AUXILIARY POWER SOURCE DEVICE FOR VEHICLE AND OVERCURRENT PROTECTION METHOD

A vehicle auxiliary power supply device includes a resonant inverter circuit 1 that converts DC input into a desired AC voltage and outputs the AC voltage and a control unit 10. The control unit 10 includes a resonance-time managing unit 13 managing resonance time of current flowing in the resonant inverter circuit 1, a gate-off-command generating unit 12 detecting overcurrent flowing in the resonant inverter circuit 1 based on detected current of a current detector CT1, and, when the overcurrent is detected, generating, based on detected current of the current detector CT1 and resonance time managed by the resonance-time managing unit 13, a gate-off command to turn off switching elements HGU1 and HGV2 included in the resonant inverter circuit 1 after the elapse of time after which current flowing in the switching elements HGU1 and HGV2 becomes zero for the first time, and a gate-signal generating unit 14 generating a gate signal that controls the switching elements HGU1 and HGV2 to be turned off when the gate-off command is input.