The power conversion circuit in the figure is divided into two ways for conversion. The converted power supply is used as the power supply connecting the internal and external signals respectively, which plays the role of isolating the internal and external signals. The power conversion chips ba12t and ba05t with high reliability and stable conversion and wide range input are used. There are over-current protection circuit and over temperature protection circuit inside the chip, which can protect other electronic components in the circuit. Ba12t is 13-25v input and output 12V DC voltage stably; ba05t is 6-25v input and output 5V DC voltage stably. Among them, diodes D1, D2, D11 and D12 have the functions of reducing voltage, preventing power supply from reverse connection, protecting electronic circuit, and diodes and their negative end capacitors have the functions of isolation and filtering.