Abstract: Due to the high requirements for electromagnetic interference(EMI) resistance in the rail transit sector, large-capacity filter capacitors are installed at the input end, which consequently generates significant surge current during the startup process. By analyzing the mechanism of surge current generation and combining the shortcomings of existing typical circuits, a new surge current suppression circuit based on a combination of negative temperature coefficient(NTC) thermistors and MOSFET devices was designed. This design combines the advantages of both devices while avoiding their shortcomings. Through simulation calculations and experimental verification, the circuit's ability to suppress surge current during startup has been validated, with surge current controlled to within three times the rated current. This effectively addresses the issue of excessive inrush current during power-on in board-level power supplies for rail transit applications, demonstrating significant engineering application value.

    Key words: filter capacitor; surge current; thermistor; MOSFET device