Patent ID: 7123489

Claim:
A variable-frequency flyback converter with a synchronous rectification function, comprising: a flyback transformer having a primary winding connected to an input voltage, a secondary winding for drive for providing a first induced voltage induced from said input voltage in a first turn ratio with said primary winding, and a secondary winding for detection for providing a second induced voltage induced from said input voltage in a second turn ratio with said primary winding; a voltage detector for detecting said second induced voltage; switching control means for determining, on the basis of a level of the voltage detected by said voltage detector, whether a current load state is a mini load state with a predetermined load or less and outputting a first switching signal according to a result of the determination; a first switch for switching the supply of said second induced voltage in response to said second induced voltage and said first switching signal from said switching control means; and a synchronous rectifier for performing a switching operation depending on a state of said first switch, said synchronous rectifier having its source and drain connected to any one of a voltage output line or ground line connected to said drive secondary winding and its gate connected to said first switch.