The input capacitance of the three-terminal voltage regulator is determined according to the load. If a high-power relay with a small DC resistance is used, the capacitance above 470UF should be used. Because the resistance of this relay is relatively large, the actual measurement is about 1K , That is, the current consumption of this circuit should be below 20MA. The 47UF capacitor can work normally in the experiment. It is feasible to use a 100UF capacitor in the circuit. If this capacitor is too large, it will not be able to shut off the load and the amplifier even when shutting down. Connected, causing impact on the headphones. Since the working current of this circuit is very small, it is possible to replace the three-terminal voltage regulator circuit with 78M15 or 78L15.
Schematic diagram:
The basic functions are:
1. Turn on the headset after the start-up delay. According to the board I made, the headset will be connected for about 3-5 seconds after the start-up to protect the headset from the impact of the start-up current.
2. When the power is turned off, the filter capacitor of the power supply is selected relatively small. After the power is turned off, the connection between the earphone and the amplifier is almost simultaneously disconnected to protect the earphone from the current impact of the shutdown.
3. Abnormal output DC voltage protection. After a simple experiment, when an output voltage of + 1.5V appears at the output of the amplifier, it can be disconnected within 1 second, and when the amplifier has a negative voltage output, the protection operating voltage is relatively high. .
It took 3 hours to finally solder the amp's protection circuit. Because the components are not handy, the parameters are inconsistent with the above schematic. It is gratifying that the welding is successful. Pay attention to the small black between the input and output terminals The rectangular parallelepiped is the miniature relay of Japan. It is the most suitable for protecting earphones. Of course, you can also use a large relay and use it as a horn protection. The PCB board has been made in the form of dual relay installation.
Relays used in the circuit:
Is the finished circuit board made small? The area of ​​the PCB spanner is 10CM * 4CM
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