Audio equipment and control circuit thereof for automatically cutting off output when no signal exists

Abstract

The utility model relates to audio equipment and a control circuit thereof for automatically cutting off output when no signal exists, the control circuit for automatically cutting off output when no signal exists comprises a pre-stage control circuit and a switch unit connected in series between a power amplifier circuit and a loudspeaker; the pre-stage control circuit comprises a polar capacitor C20, a first operational amplifier, a first voltage stabilizing diode, a resistor R27, a diode D3, a triode Q4, a triode Q5, a resistor R31, a resistor R32, a resistor R34, a diode D6, a polar capacitor C21 and a second operational amplifier; the switch unit is configured to connect or disconnect the power amplifier circuit and the loudspeaker based on the received high and low level signals output by the second operational amplifier; when no signal exists, the connection between the power amplifier circuit and the loudspeaker is cut off, so that the loudspeaker is in a mute state, and noise is not generated when the audio equipment stops performance in a power-on state; and the cost is low, the design is simple, and the development period is shortened.

Description

Technical Field

[0001] The utility model relates to the technical field of audio equipment, in particular to an audio equipment and a control circuit for automatically cutting off the output when there is no signal. Background Art

[0002] Audio equipment mainly refers to the general term for audio input and output equipment, and there are many types of products it includes. Generally, it can be divided into the following categories:

[0003] Power amplifiers, speakers, multimedia consoles, digital mixers, audio sampling cards, synthesizers, mid-high frequency speakers, microphones, sound cards in PCs, headphones, etc.

[0004] Other peripheral audio equipment: professional microphone series, headphones, radio and public address systems, etc.

[0005] In the audio power amplifier circuit of audio equipment, due to the audio power amplifier circuit itself or other reasons, there will be background noise. The audio power amplifier circuit outputs the background noise to the speaker, and in the case of no audio signal input, the speaker will still emit a hissing current sound or other forms of noise.

[0006] Therefore, in this utility model patent application, the applicant has carefully studied an audio equipment and a control circuit for automatically cutting off the output when there is no signal to solve the above problems. Summary of the Utility Model

[0007] Aiming at the deficiencies of the above-mentioned prior art, the main purpose of the utility model is to provide an audio equipment and a control circuit for automatically cutting off the output when there is no signal, which can disconnect the connection between the power amplifier circuit and the speaker when there is no signal, and then make the speaker in a mute state, so that no noise will be generated when the audio equipment stops playing during the power-on state; nor is a single-chip microcomputer required, with low cost, simple design, and reduced development cycle.

[0008] To achieve the above purpose, the utility model adopts the following technical solutions:

[0009] A control circuit for automatically cutting off the output when there is no signal includes a pre-stage control circuit and a switch unit connected in series between the power amplifier circuit and the speaker;

[0010] The pre-stage control circuit includes a polar capacitor C20, a first operational amplifier, a first voltage stabilizing diode, a resistor R27, a diode D3, a triode Q4, a triode Q5, a resistor R31, a resistor R32, a resistor R34, a diode D6, a polar capacitor C21, and a second operational amplifier;

[0011] The positive pole of the polarized capacitor C20 is the signal detection terminal. The negative pole of the polarized capacitor C20 is connected to the negative input terminal of the first operational amplifier through the resistor R26. The positive and negative poles of the first voltage stabilizing diode are respectively connected to the negative and positive input terminals of the first operational amplifier, and the resistor R27 is connected in parallel with the first voltage stabilizing diode;

[0012] The positive input terminal of the first operational amplifier is grounded; the output terminal of the first operational amplifier is connected to the anode of the diode D3 through the resistor R28. The cathode of the diode D3 is connected to the base of the triode Q4. The base of the triode Q4 is grounded through the resistor R29, and the emitter of the triode Q4 is grounded through the resistor R30;

[0013] The resistors R31, R32 and R34 are connected in series in sequence. The collector of the triode Q4 is connected to the non - series node of the resistor R31. The series node of the resistors R31 and R32 is connected to the base of the triode Q5. The emitter of the triode Q5 is connected to the series node of the resistors R32 and R34. The series node of the resistors R32 and R34 is used to connect to the +12V voltage terminal,

[0014] The collector of the triode Q5 is connected to the positive input terminal of the second operational amplifier through the resistor R33. The negative input terminal of the second operational amplifier is connected to the non - series node of the resistor R34. The non - series node of the resistor R34 is connected to the anode of the diode D6. The cathode of the diode D6 and the negative pole of the polarized capacitor C21 are both grounded;

[0015] The positive input terminal of the second operational amplifier is grounded through the resistor R35. The positive pole of the polarized capacitor C21 is connected to the positive input terminal of the second operational amplifier. The output terminal of the second operational amplifier is connected to the switch unit;

[0016] The switch unit is configured to conduct or disconnect the connection between the power amplifier circuit and the speaker based on the high and low level signals received from the output of the second operational amplifier.

[0017] As a preferred solution, the switch unit includes a relay and a relay driving circuit for driving the relay. The relay includes a coil and a contact connected in series between the power amplifier circuit and the speaker. The two ends of the relay driving circuit are respectively connected to the coil of the relay and the output terminal of the second operational amplifier, and are used to provide or not provide the instantaneous suction voltage or the holding suction voltage for the coil of the relay, so as to control the contact of the relay to suck or not suck, and then conduct or disconnect the connection between the power amplifier circuit and the speaker.

[0018] As a preferred solution, the relay driving circuit includes a second voltage stabilizing diode, a resistor R304, a triode Q302 and a triode Q301;

[0019] The base of the triode Q302 is connected to the output terminal of the second operational amplifier through the resistor R304. The emitter of the triode Q302 is connected to the base of the triode Q301. The base of the triode Q301 is connected to the anode of the second zener diode. The cathode of the second zener diode is used to connect to the power amplifier circuit. The collector of the triode Q301 is connected to the coil of the relay. The collectors of the triode Q302 and the emitter of the triode Q301 are both grounded.

[0020] An audio device includes a control circuit, and the control circuit is the control circuit for automatically cutting off the output when there is no signal.

[0021] As a preferred solution, it further includes a pre-stage processing circuit, a signal input terminal, a power amplifier circuit, and a speaker;

[0022] The pre-stage processing circuit includes a filter buffer circuit and a pre-stage amplifier circuit. The signal input terminal is connected to the input terminal of the filter buffer circuit. The output terminal of the filter buffer circuit is respectively connected to the input terminal of the pre-stage amplifier circuit and the signal detection terminal of the pre-stage control circuit. The output terminal of the pre-stage amplifier circuit is connected to the power amplifier circuit, and the power amplifier circuit is connected to the speaker through a switching unit.

[0023] As a preferred solution, the filter buffer circuit includes a capacitor C01, a capacitor C03, a capacitor C02, a capacitor C04, a resistor R02, a resistor R05, a capacitor C05, and a comparator;

[0024] The signal input terminal is a signal input interface. The pin 2 of the signal input interface is grounded. The capacitor C01 and the resistor R02 are in series. The non-series node of the capacitor C01 is connected to the pin 3 of the signal input interface. The series node of the capacitor C01 and the resistor R02 is grounded through the resistor R01. The capacitor C02 is in parallel with the resistor R01. The non-series node of the resistor R02 is connected to the positive input terminal of the comparator. The positive input terminal of the comparator is also grounded through the resistor R03;

[0025] The capacitor C03 and the resistor R05 are in series. The non-series node of the capacitor C03 is connected to the pin 1 of the signal input interface. The series node of the capacitor C03 and the resistor R05 is grounded through the resistor R04. The capacitor C04 is in parallel with the resistor R01. The non-series node of the resistor R05 is connected to the negative input terminal of the comparator. The output terminal of the comparator is connected to its negative input terminal through the resistor R06. The capacitor C05 is in parallel with the resistor R06. The output terminal of the comparator is respectively connected to the input terminal of the pre-stage amplifier circuit and the signal detection terminal of the pre-stage control circuit.

[0026] Compared with the prior art, the utility model has obvious advantages and beneficial effects. Specifically, it mainly combines a pre-stage control circuit and a switch unit, which can disconnect the connection between the power amplifier circuit and the speaker when there is no signal, thereby making the speaker in a mute state, and further preventing noise from being generated when the audio device stops playing during the power-on state. In particular, the pre-stage control circuit uses pure electronic components without a single-chip microcomputer, with low cost, simple design, and reduced development cycle.

[0027] To more clearly elaborate on the structural features and functions of the utility model, the following will be a detailed description thereof in combination with the attached drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic block diagram of the general control principle of the audio device according to an embodiment of the utility model.

[0029] Figure 2 is the first circuit schematic diagram of an embodiment of the utility model (mainly showing the pre-stage control circuit).

[0030] Figure 3 is the second circuit schematic diagram of an embodiment of the utility model (mainly showing the filter buffer circuit).

[0031] Figure 4 is the third circuit schematic diagram of an embodiment of the utility model (mainly showing the pre-stage amplification circuit).

[0032] Figure 5 is the fourth circuit schematic diagram of an embodiment of the utility model (mainly showing the power amplifier circuit).

[0033] Figure 6 is the fifth circuit schematic diagram of an embodiment of the utility model (mainly showing the switch unit).

[0034] Figure 7 is the sixth circuit schematic diagram of an embodiment of the utility model (mainly showing the power supply circuit).

[0035] DESCRIPTION OF THE REFERENCE NUMERALS IN THE DRAWINGS:

[0036] 11. Pre-stage control circuit

[0037] 12. Switch unit

[0038] 20. Signal input terminal

[0039] 30. Pre-stage processing circuit

[0040] 31. Filter buffer circuit 32. Pre-stage amplification circuit

[0041] 40. Power amplifier circuit

[0042] 50. Speaker. Detailed implementation manners

[0043] The present utility model will be further described below in conjunction with the accompanying drawings and specific implementation manners.

[0044] As Figures 1 to 7 shown, a control circuit for automatically cutting off the output when there is no signal includes a pre-stage control circuit 11 and a switch unit 12 connected in series between a power amplifier circuit 40 and a speaker 50;

[0045] The pre-stage control circuit 11 includes a polar capacitor C20, a first operational amplifier, a first zener diode, a resistor R27, a diode D3, a triode Q4, a triode Q5, a resistor R31, a resistor R32, a resistor R34, a diode D6, a polar capacitor C21 and a second operational amplifier;

[0046] The positive electrode of the polar capacitor C20 is a signal detection terminal, the negative electrode of the polar capacitor C20 is connected to the negative input terminal of the first operational amplifier through a resistor R26, the positive and negative electrodes of the first zener diode are respectively connected to the negative and positive input terminals of the first operational amplifier, and the resistor R27 is connected in parallel with the first zener diode;

[0047] The positive input terminal of the first operational amplifier is grounded; the output terminal of the first operational amplifier is connected to the anode of the diode D3 through a resistor R28, the cathode of the diode D3 is connected to the base of the triode Q4, the base of the triode Q4 is grounded through a resistor R29, and the emitter of the triode Q4 is grounded through a resistor R30;

[0048] The resistor R31, the resistor R32 and the resistor R34 are connected in series in sequence, the collector of the triode Q4 is connected to the non-series node of the resistor R31, the series node of the resistor R31 and the resistor R32 is connected to the base of the triode Q5, the emitter of the triode Q5 is connected to the series node of the resistor R32 and the resistor R34, and the series node of the resistor R32 and the resistor R34 is used to connect to the +12V voltage terminal,

[0049] The collector of the triode Q5 is connected to the positive input terminal of the second operational amplifier through a resistor R33, the negative input terminal of the second operational amplifier is connected to the non-series node of the resistor R34, the non-series node of the resistor R34 is connected to the anode of the diode D6, and the cathode of the diode D6 and the negative electrode of the polar capacitor C21 are both grounded;

[0050] The positive input terminal of the second operational amplifier is grounded through a resistor R35, the positive electrode of the polar capacitor C21 is connected to the positive input terminal of the second operational amplifier, and the output terminal of the second operational amplifier is connected to the switch unit 12;

[0051] The switch unit 12 is configured to conduct or disconnect the connection between the power amplifier circuit 40 and the speaker 50 based on the high and low level signals received from the output of the second operational amplifier.

[0052] In this embodiment, the switch unit 12 includes a diode D304, a relay, and a relay driving circuit for driving the relay. The relay includes a coil and a contact connected in series between the power amplifier circuit 40 and the speaker 50. The two ends of the relay driving circuit are respectively connected to the coil of the relay and the output terminal of the second operational amplifier, and are used to provide or not provide the instantaneous suction voltage or the holding suction voltage for the coil of the relay, so as to control the contact of the relay to be attracted or not attracted, and then conduct or disconnect the connection between the power amplifier circuit 40 and the speaker 50.

[0053] One end of the coil of the relay is connected to the relay driving circuit, and the other end of the coil of the relay is used to connect to the 13V voltage terminal. The positive and negative electrodes of the diode D304 are connected to one end and the other end of the coil of the relay.

[0054] In this embodiment, the relay driving circuit includes a second zener diode, a resistor R304, a triode Q302, and a triode Q301;

[0055] The base of the triode Q302 is connected to the output terminal of the second operational amplifier through the resistor R304. The emitter of the triode Q302 is connected to the base of the triode Q301. The base of the triode Q301 is connected to the anode of the second zener diode. The cathode of the second zener diode is used to connect to the power amplifier circuit 40. The collector of the triode Q301 is connected to the coil of the relay. The collectors of the triode Q302 and the emitter of the triode Q301 are both grounded.

[0056] Next, the working principle will be briefly described:

[0057] When a signal is received at the signal detection terminal, the signal is input to the first operational amplifier through the polarizing capacitor C20. After being amplified by the first operational amplifier, it is rectified by the diode D3 and a direct current is output. The triode Q4 is first turned on. The collector of the triode Q4 is at a low level. Then the triode Q5 is turned on. The negative input terminal of the second operational amplifier is 0.7V. The positive input terminal of the second operational amplifier is 12V. Then the output terminal of the second operational amplifier outputs a high level, causing the contact of the relay of the switch unit 12 to be attracted and then conducting the connection between the power amplifier circuit 40 and the speaker 50, so as to realize the normal operation of the speaker 50;

[0058] Accordingly, when no signal is received at the signal detection terminal, the triode Q4 is cut off, and then the triode Q5 is also cut off. The polarized capacitor C21 continuously discharges the resistor R35. When the voltage at the positive input terminal of the second operational amplifier is lower than 0.7V, the output terminal of the second operational amplifier outputs a low level, causing the contact of the relay of the switch unit 12 not to be attracted and then disconnecting the connection between the power amplifier circuit 40 and the speaker 50, so that the speaker 50 cannot work, that is, it cannot emit sound;

[0059] It should be noted that the calculation formula for the discharge time is: T = RC = 270s. In this embodiment, it is generally considered that it takes 5T time to basically complete the discharge, that is, 5 * 270 = 1350s.

[0060] A control method for automatically cutting off the output when there is no signal, which is based on the control circuit for automatically cutting off the output when there is no signal. The control method includes the following steps:

[0061] When a signal is received at the signal detection terminal, the output terminal of the second operational amplifier outputs a high level to the switch unit 12. After receiving the high level, the switch unit 12 conducts the connection between the power amplifier circuit 40 and the speaker 50, that is, the speaker 50 can emit sound;

[0062] When no signal is received at the signal detection terminal, the output terminal of the second operational amplifier outputs a low level to the switch unit 12. After receiving the low level, the switch unit 12 disconnects the connection between the power amplifier circuit 40 and the speaker 50, that is, the speaker 50 cannot emit sound.

[0063] An audio device includes a control circuit, a pre-stage processing circuit 30, a signal input terminal 20, a power amplifier circuit 40, a speaker 50, and a power supply circuit 60 for power supply. The control circuit is the control circuit for automatically cutting off the output when there is no signal. In this embodiment, the power amplifier circuit 40 is a dual-power OCL power amplifier circuit.

[0064] The pre-stage processing circuit 30 includes a filter buffer circuit 31 and a pre-stage amplifier circuit 32. The signal input terminal 20 is connected to the input terminal of the filter buffer circuit 31. The output terminal of the filter buffer circuit 31 is respectively connected to the input terminal of the pre-stage amplifier circuit 32 and the signal detection terminal of the pre-stage control circuit 11. The output terminal of the pre-stage amplifier circuit 32 is connected to the power amplifier circuit 40. The power amplifier circuit 40 is connected to the speaker 50 through the switch unit 12.

[0065] In this embodiment, the filter buffer circuit 31 includes a capacitor C01, a capacitor C03, a capacitor C02, a capacitor C04, a resistor R02, a resistor R05, a capacitor C05, and a comparator;

[0066] The signal input terminal 20 is a signal input interface. The pin 2 of the signal input interface is grounded. The capacitor C01 and the resistor R02 are connected in series. The non - series node of the capacitor C01 is connected to the pin 3 of the signal input interface. The series node of the capacitor C01 and the resistor R02 is grounded through the resistor R01. The capacitor C02 is connected in parallel with the resistor R01. The non - series node of the resistor R02 is connected to the positive input terminal of the comparator. The positive input terminal of the comparator is also grounded through the resistor R03;

[0067] The capacitor C03 and the resistor R05 are connected in series. The non - series node of the capacitor C03 is connected to the pin 1 of the signal input interface. The series node of the capacitor C03 and the resistor R05 is grounded through the resistor R04. The capacitor C04 is connected in parallel with the resistor R01. The non - series node of the resistor R05 is connected to the negative input terminal of the comparator. The output terminal of the comparator is connected to its negative input terminal through the resistor R06. The capacitor C05 is connected in parallel with the resistor R06. The output terminal of the comparator is respectively connected to the input terminal of the pre - amplifier circuit 32 and the signal detection terminal of the pre - control circuit 11.

[0068] The design key point of the present utility model lies in the cooperation between the pre - control circuit and the switch unit, which can disconnect the connection between the power amplifier circuit and the speaker when there is no signal, thereby making the speaker in a mute state, and further enabling the audio device not to generate noise when stopping playing during the power - on state; in particular, the pre - control circuit adopts pure electronic devices without a single - chip microcomputer, with low cost, simple design, and reduced development cycle.

[0069] The above - mentioned is only a preferred embodiment of the present utility model, and does not impose any limitation on the technical scope of the present utility model. Therefore, any minor modification, equivalent change and modification made to the above - mentioned embodiment according to the technical essence of the present utility model still fall within the scope of the technical solution of the present utility model.

Claims

1. A control circuit for automatically cutting off output when there is no signal, characterized in that: It includes a pre-stage control circuit and a switch unit connected in series between the power amplifier circuit and the speaker; The front-stage control circuit includes a polarity capacitor C20, a first operational amplifier, a first voltage-stabilizing diode, a resistor R27, a diode D3, a transistor Q4, a transistor Q5, a resistor R31, a resistor R32, a resistor R34, a diode D6, a polarity capacitor C21 and a second operational amplifier; The positive electrode of the polarity capacitor C20 is the signal detection terminal, the negative electrode of the polarity capacitor C20 is connected to the negative input terminal of the first operational amplifier through the resistor R26, the positive and negative electrodes of the first voltage zener diode are respectively connected to the negative and positive input terminals of the first operational amplifier, and the resistor R27 is connected in parallel with the first voltage zener diode; The positive input terminal of the first operational amplifier is grounded; the output terminal of the first operational amplifier is connected to the anode of the diode D3 through the resistor R28, the cathode of the diode D3 is connected to the base of the transistor Q4, the base of the transistor Q4 is grounded through the resistor R29, and the emitter of the transistor Q4 is grounded through the resistor R30; The resistors R31, R32 and R34 are connected in series in sequence. The collector of the transistor Q4 is connected to the non-series node of the resistor R31. The series node of the resistors R31 and R32 is connected to the base of the transistor Q5. The emitter of the transistor Q5 is connected to the series node of the resistors R32 and R34. The series node of the resistors R32 and R34 is used to connect to the +12V voltage terminal. The collector of transistor Q5 is connected to the positive input terminal of the second operational amplifier through resistor R33, the negative input terminal of the second operational amplifier is connected to the non-series node of resistor R34, the non-series node of resistor R34 is connected to the anode of diode D6, the cathode of diode D6 and the negative electrode of polar capacitor C21 are both grounded; The positive input terminal of the second operational amplifier is grounded through a resistor R35, the positive electrode of the polarity capacitor C21 is connected to the positive input terminal of the second operational amplifier, and the output terminal of the second operational amplifier is connected to the switch unit; The switch unit is configured to switch on or off the connection between the power amplifier circuit and the speaker based on the high or low level signal received from the second operational amplifier output.

2. The control circuit for automatically cutting off output when there is no signal according to claim 1, characterized in that: The switch unit includes a relay and a relay driving circuit for driving the relay. The relay includes a coil and contacts connected in series between the power amplifier circuit and the speaker. The two ends of the relay driving circuit are respectively connected to the coil of the relay and the output end of the second operational amplifier, and are used to provide or not provide the coil of the relay with an instantaneous voltage for closing or a holding voltage for closing, so as to control the closing or not closing of the contacts of the relay and then to conduct or disconnect the connection between the power amplifier circuit and the speaker.

3. The control circuit for automatically cutting off output when there is no signal according to claim 2, characterized in that: The relay driving circuit includes a second voltage stabilizing diode, a resistor R304, a transistor Q302 and a transistor Q301; The base of the transistor Q302 is connected to the output end of the second operational amplifier through the resistor R304, the emitter of the transistor Q302 is connected to the base of the transistor Q301, the base of the transistor Q301 is connected to the anode of the second voltage-stabilizing diode, the cathode of the second voltage-stabilizing diode is used to connect to the power amplifier circuit, the collector of the transistor Q301 is connected to the coil of the relay, and the collector of the transistor Q302 and the emitter of the transistor Q301 are both grounded.

4. An audio device, characterized in that: A control circuit is included, and the control circuit is the control circuit for automatically cutting off output when there is no signal as described in any one of claims 1 to 3.

5. The audio device according to claim 4, characterized in that: It also includes a pre-stage processing circuit, a signal input terminal, a power amplifier circuit and a speaker; The pre-stage processing circuit includes a filter buffer circuit and a pre-stage amplifier circuit. The signal input end is connected to the input end of the filter buffer circuit. The output end of the filter buffer circuit is respectively connected to the input end of the pre-stage amplifier circuit and the signal detection end of the pre-stage control circuit. The output end of the pre-stage amplifier circuit is connected to the power amplifier circuit, and the power amplifier circuit is connected to the speaker through a switch unit.

6. The audio device according to claim 5, characterized in that: The filter buffer circuit includes a capacitor C01, a capacitor C03, a capacitor C02, a capacitor C04, a resistor R02, a resistor R05, a capacitor C05 and a comparator; The signal input end is a signal input interface, pin 2 of the signal input interface is grounded, capacitor C01 and resistor R02 are connected in series, a non-series node of capacitor C01 is connected to pin 3 of the signal input interface, a series node of capacitor C01 and resistor R02 is grounded through resistor R01, capacitor C02 is connected in parallel with resistor R01, a non-series node of resistor R02 is connected to a positive input end of a comparator, and the positive input end of the comparator is also grounded through resistor R03; Capacitor C03 and resistor R05 are connected in series, the non-series node of capacitor C03 is connected to pin 1 of the signal input interface, the series node of capacitor C03 and resistor R05 is grounded through resistor R04, capacitor C04 is connected in parallel with resistor R01, the non-series node of resistor R05 is connected to the negative input terminal of the comparator, the output terminal of the comparator is connected to its negative input terminal through resistor R06, capacitor C05 is connected in parallel with resistor R06, and the output terminal of the comparator is respectively connected to the input terminal of the pre-stage amplifier circuit and the signal detection terminal of the pre-stage control circuit.

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