Current resonance type power supply device

A current resonance type power supply device, comprising:

• a first switch element and a second switch element connected in series across ends of a DC power supply;
• a series circuit connected to a junction of the first switch element and the second switch element and to one end of the DC power supply, and having a series connection of a reactor, a primary winding of a transformer, and a capacitor;
• a full-wave rectifier/smoothing circuit configured to perform full-wave rectification and smoothing on a voltage generated in a secondary winding of the transformer thereby to extract a DC voltage;
• a control circuit configured to set a first ON time of the first switch element and a second ON time of the second switch element to a same predetermined time thereby to alternately turn on and off the first switch element and the second switch element, and configured to control a switching frequency of the first switch element and the second switch element according to a value of the DC voltage;
• a voltage detector configured to detect a voltage of the capacitor;
• and
• an ON time controller configured to set one of the first ON time and the second ON time shorter than the predetermined time and set the other of the first ON time and the second ON time longer than the predetermined time, under light-load conditions, based on a value of the voltage of the capacitor detected by the voltage detector.