Abstract: Auxiliary converter is an important power supply device providing 380 V AC and 24 V DC power for the guided vehicle. At present, auxiliary converters are usually designed with IGBT (insulated gate bipolar transistor) power modules, but the large volume, low switching frequency and low power density cannot meet the requirements of miniaturization and light weight for auxiliary converter installed on the guided vehicle. Therefore, a new SiC (silicon carbide) MOSFET (metal\|oxide\|semiconductor field\|effect transistor) power device is adopted in the design of auxiliary converters to replace IGBT, for the purpose of improving the system switching frequency, optimizing the design of peripheral passive components, and suppressing the spike voltage caused by high switching frequency with the new clamp circuit. Through calculation and test, the advantages of the new rail tram auxiliary converter based on SiC design in terms of volume and performance are verified, which has positive impact on the application of SiC MOSFET devices.