AC ADAPTOR, POWER SUPPLY UNIT, ELECTRICAL APPARATUS, AND CONTROLLING METHOD FOR POWER SUPPLY UNIT

摘要

PROBLEM TO BE SOLVED: To reduce power loss by reducing the operating frequency of a power supply unit on standby, for example, in soft-off or suspended state or when a line has not been connected. SOLUTION: An AC adaptor 10 is installed so that the adaptor is connectable to equipment main body through a power line, and is provided with a rectification bridge diode 11 for rectifying inputted alternating-current voltage; a capacitor 12 for smoothing the voltage; a switching transistor 13 that performs switching of the rectified and smoothed voltage; and a pulse width modulation IC 15 that provides an operating frequency for the performed switching. The pulse width modulation IC 15 provides a first operating frequency to the switching transistor 13 when the equipment main body performs normal operation, and a second operating frequency lower than the first operating frequency to the switching transistor 13 when the power line between the adaptor and the equipment main body is disconnected or when the equipment main body is in a specified standby state.