POWER SUPPLY UNIT

PROBLEM TO BE SOLVED: To provide a power supply unit capable of stably achieving an operation at high power factor even if the power supply frequency of an AC power supply is fluctuated. SOLUTION: The power supply unit includes: a rectifier circuit 2 for rectifying AC voltage from the AC power supply 1; a reactor 6 connected in series with the AC power supply 1; switching means 7 for shorting/opening the AC power supply 1 through the reactor 6; voltage phase detection means 8 for generating a pulse signal synchronized with the AC power supply 1; and control means 9 for driving the switching means 7 based on the pulse signal output from the voltage phase detection means 8. The power supply unit shorts/opens the AC power supply 1 once or a plurality of times during a half period of the AC power supply 1 in synchronization with the voltage phase of the AC power supply 1. Only when the period T of the pulse signal obtained from the voltage phase detection means 8 is in a range from a first predetermined time T1 to a second predetermine time T2, a plurality of shorting/opening operations are performed. COPYRIGHT: (C)2010,JPO&INPIT