Control circuit and method for suppressing audio noise

Abstract

The present application relates to a control circuit and method for suppressing audio noise, wherein the control circuit comprises: an amplification module, outputting a first amplified signal; a compensation module, receiving the first amplified signal and outputting a second amplified signal; a frequency control module, receiving the second amplified signal and outputting a minimum period drive signal; a detection module, used to detect the valley of the resonance signal and output a valley detection output signal; a logic and gate control module, receiving the minimum period drive signal and the valley detection output signal, and outputting a drive start control signal; a peak current control module, receiving the first amplified signal and outputting a maximum current control signal; a comparison module, receiving the maximum current control signal and combining the maximum current detection signal to output a drive shutdown control signal; a trigger module, receiving a drive start control signal and a drive shutdown control signal to output a drive signal, and the drive signal is used to drive the switch tube to operate. It can achieve the effect of avoiding the occurrence of audio noise, and is simple, convenient and fast.

Description

Technical Field

[0001] The invention relates to a control circuit and method for suppressing audio noise, belonging to the technical field of switch power supply control. Background Art

[0002] With the continuous development of society, electronic products continue to appear in people's lives. However, not every electronic product is relatively perfect, and each has its own advantages and disadvantages. Among them, when the oscillation frequency of electronic and magnetic components is within the hearing range of the human ear, an audible audio signal will be generated. This phenomenon of audio noise is well known. For example, transformers with an operating frequency of 50Hz and 60Hz often generate audible noise.

[0003] Flyback switching power supply output power Where I is the average current flowing through the coil, L is the coil inductance, and f is the power switching frequency. From the formula for the output power of the flyback switching power supply, it can be seen that its power is mainly related to the current and frequency. When the power required by the load increases, the output power is increased by adjusting the switching power supply chip to increase the current or increase the frequency; similarly, when the power required by the load decreases, the output power is reduced by adjusting the switching power supply chip to reduce the current or reduce the frequency, thereby ensuring the balance of the system.

[0004] In a quasi-resonant flyback switching power supply, the power switching frequency is also affected by the resonant signal. To reduce the switching loss of the switch tube, the power supply is only allowed to turn on the power switch at the bottom of the resonant signal. Therefore, in actual operation (non-heavy load / light load mode), if the switching frequency is not controlled, the frequency change will be discontinuous. Once it enters the audio range, audio noise will appear in the power system. Summary of the invention

[0005] The object of the present invention is to provide a control circuit and method for suppressing audio noise, which can prevent the occurrence of discontinuous changes in the switching frequency of a switching power supply, thereby achieving the effect of avoiding the occurrence of audio noise, and is simple, convenient and fast.

[0006] To achieve the above object, the present invention provides the following technical solution: a control circuit for suppressing audio noise, arranged in a quasi-resonant flyback switching power supply, the control circuit comprising:

[0007] an amplification module, receiving a signal proportional to the output voltage and a reference voltage to output a first amplified signal;

[0008] a compensation module, receiving the first amplified signal and performing compensation processing on the first amplified signal to output a second amplified signal;

[0009] A frequency control module, receiving the second amplified signal and outputting a minimum period driving signal;

[0010] A detection module, used for detecting the valley of the resonance signal and outputting a valley detection output signal;

[0011] A logic and gate control module receives the minimum period drive signal and the valley detection output signal, and outputs a drive start control signal;

[0012] A peak current control module receives the first amplified signal and outputs a maximum current control signal;

[0013] A comparison module receives the maximum current control signal and combines the maximum current detection signal to output a drive shutdown control signal;

[0014] The trigger module receives the driving on control signal and the driving off control signal to output a driving signal, wherein the driving signal is used to drive the switch tube to operate.

[0015] Furthermore, the amplification module comprises an error amplifier, a reverse input terminal of the error amplifier is connected to a signal proportional to the output voltage, and a forward input terminal of the error amplifier is connected to a reference voltage.

[0016] Furthermore, the comparison module includes a comparator, a reverse input terminal of the comparator is connected to the maximum current control signal, and a forward input terminal of the comparator is connected to the maximum current detection signal.

[0017] Further, the trigger module includes an RS trigger, a set end of the RS trigger is connected to the drive-on control signal, and a reset end of the RS trigger is connected to the drive-off control signal.

[0018] The present invention also provides a control method for suppressing audio noise, the control method adopts the control circuit for suppressing audio noise as described above, and the method comprises the following steps:

[0019] Obtaining a first amplified signal and a maximum current detection signal;

[0020] Obtaining a second amplified signal and a maximum current control signal according to the first amplified signal;

[0021] Obtaining a minimum period driving signal according to the second amplified signal;

[0022] detecting a valley of the resonance signal to obtain a valley detection output signal;

[0023] Obtaining a drive start control signal according to the minimum period drive signal and the valley detection output signal;

[0024] Obtaining a drive shutdown control signal according to the maximum current control signal and the maximum current detection signal;

[0025] A driving signal is obtained according to the driving on control signal and the driving off control signal, and the switching tube is driven to operate by the driving signal.

[0026] Further, obtaining a second amplified signal according to the first amplified signal includes:

[0027] The first amplified signal is compensated by the compensation module to obtain the second amplified signal;

[0028] The compensation module includes a subtraction module and an addition module. When the output voltage decreases and the first amplified signal increases, the first amplified signal is processed by the subtraction module to obtain the second amplified signal; when the output voltage increases and the first amplified signal decreases, the first amplified signal is processed by the addition module to obtain the second amplified signal.

[0029] Furthermore, the maximum current control signal changes with the change of the first amplified signal.

[0030] Further, obtaining the first amplified signal includes:

[0031] The amplification module includes an error amplifier, a reverse input terminal of the error amplifier is connected to a signal proportional to the output voltage, a forward input terminal of the error amplifier is connected to a reference voltage, and an output terminal of the error amplifier outputs an amplified voltage value to obtain a first amplified signal.

[0032] The beneficial effects of the present invention are as follows: by providing a compensation circuit, the compensation circuit processes the first amplified signal to obtain the second amplified signal, so that the switching frequency of the final output changes continuously, thereby preventing the power supply switching frequency from entering the audio range; the present invention has a simple structure and is convenient and fast.

[0033] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a waveform diagram of a driving signal DRV of a switch tube of a switching power supply in the prior art.

[0035] Figure 2 It is a structural block diagram of the control circuit for suppressing audio noise of the present invention.

[0036] Figure 3 It is a waveform diagram of the audio noise suppression control circuit of the present invention. DETAILED DESCRIPTION

[0037] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0038] See also Figure 1 , the drive signal DRV waveform of the switch tube in the switching power supply in the prior art, where VS is the voltage waveform of the auxiliary coil after voltage division. When the switch is disconnected and there is current on the coil, the VS signal is a signal proportional to the output voltage; when the switch is disconnected and the current on the coil is zero, the VS signal is a signal proportional to the resonant voltage. TMIN is the switching frequency control signal. During the time when TMIN=1, the drive signal cannot be turned on for the second time. Only when TMIN=0 and VS reaches the bottom, the drive signal can be turned on again. Therefore, the longer TMIN=1 is maintained, the lower the switching frequency of the switching power supply; otherwise, the higher the switching frequency.

[0039] In a switching power supply that controls output power simultaneously with current and frequency, when the load power increases slightly, the system will adjust and shorten the TMIN=1 time to increase the switching frequency. Due to the limitation of valley detection, when the maintenance time of TMIN=1 is reduced from the Nth resonance valley to the N-1th resonance valley, the difference between the two system switching cycles will be one resonance cycle, resulting in the switching frequency of the entire switching power supply being reduced to the audio range. Figure 1 As shown in the figure, in the first switching cycle, TMIN=1 is maintained after the second resonance valley, so the drive signal of the switch tube is always turned on at the third resonance valley; in the second switching cycle, TMIN=1 is maintained before the second resonance valley, and the drive signal of the switch tube in this cycle is turned on at the second resonance valley, so T2 is one resonance cycle smaller than T1. When the load power decreases slightly, the above-mentioned discontinuous switching frequency change will also occur. Once it enters the audio range, the switching power supply will have audio noise.

[0040] See also Figure 2A control circuit for suppressing audio noise in a preferred embodiment of the present invention is arranged in a quasi-resonant flyback switching power supply, and the control circuit includes: an amplification module connected to a signal proportional to an output voltage and a reference voltage to output a first amplified signal, a compensation module receiving the first amplified signal and performing compensation processing on the first amplified signal to output a second amplified signal, a frequency control module receiving the second amplified signal and outputting a minimum period drive signal, a detection module for detecting the bottom of the resonance signal and outputting a bottom detection output signal, a logic and gate control module for receiving the minimum period drive signal and the bottom detection output signal and outputting a drive start control signal, a peak current control module receiving the first amplified signal and outputting a maximum current control signal, a comparison module for receiving the maximum current control signal and combining the maximum current detection signal to output a drive shutdown control signal, and a drive module receiving the drive start control signal and the drive shutdown control signal to output a drive signal, wherein the drive signal is used to drive the switch tube to operate. In this embodiment, the amplification module includes an error amplifier, the inverting input terminal of the error amplifier is connected to a signal proportional to the output voltage, the positive input terminal of the error amplifier is connected to a reference voltage, and the output terminal of the error amplifier outputs an amplified voltage value to output a first amplified signal. The auxiliary coil voltage after voltage division is VS, the reference voltage is Vref1, and the first amplified signal is eaout1.

[0041] The comparison module includes a comparator, the inverting input terminal of the comparator is connected to the maximum current control signal VCS, and the positive input terminal of the comparator is connected to the maximum current detection signal CS. The trigger module includes an RS trigger, the set terminal (S terminal) of the RS trigger is connected to the drive start control signal Son, and the reset terminal (R terminal) of the RS trigger is connected to the drive shutdown control signal Soff.

[0042] The peak current control module is a circuit for controlling the peak current flowing through the coil, the frequency control module is a circuit for controlling the switching frequency, and the detection module is a detection circuit for detecting the valley of the resonant signal. Of course, in other embodiments, the peak current control module, frequency control module and detection module may also be other, depending on the actual situation, and are not specifically limited here. Among them, the minimum period drive signal is tmin, the maximum current control signal is Vcs, and the valley detection output signal is Svall.

[0043] The compensation module includes a subtraction module and an addition module. When the output voltage decreases and the first amplified signal increases, the first amplified signal is processed by the subtraction module to obtain the second amplified signal; when the output voltage increases and the first amplified signal decreases, 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 eaout2. When the load power increases slightly, the output voltage decreases, VS decreases slightly, and the first amplified signal increases. eaout1 is obtained by the subtraction circuit to obtain eaout2, and eaout2=eaout1-Vcomp1. At this time, the maximum current control signal Vcs flowing through the coil can be obtained from eaout1, and the minimum period control signal tmin can be obtained from eaout2. Finally, the driving signal DRV of the final switch tube is obtained by the judgment of the valley detection output circuit.

[0044] When the load power decreases slightly, the output voltage rises, VS rises slightly, and the first amplified signal decreases, eaout1 is obtained through the addition circuit to obtain eaout2, and eaout2=eaout1+Vcomp2. At this time, the maximum current control signal Vcs flowing through the coil can be obtained from eaout1, and the minimum period control signal tmin can be obtained from eaout2. Finally, after the judgment of the valley detection output circuit, the final switch tube drive signal DRV is obtained.

[0045] like Figure 3 As shown, from the first cycle T1 to the second cycle T2, eaout2=eaout1-Vcomp1 is satisfied, from the second cycle T2 to the third cycle T3, eaout2=eaout1+Vcomp2 is satisfied, and from the third cycle T3 to the fourth cycle T4, eaout2=eaout1-Vcomp1 is satisfied. It can be found from the above changes that the change in output power mainly comes from the control of the peak current by eaout1. Combined with the judgment signal Svall of the valley detection output circuit, the power switching frequency changes more continuously.

[0046] Since the tmin signal of the control cycle is controlled by the compensated eaout2 signal, when the output voltage changes, the power chip first adjusts the output power by changing the size of Vcs, while the change of the cycle control signal tmin is relatively slow. Until the power required by the load changes significantly, tmin will change significantly, causing the switching frequency to change.

[0047] The present invention also provides a control method for suppressing audio noise, the control method adopts the control circuit for suppressing audio noise as described above, and the method comprises the following steps:

[0048] Obtaining a first amplified signal and a maximum current detection signal;

[0049] Obtaining a second amplified signal and a maximum current control signal according to the first amplified signal;

[0050] Obtaining a minimum period driving signal according to the second amplified signal;

[0051] detecting a valley of the resonance signal to obtain a valley detection output signal;

[0052] Obtaining a drive start control signal according to the minimum period drive signal and the valley detection output signal;

[0053] Obtaining a drive shutdown control signal according to the maximum current control signal and the maximum current detection signal;

[0054] A driving signal is obtained according to the driving on control signal and the driving off control signal, and the switching tube is driven to operate by the driving signal.

[0055] The step of obtaining a second amplified signal according to the first amplified signal comprises:

[0056] The first amplified signal is compensated by the compensation module to obtain the second amplified signal;

[0057] The compensation module includes a subtraction module and an addition module. When the output voltage decreases and the first amplified signal increases, the first amplified signal is processed by the subtraction module to obtain the second amplified signal; when the output voltage increases and the first amplified signal decreases, the first amplified signal is processed by the addition module to obtain the second amplified signal.

[0058] The obtaining of the first amplified signal comprises:

[0059] The amplification module includes an error amplifier, a reverse input terminal of the error amplifier is connected to a signal proportional to the output voltage, a forward input terminal of the error amplifier is connected to a reference voltage, and an output terminal of the error amplifier outputs an amplified voltage value to obtain a first amplified signal.

[0060] The maximum current control signal changes with the change of the first amplified signal. When the output voltage changes, the power chip first adjusts the output power by changing the size of the maximum current control signal, while the minimum period control signal changes more slowly.

[0061] In summary: by providing a compensation circuit, the compensation circuit processes the first amplified signal to obtain the second amplified signal, so that the change of the second amplified signal finally outputted is continuous, thereby avoiding the power switching frequency from entering the audio range; the present invention has a simple structure and is convenient and fast.

[0062] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0063] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A control circuit for suppressing audio noise, arranged in a quasi-resonant flyback switching power supply, characterized in that: The control circuit comprises: an amplification module, receiving a signal proportional to the output voltage and a reference voltage to output a first amplified signal; a compensation module, receiving the first amplified signal and performing compensation processing on the first amplified signal to output a second amplified signal; A frequency control module, receiving the second amplified signal and outputting a minimum period driving signal; A detection module, used for detecting the valley of the resonance signal and outputting a valley detection output signal; A logic and gate control module receives the minimum period drive signal and the valley detection output signal, and outputs a drive start control signal; A peak current control module receives the first amplified signal and outputs a maximum current control signal; A comparison module receives the maximum current control signal and combines the maximum current detection signal to output a drive shutdown control signal; The trigger module receives the driving on control signal and the driving off control signal to output a driving signal, wherein the driving signal is used to drive the switch tube to operate.

2. The control circuit for suppressing audio noise according to claim 1, characterized in that: The amplification module comprises an error amplifier, a signal proportional to the output voltage is connected to the inverting input terminal of the error amplifier, and a reference voltage is connected to the forward input terminal of the error amplifier.

3. The control circuit for suppressing audio noise according to claim 1, characterized in that: The comparison module includes a comparator, the inverting input terminal of the comparator is connected to the maximum current control signal, and the forward 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, characterized in that: The trigger module includes an RS trigger, a set end of the RS trigger is connected to the drive-on control signal, and a reset end of the RS trigger is connected to the drive-off control signal.

5. A control method for suppressing audio noise, characterized in that: The control method adopts the control circuit for suppressing audio noise according to any one of claims 1 to 4, and the method 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 of the resonance signal to obtain a valley detection output signal; Obtaining a drive start control signal according to the minimum period drive signal and the valley detection output signal; Obtaining a drive shutdown control signal according to the maximum current control signal and the maximum current detection signal; A driving signal is obtained according to the driving on control signal and the driving off control signal, and the switching tube is driven to operate by the driving signal.

6. The control method for suppressing audio noise according to claim 5, characterized in that: The step of obtaining a second amplified signal according to the first amplified signal comprises: The first amplified signal is compensated by the compensation module to obtain the second amplified signal; The compensation module includes a subtraction module and an addition module. When the output voltage decreases and the first amplified signal increases, the first amplified signal is processed by the subtraction module to obtain the second amplified signal; when the output voltage increases and the first amplified signal decreases, 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, characterized in that: The maximum current control signal changes with the change of the first amplified signal.

8. The control method for suppressing audio noise according to claim 5, characterized in that: The obtaining of the first amplified signal comprises: The amplification module includes an error amplifier, a reverse input terminal of the error amplifier is connected to a signal proportional to the output voltage, a forward input terminal of the error amplifier is connected to a reference voltage, and an output terminal of the error amplifier outputs an amplified voltage value to obtain a first amplified signal.

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