CN111181380A - Control circuit and method for suppressing audio noise - Google Patents
Control circuit and method for suppressing audio noise Download PDFInfo
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- CN111181380A CN111181380A CN202010116460.6A CN202010116460A CN111181380A CN 111181380 A CN111181380 A CN 111181380A CN 202010116460 A CN202010116460 A CN 202010116460A CN 111181380 A CN111181380 A CN 111181380A
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- 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
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Abstract
The application relates to a control circuit and a method for suppressing audio noise, wherein the control circuit comprises: the amplifying module outputs a first amplified signal; the compensation module receives the first amplified signal and outputs a second amplified signal; the frequency control module receives the second amplified signal and outputs a minimum period driving signal; the detection module is used for detecting the valley bottom of the resonance signal and outputting a valley bottom detection output signal; the logic and gate control module receives the minimum period driving signal and the valley bottom detection output signal and outputs a driving opening control signal; the peak current control module receives the first amplified signal and outputs a maximum current control signal; the comparison module receives the maximum current control signal and combines the maximum current detection signal to output a drive turn-off control signal; and the trigger module receives the drive starting control signal and the drive stopping control signal to output a drive signal, and the drive signal is used for driving the switching tube to operate. The method can achieve the effect of avoiding audio noise, and is simple, convenient and quick.
Description
Technical Field
The invention relates to a control circuit and a control method for inhibiting audio noise, and belongs to the technical field of switching power supply control.
Background
With the continuous development of society, electronic products continuously appear in the lives of people, and each electronic product is not relatively perfect and has respective advantages and disadvantages; it is known that the oscillation frequency of electronic and magnetic elements is in the range of human ear, which generates audible audio signals, and this phenomenon of audio noise. For example, transformers operating at 50Hz and 60Hz often produce audible noise.
Flyback switching power supply output power
Wherein I is the average current flowing through the coil, L is the inductance of the coil, and f is the switching frequency of the power supply. As can be known from the formula of the output power of the flyback switching power supply, the power is mainly related to the magnitude of the current and the frequency. When the power required by the load becomes large, the output power is improved by adjusting the increasing current or increasing the frequency through the switching power supply chip; similarly, when the power required by the load is reduced, the output power is reduced by adjusting the reduced current or the reduced frequency through the switching power supply chip, so that the balance of the system is ensured.
In the quasi-resonant flyback switching power supply, the switching frequency of the power supply is also influenced by the resonant signal, and in order to reduce the switching loss of the switching tube, the power supply only allows the power supply switch to be started at the valley of the resonant signal, so that when the quasi-resonant flyback switching power supply is in actual work (in a non-heavy load/light load mode), if the switching frequency is not controlled, the frequency change is discontinuous. Once in the audio range, audio noise is present in the power supply system.
Disclosure of Invention
The invention aims to provide a control circuit and a control method for inhibiting audio noise, which can prevent the discontinuous change of the switching frequency of a switching power supply so as to achieve the effect of avoiding the audio noise, and are simple, convenient and quick.
In order to achieve the purpose, the invention provides the following technical scheme: a control circuit for suppressing audio noise disposed within a quasi-resonant flyback switching power supply, the control circuit comprising:
the amplifying module is used for accessing a signal proportional to the output voltage and a reference voltage to output a first amplifying signal;
the compensation module receives the first amplified signal and performs compensation processing on the first amplified signal to output a second amplified signal;
the frequency control module receives the second amplified signal and outputs a minimum period driving signal;
the detection module is used for detecting the valley bottom of the resonance signal and outputting a valley bottom detection output signal;
the logic and gate control module receives the minimum period driving signal and the valley bottom detection output signal and outputs a driving opening control signal;
the peak current control module receives the first amplified signal and outputs a maximum current control signal;
the comparison module receives the maximum current control signal and combines the maximum current detection signal to output a drive turn-off control signal;
and the trigger module is used for receiving the drive starting control signal and the drive switching-off control signal so as to output a drive signal, and the drive signal is used for driving the switching tube to operate.
Furthermore, the amplifying module comprises an error amplifier, a signal proportional to the output voltage is connected to the inverting input end of the error amplifier, and a reference voltage is connected to the forward input end of the error amplifier.
Further, the comparing module comprises a comparator, a reverse input end of the comparator is connected to the maximum current control signal, and a forward input end of the comparator is connected to the maximum current detection signal.
Furthermore, the trigger module comprises an RS trigger, a set end of the RS trigger is connected to the drive turn-on control signal, and a reset end of the RS trigger is connected to the drive turn-off control signal.
The invention also provides a control method for suppressing audio noise, which adopts the control circuit for suppressing audio noise, and comprises the following steps:
obtaining a first amplified signal and a maximum current detection signal;
obtaining a second amplified signal and a maximum current control signal according to the first amplified signal;
obtaining a minimum period driving signal according to the second amplified signal;
detecting a valley bottom of the resonance signal to obtain a valley bottom detection output signal;
obtaining a driving starting control signal according to the minimum period driving signal and the valley bottom detection output signal;
obtaining a driving turn-off control signal according to the maximum current control signal and the maximum current detection signal;
and obtaining a driving signal according to the driving starting control signal and the driving stopping control signal, and driving the switching tube to operate through the driving signal.
Further, the obtaining a second amplified signal from the first amplified signal includes:
the first amplified signal is compensated by the compensation module to obtain the second amplified signal;
the compensation module comprises a subtraction module and an addition module, and when the output voltage is reduced and the first amplified signal rises, the first amplified signal is processed by the subtraction module to obtain the second amplified signal; when the output voltage rises and the first amplified signal falls, the first amplified signal is processed by the addition module to obtain the second amplified signal.
Further, the maximum current control signal varies with a variation of the first amplified signal.
Further, the obtaining the first amplified signal includes:
the amplifying module comprises an error amplifier, a signal in direct proportion to output voltage is connected to the reverse input end of the error amplifier, reference voltage is connected to the forward input end of the error amplifier, and the output end of the error amplifier outputs an amplifying voltage value to obtain a first amplifying signal.
The invention has the beneficial effects that: the compensation circuit is arranged and processes the first amplified signal to obtain a second amplified signal, so that the finally output switching frequency is continuously changed, and the switching frequency of the power supply is prevented from entering an audio frequency range; the invention has simple structure, and is convenient and fast.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.
Drawings
Fig. 1 is a waveform diagram of a driving signal DRV of a switching tube of a switching power supply in the prior art.
Fig. 2 is a block diagram of the control circuit for suppressing audio noise according to the present invention.
Fig. 3 is a waveform diagram of the audio noise suppression control circuit according to the present invention.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
Referring to fig. 1, a waveform diagram of a driving signal DRV of a switching tube in a switching power supply in the prior art is shown, where VS is a voltage waveform of an auxiliary coil after voltage division, and when a switch is turned off and a current exists in the coil, a VS signal is a signal proportional to an output voltage; when the switch is open and the current on the coil is zero, the VS signal is a signal proportional to the resonant voltage. TMIN is a switching frequency control signal, and the driving signal cannot be turned on for the second time within the time when TMIN is 1, and the driving signal can be turned on again only when TMIN is 0 and VS reaches the bottom of the valley, so that the longer the time when TMIN is 1 is, the smaller the switching frequency of the switching power supply is; whereas the switching frequency is larger.
In the switching power supply which controls the output power simultaneously by current and frequency, when the load power is increased slightly, the system adjusts and shortens the time of TMIN equal to 1 to improve the switching frequency, and because of the limitation condition of valley bottom detection, when the maintaining time of TMIN equal to 1 is reduced from the Nth resonance valley bottom to the Nth-1 th resonance valley bottom, the switching periods of the front and the back systems are different by one resonance period, thereby leading the switching frequency of the whole switching power supply to be reduced to the audio frequency range. As shown in fig. 1, in the first switching period, TMIN ═ 1 is maintained after the second resonance valley, so that the driving signal of the switching tube is always turned on at the third resonance valley; in the second switching period, TMIN ═ 1 holding time is shortened to the second resonance valley, and the driving signal of the switching tube in the period is turned on at the second resonance valley, so T2 is one resonance period less than T1. When the load power is reduced to a small extent, the situation that the switching frequency is discontinuously changed also occurs, and once the audio frequency range is entered, audio frequency noise occurs in the switching power supply.
Referring to fig. 2, in a preferred embodiment of the present invention, a control circuit for suppressing audio noise is disposed in a quasi-resonant flyback switching power supply, and the control circuit includes: an amplifying module for receiving a signal proportional to an output voltage and a reference voltage to output a first amplified signal, a compensating module for receiving the first amplified signal and performing a compensation process on the first amplified signal to output a second amplified signal, a frequency control module for receiving the second amplified signal and outputting a minimum period driving signal, a detecting module for detecting a valley bottom of a resonance signal and outputting a valley bottom detection output signal, a logic and gate control module for receiving the minimum period driving signal and the valley bottom detection output signal and outputting a driving start control signal, a peak current control module for receiving the first amplified signal and outputting a maximum current control signal, a comparing module for receiving the maximum current control signal and outputting a driving stop control signal in combination with the maximum current detection signal, and a driving module for receiving the driving start control signal and the driving stop control signal to output a driving signal, the driving signal is used for driving the switching tube to operate. In this embodiment, the amplifying module includes an error amplifier, a signal proportional to the output voltage is connected to an inverting input terminal of the error amplifier, a reference voltage is connected to a forward input terminal of the error amplifier, and the output terminal of the error amplifier outputs an amplified voltage value to output a first amplified signal. The divided auxiliary winding voltage is VS, the reference voltage is Vref1, and the first amplified signal is eaout 1.
The comparison module comprises a comparator, the reverse input end of the comparator is connected with the maximum current control signal VCS, and the forward input end of the comparator is connected with the maximum current detection signal CS. The trigger module comprises an RS trigger, a set end (S end) of the RS trigger is connected to the drive starting control signal Son, and a reset end (R end) of the RS trigger is connected to the drive switching-off control signal Soff.
The peak current control module is a circuit for controlling a peak current flowing through the coil, the frequency control module is a circuit for controlling a switching frequency, and the detection module is a detection circuit for detecting a valley bottom of the resonance signal. Indeed, in other embodiments, the peak current control module, the frequency control module and the detection module may be other modules, which are determined according to practical situations and are not limited herein. The minimum period driving signal is tmin, the maximum current control signal is Vcs, and the valley bottom detection output signal is svell.
The compensation module comprises a subtraction module and an addition module, and when the output voltage is reduced and the first amplified signal rises, the first amplified signal is processed by the subtraction module to obtain the second amplified signal; when the output voltage rises and the first amplified signal falls, the first amplified signal is processed by the addition module to obtain the second amplified signal. More specifically, the compensation module is an error compensation circuit, and the error compensation circuit includes a subtraction circuit and an addition circuit. In this embodiment, the second amplified signal is eaout 2. When the load power is increased slightly, the output voltage is reduced, VS is reduced slightly, the first amplified signal is increased, eaout1 is subjected to a subtraction circuit to obtain eaout2, and eaout2 is equal to eaout1-Vcomp1, at this time, the maximum current control signal Vcs flowing through the coil can be obtained from eaout1, the minimum period control signal tmin can be obtained from eaout2, and finally, the driving signal DRV of the final switching tube is obtained through the judgment of the valley detection output circuit.
When the load power is reduced slightly, the output voltage rises, VS rises slightly, and the first amplified signal falls, eaout1 passes through an adder circuit to obtain eaout2, and eaout2 is equal to eaout1+ Vcomp2, at this time, the maximum current control signal Vcs flowing through the coil can be obtained from eaout1, the minimum period control signal tmin can be obtained from eaout2, and finally, the driving signal DRV of the final switching tube is obtained through the judgment of the valley detection output circuit.
As shown in fig. 3, from the first period T1 to the second period T2, eaout2 is satisfied as eaout1-Vcomp1, from the second period T2 to the third period T3, eaout2 is satisfied as eaout1+ Vcomp2, and from the third period T3 to the fourth period T4, eaout2 is satisfied as eaout1-Vcomp1, and it can be found that the output power change mainly comes from the control of the peak current by the eaout1, and the power supply switching frequency change is more continuous in conjunction with the determination signal svell of the bottom detection output circuit.
Because tmin signal of the control period is controlled by the compensated eaout2 signal, when the output voltage changes, the power chip firstly adjusts the output power by changing the magnitude of Vcs, and the change of the period control signal tmin is relatively slow, and tmin does not change greatly until the power required by the load changes greatly, so that the switching frequency changes.
The invention also provides a control method for suppressing audio noise, which adopts the control circuit for suppressing audio noise, and comprises the following steps:
obtaining a first amplified signal and a maximum current detection signal;
obtaining a second amplified signal and a maximum current control signal according to the first amplified signal;
obtaining a minimum period driving signal according to the second amplified signal;
detecting a valley bottom of the resonance signal to obtain a valley bottom detection output signal;
obtaining a driving starting control signal according to the minimum period driving signal and the valley bottom detection output signal;
obtaining a driving turn-off control signal according to the maximum current control signal and the maximum current detection signal;
and obtaining a driving signal according to the driving starting control signal and the driving stopping control signal, and driving the switching tube to operate through the driving signal.
The obtaining a second amplified signal from the first amplified signal comprises:
the first amplified signal is compensated by the compensation module to obtain the second amplified signal;
the compensation module comprises a subtraction module and an addition module, and when the output voltage is reduced and the first amplified signal rises, the first amplified signal is processed by the subtraction module to obtain the second amplified signal; when the output voltage rises and the first amplified signal falls, the first amplified signal is processed by the addition module to obtain the second amplified signal.
The obtaining a first amplified signal includes:
the amplifying module comprises an error amplifier, a signal in direct proportion to output voltage is connected to the reverse input end of the error amplifier, reference voltage is connected to the forward input end of the error amplifier, and the output end of the error amplifier outputs an amplifying voltage value to obtain a first amplifying signal.
The maximum current control signal changes with the change of the first amplification signal, when the output voltage changes, the power supply chip firstly adjusts the output power by changing the magnitude of the maximum current control signal, and the change of the minimum period control signal is slower.
In summary, the following steps: the compensation circuit is arranged and processes the first amplified signal to obtain a second amplified signal, so that the change of the finally output second amplified signal is changed continuously, and the switching frequency of the power supply is prevented from entering an audio frequency range; the invention has simple structure, and is convenient and fast.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (8)
1. A control circuit for suppressing audio noise disposed in a quasi-resonant flyback switching power supply, the control circuit comprising:
the amplifying module is used for accessing a signal proportional to the output voltage and a reference voltage to output a first amplifying signal;
the compensation module receives the first amplified signal and performs compensation processing on the first amplified signal to output a second amplified signal;
the frequency control module receives the second amplified signal and outputs a minimum period driving signal;
the detection module is used for detecting the valley bottom of the resonance signal and outputting a valley bottom detection output signal;
the logic and gate control module receives the minimum period driving signal and the valley bottom detection output signal and outputs a driving opening control signal;
the peak current control module receives the first amplified signal and outputs a maximum current control signal;
the comparison module receives the maximum current control signal and combines the maximum current detection signal to output a drive turn-off control signal;
and the trigger module is used for receiving the drive starting control signal and the drive switching-off control signal so as to output a drive signal, and the drive signal is used for driving the switching tube to operate.
2. The control circuit for suppressing audio noise according to claim 1, wherein the amplifying block comprises an error amplifier, a signal proportional to the output voltage is connected to a negative input terminal of the error amplifier, and a reference voltage is connected to a positive input terminal of the error amplifier.
3. The control circuit for suppressing audio noise according to claim 1, wherein the comparing module comprises a comparator, a negative input terminal of the comparator is connected to the maximum current control signal, and a positive input terminal of the comparator is connected to the maximum current detection signal.
4. The control circuit for suppressing audio noise according to claim 1, wherein the trigger module includes an RS flip-flop, a set terminal of the RS flip-flop is connected to the driving-on control signal, and a reset terminal of the RS flip-flop is connected to the driving-off control signal.
5. A control method of suppressing audio noise, characterized in that the control method employs the control circuit of suppressing audio noise according to any one of claims 1 to 4, the method comprising the steps of:
obtaining a first amplified signal and a maximum current detection signal;
obtaining a second amplified signal and a maximum current control signal according to the first amplified signal;
obtaining a minimum period driving signal according to the second amplified signal;
detecting a valley bottom of the resonance signal to obtain a valley bottom detection output signal;
obtaining a driving starting control signal according to the minimum period driving signal and the valley bottom detection output signal;
obtaining a driving turn-off control signal according to the maximum current control signal and the maximum current detection signal;
and obtaining a driving signal according to the driving starting control signal and the driving stopping control signal, and driving the switching tube to operate through the driving signal.
6. The control method for suppressing audio noise according to claim 5, wherein said obtaining a second amplified signal from said first amplified signal comprises:
the first amplified signal is compensated by the compensation module to obtain the second amplified signal;
the compensation module comprises a subtraction module and an addition module, and when the output voltage is reduced and the first amplified signal rises, the first amplified signal is processed by the subtraction module to obtain the second amplified signal; when the output voltage rises and the first amplified signal falls, the first amplified signal is processed by the addition module to obtain the second amplified signal.
7. The control method for suppressing audio noise according to claim 6, wherein the maximum current control signal is changed in accordance with a change in the first amplified signal.
8. The control method for suppressing audio noise according to claim 5, wherein said obtaining a first amplified signal comprises:
the amplifying module comprises an error amplifier, a signal in direct proportion to output voltage is connected to the reverse input end of the error amplifier, reference voltage is connected to the forward input end of the error amplifier, and the output end of the error amplifier outputs an amplifying voltage value to obtain a first amplifying signal.
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| CN202010116460.6A CN111181380A (en) | 2020-02-25 | 2020-02-25 | Control circuit and method for suppressing audio noise |
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Cited By (1)
| 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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2020
- 2020-02-25 CN CN202010116460.6A patent/CN111181380A/en active Pending
Cited By (2)
| 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 |
| CN117526685B (en) * | 2024-01-08 | 2024-05-03 | 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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