POWER SUPPLY UNIT AND AIR CONDITIONER

PROBLEM TO BE SOLVED: To provide a power supply unit of a simple structure in which the stability of an output voltage is high and the distortion of an input current is less over a wide load range. SOLUTION: The power supply unit includes: a rectifier circuit 2, which rectifies an AC voltage from an AC power source 1; a reactor 6, which is connected in series to the AC power source 1; a bidirectional switching means 7, which short-circuits or opens the AC power source 1 via the reactor 6; a zero-cross detection means 8, which detects the zero-cross of the AC power source 1; and a switching element drive means 9, which drives the switching means 7 based on a pulse signal from the zero-cross detection means 8. The AC power source 1 is short-circuited by a short-circuit period Δt by the switching means 7 via the reactor 6 once every half a period of the AC power source 1 synchronizing the voltage phase of the AC power source 1. In this power supply unit, the short-circuit period Δt, during which the AC power source 1 is short-circuited, is increased or decreased so as to make the output voltage equal to a target voltage. Simultaneously, a time Δd from the zero-cross of the AC power source 1 up to the start of the short-circuit is controlled so as to satisfy Δd=Δd0-α×Δt. COPYRIGHT: (C)2010,JPO&INPIT