Power supply device for supplying standby voltage by using main voltage

A power supply device, comprising:

• a standby power unit converting a DC voltage to an operating voltage and a first standby voltage and providing the first standby voltage to a standby output terminal;
• a DC/DC converting unit receiving the operating voltage from the standby power unit, converting the DC voltage to a main voltage, and providing the main voltage to a main output terminal;
• a main/standby power unit converting the main voltage from the DC/DC converting unit to a second standby voltage and providing the second standby voltage to the standby output terminal;
• and
• a sensing unit sensing whether or not the second standby voltage is supplied to the standby output terminal,
• wherein the sensing unit outputs a switching signal varying a magnitude of the first standby voltage to the standby power unit when the second standby voltage is supplied to the standby output terminal.