Phenomenon 1: (Two 7805 in parallel) After working for about 1 minute after power on, the power amplifier is seriously hot, output noise, the current reaches 800 mA, and the speaker is disconnected and connected again. The above phenomenon is repeated after tens of seconds, and the components are eliminated problem.
Phenomenon 2: With a 7805, the sound is intermittent after being powered on for 5 minutes, and the current is gradually increased to 500 mA to protect it from power failure and restart.
If you use the 5v power supply of this problem board to power the amplifier 8002 of the same model of another board (the board with the above problem), it works normally (single 7805 or two in parallel are no problem) using an external 5V power amplifier for the problem board also works normally , Solve. The circuit board is shown in the attached picture.
Kennan postado em December 22, 2020
The power amplifier circuit is self-excited!
Phyllis postado em December 22, 2020
Self-excited oscillation is generated, check the grounding power supply filter capacitor high frequency filter capacitor input signal path anti-interference measures.
Daley postado em December 22, 2020
Judging from the schematic, it feels like it is oscillating.
