How does the power amplifier circuit diagram work?

You may have heard of power amplifier circuits, but do you know how it works? With the development of technology, power amplifier protection circuits will be more and more widely used in society. I will explain the content of power amplifier protection circuits to you. The following content mainly analyzes the power amplifier protection circuit and the detection of the power amplifier protection circuit.

When overhauling the output circuit of a power amplifier, we often encounter a fault that the relay cannot close. In addition to the circuit protection caused by the offset of the midpoint voltage of the power amplifier, the abnormality of the protection circuit itself is also one of the causes of the fault.

There are two common power amplifier protection circuits, one is a circuit composed of discrete components, and the other is a protection circuit composed of integrated circuits. Both circuits are very common in practical applications. The following uses the power amplifier protection circuit composed of μPCI237 as an example to introduce its circuit principles and maintenance methods.

A protection circuit composed of μPCI237. The protection scope includes: midpoint voltage drift protection, power amplifier final stage overcurrent protection, etc. The protection of the circuit is very sensitive, and the action time of the protection circuit is less than 1 second. As long as the components of the peripheral circuit are properly selected, the circuit operation is very reliable. However, because the sensitivity of this type of protection circuit is too high, false protection faults may sometimes occur. At this time, if a capacitor of 104 is connected to the two pins of the integrated circuit to the ground, it can effectively prevent the occurrence of false protection. .

Both pins in the circuit are the input terminals of the protection circuit. When positive or negative voltage appears on the periphery of the circuit, the relay output pin of the circuit outputs a high level. The relay cannot pull in because there is no loop current, which plays a role. The role of circuit protection. The maintenance of this circuit is very simple. As long as you check whether the peripheral circuits and power supply of both legs are normal, you can quickly find out the fault location. If the voltage at the pin is positive or negative and the relay does not close, it means that the final stage of the power amplifier is faulty. The fault of the final circuit of the power amplifier should be checked and eliminated first. In addition, when there are other pulse interferences in the circuit, it will also cause false protection of the relay. If the power amplifier is controlled by the CPU function, interference pulses will appear when the CPU is working, which will also cause the protection of this circuit. Adding two capacitors to pins 1 and 2 can prevent the working pulse of the CPU circuit from interfering with the circuit and causing false protection. Actually in application. Adding this capacitor can also improve the stability of the circuit.

Common faulty components of this circuit are: pin supply voltage diode D21N4007, pin peripheral to ground capacitor C4 is damaged. In most cases, the capacitor pin is rusty and broken, etc.

Power amplifier protection circuit

Such as a Shenbao BD808 amplifier. There is a phenomenon of irregular automatic protection, and automatic protection occurs frequently when the volume is turned up. After power-on inspection, it was found that there is no distortion when the power amplifier plays normally, which means that the final amplification circuit of the power amplifier is normal. If the playback is distorted, it means that the output of the final amplification circuit has DC voltage.

At this time, the relay protection is protected by midpoint voltage drift. You can determine which part of the cause is based on whether the sound output is distorted, and you should focus on checking the protection circuit.

The protection circuit is composed of integrated circuit UPCI237. Its typical application circuit is basically the same as the circuit in the attached picture. So the components in the circuit were checked and replaced, but the fault remained. Replacing the integrated circuit did not eliminate the fault. During circuit protection, unstable voltage appears at the pin of the integrated circuit UPC1237. After analysis, most of this is caused by AC components entering the circuit and causing integrated circuit protection. For this phenomenon, as long as a ceramic capacitor with a nominal capacity of 104 is connected from the pin of the circuit to the ground, the fault can be eliminated. To develop excellent power amplifier circuits, you need to continuously accumulate experience in practice.