Patent ID: 8218342

Claim:
A power supply device which converts alternating-current power into direct-current power and supplies the direct-current power to a load, comprising: a buffer; a control section; a rectifier circuit which rectifies the alternating-current power; a smoothing circuit which includes a first capacitor and a second capacitor connected in series, smoothes an output of the rectifier circuit, and outputs the direct-current power; and a switch provided between the rectifier circuit and a connection point between the first capacitor and the second capacitor, wherein the control section is configured to: detect a zero cross point of the alternating-current power input to the rectifier circuit; calculate in advance, at any stage prior to the detection of a predetermined zero cross point, predetermined parameters which are used when a generation timing of a PAM interrupt pulse is calculated, the PAM interrupt pulse being used when a PAM waveform having at least two or more pulses in a half period of the alternating-current power is generated and being input to the switch; retain the calculated predetermined parameters in the buffer; use in common, after the detection of predetermined zero cross point, the predetermined parameters retained in the buffer in calculating the generation timing of the PAM interrupt pulse over a predetermined period of the alternating-current power; calculate in advance the predetermined parameters again at any stage prior to a lapse of the predetermined period; retain, in the buffer, the predetermined parameters after being calculated again; and use, after the lapse of the predetermined period, the predetermined parameters after being calculated again in calculating the generation timing of the PAM interrupt pulse.