Patent ID: 7372710

Claim:
A switching power source device comprising: a primary winding of a transformer and a primary switching element connected in series to a DC power source wherein said primary switching element is turned on and off to cause electric current to flow through said primary winding and primary switching element in order to generate DC power from output terminals connected to a secondary winding of said transformer; a secondary switching element for synchronous rectification connected between said secondary winding of said transformer and output terminals, a reactor connected in parallel to said secondary winding of the transformer for accumulating energy during the on-period of said primary switching element, and a secondary control circuit connected to said reactor and a control terminal of said secondary switching element, wherein said secondary control circuit serves to retain said secondary switching element off during the period for accumulating energy in reactor, retain said secondary switching element on during the period for discharging energy accumulated in said reactor, and turn said secondary switching element off upon completion of energy release from said reactor.