Patent ID: 7698574

Claim:
A power supply device, comprising: a main power supply circuit for supplying power to a main control section of a main apparatus, the main apparatus including a plurality of interface sections for communicating with an external device, each of the interface sections having a signal detection circuit for detecting an external signal; an auxiliary power supply circuit for supplying power to only the signal detection circuit, the auxiliary power supply circuit being connected to a commercial power supply; and a power control section configured to control the main power supply circuit and the auxiliary power supply circuit respectively, the power control section being configured to turn the main power supply circuit off and turn the auxiliary power supply circuit on when the main apparatus is in power saving mode, and to restart the main power supply circuit upon the detection of external signal by the signal detection circuit, wherein the power control section is configured to determine that external signal input to the signal detection circuit is valid only when the signal matches a predetermined pattern.