The invention provides an overvoltage protection circuit and a transponder A interface protection circuit. The protection circuit comprises a resonant circuit and a voltage-limiting protection circuit, and the resonant circuit and the voltage-limiting protection circuit are connected through a rectifier bridge circuit. Through the overvoltage protection circuit and the transponder A interface protection circuit, the problem that the transponder is damaged as energy transmitted to the transponder by a vehicle-mounted unit is over large can be effectively solved.