Patent ID: 7176660

Claim:
A switching power source apparatus having a power factor corrector and a DC-DC converter, the power factor corrector being connected to an AC power source and providing a first DC voltage, the DC-DC converter applying the first DC voltage to a primary winding of a transformer, carrying out an ON/OFF switching operation with a switching element, to convert the first DC voltage into a second DC voltage, and decreasing the frequency of the switching operation or shifting to an intermittent oscillation in case of a light- or no-load state, comprising: a first rectifying/smoothing circuit configured to rectify a voltage generated by a secondary winding of the transformer, smooth the rectified voltage with a first smoothing capacitor, and supply the rectified-and-smoothed voltage to a load; a second rectifying/smoothing circuit configured to rectify a voltage generated by a control winding of the transformer and smooth the rectified voltage with a second smoothing capacitor; and a light-load detector configured to detect if an output ripple of the second rectifying/smoothing circuit is equal to or greater than a predetermined value, determine upon detection that the switching operation has decreased the frequency thereof or has shifted to an intermittent oscillation, and make the power factor corrector inoperative.