US Patent 7375987 Resonant switching power source apparatus

A resonant switching power source apparatus has a first switching element and second switching element being connected in series between output terminals of a DC power source and are alternately turned on and off; a series resonant circuit having a primary winding of a transformer and a current resonance capacitor and connected in parallel with the second switching element; a controller to control the first and second switching elements; a rectifying/smoothing circuit to rectify and smooth a voltage, which is generated on a secondary winding of the transformer during an ON period of the second switching element, and output the rectified-smoothed voltage; a current detector to detect a current passing through the series resonant circuit; and an overcurrent protector to turn off the first and second switching elements for a predetermined period so that excitation energy of the transformer is reset, if the current detector detects a predetermined current value.