state, when the main inductance Lp of the transformer T is demagnetized, the main inductance Lp of the transformer T and the parasitic capacitance Cp of the power switch S1 resonate freely. At this time, the quasi-resonant controller in the system shown in FIG. 1 can control the power switch S1 to switch from the off state to the on state at the resonance valley of the drain voltage of the power switch S1 to reduce the system shown in FIG. 1 Switching losses and electromagnetic interference (Electromagnetic Interference, EMI). The resonant period of the LC resonator formed by the main inductance Lp of the transformer T and the parasitic capacitance Cp of the power switch S1 is smaller than the switching period of the power switch S1, so the system shown in FIG. 1 is approximately operating in the critical conduction mode.

In the system shown in Figure 1, the system output power and the system operating frequency (that is, the switching frequency of the power switch S1) can be expressed as formula (1) and formula (2):

In formula (1) and formula (2), P _OUT is the system output power, f _s is the system operating frequency, η is the system power conversion efficiency, and V _OUT is the system output voltage (ie, the secondary output voltage of the transformer T) , V _in is the system input voltage (ie, line input rectified voltage), I _PK is the peak current flowing through the primary winding of the transformer T (ie, the peak current flowing through the power switch S1), and N is the primary winding of the transformer T and The turns ratio of the secondary winding, V _F is the voltage drop of the rectifier diode D1 on the secondary side of the transformer T, and D is the on-time duty cycle of the power switch S1.

It can be seen from formula (1) and formula (2) that the system operating frequency is basically unchanged when the system output power and system input voltage are unchanged. Therefore, the EMI when the system shown in Figure 1 works in the critical conduction mode will be worse in the low frequency band.

FIG. 3 shows a schematic diagram of the quasi-resonant controller in the system shown in FIG. 1. As shown in Figure 3, the FB terminal of the quasi-resonant controller receives the output voltage or current feedback signal generated by the error amplification and isolation module based on the system output voltage or system output current and used to characterize the system output voltage or system output current; The CS terminal of the quasi-resonant controller receives the transformer primary winding current characterization signal generated by the current flowing through the primary winding of the transformer T on the current sensing resistor Rsense to characterize the current flowing through the primary winding of the transformer T; A Pulse Width Modulation (PWM) comparator controls the power switch S1 on and off based on the output voltage or current characterization signal and the transformer primary winding current characterization signal, thereby controlling the system output voltage or system output current.

In order to improve the EMI when the system shown in Figure 1 works in the critical conduction mode, the system operating frequency cannot be too concentrated, so it is necessary to realize the jitter of the system operating frequency. Here, the system operating frequency can also be expressed as formula (3):

In equation (3), the system input voltage V _in , the turns ratio N of the primary and secondary windings of the transformer T, and the voltage drop V _F of the rectifier diode D1 on the secondary side of the transformer T are system parameters . From formula (3), the system operating frequency is inversely proportional to the peak current flowing through the primary winding of the transformer T. Therefore, the system operating frequency can be dithered by disturbing the peak current flowing through the primary winding of the transformer T.

FIG. 4 shows a waveform diagram of the peak current I _PK flowing through the primary winding of the transformer T and the system operating frequency f _s when the triangular wave frequency dithering scheme is implemented in the system shown in FIG. 1. FIG. 5 shows a waveform diagram of the peak current I _PK flowing through the primary winding of the transformer T and the system operating frequency f _s when the pseudo-random frequency jitter scheme is implemented in the system shown in FIG. 1.

As shown in Figures 4 and 5, the system operating frequency f _{s is} inversely proportional to the peak current I _PK flowing through the primary winding of the transformer T. When the jitter frequency of the peak current I _PK is much greater than the loop bandwidth of the system, the adjustment of the system operating frequency f _s can be achieved by adjusting the peak current I _PK flowing through the primary winding of the transformer T, where the flow through the transformer The periodic change of the peak current I _PK of the primary winding of T can cause the periodic change of the operating frequency of the system.

In addition to realizing the jitter of the system operating frequency by disturbing the peak current I _PK flowing through the primary winding of the transformer T, the jitter of the system operating frequency f _s can also be achieved by adding a certain amplitude and varying delay in the loop. For example, the moment when the power switch S1 is switched from the off state to the on state can be changed within a short period of time near the resonance valley bottom of the drain voltage of the power switch S1. FIG. 6 shows a waveform diagram of the drain voltage Vd of the power switch S1 and the system operating frequency f _s when the control delay frequency jitter scheme is implemented in the system shown in FIG. 1. The control delay frequency dithering scheme shown in FIG. 6 will reduce the efficiency of the system shown in FIG. 1 to a certain extent compared to turning on the resonance valley bottom where the control power switch S1 is fixed at the drain voltage Vd. However, as long as the delay amplitude is controlled, the efficiency loss of the system shown in Figure 1 can be controlled within an acceptable range.

In many application scenarios, the operating frequency of the quasi-resonant flyback converter power system will be limited to a certain range. For a quasi-resonant flyback converter power supply system with frequency jitter, when the system operating frequency is close to the set upper or lower frequency limit, the system operating frequency after superimposing the frequency jitter may fall outside the predetermined frequency interval, which may result in The moment when the power switch is switched from the off state to the on state repeatedly jumps between several adjacent resonance valley bottoms of its drain voltage. This repeated bounce will cause the system output voltage or current and the system output voltage or current feedback signal to fluctuate, resulting in a larger system output ripple. In addition, when the system's operating frequency fluctuates greatly, the frequency components that fall in the audio area will also increase, which will greatly deteriorate the system noise index.

In view of the above one or more problems, the present invention provides a combination The power system of quasi-resonant flyback converter with frequency jitter and valley control is introduced.

A quasi-resonant flyback converter power supply system according to an embodiment of the present invention includes a transformer, a power switch, and a quasi-resonant controller including a frequency-jittering module and a valley control module. Frequency dithering module adjusts the switching frequency of the power switch by adjusting the peak current flowing through the primary winding of the transformer, or by adding an advance or delay to the resonance valley of the drain voltage of the power switch to adjust the switching frequency of the power switch; The control module obtains the first voltage signal reflecting the switching frequency of the power switch by performing frequency/voltage conversion on the switching frequency of the power switch, and the first voltage signal is integrated or filtered to remove glitches or high-frequency disturbances to obtain the first Two voltage signals, by comparing the second voltage signal with the first reference voltage reflecting the first reference frequency and the second reference voltage reflecting the second reference frequency to generate an increased valley signal and a reduced valley signal, and according to the increased valley signal and Reduce the valley signal to control the power switch to switch from the off state to the on state at the predetermined resonance valley of its drain voltage, or generate the first frequency comparison by comparing the switching frequency of the power switch with the first reference frequency and the second reference frequency, respectively Output signal and second frequency comparator output signal, by integrating or filtering the first frequency comparator output signal and the second frequency comparator output signal, the first frequency comparator output signal and the second frequency comparison are filtered out The glitches or high-frequency disturbances in the output signal of the converter obtain the increased valley signal and the reduced valley signal, and control the power switch to switch from the off state to the on state at the predetermined resonance valley of its drain voltage according to the increased valley signal and the reduced valley signal.

The quasi-resonant flyback converter power supply system according to the embodiment of the present invention can solve the EMI problem of the conventional quasi-resonant flyback converter power supply system, and also avoids the The problem of increased system output ripple and noise caused by the introduction of frequency jitter.

S1: Power switch

Vd: drain voltage

Vg: gate voltage

T: transformer

Ip: primary winding current

Ton: On-time of power switch S1

Toff: off time of power switch S1

Lp: main inductance of transformer T

Cp: parasitic capacitance

P _OUT : system output power

f _s : system operating frequency

η: system power conversion efficiency

I _PK : peak current

FB, CS, dem: terminal

R0, R1R2, R3: resistance

D: On-time duty cycle of power switch S1

V _F : voltage drop of the rectifier diode D1 on the secondary side of the transformer T

Rsense: resistance

N: turns ratio

D1: rectifier diode

Vf, Vavg: voltage signal

fup, fdw: reference frequency

Vup, Vdw: reference level

de-mag: demagnetization sensing signal

Gate: drive signal

Q1, Q2: switch

I _{cs_jitter} : jitter current

V _{FB_jitter} : jitter frequency voltage

V _OUT : system output voltage

V _in : system input voltage

S: RS latch set terminal

Q: RS latch output

R: RS latch reset terminal

The present invention can be better understood from the following description of specific embodiments of the present invention with reference to the drawings, in which: FIG. 1 shows a schematic diagram of a conventional quasi-resonant flyback converter power supply system; FIG. 2 shows The waveform diagram of the drain voltage Vd, the gate voltage Vg, and the current Ip flowing through the primary winding of the transformer T in the system shown in FIG. 1; FIG. 3 shows the diagram shown in FIG. The schematic diagram of the quasi-resonant controller in the system; Figure 4 shows the peak current I _PK flowing through the primary winding of the transformer T and the system operating power frequency when the triangular wave frequency jitter scheme is implemented in the system shown in Figure 1 The waveform diagram of f _s ; the fifth is the waveform diagram of the peak current I _PK flowing through the primary winding of the transformer T and the system operating frequency f _s when the pseudo-random frequency jitter scheme is implemented in the system shown in FIG. 1; 6 shows the waveform diagram of the drain voltage Vd of the power switch S1 and the system operating frequency f _s when the control delay frequency dithering scheme is implemented in the system shown in FIG. 1; FIG. 7 shows the application of FIG. 1 A schematic diagram of a quasi-resonant controller according to an embodiment of the present invention of the system shown; FIG. 8 shows a schematic diagram of a quasi-resonant controller according to another embodiment of the present invention to which the system shown in FIG. 1 can be applied; 9 shows a schematic diagram of a quasi-resonant controller according to yet another embodiment of the present invention to which the system shown in FIG. 1 can be applied; FIG. 10 shows a quasi-resonant controller that can be applied to FIGS. 7 to 9 The principle diagram of the valley bottom control module of the controller according to the embodiment of the present invention; FIG. 11 shows the valley bottom control according to another embodiment of the present invention applicable to the quasi-resonant controller shown in FIGS. 7 to 9 The schematic diagram of the module; Figure 12 shows the specific implementation circuit of the valley control module shown in Figure 10; Figure 13 shows the specific implementation circuit of the valley control module shown in Figure 11; The figure shows the principle diagram of the frequency comparator #1 shown in FIG. 13; FIG. 15 shows the specific realization circuit of the quasi-resonant controller shown in FIG. 7; FIG. 16 shows the figure 8 Figure 17 shows the specific implementation circuit of the quasi-resonant controller; Figure 17 shows another specific implementation circuit of the quasi-resonant controller shown in Figure 8; Figure 18 shows the quasi-resonant controller shown in Figure 8 Fig. 19 shows the specific realization circuit of the quasi-resonant controller shown in Fig. 9.

The features and exemplary embodiments of the various aspects of the invention will be described in detail below. In the following detailed description, many specific details are presented in order to provide a comprehensive understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without some of these specific details. The following description of the embodiment is only In order to provide a better understanding of the present invention by showing examples of the present invention. The present invention is by no means limited to any specific configurations and algorithms proposed below, but covers any modification, replacement, and improvement of elements, components, and algorithms without departing from the spirit of the present invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.

As can be seen from the above, in the conventional quasi-resonant flyback converter power supply system, when the system input voltage and the system output power are constant, the system operating frequency is basically unchanged, so there is a problem of insufficient conducted EMI margin in the low frequency band. Adding random frequency jitter to the power system of quasi-resonant flyback converter is a method to improve the electromagnetic interference of the system. However, for a quasi-resonant flyback converter power supply system with an upper or lower operating frequency, when operating near the upper or lower operating frequency of the system, the jitter of the operating frequency of the system will cause the power switch to switch from the off state to the The moment of the on-state repeatedly jumps between several adjacent resonance valley bottoms of its drain voltage, so the system operating frequency will fluctuate greatly. Large fluctuations in the operating frequency of the system on the one hand will cause a larger ripple in the output voltage or current, on the other hand, it will also generate more frequency components in the audio section, thus making the system have a higher noise level.

In the quasi-resonant flyback converter power supply system where the operating frequency of the system is limited, in order to take into account the EMI, noise and ripple indicators of the system, a new method must be provided to achieve frequency jitter, valley lock, and system operating frequency limits.

The present invention provides a novel quasi-resonant controller applicable to the system shown in FIG. 1. The quasi-resonant controller needs to realize the following functions: 1) realizing jitter of the system operating frequency; 2) when flowing through the transformer T1 When the peak current I _{PK of the} primary winding is disturbed by high-frequency changes, the moment when the power switch S1 is switched from the off state to the on state will not switch between the resonance valley bottoms of its drain voltages due to the disturbance; 3) only When the system input voltage or system output power changes to cause the system operating frequency to exceed the upper limit frequency or lower than the lower limit frequency, the resonance valley of the drain voltage at the moment when the power switch S1 is switched from the off state to the on state is adjusted, thereby averaging the system The operating frequency is adjusted between the upper and lower frequency limits.

FIG. 7 shows a schematic diagram of a quasi-resonant controller according to an embodiment of the present invention to which the system shown in FIG. 1 can be applied. Compared to the quasi-resonant controller shown in FIG. 3, the quasi-resonant controller according to the embodiment of the present invention includes both a valley control module and a frequency-jittering module. Here, the frequency-jittering module implements regulation of the flow through the transformer by superimposing a varying voltage on the transformer primary winding current characterization signal received at the CS terminal of the quasi-resonant controller and characterizing the current Ip flowing through the primary winding of the transformer T The function of the peak current I _PK of the primary winding of T, thereby realizing the adjustment of the system operating frequency. The superimposed voltage may be continuously changed or randomly changed, and the frequency of change is greater than the bandwidth of the feedback loop of the system shown in FIG. 1.

FIG. 8 shows a schematic diagram of a quasi-resonant controller according to another embodiment of the present invention to which the system shown in FIG. 1 can be applied. Similarly, compared to the quasi-resonant controller shown in FIG. 3, a quasi-resonant controller according to another embodiment of the present invention includes both a valley control module and a frequency-jittering module. Here, the frequency-jittering module realizes the regulation of the primary winding flowing through the transformer T by superimposing a pseudo-random voltage on the output voltage or current feedback signal that is used to characterize the system output voltage or system output current received by the FB terminal of the quasi-resonant controller The function of the peak current I _PK to achieve the adjustment of the system operating frequency.

FIG. 9 shows a schematic diagram of a quasi-resonant controller according to yet another embodiment of the present invention to which the system shown in FIG. 1 can be applied. Similarly, compared to the quasi-resonant controller shown in FIG. 3, a quasi-resonant controller according to another embodiment of the present invention includes both a valley control module and a frequency-jittering module. Here, the frequency dithering module adjusts the operating frequency of the system by adding a small amount of advance or a small amount of delay (ie, positive or negative delay) near the resonance valley of the drain voltage of the power switch S1. As long as the magnitude of the added delay is controlled so that the power switch S1 still switches from the off state to the on state near the resonance valley bottom of its drain voltage, the efficiency loss of the system shown in Figure 1 can be controlled to be sufficiently small Degree.

FIG. 10 shows a schematic diagram of a valley control module according to an embodiment of the present invention that can be applied to the quasi-resonant controller shown in FIGS. 7 to 9. As shown in FIG. 10, the signal processing unit obtains a first voltage signal reflecting the system operating frequency fs by performing frequency/voltage conversion on the system operating frequency fs, and integrating or filtering the first voltage signal reflecting the system operating frequency fs Processing, filtering out glitches or high-frequency disturbances in the operating frequency fs of the system to obtain a second voltage signal; the voltage comparing unit respectively compares the second voltage signal with the first reference voltage reflecting the first reference frequency and the second reflecting the second reference frequency Compare the reference voltage to determine whether to change the currently locked resonance valley bottom number (for example, from locking to the second resonance valley bottom to locking the third resonance valley bottom or the first resonance valley bottom), and output an increase valley signal (+1) And reduce valley letters No. (-1); the valley selection unit masks a certain number of resonance valleys according to increasing valley signals and decreasing valley signals, thereby controlling the power switch S1 to switch from an off state to an on state at a predetermined resonance valley of its drain voltage.

FIG. 11 shows a schematic diagram of a valley control module according to another embodiment of the present invention that can be applied to the quasi-resonant controller shown in FIGS. 7 to 9. As shown in Figure 11, the frequency comparison unit directly compares the system operating frequency fs with the first reference frequency and the second reference frequency, respectively, to generate the first frequency comparator output signal and the second frequency comparator output signal; the signal processing unit passes The analog circuit or digital circuit respectively integrates, filters or otherwise processes the output signal of the first frequency comparator and the output signal of the second frequency comparator to filter out glitches in the output signal of the first frequency comparator and the output signal of the second frequency comparator Or high-frequency disturbances to obtain the increased valley signal and reduced valley signal; the valley selection unit controls the power switch S1 to switch from the off state to the on state at the predetermined resonance valley of its drain voltage according to the increased valley signal and the reduced valley signal.

In the quasi-resonant controller shown in Figs. 10 to 11, when the valley signal (+1) is effective, the valley selection unit will increase the number of resonant valleys that are masked; when the valley signal (-1) is reduced When effective, the valley selection unit will reduce the number of resonant valleys that are masked; when both increasing and decreasing valley signals are invalid, the valley selection unit will maintain the current number of resonant valleys that are masked unchanged.

FIG. 12 shows a specific implementation circuit of the valley control module shown in FIG. 10. In the circuit shown in FIG. 12: Frequency/voltage conversion is performed on the drive signal (Gate) that can characterize the system operating frequency fs and used to drive the power switch S1 on and off to obtain a voltage that reflects the system operating frequency fs Signal Vf; low-pass filtering the voltage signal Vf to obtain a voltage signal Vavg reflecting the average frequency of the system operating frequency fs; the voltage signal Vavg is performed with two reference levels Vup and Vdw corresponding to two reference frequencies fup and fdw, respectively In comparison, the increase of the bottom signal (+1) and the decrease of the bottom signal (-1) are obtained. Here, Vavg>Vup means that the system operating frequency fs is greater than the reference frequency fup, at this time increasing the valley signal (+1) is effective; Vavg>Vdw means that the system operating frequency fs is less than the reference frequency fdw, and reducing the valley signal (-1) is effective. The valley selection unit may include a bidirectional counter, an accumulator, and several logic gates, wherein: the bidirectional counter receives an increase valley signal (+1) and a decrease valley signal (- 1) Increase or decrease or maintain the n-bit register Q[(n-1): 0]; the accumulator uses the falling edge pair of the demagnetization sensing signal de-mag for the transformer T received from the dem terminal of the quasi-resonant controller The number C[(n-1):0] of the resonant valley bottoms that have been masked in the current switching cycle is counted. The working principle of the valley selection unit is: in each switching cycle, after the power switch S1 is switched from the on state to the off state (ie, after driving the gate signal low), the accumulator starts to demagnetize the sensing signal from zero Count the falling edge of de-mag and record the number of resonance valleys that have been masked in the current switching cycle; when C<Q, the mask demagnetization sensing signal de-mag; when C>=Q, the demagnetization is no longer masked Sensing signal de-mag, the Q[(n-1): 0]+1 resonance valleys within the current switching cycle to switch the power switch S1 from the off state to the on state (ie, the drive signal Gate is pulled high ); driving the signal high will reset the accumulator C[(n-1): 0] to zero until the next time the driving signal Gate is pulled low to restart counting.

FIG. 13 shows a specific implementation circuit of the valley control module shown in FIG. 11. In the circuit shown in Figure 13, two frequency comparators compare the system operating frequency fs with the reference frequencies fup and fdw; the signal processing unit performs calculation and processing on the output result of the frequency comparator; the two-way counter uses frequency comparison The comparison result of the output of the multiplexer (that is, increase the valley signal and decrease the valley signal) to control the increase and decrease of the resonance valley; the multiplexer realizes the valley control function based on the output of the bidirectional counter.

FIG. 14 shows a schematic diagram of the frequency comparator #1 shown in FIG. 13. As shown in FIG. 14, the working principle of the frequency comparator #1 is as follows: the delay amount T=1/ corresponding to the period Tsw of the drive signal Gate (that is, the switching period corresponding to the switching frequency of the power switch S1) and the reference frequency fup fup is compared, and the result obtained corresponds to the size relationship between fsw and fup (that is, the valley signal can be generated by comparing fsw and fup). The frequency comparator #1 also performs an integration operation on the comparison result by using a pulse current source to charge the capacitor (that is, the glitch in the increased valley signal can be filtered through integration processing). The circuit schematic of frequency comparator #2 is compared with frequency comparator #1, and the delay of the delay unit needs to be changed from T=1/fup to T=1/fdw, and the switches Q1 and Q2 are exchanged to achieve inversion .

FIG. 15 shows a specific implementation circuit of the quasi-resonant controller shown in FIG. 7. In the circuit shown in Figure 15, the frequency- _jittering module is implemented by a resistor R0 and a frequency- _jittering current source I _{cs_jitter} . Here, the voltage V _{cs_jitter} =I _{cs_jitter} ×R0, which is superimposed on the transformer primary winding current characterization signal used to characterize the current Ip flowing through the primary winding of the transformer T1, changes periodically, and its change frequency is higher than that of the error amplification and isolation module bandwidth. The signal amplitude of the frequency- _jittering current I _{cs_jitter} may change continuously or randomly during a switching period. The frequency- _jittering current I _{cs_jitter} can adjust the peak current I _PK flowing through the primary winding of the transformer T. By adjusting the I _{PK, the} system operating frequency fs can be controlled to change periodically.

FIG. 16 shows a specific implementation circuit of the quasi-resonant controller shown in FIG. 8. In the circuit shown in Figure 16, a dithering voltage is superimposed before the output voltage or current feedback signal used to characterize the system output voltage or system output current received at the FB terminal of the quasi-resonant controller enters the PWM comparator V _{FB_jitter} realizes the adjustment of the peak current I _PK flowing through the primary winding of the transformer T. By adjusting I _{PK, the} system operating frequency fs can be controlled to change periodically.

FIG. 17 shows another specific implementation circuit of the quasi-resonant controller shown in FIG. 8. In the circuit shown in Figure 17, a resistor R3 is inserted between the voltage dividing resistor network composed of R1 and R2 and the PWM comparator, and a periodically varying jitter current I _{cs_jitter} is superimposed on the resistor R3, V _{cs_jitter} =I _{cs_jitter} *R3 changes periodically, and its change frequency is higher than the bandwidth of the feedback loop of the system shown in Figure 1 to achieve the adjustment of the peak current I _PK flowing through the primary winding of the transformer T, which can be controlled by adjusting I _PK The system operating frequency fs changes periodically.

FIG. 18 shows another specific implementation circuit of the quasi-resonant controller shown in FIG. 8. In the circuit shown in Figure 18, the jitter frequency V _{FB_jitter is} superimposed under the resistor divider network R1 and R2. The jitter frequency V _{FB_jitter} changes periodically, and the frequency of its change is higher than the feedback of the system shown in Figure 1 The bandwidth of the loop can adjust the peak current I _PK flowing through the primary winding of the transformer T. By adjusting I _{PK, the} system operating frequency fs can be controlled to change periodically.

FIG. 19 shows a specific implementation circuit of the quasi-resonant controller shown in FIG. 9. In the circuit shown in Figure 19, the signal provided by the valley control module is superimposed on a delay by the delay unit. The magnitude of this delay is determined by the jitter current I _jitter and the capacitance Cd. The frequency of _jitter current I _jitter is slightly higher than the bandwidth of the system shown in the first. Controlling the frequency and amplitude of the _jitter current I _jitter can control the size and amplitude of the jitter of the system operating frequency fs, and controlling the waveform of the _jitter current I _jitter can control the jitter mode of the system operating frequency fs.

The valley control module in the 15th to 19th can directly adopt the 12th to the The implementation shown in 13 can also be modified, replaced, or recombined.

The quasi-resonant flyback converter power supply system according to the embodiment of the present invention can solve the EMI problem of the traditional quasi-resonant switchable power supply system, and at the same time avoids the introduction of jitter in the quasi-resonant flyback converter power supply system with upper and lower frequency limits. The problem of increased system output ripple and noise due to high frequency.

The present invention can be implemented in other specific forms without departing from its spirit and essential characteristics. 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 current embodiment is considered to be exemplary rather than limiting in all respects, the scope of the present invention is defined by the appended claims rather than the above description, and falls within the meaning and equivalent of the claims All changes within the scope are thus included in the scope of the present invention.

S1: Power switch

T: transformer

R1, R2: resistance

Gate: drive signal

FB, CS, dem: terminal

Vin: input voltage

Rsense: resistance

Qb: RS latch inverting output

S: RS latch set terminal

Q: RS latch output

R: RS latch reset terminal

Claims (6)

A quasi-resonant flyback converter power supply system includes a transformer, a power switch, and a quasi-resonant controller including a frequency-jittering module and a valley control module, wherein: the frequency-jittering module adjusts the flow of the primary winding flowing through the transformer Peak current, to adjust the switching frequency of the power switch, or to adjust the switching frequency of the power switch by adding an advance or delay to the resonance valley of the drain voltage of the power switch; the valley control module Perform a frequency/voltage conversion on the switching frequency of the switch to obtain a first voltage signal reflecting the switching frequency of the power switch, and obtain a second voltage signal by integrating or filtering the first voltage signal to remove glitches or high-frequency disturbances, The second voltage signal is compared with the first reference voltage reflecting the first reference frequency and the second reference voltage reflecting the second reference frequency to generate an increased valley signal and a reduced valley signal, and according to the increased valley signal and the decrease The valley signal controls the power switch to switch from the off state to the on state at a predetermined resonance valley of its drain voltage, or to generate the first by comparing the switching frequency of the power switch with the first reference frequency and the second reference frequency, respectively A frequency comparator output signal and a second frequency comparator output signal, by integrating or filtering the first frequency comparator output signal and the second frequency comparator output signal, the first frequency comparator output is filtered out Glitches or high-frequency disturbances in the signal and the output signal of the second frequency comparator to obtain the increased valley signal and the reduced valley signal, and according to the increased valley signal and the reduced valley signal, the power switch is controlled at its drain voltage The predetermined resonance valley bottom is switched from the off state to the on state. The quasi-resonant flyback converter power supply system as claimed in item 1 of the patent scope, wherein the frequency-jittering module superimposes the change on the transformer primary winding current characterization signal used to characterize the current flowing through the primary winding of the transformer Voltage to regulate the peak current flowing through the primary winding of the transformer. The quasi-resonant flyback converter power supply system as claimed in item 1 of the patent scope, in which The frequency-jittering module adjusts the peak current flowing through the primary winding of the transformer by superimposing a pseudo-random voltage on the output voltage or current feedback signal that characterizes the quasi-resonant flyback converter power system . The quasi-resonant flyback converter power supply system as described in item 1 of the patent scope, wherein the valley control module includes a signal processing unit, a voltage comparison unit, and a valley selection unit, wherein: the signal processing unit is used to drive The on/off driving signal of the power switch performs frequency/voltage conversion to obtain the first voltage signal reflecting the switching frequency of the power switch, and the low voltage filtering process is performed on the first voltage signal to obtain the reflection of the power switch. The second voltage signal of the average switching frequency; the voltage comparison unit generates the increased valley signal and the decreased valley signal by comparing the second voltage signal with the first reference voltage and the second reference voltage, respectively; the valley floor The selection unit controls the power switch to switch from an off state to an on state at a predetermined resonance valley bottom of its drain voltage according to the increasing valley signal and the decreasing valley signal. The quasi-resonant flyback converter power supply system as claimed in item 4 of the patent scope, wherein the valley selection unit controls the power switch to switch from the off state to the on state in the next switching cycle when the increased valley signal is valid The time is delayed by one resonance trough from the current switching cycle; when the reduction trough signal is valid, the time when the power switch is controlled to switch from the off state to the on state in the next switching cycle is advanced by one resonance trough from the current switching cycle; when the reduction trough When both the signal and the increased valley signal are invalid, the power switch is controlled to switch from the off state to the on state in the next switching cycle at the same resonance valley as the current switching cycle. The quasi-resonant flyback converter power supply system as claimed in item 1 of the patent scope, wherein the valley control module includes a frequency comparison unit, a signal processing unit, and a valley selection unit, wherein: the frequency comparison unit includes a first frequency comparison And a second frequency comparator, the first frequency comparator generates the first frequency comparator output signal by comparing the switching period corresponding to the switching frequency of the power switch with the first reference period corresponding to the first reference frequency, The second frequency The comparator generates the output signal of the second frequency comparator by comparing the switching period corresponding to the switching frequency of the power switch with the second reference period corresponding to the second reference frequency; the signal processing unit compares the first frequency by respectively The output signal of the comparator and the output signal of the second frequency comparator are integrated or filtered in the analog domain or the digital domain to filter out glitches or high-frequency disturbances in the output signal of the first frequency comparator and the output signal of the second frequency comparator To obtain the increased valley signal and the reduced valley signal; the valley selection unit controls the power switch to switch from an off state to an on state at a predetermined resonance valley of its drain voltage according to the increased valley signal and the reduced valley signal.

Images