Abstract: A DC power-supply unit convening AC into DC power is provided to, when AC voltage and/or AC current of an AC power supply passes through a zero point, close a switch after a preset first delay time from a passing through time, and open the switch after a preset second delay time from a passing through time. The unit includes a rectifier switch for convening AC power output from the AC power supply into DC power, an inductive element connected to the rectifying element, a switching element connected to the inductive element, and the rectifying element, a smoothing unit connected in parallel with the switching element, and a switch control unit for controlling the switch according to the predetermined delay times.