Patent ID: 8253276

Claim:
A power supply device, comprising: a first power supply, a voltage step-up transformer that steps up an output voltage of the first power supply; a voltage step-down transformer that steps down an output voltage of the voltage step-up transformer, and outputs the stepped-down voltage to a load; wherein the voltage step-up transformer steps up the output voltage of the first power supply to an operating voltage of the load, wherein the stepped-up output voltage includes a voltage equal to a voltage that is stepped-down by the voltage step-down transformer, and wherein a lower limit of the operating voltage of the load is obtained by deducting the voltage stepped-down by the voltage step-down transformer from the stepped-up output voltage; a second power supply that supplies electric power in a usual operation of the power supply device; and a power supply switching unit that, when the second power supply stops supplying power and the first power supply starts to supply electric power, switches its output to the output voltage of the first power supply stepped up by the voltage step-up transformer from an output voltage of the second power supply, and supplies the output voltage of the first power supply to the voltage step-down transformer.