Patent ID: 8289744

Claim:
A power supply unit, comprising: a power supply circuit; a first switch to connect a main power source to the power supply circuit; a controlling unit configured to switch an operational state of an apparatus between an operating mode in which the power supply circuit supplies a first-level power to the apparatus and a power-saving mode in which the power supply circuit supplies a second-level power that is lower than the first-level power to the apparatus; a monitoring unit that monitors whether a returning factor required to switch the operational state of the apparatus from the power-saving mode to the operating mode is generated; an antenna unit that receives external electrical waves; a power generation unit that includes a tuning circuit connected to the antenna unit so as to generate electricity from the electrical waves received by the antenna unit and supplies the electricity to the power supply circuit and to the monitoring unit; and a second switch to switch the power generation unit between a state in which the power generation unit supplies the electricity, and a state in which the power generation unit stops supplying the electricity, the second switch being open or closed in unison with the first switch, wherein the second switch is open when the first switch is open and the main power source is not supplied to the power supply circuit, causing the power generation unit to stop supplying electricity to the power supply circuit and the monitoring unit; and the controlling unit switches the operational state of the apparatus from the power-saving mode to the operating mode when the monitoring unit detects generation of a returning factor.