Electric driven cars are composed of electric converters (inverter, DCDC convert,), which converts high voltage and current. Distinct from conventional ECU, high voltage system and low voltage system exist in the converters. High voltage and current generates high electric and magnetic noise and require shorter response time than conventional ECU’s. As failsafe requirements for vehicle is getting higher, building reliable fault detection system becomes more important. Due to these two requirements, converters need to have a protection system with high reliability and immediacy compared to conventional ECUs. This paper investigates conventional method to detect fault signal, which was used for an internal combustion vehicle and propose a new method to have a reliability and immediacy for electric driven cars. This proposed method achieves a protection system with high reliability and immediacy using CPLD device.