Patent ID: 8199533

Claim:
A switching power supply device, comprising: a transformer comprising a primary winding and a secondary winding; a switching element connected to the primary winding of the transformer; a control circuit that controls the switching element to be turned on/off in a case where a voltage is inputted to the primary winding of the transformer, and thereby induces a voltage in the secondary winding of the transformer; and a rectifying/smoothing circuit that rectifies and smoothes the voltage induced in the secondary winding of the transformer, and outputs the rectified and smoothed voltage to a load, wherein the control circuit includes: a current control unit that controls the switching element to prevent a current flowing through the switching element from being lowered to a fixed value or less in a case where the load is light; and an intermittent control unit that, in the case where the load is light, controls the switching element to perform an intermittent oscillation operation based on a feedback signal corresponding to an output voltage to the load.