Automatic power on / off circuit for power amplifier

Abstract

The present invention discloses an automatic power on / off circuit for a power amplifier, and relates to the field of vehicle-mounted power amplifier control. The input end of the automatic power on / off circuit for the power amplifier is connected to the audio source input of the power amplifier, and the output end is connected to the state selection pin of the power amplifier, so as to control the difference between the state selection pin and the positive power supply of the power amplifier, and then control the working state of the power amplifier, and the state includes PLAY state, ST-BY state and MUTE state; when there is an audio signal, the automatic power on / off circuit controls the power amplifier to switch from ST-BY state to MUTE state, and after time T, from MUTE state to PLAY state; when there is no audio signal, the automatic power on / off circuit controls the power amplifier to switch from PLAY state to ST-BY state. The automatic power on / off circuit of the present invention realizes that the power amplifier automatically turns on when there is an audio source input, and automatically turns off when there is no audio source input, and at the same time improves the startup noise, and ensures that the power amplifier is in a low power consumption state when it is turned off, thereby avoiding unnecessary loss of the power supply on the vehicle.

Description

Technical Field

[0001] The present invention relates to the field of vehicle-mounted power amplifier control, and in particular to an automatic power on / off circuit of a power amplifier. Background Art

[0002] With the rapid development of the automobile market, the application of in-vehicle multimedia entertainment terminals in buses is becoming more and more widespread. At the same time, in order to meet the requirements of separate audio sources for passengers and drivers, the driver is often equipped with an independent external amplifier. As for the control of the external amplifier, due to the long-distance transmission problem, it is impossible to use the CPU's I / O port to control it. Generally, a mechanical control switch is added to the instrument panel to control the switch of the external amplifier. However, sometimes due to the limitations of the in-vehicle installation environment, there are not enough switch installation positions reserved, and there are already many mechanical buttons on the bus itself. Adding mechanical buttons will bring additional operation troubles to the driver. Another problem is that when designing an external amplifier, we often use a Class AB high-power amplifier chip, and some amplifier ICs have only one state control pin. By adjusting the voltage difference between the state control pin and the power supply, the amplifier can achieve three states: ST-BY, MUTE, and PLAY. ST-BY is the standby state, in which the amplifier output is turned off and has a small holding current. MUTE is the mute state, in which the amplifier output is turned off and the noise is minimal. PLAY is the play state, in which the output is turned on to drive the speaker to sound. Figure 1 The figure shows the amplifier circuit of the TDA7265 dual-channel power amplifier, whose control pin is MUTE / ST-BY (mute / standby). By combining switch SW1 and switch SW2, the voltage difference between the pin MUTE / ST-BY and the power supply +Vs of the amplifier is adjusted, that is, the two switches can be used to control the amplifier to enter the MUTE or ST-BY state. When the amplifier switches from the ST-BY or MUTE state to the PLAY state, it can output audio, which can be considered as the amplifier is turned on; when the amplifier switches from the PLAY state to the ST-BY or MUTE state, there is no audio output, which can be considered as the amplifier is turned off.

[0003] Sometimes, for the convenience of design, a switch is often used to control the power amplifier to work in two states: ST-BY and PLAY, or in two states: MUTE and PLAY. In the former case, it is more difficult to deal with the "pop" noise when the power is turned on, and in the latter case, the static current of the power amplifier in the MUTE state will be relatively large. Therefore, when designing an amplifier with only one state control pin, it is best to make the device work in the MUTE state at the moment of power-on; when the power amplifier is turned off, it is best to make the power amplifier in the ST-BY state. Summary of the invention

[0004] The purpose of the present invention is to provide an automatic power on / off circuit for a power amplifier, which performs automatic power on / off control of the power amplifier without using external switch signals such as buttons or system IO control, improves startup noise, and ensures that the power amplifier is in a low power consumption state when not working, thereby avoiding unnecessary loss of vehicle power supply.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An automatic power on / off circuit for a power amplifier, the power amplifier having a state selection pin, and the state of the power amplifier is controlled by adjusting the difference between the state selection pin and the positive power supply of the power amplifier, the state including the PLAY state, the ST-BY state and the MUTE state;

[0007] The input end of the automatic power on / off circuit is electrically connected to an audio input end of the power amplifier, and the output end of the automatic power on / off circuit is electrically connected to a state selection pin of the power amplifier.

[0008] When there is an audio signal, the automatic on / off circuit controls the power amplifier to switch from the ST-BY state to the MUTE state, and after a time T, switch from the MUTE state to the PLAY state;

[0009] When there is no audio signal, the automatic on / off circuit controls the power amplifier to switch from the PLAY state to the ST-BY state.

[0010] Furthermore, the absolute values ​​of the differences in each state are, from small to large, ST-BY state, MUTE state and PLAY state.

[0011] Furthermore, the automatic on / off circuit includes an audio amplification and shaping circuit and a state gating circuit;

[0012] The audio amplification and shaping circuit is used to input an audio signal and smoothly output a first switch signal. When the first switch signal is a low-level signal, it indicates that there is audio input, and when the first switch signal is a high-level signal, it indicates that there is no audio input;

[0013] The state gating circuit includes a first control unit, a second control unit and a third control unit.

[0014] The second control unit receives the first switch signal and outputs a second switch signal in an inverted manner;

[0015] The third control unit receives the first switch signal and outputs a third switch signal in an inverted manner after a delay;

[0016] The first control unit comprises a voltage divider network, the voltage divider network comprises a pull-up resistor and a ground resistor connected in series, an intermediate node of the voltage divider network is connected to a state selection pin, connected to the positive power supply of the power amplifier through the pull-up resistor, and grounded through the ground resistor;

[0017] When the second switch signal is a low level signal, the intermediate node and the ground are disconnected;

[0018] When the second switch signal is a high level signal, the intermediate node is connected to the ground;

[0019] When the third switch signal changes from a low level signal to a high level signal, the grounding resistance decreases.

[0020] Further, the first control unit includes a first transistor, a fourth transistor, a fifteenth resistor, a sixteenth resistor, a second capacitor, and a second resistor, and the first transistor and the fourth transistor are NPN transistors;

[0021] The pull-up resistor is a second resistor; the grounding resistor includes a fifteenth resistor and a sixteenth resistor;

[0022] The collector of the first transistor is connected to the state selection pin, the collector of the first transistor is connected to the positive power supply of the power amplifier through a second capacitor and a second resistor connected in parallel, the emitter of the first transistor is grounded through a sixteenth resistor, and the base of the first transistor is connected to the output end of the second control unit;

[0023] The collector of the fourth transistor is connected to the emitter of the first transistor through the fifteenth resistor, the emitter of the fourth transistor is grounded, and the base of the fourth transistor is connected to the output end of the third control unit.

[0024] Further, the second control unit includes a second transistor, a first voltage regulator, a fourth resistor, a fifth resistor and a ninth resistor, and the second transistor is an NPN transistor;

[0025] The input terminal of the second control unit is connected to the base of the second transistor;

[0026] The output terminal of the second control unit is connected to the collector of the second triode;

[0027] The collector of the second triode is connected to the first node through the fifth resistor and to the ground through the ninth resistor, the first node is grounded through the first voltage regulator and connected to the positive electrode of the signal power supply through the fourth resistor, and the emitter of the second triode is grounded;

[0028] The third control unit includes a fifth transistor, a seventeenth resistor, a twenty-second resistor, a nineteenth resistor and a tenth capacitor, and the fifth transistor is an NPN transistor;

[0029] The input end of the third control unit is connected to the base of the fifth transistor;

[0030] The output end of the third control unit is connected to the collector of the fifth transistor through the nineteenth resistor;

[0031] The collector of the fifth transistor is connected to the positive electrode of the signal power supply through the seventeenth resistor and is grounded through the twenty-second resistor and the tenth capacitor connected in parallel. The emitter of the fifth transistor is grounded.

[0032] Further, the audio amplification and shaping circuit includes an audio amplification unit, a third triode, a second diode, a seventh resistor, a fourteenth resistor and a seventh capacitor;

[0033] The output end of the audio amplification and shaping circuit is connected to the input end of the audio amplification unit;

[0034] The output end of the audio amplification and shaping circuit is connected to the collector of the third triode;

[0035] The audio amplification unit amplifies the audio signal and inputs it into the base of the third transistor after being DC-isolated by a capacitor;

[0036] The collector of the third triode is connected to the positive electrode of the signal power supply through the seventh resistor, and is grounded through the seventh capacitor and the fourteenth resistor connected in parallel;

[0037] The cathode of the second diode is connected to the base of the third transistor, and the anode of the second diode is grounded.

[0038] Furthermore, the audio amplification unit is a second-order low-pass audio amplifier circuit.

[0039] The present invention achieves the following technical effects:

[0040] The present invention realizes automatic on / off control of the power amplifier through the input of the power amplifier sound source. The power amplifier automatically turns on when there is sound source input, and automatically turns off when there is no sound source input. At the same time, the startup noise is improved, and it is ensured that the power amplifier is in a low power consumption state when it is turned off, thereby avoiding unnecessary loss of power supply on the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the schematic diagram of the power amplifier control;

[0042] Figure 2 It is a principle block diagram of the automatic power on / off control of the power amplifier of the present invention;

[0043] Figure 3 It is a circuit diagram of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0044] To further illustrate the various embodiments, the present invention provides drawings. These drawings are part of the disclosure of the present invention, which are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, a person of ordinary skill in the art should be able to understand other possible implementations and advantages of the present invention. The components in the figures are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0045] The present invention will now be further described with reference to the accompanying drawings and specific implementation methods.

[0046] like Figure 2 As shown, the present invention discloses an automatic power on / off circuit of a power amplifier, comprising an audio amplification and shaping circuit 40 and a state selection control circuit 30, wherein the input end of the automatic power on / off circuit is connected to one of the left and right channels AUXL / AUXR of the power amplifier 20 (i.e., connected to one of the left and right channels AUXL / AUXR of the sound source 10), and the output end of the automatic power on / off circuit is electrically connected to the state selection pin of the power amplifier 20, and the difference between the state selection pin 201 and the positive pole of the power supply of the power amplifier is adjusted to control the state of the power amplifier 20, wherein the state includes a PLAY state, a ST-BY state and a MUTE state.

[0047] When there is an audio signal, the automatic on / off circuit controls the power amplifier 20 to switch from the ST-BY state to the MUTE state, and after a time T, from the MUTE state to the PLAY state;

[0048] When there is no audio signal, the power amplifier automatic on / off circuit controls the power amplifier 20 to switch from the PLAY state to the ST-BY state.

[0049] Figure 3 The figure shows a preferred embodiment of the automatic power on / off circuit of the power amplifier of the present invention, which is specifically described as follows:

[0050] The audio amplification and shaping circuit 40 of the automatic on / off circuit includes an audio amplification unit and a shaping unit. The audio amplification unit includes an operational amplifier U1A, capacitors C4, C5, resistors R6, R10, R11, R12 and R13, wherein U1A is an audio operational amplifier. These resistors, capacitors and operational amplifier U1A form a second-order low-pass audio power amplifier circuit. The output of the audio amplification unit is defined as node A. The maximum amplification factor of the audio amplification unit is between 50-100 times, and the input small audio signal can be amplified into a large audio signal. When the input audio signal is large, it is limited and output through the audio amplification unit. The audio amplification unit can also use other audio power amplifier circuits with low-pass filtering in the prior art to amplify the audio signal and suppress high-frequency noise signals.

[0051] The shaping unit includes a diode D2, a transistor Q3, resistors R7, R14, capacitors C6 and C7, wherein the transistor Q3 is an NPN transistor, the collector of which is connected to the output of the shaping part, defined as node B, the capacitor C6 is a DC blocking capacitor, allowing the AC audio signal to pass, the diode D2 provides a negative bias for the base of the transistor Q3, when the signal at node A is a small signal, the base of the transistor Q3 cannot generate a positive bias, the transistor Q3 is in a closed state, and the node The state of point B is controlled by capacitor C7, resistor R7 and resistor R14. When the signal at node A is a large signal, the base of transistor Q3 generates a positive bias, the collector and emitter of transistor Q3 are turned on, and the voltage of node B is pulled down to close to 0V; capacitor C7 is a filter capacitor, which is used to smooth the voltage fluctuation of node B. Resistors R7 and R14 form a voltage divider circuit. When transistor Q3 is turned off, the voltage of node B gradually increases to VCC*R14 / (R7+R14).

[0052] Whether there is audio input is determined by the switch state of transistor Q3. When transistor Q3 is turned on, we believe that there is audio input; when transistor Q3 is turned off, we believe that there is no audio input. We can adjust the input threshold of the audio signal to suppress the noise introduced by the audio system, and provide a good signal-to-noise ratio when it is determined that there is audio signal input.

[0053] The state selection control circuit 30 of the automatic on / off circuit is divided into a first control unit, a second control unit and a third control unit, wherein: the first control unit includes transistors Q1, Q4, resistors R15, R16, R2 and capacitor C2, wherein transistors Q1 and Q4 are NPN transistors.

[0054] In the first control unit, the collector of transistor Q1 and the state selection pin 201 are connected to node F, point F is connected to the positive power supply BATT of the power amplifier 20 through capacitor C2 and resistor R2, the emitter of transistor Q1 is grounded through resistor R16, the collector of transistor Q4 is connected to node E through R15 and the emitter of transistor Q1, the emitter of transistor Q4 is grounded, and the parameters of resistors R2, R15, and R16 are adjusted so that:

[0055] When transistor Q1 is turned off, the voltage VF at node F is pulled up to BATT through resistor R2, and the voltage of VF is approximately equal to BATT, and the power amplifier is in the ST-BY state;

[0056] When transistor Q1 is turned on and transistor Q4 is turned off, the voltage VF of node F is between BATT-2.5V and BATT-6V, and the power amplifier is in MUTE state;

[0057] When transistor Q1 is turned on and transistor Q4 is turned on, the voltage VF of node F is less than BATT-6V, and the power amplifier is in the PLAY state.

[0058] In other specific embodiments, the first control unit may also adopt other circuits, which can be understood as: including a voltage divider network, the voltage divider network includes a pull-up resistor and a grounding resistor connected in series, the middle node of the voltage divider network is connected to the state selection pin 201, connected to the positive power supply BATT of the power amplifier through the pull-up resistor, and grounded through the grounding resistor; when the transistor Q2 is turned on, the output control signal controls the first control switch to disconnect the middle node and the ground, so that the middle node is pulled up through the pull-up resistor to enter the ST-BY state, and when the transistor Q2 is turned off, the output control signal connects the middle node to the ground.

[0059] The grounding resistor is composed of two resistors, which can be set to a series mode or a parallel mode. One of the resistors is controlled by the second control switch and connected in parallel or series, thereby causing the resistance value of the grounding resistor to change, resulting in a voltage change at the state selection pin 201. By selecting suitable resistance values ​​for the pull-up resistor and the grounding resistor, the power amplifier 20 can be controlled to enter the MUTE state or the PLAY state.

[0060] The second control unit is used to control the conduction of transistor Q1, and the third unit is used to control the conduction of transistor Q4. There is almost no noise when the power amplifier switches from MUTE state to PLAY state. When the second control unit and the third unit use the same control input, a delay circuit is set in the third power supply to realize that transistor Q4 is turned on later than transistor Q1, so that when the power amplifier is turned on, the state of the power amplifier transitions from ST-BY state to MUTE state, and then enters PLAY state, thereby solving the problem of power-on noise. When the power amplifier is turned off, transistor Q1 is turned off, and the power amplifier enters the low-power ST-BY state from PLAY state.

[0061] Specifically, in this embodiment, the second control unit includes: transistor Q2, resistors R4, R5, R9 and voltage regulator D1; wherein the transistor Q2 is an NPN transistor, the voltage regulator D1 has a voltage regulator voltage of VZ, the voltage regulator D1 and the resistor R4 are connected in series to the positive electrode VCC of the signal power supply and the ground GND to form a voltage regulator circuit to provide a stable voltage. The base of the transistor Q2 is connected to the node B through the resistor R8, the collector of the transistor Q2 is defined as the node C, the node C is connected to the middle node of the voltage regulator D1 and the resistor R4 through the resistor R5, is grounded through the resistor R9, and is connected to the base of the transistor Q1 to control the conduction and shutdown of the transistor Q1, and the emitter of the transistor Q2 is grounded. When transistor Q2 is turned on, the voltage VC at node C is close to 0V, and transistor Q1 is turned off; when transistor Q2 is turned off, the voltage VC at node C is VZ*R9 / (R5+R9), and resistors R5 and R9 are adjusted so that transistor Q1 is turned on at this voltage.

[0062] The third unit includes transistor Q5, resistors R21, R17, R22, R19 and capacitor C10, wherein transistor Q5 is an NPN transistor, the base of transistor Q5 is connected to node B through resistor R21, the collector of transistor Q5 is connected to the positive electrode VCC of the signal power supply through resistor R17, and is grounded through parallel resistor R17 and capacitor C10, and is connected to the base of transistor Q4 through resistor R19, and the emitter of transistor Q5 is grounded. When transistor Q5 is turned on, the voltage VD of node D is close to 0V, and transistor Q4 is turned off. When Q5 is turned off, node D is boosted from close to 0V to VCC*R22 / (R17+R22) after time T under the action of the delay circuit composed of resistor R17 and capacitor C10, and transistor Q4 is turned on.

[0063] Under the joint control of the second control unit and the third unit, the transistor Q1 is turned on before the transistor Q4.

[0064] In actual use, the second control unit and the third unit can also use other control circuits, as long as the transistor Q1 of the first control unit is turned on before the transistor Q4, so that when the power is turned on, the power amplifier switches from the ST-BY state to the MUTE state, and then switches from the MUTE state to the PLAY state. Through the above circuit, the automatic power on and off control of the power amplifier is realized, and the startup noise is reduced; when the power amplifier is turned off, the power amplifier enters the low-power ST-BY mode, thereby avoiding unnecessary loss of the power supply on the vehicle.

[0065] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, it should be understood by those skilled in the art that various changes may be made to the present invention in form and details without departing from the spirit and scope of the present invention as defined by the appended claims, all of which are within the scope of protection of the present invention.

Claims

1. An automatic power on / off circuit for a power amplifier, characterized in that: The power amplifier has a state selection pin, and the state of the power amplifier is controlled by adjusting the difference between the state selection pin and the positive power supply of the power amplifier, and the state includes a PLAY state, a ST-BY state and a MUTE state; The input end of the automatic power on / off circuit is electrically connected to an audio input end of the power amplifier, and the output end of the automatic power on / off circuit is electrically connected to a state selection pin of the power amplifier. When there is an audio signal, the automatic on / off circuit controls the power amplifier to switch from the ST-BY state to the MUTE state, and after a time T, switch from the MUTE state to the PLAY state; When there is no audio signal, the automatic on / off circuit controls the power amplifier to switch from the PLAY state to the ST-BY state.

2. The automatic on / off circuit according to claim 1, characterized in that: The absolute values ​​of the difference in each state are, from small to large, ST-BY state, MUTE state and PLAY state.

3. The automatic on / off circuit according to claim 2, characterized in that: Including audio amplification and shaping circuit and state gating circuit; The audio amplification and shaping circuit is used to input an audio signal and smoothly output a first switch signal. When the first switch signal is a low-level signal, it indicates that there is audio input, and when the first switch signal is a high-level signal, it indicates that there is no audio input; The state gating circuit includes a first control unit, a second control unit and a third control unit; The second control unit receives the first switch signal and outputs a second switch signal in an inverted manner; The third control unit receives the first switch signal and outputs a third switch signal in an inverted manner after a delay; The first control unit comprises a voltage divider network, the voltage divider network comprises a pull-up resistor and a ground resistor connected in series, an intermediate node of the voltage divider network is connected to a state selection pin, connected to the positive power supply of the power amplifier through the pull-up resistor, and grounded through the ground resistor; When the second switch signal is a low level signal, the intermediate node and the ground are disconnected; When the second switch signal is a high level signal, the intermediate node is connected to the ground; When the third switch signal changes from a low level signal to a high level signal, the grounding resistance decreases.

4. The automatic on / off circuit according to claim 3, characterized in that: The first control unit includes a first transistor, a fourth transistor, a fifteenth resistor, a sixteenth resistor, a second capacitor, and a second resistor, and the first transistor and the fourth transistor are NPN transistors; The pull-up resistor is a second resistor; the grounding resistor includes a fifteenth resistor and a sixteenth resistor; The collector of the first transistor is connected to the state selection pin, the collector of the first transistor is connected to the positive power supply of the power amplifier through a second capacitor and a second resistor connected in parallel, the emitter of the first transistor is grounded through a sixteenth resistor, and the base of the first transistor is connected to the output end of the second control unit; The collector of the fourth transistor is connected to the emitter of the first transistor through the fifteenth resistor, the emitter of the fourth transistor is grounded, and the base of the fourth transistor is connected to the output end of the third control unit.

5. The automatic on / off circuit according to claim 3, characterized in that: The second control unit includes a second transistor, a first voltage regulator, a fourth resistor, a fifth resistor and a ninth resistor, and the second transistor is an NPN transistor; The input terminal of the second control unit is connected to the base of the second transistor; The output terminal of the second control unit is connected to the collector of the second triode; The collector of the second triode is connected to the first node through the fifth resistor and to the ground through the ninth resistor, the first node is grounded through the first voltage regulator and connected to the positive electrode of the signal power supply through the fourth resistor, and the emitter of the second triode is grounded; The third control unit includes a fifth transistor, a seventeenth resistor, a twenty-second resistor, a nineteenth resistor and a tenth capacitor, and the fifth transistor is an NPN transistor; The input end of the third control unit is connected to the base of the fifth transistor; The output end of the third control unit is connected to the collector of the fifth transistor through the nineteenth resistor; The collector of the fifth transistor is connected to the positive electrode of the signal power supply through the seventeenth resistor and is grounded through the twenty-second resistor and the tenth capacitor connected in parallel. The emitter of the fifth transistor is grounded.

6. The automatic on / off circuit according to claim 3, characterized in that: The audio amplification and shaping circuit comprises an audio amplification circuit, a third triode, a second diode, a seventh resistor, a fourteenth resistor and a seventh capacitor; The output end of the audio amplification and shaping circuit is connected to the input end of the audio amplification circuit; The output end of the audio amplification and shaping circuit is connected to the collector of the third triode; The audio amplifier circuit amplifies the audio signal and inputs it into the base of the third transistor after being DC-isolated by a capacitor; The collector of the third triode is connected to the positive electrode of the signal power supply through the seventh resistor, and is grounded through the seventh capacitor and the fourteenth resistor connected in parallel; The cathode of the second diode is connected to the base of the third transistor, and the anode of the second diode is grounded.

7. The automatic on / off circuit according to claim 6, characterized in that: The audio amplifier circuit is a second-order low-pass audio amplifier circuit.

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