A power amplifier adaptive power matching circuit

Abstract

The invention discloses an adaptive power matching circuit for a power amplifier, comprising an input attenuation control circuit, an input buffer circuit, a hysteresis comparison circuit, a temperature compensation driving circuit and a current mutual inductance rectification and filtering circuit, wherein the input end of the input attenuation control circuit is connected to an external sound source, the output end is respectively connected to the input end of the input buffer circuit, the output end of the input buffer circuit is respectively connected to the hysteresis comparison circuit and the input end of the power amplifier, the output end of the hysteresis comparison circuit is connected to the input end of the input attenuation control circuit, the output end of the power amplifier is connected to an external load, the output end of the power amplifier is also connected to the input end of the current mutual inductance rectification and filtering circuit, the output end of the current mutual inductance rectification and filtering circuit is connected to the input end of the temperature compensation driving circuit, and the output end of the temperature compensation driving circuit is connected to the input end of the hysteresis comparison circuit. The invention can adaptively match the load in a wide range to adjust the maximum output power, thereby improving the stability and safety of the circuit.

Description

Technical Field

[0001] The invention relates to the technical field of power amplifier output power control circuits, and in particular to a power amplifier adaptive power matching circuit. Background Art

[0002] The power amplifiers in the existing market have a relatively narrow applicable range for load impedance. When the rated power of the power amplifier is exceeded, overcurrent protection is likely to occur, or the user mistakenly connects a speaker that does not match the load of the power amplifier to the power amplifier. That is, the output power of the power amplifier cannot be adaptively matched according to the load speaker, which leads to the phenomenon of burning the power amplifier and the speaker, causing property loss to the user. Therefore, it is necessary to protect the power amplifier and the load connected to the power amplifier through a power amplifier output power adaptive matching circuit, so that the power amplifier can adaptively match the load in a wide range to adjust the maximum output power, and can perfectly protect the power amplifier from being damaged or burned by the wrong load. Summary of the invention

[0003] In view of the deficiencies in the prior art, an object of the present invention is to provide an adaptive power matching circuit for a power amplifier, which can solve the problem of automatic matching of the output power of the power amplifier.

[0004] The technical scheme for achieving the purpose of the present invention is: an adaptive power matching circuit for a power amplifier, comprising an input attenuation control circuit, an input buffer circuit, a hysteresis comparison circuit, a temperature compensation driving circuit and a current mutual inductance rectification and filtering circuit, wherein the input end of the input attenuation control circuit is connected to an external sound source, and the output end is respectively connected to the input end of the input buffer circuit, the output end of the input buffer circuit is respectively connected to the hysteresis comparison circuit and the input end of the power amplifier, the output end of the hysteresis comparison circuit is connected to the input end of the input attenuation control circuit, the output end of the power amplifier is connected to an external load, the output end of the power amplifier is also connected to the input end of the current mutual inductance rectification and filtering circuit, the output end of the current mutual inductance rectification and filtering circuit is connected to the input end of the temperature compensation driving circuit, the output end of the temperature compensation driving circuit is connected to the input end of the hysteresis comparison circuit,

[0005] Among them, the input attenuation control circuit is used to attenuate the sound source signal input from the external sound source and filter out the high-frequency interference signal when the circuit is in closed-loop operation, so as to attenuate the high voltage of the sound source signal to a low voltage.

[0006] The input buffer circuit is used to buffer the output voltage received from the input attenuation control circuit and then input it to the power amplifier and hysteresis comparison circuit.

[0007] The hysteresis comparator circuit is used to compare the output voltage of the input buffer circuit and then output a reference comparison voltage value, so that the maximum output amplitude of the power amplifier can be set based on the reference comparison voltage value.

[0008] The temperature compensation driving circuit is used to compensate for the change of the HFE value of the transistor in the temperature compensation driving circuit caused by the temperature change of the ambient temperature and the temperature of the power amplifier itself, and to drive the light-emitting diode inside the optocoupler in the input attenuation control circuit to attenuate the sound source signal.

[0009] The current mutual inductance rectification and filtering circuit is used to convert and couple the current value of the external load, and perform full-wave rectification on the coupled current to obtain direct current, and then output the direct current to the temperature compensation drive circuit.

[0010] Furthermore, the input attenuation control circuit includes capacitors C1, C2, resistors R1, R2, R3 and optocoupler U1, the optocoupler U1 includes a light emitting diode, the capacitor C1 and the resistor R1 are connected in series to form a first series circuit, the capacitor C2 and the resistor R2 are connected in parallel to form a first parallel circuit, one end of the first series circuit is connected to an external sound source, and the other end is respectively connected to one end of the first parallel circuit, pin 3 of the optocoupler U1, and the input buffer circuit, the other end of the first parallel circuit and pin 4 of the optocoupler U1 are grounded together, an internal resistor is formed between pin 3 and pin 4 of the optocoupler U1, the light emitting diode is connected in series between pin 1 and pin 2 of the optocoupler U1, pin 2 is grounded, and pin 1 is respectively connected to one end of the resistor R3 and the temperature compensation drive circuit.

[0011] Furthermore, the input buffer circuit includes a dual operational amplifier U2, resistors R5 and R6, the negative electrode of the dual operational amplifier U2 is connected to the output end, the positive electrode of the dual operational amplifier U2 is connected to the other end of the first series circuit, the output end of the dual operational amplifier U2 is respectively connected to one end of the resistors R5 and R6, the other end of the resistor R5 is connected to the power amplifier, and the other end of the resistor R6 is connected to the hysteresis comparison circuit.

[0012] Furthermore, the hysteresis comparison circuit includes resistors R4, R7, R8, R9, R10, R11, diodes D2, D7, capacitor C3, dual JFET input operational amplifier U3A and dual JFET input operational amplifier U3B. After the resistor R4 and one end of the capacitor C3 are connected, they are commonly connected to the input attenuation control circuit. The other end of the capacitor C3 is grounded. The other end of the resistor R4 is respectively connected to the negative electrodes of the diodes D7 and D2. The positive electrode of the diode D7 is connected to the output end of the dual JFET input operational amplifier U3B. The positive electrode of the diode D2 is connected to the output end of the dual JFET input operational amplifier U3A. The positive electrode of the dual JFET input operational amplifier U3B is connected to the negative electrode of the dual JFET input operational amplifier U3A and then commonly connected in series with one end of the resistor R11. The other end of the resistor R11 is grounded. The negative electrode of the dual JFET input operational amplifier U3B is respectively connected to one end of the resistors R7 and R8. The other end of the resistor R7 is connected to the positive electrode of the external power supply. The other end of the resistor R8 is grounded.

[0013] Furthermore, the temperature compensation driving circuit includes resistors R13, R15, R16, R17, R18, a thermistor RT1, a capacitor C5, a transistor Q1 and a transistor Q2, the thermistor RT1 and the resistor R15 are connected in parallel to form a second parallel circuit, the resistor 16 and the capacitor C5 are connected in parallel to form a third parallel circuit, one end of the resistor R13 is connected to the current mutual inductance rectification and filtering circuit, and the other end is respectively connected to one end of the second parallel circuit and the base of the transistor Q1, the other end of the second parallel circuit and the emitter of the transistor Q1 are commonly grounded, the collector of the transistor Q1 is connected in series with the resistor R17 and then connected to one end of the third parallel circuit and the base of the transistor Q2, the other end of the third parallel circuit is respectively connected to the emitter of the transistor Q2 and the positive electrode of the external power supply, and the transistor Q2 is connected in series with the resistor R18 and then connected to the input attenuation control circuit and the resistor R3.

[0014] Furthermore, the thermistor is a negative temperature coefficient thermistor.

[0015] Furthermore, the transistor Q1 is an NPN transistor, and the transistor Q2 is a PNP transistor.

[0016] Furthermore, the current mutual inductance rectification and filtering circuit includes a coupling inductor T1, diodes D3, D4, D5, D6, a resistor R12 and a capacitor C4, one end of the coupling inductor T1 is respectively connected to the output end of the power amplifier and the external load, the other end of the coupling inductor T1 is respectively connected between the diodes D3 and D4, and between the diodes D5 and D6, the positive electrode of the diode D4 and the negative electrode of the diode D3 are connected in series to form a second series circuit, the positive electrode of the diode D6 and the negative electrode of D5 are connected in series to form a third series circuit, the second series connection circuit, the third series connection circuit, the resistor R12, and the capacitor C4 are connected in parallel to form a fourth parallel circuit, one end of the fourth parallel circuit is grounded, and the other end is connected to the temperature compensation drive circuit.

[0017] The beneficial effects of the present invention are as follows: the present invention can enable the output function of the power amplifier to be well adaptively matched with the load, and can adaptively match the load within a wide range to adjust the maximum output power, prevent the power amplifier and the load from burning due to overvoltage or overcurrent, and improve the stability and safety of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the overall circuit diagram of the present invention;

[0019] Figure 2 is a circuit diagram of an input attenuation control circuit;

[0020] Figure 3 is a circuit diagram of an input buffer circuit;

[0021] Figure 4 is a circuit diagram of a hysteresis comparison circuit;

[0022] Figure 5 It is a circuit diagram of a current mutual inductance rectification and filtering circuit;

[0023] Figure 6 is a circuit diagram of a temperature compensation driving circuit;

[0024] Figure 7 It is a circuit principle block diagram of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings and specific implementation schemes.

[0026] like Figure 1-Figure 7 As shown, an adaptive power matching circuit for a power amplifier includes an input attenuation control circuit, an input buffer circuit, a hysteresis comparison circuit, a temperature compensation driving circuit and a current mutual inductance rectification and filtering circuit. The input end of the input attenuation control circuit is connected to an external sound source, that is, the external sound source is input into the input attenuation control circuit, the output end of the input attenuation control circuit is respectively connected to the input end of the input buffer circuit, the output end of the input buffer circuit is respectively connected to the hysteresis comparison circuit and the input end of the power amplifier, and the output end of the hysteresis comparison circuit is connected to the input end of the input attenuation control circuit. The output end of the power amplifier is connected to load devices such as speakers and sound boxes, the output end of the power amplifier is also connected to the input end of the current mutual inductance rectification and filtering circuit, the output end of the current mutual inductance rectification and filtering circuit is connected to the input end of the temperature compensation driving circuit, and the output end of the temperature compensation driving circuit is connected to the input end of the hysteresis comparison circuit.

[0027] Among them, the input attenuation control circuit is used to attenuate the audio source signal input from the external audio source and filter out the high-frequency interference signal when the circuit is in closed-loop operation. Attenuating the audio source signal means attenuating the excessively high voltage of the audio source signal to a suitable voltage, so that the output voltage after the input attenuation control circuit is not too high and is input to the input buffer circuit. When the circuit is in a non-closed loop, the audio source signal is not attenuated and the high-frequency interference signal is not filtered out. Of course, the function of filtering out high-frequency interference signals always exists, regardless of whether the circuit is working or not. Filtering out high-frequency interference signals is only for stabilizing the circuit and is not necessary. The input buffer circuit is used to buffer the output voltage received from the input attenuation control circuit and then input it to the power amplifier and hysteresis comparison circuit to prevent excessive audio source signal amplitude from being directly input to the power amplifier to prevent the power amplifier from burning out. The hysteresis comparison circuit is used to compare the voltage value output by the input buffer circuit, and output a voltage for controlling the attenuation circuit, which is finally applied to the power amplifier, so that the maximum output amplitude of the power amplifier can be limited based on a set reference voltage value, to prevent the output power of the power amplifier from not matching the load and burning the load (such as speakers, speakers, etc.), so as to achieve the purpose of adaptive matching of the output power of the power amplifier. The temperature compensation circuit is used to compensate for the change in the HFE value of the transistor due to the ambient temperature and the temperature change of the power amplifier itself, and to drive the light-emitting diode inside the optocoupler in the input attenuation control circuit, so as to attenuate the sound source signal and finally reach a dynamic balance point, so as to control the output power of the power amplifier. The current mutual inductance rectifier filter circuit is used to convert and couple the current value of the external load, and perform full-wave rectification on the coupled current to obtain direct current, and then output the direct current to the temperature compensation drive circuit.

[0028] refer to Figure 2 , the input attenuation control circuit includes capacitors C1, C2, resistors R1, R2, R3 and optocoupler U1, and the optocoupler U1 includes a light-emitting diode and a photoresistor. Capacitor C1 and resistor R1 are connected in series to form a first series circuit, capacitor C2 and resistor R2 are connected in parallel to form a first parallel circuit, one end of the first series circuit is connected to an external sound source, and the other end is respectively connected to one end of the first parallel circuit, pin 3 of the optocoupler U1, and the input buffer circuit, the other end of the first parallel circuit and pin 4 of the optocoupler U1 are grounded together, and an internal resistor (i.e., an internal photoresistor) is formed between pins 3 and 4 of the optocoupler U1. The light-emitting diode is connected in series between pins 1 and 2 of the optocoupler U1, pin 2 is grounded, and pin 1 is respectively connected to one end of the resistor R3 and the temperature compensation drive circuit. Among them, the capacitance values ​​of capacitors C1 and C2 are 1uF (microfarad) and 220pF (picofarad) respectively, the resistance values ​​of resistors R1, R2, and R3 are 10KΩ, 100KΩ, and 1KΩ respectively, and the model of optocoupler U1 is LCR-0202 (DIP-4).

[0029] refer to Figure 3 , the input buffer circuit includes a dual-channel operational amplifier U2, resistors R5 and R6, the negative electrode (i.e., pin 2) of the dual-channel operational amplifier U2 is connected to the output end (i.e., pin 1), and the positive electrode (i.e., pin 3) of the dual-channel operational amplifier U2 is connected to the other end of the first series circuit, that is, connected to the resistor R1. The output end of the dual-channel operational amplifier U2 is respectively connected to one end of the resistors R5 and R6, the other end of the resistor R5 is connected to the power amplifier, and the other end of the resistor R6 is connected to the hysteresis comparison circuit. Among them, the resistance values ​​of the resistors R5 and R6 are both 1KΩ, and the model of the dual-channel operational amplifier U2 can be selected from NJM4580M, and of course other operational amplifiers with two-way inputs can also be selected.

[0030] refer to Figure 4 The hysteresis comparison circuit includes resistors R4, R7, R8, R9, R10, R11, diodes D2, D7, capacitor C3, dual JFET input operational amplifier U3A and dual JFET input operational amplifier U3B. One end of the resistor R4 and the capacitor C3 are connected and connected to the resistor R3 in the input attenuation control circuit. The other end of the capacitor C3 is grounded. The other end of the resistor R4 is respectively connected to the cathodes of the diodes D7 and D2. The anode of the diode D7 is connected to the output end of the dual JFET input operational amplifier U3B. The anode of the diode D2 is connected to the output end of the dual JFET input operational amplifier U3A. The positive electrode (i.e., pin 5) of the dual JFET input operational amplifier U3B is connected to the negative electrode (i.e., pin 2) of the dual JFET input operational amplifier U3A, and then connected in series with one end of the resistor R11. The other end of the resistor R11 is grounded. The negative electrode (i.e., pin 6) of the dual JFET input operational amplifier U3B is connected to one end of the resistors R7 and R8 respectively. The other end of the resistor R7 is connected to the positive electrode of the power supply, which can be provided externally. The other end of the resistor R8 is grounded. The positive electrode (i.e., pin 3) of the dual JFET input operational amplifier U3A is connected to one end of the resistors R9 and R10 respectively. The other end of the resistor R9 is connected to the negative electrode of the power supply, and the other end of the resistor R10 is grounded. Among them, the resistance values ​​of resistors R4, R7, R8, R9, R10, and R11 are 100Ω, 11KΩ, 1KΩ, 11KΩ, 1KΩ, and 39KΩ respectively, the capacitance value of capacitor C3 is 102F, the models of diodes D2 and D7 are BAV21WS, and the model of dual JFET input operational amplifiers U3A and U3B is NJM072M.

[0031] refer to Figure 5The temperature compensation driving circuit includes resistors R13, R15, R16, R17, R18, thermistor RT1, capacitor C5, transistor Q1 and transistor Q2. Thermistor RT1 is connected in parallel with resistor R15 to form a second parallel circuit, and resistor 16 and capacitor C5 are connected in parallel to form a third parallel circuit. One end of resistor R13 is connected to the current mutual inductance rectification and filtering circuit, and the other end is respectively connected to one end of the second parallel circuit and the base of transistor Q1. The other end of the second parallel circuit is grounded together with the emitter of transistor Q1. The collector of transistor Q1 is connected in series with resistor R17 and then connected to one end of the third parallel circuit and the base of transistor Q2. The other end of the third parallel circuit is respectively connected to the emitter of transistor Q2 and the positive electrode of the external power supply. Transistor Q2 is connected in series with resistor R18 and then connected to the optical coupler U1 and resistor R3 of the input attenuation control circuit. That is, the resistor R18 is connected to the pin 1 of the optocoupler U1 and one end of the resistor R3 respectively. Among them, the resistance values ​​of the resistors R13, R15, R16, R17, and R18 are 18KΩ, 2.2KΩ, 10KΩ, 3KΩ, and 3KΩ respectively. The thermistor RT1 is a negative temperature coefficient thermistor, which can reduce its resistance as the ambient temperature rises. Its model is B57421V2103J62V9. The capacitance value of the capacitor C5 is 1nF (nanofarad). The models of the transistors Q1 and Q2 are MMBT5551 and MMBT5401 respectively. The transistor Q1 is an NPN transistor, and the transistor Q2 is a PNP transistor.

[0032] refer to Figure 6 , the current mutual inductance rectification and filtering circuit includes a coupling inductor T1, diodes D3, D4, D5, D6, a resistor R12 and a capacitor C4, and one end of the coupling inductor T1 is connected to the output end of the power amplifier and the external load respectively. For example, pin 2 of the coupling inductor T1 is connected to the output end of the power amplifier, and pin 1 is connected to the external load. The other end of the coupling inductor is connected between the diodes D3 and D4 and between the diodes D5 and D6 respectively. For example, pin 3 of the coupling inductor T1 is connected between the diodes D3 and D4, and pin 4 of the coupling inductor T1 is connected between the diodes D5 and D6. The positive electrode of the diode D4 and the negative electrode of the diode D3 are connected in series to form a second series circuit, and the positive electrode of the diode D6 and the negative electrode of D5 are connected in series to form a third series circuit. The second series connection circuit, the third series connection circuit, the resistor R12, and the capacitor C4 are connected in parallel to form a fourth parallel circuit, one end of the fourth parallel circuit is grounded, and the other end is connected to the resistor R13 of the temperature compensation drive circuit. Among them, the models of diodes D3, D4, D5, and D6 are CD4148WTN, the model of coupled inductor T1 is ZEMCT131, the resistance value of resistor R12 is 2.4KΩ, and the capacitance value of capacitor C4 is 150nF.

[0033] Working principle: The audio signal is coupled by capacitor C1 and then passes through the attenuation circuit composed of resistors R1, R2 and the internal resistor of optocoupler U1 in parallel. Resistor R2 is selected with a larger resistance value. The internal resistor of optocoupler U1 presents a large resistance value when the light-emitting diode inside optocoupler U1 is not lit. When the control signal in the audio source signal does not work, it will hardly attenuate the signal. Capacitor C2 is a small-capacitance capacitor that can filter out high-frequency interference signals and improve the stability of the entire circuit. The unattenuated audio signal (i.e., the audio source signal) is buffered by the emitter-follower circuit composed of U2 and then output to the power amplifier of the next stage. At the same time, the audio signal output by U2 is attenuated by the attenuation circuit composed of R6 and R11 and then sent to the comparator circuit composed of U3. R7 and R8 divide the voltage to provide a positive reference value to U3B, and R9 and R10 divide the voltage to provide a negative reference value to U3A, thereby providing a reference comparison value to the positive input and negative input of U3A and U3B respectively; through the hysteresis comparator composed of U3A and U3B, a set voltage value can be compared at the input end.

[0034] For example: we set the comparison circuit of the hysteresis comparator composed of U3A and U3B to ±1V, that is, the voltage value of the audio signal after being buffered by U2 and then divided by R6 and R11 changes within ±1V, which will not trigger the hysteresis comparator to work (the input single-ended audio signal is a positive and negative voltage value with the ground wire of this system as the reference), and thus will not trigger the optocoupler U1 to work, so the audio signal is almost not affected by attenuation. When the audio signal continues to increase and exceeds ±1V, the hysteresis comparator will output a voltage of the working voltage value, which is rectified into a unidirectional direct current by D1 and D2 and filtered by R4 and C3. After R3 limits the current, it lights up the light-emitting diode in the optocoupler U1, thereby changing the resistance between pins 3 and 4 of the optocoupler U1 (that is, changing the resistance of the internal resistor of the optocoupler U1), and then attenuating the input signal through the voltage divider of R1, and completing a stable state over and over again.

[0035] The amplified audio signal at the output end is coupled by the coupling inductor T1 and then output. The coupling inductor T1 is also a current transformer. It is rectified by the full-wave rectifier circuit composed of D3, D4, D5, and D6, and filtered by C4. R12 provides a fixed value load stable output to the circuit. The voltage divider circuit composed of R13 and R15 divides the DC signal of the current transformer and inputs it into the base of the NPN transistor Q1. When the output load is within a reasonable range, the voltage value coupled by the current transformer is relatively low. This voltage value is not enough to turn on the transistor Q1 after being divided by R13 and R15. At this time, the output audio is not affected. When the load continues to increase (heavier), until the audio signal coupled by the current transformer turns on the transistor, it will flip the level through the PNP transistor Q2 to drive the optocoupler U1. Thermistor RT1 is a negative temperature coefficient thermistor. As the ambient temperature rises, the resistance value decreases, which can compensate for the problem of the increase in the DC amplification factor of the transistor HFE caused by the increase in ambient temperature and stabilize the system output. When the load exceeds the rated value, the current transformer T1 is triggered, thereby lighting up the light-emitting diode of the optocoupler U1. The resistance value is then changed to attenuate the input signal, and finally the output signal is attenuated. The load current is maintained within the rated value range, thus completing the control requirements.

[0036] Through the circuit of the present invention, the output function of the power amplifier can be well adaptively matched with the load, and the maximum output power can be adjusted by adaptively matching the load within a wide range, preventing the power amplifier and the load from burning due to overvoltage or overcurrent, thereby improving the stability and safety of the circuit.

[0037] The embodiment disclosed in this specification is only an example of a unilateral feature of the present invention, and the protection scope of the present invention is not limited to this embodiment, and any other functionally equivalent embodiments fall within the protection scope of the present invention. For those skilled in the art, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all of these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A power amplifier adaptive power matching circuit, characterized in that: The invention comprises an input attenuation control circuit, an input buffer circuit, a hysteresis comparison circuit, a temperature compensation driving circuit and a current mutual inductance rectification and filtering circuit. The input end of the input attenuation control circuit is connected to an external sound source, and the output end is respectively connected to the input end of the input buffer circuit. The output end of the input buffer circuit is respectively connected to the input end of the hysteresis comparison circuit and the input end of the power amplifier. The output end of the hysteresis comparison circuit is connected to the input end of the input attenuation control circuit. The output end of the power amplifier is connected to an external load. The output end of the power amplifier is also connected to the input end of the current mutual inductance rectification and filtering circuit. The output end of the current mutual inductance rectification and filtering circuit is connected to the input end of the temperature compensation driving circuit. The output end of the temperature compensation driving circuit is connected to the input end of the hysteresis comparison circuit. Among them, the input attenuation control circuit is used to attenuate the sound source signal input from the external sound source and filter out the high-frequency interference signal when the circuit is in closed-loop operation, so as to attenuate the high voltage of the sound source signal to a low voltage. The input buffer circuit is used to buffer the output voltage received from the input attenuation control circuit and then input it to the power amplifier and hysteresis comparison circuit. The hysteresis comparator circuit is used to compare the output voltage of the input buffer circuit and then output a reference comparison voltage value, so that the maximum output amplitude of the power amplifier can be set based on the reference comparison voltage value. The temperature compensation driving circuit is used to compensate for the change of the HFE value of the transistor in the temperature compensation driving circuit caused by the temperature change of the ambient temperature and the temperature of the power amplifier itself, and to drive the light-emitting diode inside the optocoupler in the input attenuation control circuit to attenuate the sound source signal. The current mutual inductance rectifier filter circuit is used to convert and couple the current value of the external load, and perform full-wave rectification on the coupled current to obtain direct current, and then output the direct current to the temperature compensation drive circuit. The input attenuation control circuit includes capacitors C1, C2, resistors R1, R2, R3 and an optocoupler U1, wherein the optocoupler U1 includes a light emitting diode, the capacitor C1 and the resistor R1 are connected in series to form a first series circuit, the capacitor C2 and the resistor R2 are connected in parallel to form a first parallel circuit, one end of the first series circuit is connected to an external sound source, and the other end is respectively connected to one end of the first parallel circuit, pin 3 of the optocoupler U1, and an input buffer circuit, the other end of the first parallel circuit and pin 4 of the optocoupler U1 are grounded together, an internal resistor is formed between pins 3 and 4 of the optocoupler U1, the light emitting diode is connected in series between pins 1 and 2 of the optocoupler U1, pin 2 is grounded, and pin 1 is respectively connected to one end of the resistor R3 and a temperature compensation drive circuit, The input buffer circuit includes a dual operational amplifier U2, resistors R5 and R6, the negative electrode of the dual operational amplifier U2 is connected to the output end, the positive electrode of the dual operational amplifier U2 is connected to the other end of the first series circuit, the output end of the dual operational amplifier U2 is respectively connected to one end of the resistors R5 and R6, the other end of the resistor R5 is connected to the power amplifier, and the other end of the resistor R6 is connected to the hysteresis comparison circuit.

2. The power amplifier adaptive power matching circuit according to claim 1, characterized in that: The hysteresis comparison circuit includes resistors R4, R7, R8, R9, R10, R11, diodes D2, D7, capacitor C3, dual JFET input operational amplifier U3A and dual JFET input operational amplifier U3B. After one end of the resistor R4 and the capacitor C3 are connected, they are commonly connected to the input attenuation control circuit. The other end of the capacitor C3 is grounded. The other end of the resistor R4 is respectively connected to the negative electrodes of the diodes D7 and D2. The positive electrode of the diode D7 is connected to the output end of the dual JFET input operational amplifier U3B. The positive electrode of the diode D2 is connected to the output end of the dual JFET input operational amplifier U3A. After the positive electrode of the dual JFET input operational amplifier U3B is connected to the negative electrode of the dual JFET input operational amplifier U3A, they are commonly connected in series with one end of the resistor R11. The other end of the resistor R11 is grounded. The negative electrode of the dual JFET input operational amplifier U3B is respectively connected to one end of the resistors R7 and R8. The other end of the resistor R7 is connected to the positive electrode of the external power supply. The other end of the resistor R8 is grounded.

3. The power amplifier adaptive power matching circuit according to claim 1, characterized in that: The temperature compensation driving circuit includes resistors R13, R15, R16, R17, R18, a thermistor RT1, a capacitor C5, a transistor Q1 and a transistor Q2. The thermistor RT1 and the resistor R15 are connected in parallel to form a second parallel circuit. The resistor R16 and the capacitor C5 are connected in parallel to form a third parallel circuit. One end of the resistor R13 is connected to the current mutual inductance rectification and filtering circuit, and the other end is respectively connected to one end of the second parallel circuit and the base of the transistor Q1. The other end of the second parallel circuit and the emitter of the transistor Q1 are grounded together. The collector of the transistor Q1 is connected in series with the resistor R17 and then connected to one end of the third parallel circuit and the base of the transistor Q2. The other end of the third parallel circuit is respectively connected to the emitter of the transistor Q2 and the positive electrode of the external power supply. The transistor Q2 is connected in series with the resistor R18 and then connected to the input attenuation control circuit and the resistor R3.

4. The power amplifier adaptive power matching circuit according to claim 3, characterized in that: The thermistor is a negative temperature coefficient thermistor.

5. The power amplifier adaptive power matching circuit according to claim 3, characterized in that: The transistor Q1 is an NPN transistor, and the transistor Q2 is a PNP transistor.

6. The power amplifier adaptive power matching circuit according to claim 1, characterized in that: The current mutual inductance rectification and filtering circuit includes a coupling inductor T1, diodes D3, D4, D5, D6, a resistor R12 and a capacitor C4, one end of the coupling inductor T1 is respectively connected to the output end of the power amplifier and the external load, the other end of the coupling inductor T1 is respectively connected between the diodes D3 and D4, and between the diodes D5 and D6, the positive electrode of the diode D4 and the negative electrode of the diode D3 are connected in series to form a second series circuit, the positive electrode of the diode D6 and the negative electrode of D5 are connected in series to form a third series circuit, the second series connection circuit, the third series connection circuit, the resistor R12, and the capacitor C4 are connected in parallel to form a fourth parallel circuit, one end of the fourth parallel circuit is grounded, and the other end is connected to the temperature compensation drive circuit.

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