Patent ID: 7397644

Claim:
A power supply device used as a power source for a load, comprising: an FET for power-source output control connected in series in a power output line, an FET for malfunction check connected between the gate and source of the FET for power-source output control, and a malfunction determination circuit for determining whether the FET for power-source output control is operating normally or not, by monitoring output voltage of the FET for malfunction check, wherein the FET for power-source output control is controlled to be in on- or off-state by a charge/discharge control circuit controlling gate voltage of the FET for power-source output control, and when the output voltage of the FET for malfunction check disappears while the FET for power-source output control is controlled to be in on-state, the malfunction determination circuit determines that this indicates malfunction of the FET for power-source output control due to short-circuiting.