CN117277748A - Control device for selecting, switching and locking conduction trough of flyback switching power supply - Google Patents

Control device for selecting, switching and locking conduction trough of flyback switching power supply Download PDF

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Publication number
CN117277748A
CN117277748A CN202311269464.8A CN202311269464A CN117277748A CN 117277748 A CN117277748 A CN 117277748A CN 202311269464 A CN202311269464 A CN 202311269464A CN 117277748 A CN117277748 A CN 117277748A
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China
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signal
valley
output
input end
power supply
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Inventor
孙铭
何乐年
奚剑雄
汪涛
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Zhejiang University ZJU
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Zhejiang University ZJU
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Priority to CN202311269464.8A priority Critical patent/CN117277748A/en
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0025—Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33515—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with digital control
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/06—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes without control electrode or semiconductor devices without control electrode

Abstract

The invention provides a control device for selecting, switching and locking conduction troughs of a flyback switching power supply, which comprises a load detection module, a trough selection oscillator, a trough detection module, a logic operation module and a switch control module, wherein in a quasi-resonance control mode, a frequency control method is adopted according to the load of the switching power supply, and a proper resonance trough is selected to turn on a switching tube; meanwhile, hysteresis frequencies between valley adding frequency and valley subtracting frequency are set up when switching between adjacent valley bottoms, and the hysteresis frequency difference is related to the output power of the system, so that the phenomenon of jumping between valleys, the problem of output envelope ripple and the problem of audio noise are avoided. Therefore, the control device has higher suitability in the current AC-DC flyback switching power supply which is suitable for mobile phones and notebook computers.

Description

Control device for selecting, switching and locking conduction trough of flyback switching power supply
Technical Field
The invention belongs to the technical field of switching power supplies, and particularly relates to a control device for selecting, switching and locking a conduction trough of a flyback switching power supply.
Background
The AC-DC switching power supply is an important component in the power supply management market, and has the function of safely and reliably converting the commercial power into stable direct current voltage; in power products of personal electronics with low power, AC-DC switching power supplies with flyback topology have been widely used. Fig. 1 is a schematic diagram of a typical flyback switching power supply for mobile phones and notebook chargers, wherein the input is AC voltage, the AC voltage is converted into DC voltage after being rectified by an EMI filter and a rectifier bridge, and then energy is transferred to a secondary side through a transformer, so that high-voltage AC input is converted into stable low-voltage DC output. The primary side transformer stores energy during the on period of the main switching tube M1, and releases energy to the secondary side transformer during the off period of the main switching tube M1; the signal for controlling the on or off of the main switching tube M1 is generated by a power management IC, which receives the signal fed back to the primary side by the secondary side output end, and determines the on time and the off time of the main switching tube M1 according to the feedback quantity; during this time, the RCD loop absorbs the energy stored by the leakage inductance, and the protocol and interface circuits determine the output voltage value of the flyback switching power supply.
In the working process of the flyback switching power supply, the turn-on loss of the main switching tube is an important component of the total loss of the system, and the smaller the product of the current flowing through the main switching tube and the voltages at the two ends of the source drain parasitic capacitor is at the turn-on moment, the lower the turn-on loss is. Therefore, the QR (quick-reset) Quasi-resonance control mode gradually replaces the traditional PWM and PFM control modes with higher transmission efficiency, and is widely applied; as shown in fig. 2, in the quasi-resonance control mode, the primary inductor resonates with the parasitic capacitance of the main switching tube, and the main switching tube is turned on at the bottom of a proper resonance valley according to the load size of the switching power supply, the voltage at two ends of the source drain parasitic capacitance is the lowest, and the current flowing through the main switching tube is approximately zero.
However, in the control method of the quasi-resonance control mode, the change of the load at the output end of the flyback switching power supply changes the sequence number of the trough selected when the main switching tube is turned on, and the switching threshold value of the conduction trough is related to the feedback quantity corresponding to the load. If the load is stable, the corresponding feedback quantity is the same as the valley switching threshold value, so that the main switching tube can continuously switch between two or even a plurality of adjacent valleys to cause the output envelope ripple problem and the audio noise problem to be solved.
The Chinese patent application with publication number CN115864853A provides a control circuit and a control method based on trough latching and switching of output power, and the detection value of the output power of the switching power supply is obtained by calculation according to the detection value of the output voltage and the detection value of the output current of the switching power supply; comparing the output power detection value of the switching power supply with a preset trough switching power threshold value, and outputting a comparison result; and performing trough latching and switching according to the comparison result. However, this solution requires monitoring the output current of the secondary side on the primary side of the flyback converter, requires additional peripheral devices such as auxiliary windings, and has high requirements on circuit design for monitoring the output current, complex circuit scale and high cost.
The Chinese patent application with publication number of CN209963955U provides a quasi-resonance valley locking method without feedback reference, and in order to solve the problem that under a specific load, the dithering frequency caused by alternately opening two adjacent valleys is in the audible frequency range of human ears, so that the transformer generates audio noise, a power supply controller is designed, and the power supply controller comprises a first counter configured to reference the valley number and a second counter configured to the valley number which is required to be conducted currently, and when the first counter and the second counter are equal in count, a driving switch tube is turned on, so that the stability of a valley locking system of the power supply converter is improved. However, the solution is not provided with feedback reference, the threshold values of the valley adding and the valley subtracting are kept consistent, when the load is in a special condition of periodical fluctuation, the influence of audio noise cannot be avoided, and meanwhile, the technology has the problem that the reference valley number is difficult to obtain.
Disclosure of Invention
In view of the above, the invention provides a control device for selecting, switching and locking the conduction trough of a flyback switching power supply, which can solve the problems of output envelope ripple and audio noise caused by low-frequency trough switching in the traditional quasi-resonance control mode.
A control device for selecting, switching and locking a conduction trough of a flyback switching power supply comprises:
the load detection module is used for detecting the load feedback voltage of the flyback switching power supply and converting the load feedback voltage into a current feedback signal reflecting the load condition;
the valley bottom selection oscillator takes the leading edge blanking pulse (high level at each turn-on time of the main switching tube) of the main switching tube of the flyback switching power supply as a reset signal, and performs oscillation sampling output addition and subtraction Gu Xinhao on the current feedback signal;
the valley bottom detection module is used for detecting the moment that the resonance valley bottom reaches the valley bottom when the flyback switching power supply enters a resonance state and outputting a valley bottom detection signal; meanwhile, counting the resonant wave trough reaching the bottom each time, and outputting a current conduction bottom counting signal;
the logic operation module outputs a conduction signal for determining the resonant trough ordinal number of the main switching tube at the turn-on moment through digital logic operation according to the valley adding and subtracting signal and the current conduction trough counting signal;
and the switch control module is used for providing an output switch control signal for the grid electrode of the main switch tube through logic control according to the conduction signal, the valley detection signal, the current sampling signal of the primary side excitation inductance of the flyback switch power supply and the load feedback voltage.
Further, the load detection module includes:
the oscillator circuit is used for carrying out oscillation control on the current feedback signal by taking the front edge blanking pulse as a reset signal to generate a square wave signal;
the adding and subtracting valley signal generating circuit is used for sampling the square wave signal when the main switching tube is turned on each time to generate adding and subtracting Gu Xinhao Vosc1 and Vosc2, and the adding and subtracting signals respectively reflect whether the resonant valley ordinal number at the current turn-on moment of the main switching tube needs to move forwards and backwards.
Further, the oscillator circuit includes a PMOS tube M1, a charging current source, a discharging current source, NMOS tubes M2 and M3, a capacitor C1, comparators CMP1 and CMP2, an inverter and an RS flip-flop, where the source of M1 is connected to a power supply voltage, the drain of M1 is connected to the input of the charging current source, the output of the charging current source is connected to the input of the discharging current source, the drain of M3, one end of C1, the inverting input of CMP1 and the non-inverting input of CMP2, the non-inverting input of CMP1 is connected to a reference voltage Vref2, the inverting input of CMP2 is connected to a reference voltage Vref1, the output of CMP1 is connected to the S input of the RS flip-flop, the output of CMP2 is connected to the R input of the RS flip-flop, the output of the inverter is connected to the gate of M1 and the gate of M2 to generate a square wave signal, the gate of M3 is connected to the reset signal, the output of the discharging current source is connected to the drain of M2, the source of M2 is connected to the source of M3 and the other end of C1 to ground; the current of the charging current source depends on the current feedback signal, and the current of the discharging current source is a given constant.
Further, the valley-adding signal generating circuit is composed of two D flip-flops D1 and D2 and an inverter, wherein the input end of the inverter is connected with the clock end of D1 and connected with the square wave signal in parallel, the input ends of D1 and D2 are both connected with the power supply voltage, the output end of D1 generates a valley-adding signal Gu Xinhao Vosc1, and the output end of D2 generates a valley-adding signal Vosc2.
Further, the reset ends of the triggers D1 and D2 are controlled by the reset signal after being delayed briefly, so that the two triggers can read out the square wave signal of the previous period before being reset, and the addition and subtraction Gu Xinhao Vosc1 and Vosc2 can be output.
Further, the logic operation module includes a signal generator, a preset valley counter, a current valley counter, two and gates AG1 and AG2, two exclusive OR gates OR1 and OR2, and an exclusive OR gate, where the signal generator receives up-down Gu Xinhao Vosc1 and Vosc2, outputs a valley adding signal INC and a valley subtracting signal DEC after logic operation and delay, a first input terminal of AG1 is connected to an output terminal of OR1, a second input terminal of AG1 is connected to the INC, a first input terminal of AG2 is connected to an output terminal of OR2, a second input terminal of AG2 is connected to DEC, an input terminal of the preset valley counter is connected to output terminals of AG1 and AG2, two input terminals of OR1 are respectively connected to a preset three-bit digital code [110] and a digital code signal a, two input terminals of OR2 are respectively connected to a preset three-bit digital code [000] and a digital code signal a, an input terminal of the current valley counter is connected to an output terminal of the current gate, and the two input terminals of the exclusive OR gate signal B are respectively connected to the output terminals of the digital code signal B.
Further, the operation logic of the signal generator is as follows:
when Vosc1 and Vosc2 are both high, INC is low and DEC is high;
when Vosc1 and Vosc2 are both low, INC is high and DEC is low;
when Vosc1 is low and Vosc2 is high, both INC and DEC are low;
when the three conditions occur, the output end of the signal generator is turned over to output corresponding signals after 360 PWM cycles are needed.
Further, the switch control module comprises an OR gate, an RS trigger, an error amplifier and a driving circuit, wherein two input ends of the OR gate are respectively connected with a conducting signal and a valley detection signal, the output end of the OR gate is connected with the S input end of the RS trigger, the non-inverting input end of the error amplifier is connected with a load feedback voltage, the inverting input end of the error amplifier is connected with a current sampling signal of a primary excitation inductor, the output end of the error amplifier is connected with the R input end of the RS trigger, the Q output end of the RS trigger is connected with the input end of the driving circuit, and the output end of the driving circuit outputs a switch control signal to the grid electrode of the main switching tube.
The invention also provides a charger which comprises the control device, the valley locking is realized through the control device, the stability of the charger is ensured, and the audio noise of the charger is avoided.
Based on the technical scheme, the control device can solve the problem that the switching tube is continuously switched at low frequency between two or even a plurality of adjacent valleys and the problem of output envelope ripple and audio noise caused by the problem that the corresponding feedback quantity is the same as the valley switching threshold value when the load is stable in the prior art, can avoid the phenomenon of jumping between the valleys and the problem of the output envelope ripple and the problem of the audio noise, and has higher suitability in the current AC-DC flyback switching power supplies which are suitable for mobile phones and notebook computers.
Drawings
Fig. 1 is a schematic diagram of a typical flyback switching power supply.
Fig. 2 is a waveform diagram of drain voltage, gate driving signal and current flowing through the switching transistor M1 in fig. 1.
FIG. 3 is a diagram showing the relationship between the feedback voltage and the turn-on valley number and the switching frequency in the conventional quasi-resonant control mode.
Fig. 4 is a block diagram of a control device for selecting, switching and locking a conduction trough according to the present invention.
Fig. 5 is a block diagram of the application of the control device of the present invention in an AC-DC switching power supply system using flyback as a topology.
Fig. 6 is a schematic circuit diagram of a valley-bottom selection oscillator.
Fig. 7 is a schematic diagram of output waveforms of key nodes in the valley-select oscillator circuit.
Fig. 8 is a schematic circuit diagram of a logic operation module.
FIG. 9 is a schematic diagram of the logic operation of the signal generator in the logic operation module.
FIG. 10 is a graph showing the relationship between feedback voltage and turn-on valley number and switching frequency under the control of the device of the present invention.
Detailed Description
In order to more particularly describe the present invention, the following detailed description of the technical scheme of the present invention is provided with reference to the accompanying drawings and the specific embodiments.
In the conventional quasi-resonance control mode, for switching between conduction troughs of adjacent ordinal numbers, the corresponding valley adding threshold is the same as the valley subtracting threshold, and the valley adding threshold and the valley subtracting threshold are usually frequency signals, and the frequency is obtained by monitoring feedback signals corresponding to loads. When the load changes, so that the output power is changed from high to low, the switching tube is gradually reduced in the on state of the trough bottom of the trough of the same ordinal number, so that the switching frequency is increased, and when the switching frequency reaches a threshold value corresponding to the valley adding threshold value, the trough bottom of the trough is switched backwards; when the load changes and the output power is changed from low to high, the on time of the switching tube is gradually increased under the conduction state of the trough bottom of the trough of the same ordinal number, the switching frequency is reduced, and when the switching frequency reaches a threshold corresponding to the valley reduction threshold, the conducting valley ordinal number is switched forward. Fig. 3 shows the relationship between the feedback voltage and the turn-on trough number and the switching frequency in the conventional quasi-resonant control mode, if the load is stable and the corresponding power stabilization point is near the power corresponding to the switch Gu Shi, the turn-on trough number of the switching tube at the turn-on time will jump back and forth at the corresponding turn-on trough with a lower frequency.
In order to solve the problems of output envelope ripple and audio noise caused by low-frequency valley switching in the traditional quasi-resonance control mode, the invention provides a control device for selecting, switching and locking the conduction valleys of a flyback switching power supply.
Fig. 4 shows a structural principle framework of an embodiment of a control device of the present invention, where the control device includes a load detection module, a valley bottom selection oscillator, a valley bottom detection module, and a logic operation module, where the load detection module detects a load size of a flyback converter, the valley bottom selection oscillator uses a front edge blanking pulse as a reset period, receives a current signal reflecting the load size output by the load detection module, and outputs a plus or minus Gu Xinhao reflecting a current load requirement; the valley bottom detection module detects the moment that the vibration valley reaches the valley bottom, outputs a valley bottom detection signal, and outputs a current on valley bottom signal to the logic operation module; the logic operation module outputs a conduction signal through digital logic operation according to the addition and subtraction valley signal output by the valley bottom selection oscillator and the current conduction valley bottom signal output by the valley bottom detection module, and the generation of a switching tube on signal is determined through OR logic together with the valley bottom detection signal output by the valley bottom detection module.
In this embodiment, the control device may be applied to an AC-DC switching power supply system using flyback as a topology structure as shown in fig. 5, where the control device further includes a Driver, an EA error amplifier and digital logic, and a pin PRT is connected to a valley detection module, to provide a voltage waveform generated by resonance between a parasitic capacitor and a transformer excitation inductance when the switching tube M1 is turned off for the valley detection module; the pin CS is connected with the source electrode of the switching tube and the sampling resistor R1, can monitor the current of the primary inductor (namely the excitation inductor connected in parallel on the primary winding) and is input into the inverting input end of the error amplifier EA; the pin FB is connected with the output end of the feedback loop, and is input into the non-inverting input end of the error amplifier EA, and forms a peak current control loop with primary inductor current to control the turn-off time of the switching tube; simultaneously, the pin FB is connected with the load detection module and provides a feedback voltage signal of the load for the load detection module; the pin GATE is connected with the grid electrode of the switching tube M1 and the output end of the Driver, and controls the switching tube M1 to be turned on and turned off; the 1-end of the RS trigger is connected with a switching tube switching-ON signal PWM_ON, the 0-end of the RS trigger is connected with the output PWM_OFF of the error amplifier, and the output end of the RS trigger is connected with the Driver module to drive the main switching tube; meanwhile, leading edge blanking sampling is carried out on the on time of the main switching tube at the output end of the Driver, and a leading edge blanking pulse signal is output to the valley bottom selection oscillator.
As shown in fig. 6, the valley bottom selection oscillator circuit includes MOS transistors M1 to M3, a capacitor C1, a charging current source Icharge, a discharging current source Idischarge, comparators CMP1 and CMP2, and digital logic, wherein the magnitude of the charging current source Icharge is controlled by a feedback signal input by a load detection module, and the heavier the load is, the larger the charging current source Icharge is; when the charging current source Icharge charges the C1 capacitor and the threshold reaches Vref2, the 1-setting end of the RS trigger is low level, the 0-setting end is high level, the output end is 0, and the Vosc square wave signal output by the inverter is high level; when the discharging current source Idischarge discharges the capacitor C1 to make the threshold reach Vref1, the 1-setting end of the RS trigger is at high level, the 0-setting end is at low level, the output end is at 0, the Vosc square wave signal output by the inverter is at low level, the period length of the high level of the finally generated square wave signal Vosc is positively correlated with the size of the discharging current source Idischarge, the period length of the low level is positively correlated with the size of the charging current source Icharge, and the square wave signal with a certain duty ratio is obtained, wherein the duty ratio D is related to the feedback signal input by the feedback pin FB, the heavier the load is, the larger the feedback signal is, and the larger the charging current source Icharge is, and the larger the duty ratio is. The square wave signal Vosc is input into the addition and subtraction valley signal generating circuit, wherein the clock end of the trigger D1 receives the square wave signal Vosc input by the oscillator circuit, the D end is connected with high level, and when the square wave signal Vosc is a falling edge, the trigger is used for generating addition and subtraction Gu Xinhao Vosc1; the clock end of the trigger D2 receives a signal of the square wave signal Vosc which is input by the oscillator circuit and is inverted by the inverter, the D end is connected with high level, and the trigger is triggered when the signal of the square wave signal Vosc which is inverted by the inverter is a falling edge, so as to generate an addition-subtraction valley signal Vosc2. The MOS tube M3 is a reset switch and is controlled by a reset signal RST, and the reset signal RST is a leading edge blanking pulse, so that a square wave signal Vosc output by the oscillator circuit is set to zero. The reset ends of the triggers D1 and D2 are controlled by the reset signal RST after short delay, so that the trigger is ensured to read out the square wave signal Vosc of the previous period before reset, and add and subtract Gu Xinhao Vosc1 and Vosc2 are output.
Fig. 7 shows output waveforms of key nodes of the valley bottom select oscillator, and the specific working principle of the synchronous rectification control circuit can be explained in detail by combining the circuit structure.
As shown in fig. 8, the logic operation module includes a signal generator, a preset valley counter, a current valley counter, and digital logic composed of an exclusive or gate, and an and gate, wherein Vosc1 and Vosc2 signals are the addition and subtraction valley signals output by the valley selection oscillator circuit, and are input to the signal generator. Fig. 9 shows specific logic of the signal generator for generating the valley-added signal INC and the valley-subtracted signal DEC according to the level of the addition and subtraction Gu Xinhao Vosc1 and Vosc 2: when Vosc1 is low level and Vosc2 is also low level, after 360 PWM periods are needed, the output end of the signal generator turns over, and at this time, the valley adding signal INC is high level and the valley subtracting signal DEC is low level; when Vosc1 is at low level and Vosc2 is at high level, the output end of the signal generator is turned over after 360 PWM periods are needed, and the valley adding signal INC and the valley subtracting signal DEC are both at low level; when Vosc1 is at high level and Vosc2 is also at high level, the output end of the signal generator is turned over after 360 PWM periods are needed, and at this time, the valley-adding signal INC is at low level and the valley-subtracting signal DEC is at high level. As can be seen from FIG. 7, when the system is in normal operation, the condition that Vosc1 is high level and Vosc2 is low level does not occur, after the output signals INC and DEC of the signal generator are subjected to digital logic operation, the preset valley bottom is input, and the three-bit digital coding signal A [2:0] is output, so that the counting in six conducting valleys can be realized, wherein when the output signal A [2:0] is [000] or [110], the conducting valley bottom ordinal number is 1 or 6, and at this time, the output signal A [2:0] is not changed by the influence of the valley adding signal and the valley subtracting signal. The input of the current valley counter is the current conduction valley counting signal output by the valley detection module, and outputs a three-bit digital coding signal B2:0, which represents the ordinal number of the resonance valley where the drain voltage of the switching tube M1 in the current system is actually located; when the digital coding signals A2:0 are equal to B2:0, the ordinal number of the trough bottom of the resonance trough where the digital coding signals A2:0 are actually located is the same as the ordinal number of the trough bottom of the preset resonance trough, and at the moment, the logic operation module outputs a conducting signal to the RS trigger to drive the switching tube M1 to be turned on.
As shown in fig. 10, the relationship between the feedback voltage and the turn-on trough number and the switching frequency is shown under the control of the device of the present invention, and the problem of output envelope ripple caused by low-frequency trough switching in the conventional quasi-resonant mode control technology is seen from fig. 3, and the problem of audio noise is seen in the conventional technology, because the output power corresponding to the valley adding threshold and the valley subtracting threshold between adjacent troughs is equal, when the load is stable, if the corresponding power stabilizing point is near the power point corresponding to the valley cutting, the turn-on trough number at the turn-on time of the switching tube will jump back and forth at the corresponding turn-on trough with lower frequency. Under the control of the device, when switching is performed between adjacent valley bottoms, hysteresis exists between the valley adding frequency and the valley subtracting frequency, the hysteresis frequency difference is related to the load, the larger the load is, the larger the hysteresis frequency difference is, and the phenomenon of jumping between valleys is avoided. Compared with the current main flow technology of valley locking, the control method of the invention adopts the frequency signal to control, can freely adjust the adding Gu Pinlv curve and the valley reducing frequency curve, can conveniently realize the smooth transition of the switching frequency of the system if the chip works in different working modes under different loads, and has higher suitability in the current AC-DC flyback switching power supply which is suitable for mobile phones and notebook computers.
The embodiment also provides a charger, which comprises the control device, the valley locking is realized through the control device, the stability of the charger is ensured, and the audio noise of the charger is avoided.
The embodiments described above are described in order to facilitate the understanding and application of the present invention to those skilled in the art, and it will be apparent to those skilled in the art that various modifications may be made to the embodiments described above and that the general principles described herein may be applied to other embodiments without the need for inventive faculty. Therefore, the present invention is not limited to the above-described embodiments, and those skilled in the art, based on the present disclosure, should make improvements and modifications within the scope of the present invention.

Claims (9)

1. The utility model provides a control device for flyback switching power supply conduction trough is selected, is switched and is locked which characterized in that includes:
the load detection module is used for detecting the load feedback voltage of the flyback switching power supply and converting the load feedback voltage into a current feedback signal reflecting the load condition;
the valley bottom selection oscillator takes the leading edge blanking pulse at the turn-on time of the main switching tube of the flyback switching power supply as a reset signal, and performs oscillation sampling output addition and subtraction Gu Xinhao on the current feedback signal;
the valley bottom detection module is used for detecting the moment that the resonance valley bottom reaches the valley bottom when the flyback switching power supply enters a resonance state and outputting a valley bottom detection signal; meanwhile, counting the resonant wave trough reaching the bottom each time, and outputting a current conduction bottom counting signal;
the logic operation module outputs a conduction signal for determining the resonant trough ordinal number of the main switching tube at the turn-on moment through digital logic operation according to the valley adding and subtracting signal and the current conduction trough counting signal;
and the switch control module is used for providing an output switch control signal for the grid electrode of the main switch tube through logic control according to the conduction signal, the valley detection signal, the current sampling signal of the primary side excitation inductance of the flyback switch power supply and the load feedback voltage.
2. The control device according to claim 1, characterized in that: the load detection module includes:
the oscillator circuit is used for carrying out oscillation control on the current feedback signal by taking the front edge blanking pulse as a reset signal to generate a square wave signal;
the adding and subtracting valley signal generating circuit is used for sampling the square wave signal when the main switching tube is turned on each time to generate adding and subtracting Gu Xinhao Vosc1 and Vosc2, and the adding and subtracting signals respectively reflect whether the resonant valley ordinal number at the current turn-on moment of the main switching tube needs to move forwards and backwards.
3. The control device according to claim 2, characterized in that: the oscillator circuit comprises a PMOS tube M1, a charging current source, a discharging current source, NMOS tubes M2 and M3, a capacitor C1, comparators CMP1 and CMP2, an inverter and an RS trigger, wherein the source electrode of the M1 is connected with a power supply voltage, the drain electrode of the M1 is connected with the input end of the charging current source, the output end of the charging current source is connected with the input end of the discharging current source, the drain electrode of the M3, one end of the C1, the inverting input end of the CMP1 and the non-inverting input end of the CMP2 are connected with a reference voltage Vref2, the inverting input end of the CMP1 is connected with the reference voltage Vref1, the output end of the CMP1 is connected with the S input end of the RS trigger, the output end of the CMP2 is connected with the R input end of the RS trigger, the Q output end of the RS trigger is connected with the grid electrode of the M1 and the grid electrode of the M2 to generate square wave signals, the grid electrode of the discharging current source is connected with the drain electrode of the M2, and the source electrode of the M2 is connected with the other end of the C1 and grounded; the current of the charging current source depends on the current feedback signal, and the current of the discharging current source is a given constant.
4. The control device according to claim 2, characterized in that: the valley-adding and valley-adding signal generating circuit consists of two D triggers D1 and D2 and an inverter, wherein the input end of the inverter is connected with the clock end of D1 and connected with the square wave signal in parallel, the input ends of D1 and D2 are both connected with the power supply voltage, the output end of D1 generates a valley-adding and valley-adding signal Gu Xinhao Vosc1, and the output end of D2 generates a valley-adding and valley-adding signal Vosc2.
5. The control device according to claim 4, characterized in that: the reset ends of the triggers D1 and D2 are controlled by the reset signals after short delay, so that the two triggers can read out square wave signals of the previous period before reset to output addition and subtraction Gu Xinhao Vosc1 and Vosc2.
6. The control device according to claim 2, characterized in that: the logic operation module comprises a signal generator, a preset valley counter, a current valley counter, two AND gates AG1 and AG2, two exclusive OR gates OR1 and OR2 and an exclusive OR gate, wherein the signal generator receives up-down Gu Xinhao Vosc1 and Vosc2, outputs a valley adding signal INC and a valley subtracting signal DEC after logic operation and time delay, a first input end of AG1 is connected with an output end of OR1, a second input end of AG1 is connected with INC, a first input end of AG2 is connected with an output end of OR2, a second input end of AG2 is connected with DEC, input ends of the preset valley counter are respectively connected with output ends of AG1 and AG2, two input ends of OR1 are respectively connected with a preset three-bit digital code [110] and a preset three-bit digital code signal A, two input ends of OR2 are respectively connected with a preset three-bit digital code [000] and a digital code signal A, an input end of the current valley counter is connected with an output end of the digital code signal A and the output end of the exclusive OR gate through counting, and the output ends of the two exclusive OR gate are respectively connected with the output ends of the digital code signal A and the exclusive OR gate.
7. The control device according to claim 6, characterized in that: the operation logic of the signal generator is as follows:
when Vosc1 and Vosc2 are both high, INC is low and DEC is high;
when Vosc1 and Vosc2 are both low, INC is high and DEC is low;
when Vosc1 is low and Vosc2 is high, both INC and DEC are low;
when the three conditions occur, the output end of the signal generator is turned over to output corresponding signals after 360 PWM cycles are needed.
8. The control device according to claim 1, characterized in that: the switch control module comprises an OR gate, an RS trigger, an error amplifier and a driving circuit, wherein two input ends of the OR gate are respectively connected with a conduction signal and a valley detection signal, the output end of the OR gate is connected with the S input end of the RS trigger, the non-inverting input end of the error amplifier is connected with load feedback voltage, the inverting input end of the error amplifier is connected with a current sampling signal of a primary excitation inductor, the output end of the error amplifier is connected with the R input end of the RS trigger, the Q output end of the RS trigger is connected with the input end of the driving circuit, and the output end of the driving circuit outputs a switch control signal to the grid electrode of the main switch tube.
9. A charger, characterized by: comprising a control device according to any one of claims 1-8, by means of which the valley locking is achieved, the stability of the charger is ensured, and the audio noise of the charger is avoided.
CN202311269464.8A 2023-09-28 2023-09-28 Control device for selecting, switching and locking conduction trough of flyback switching power supply Pending CN117277748A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117526685A (en) * 2024-01-08 2024-02-06 深圳市力生美半导体股份有限公司 Control method and control device of switching power supply and switching power supply

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117526685A (en) * 2024-01-08 2024-02-06 深圳市力生美半导体股份有限公司 Control method and control device of switching power supply and switching power supply

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