US Patent 7123489 Variable-frequency flyback converter with synchronous rectification function

Disclosed herein is a variable-frequency flyback. The flyback converter comprises a flyback transformer having secondary windings for drive and detection for providing first and second induced voltages induced from an input voltage in first and second turn ratios with a primary winding, respectively, a voltage detector for detecting the second induced voltage, a switching controller for determining, on the basis of a level of the voltage detected by the voltage detector, whether a current load state is the mini load state and outputting a first switching signal according to a result of the determination, a first switch for switching the supply of the second induced voltage in response to the second induced voltage and the first switching signal, and a synchronous rectifier for performing a switching operation depending on a state of the first switch, the synchronous rectifier having its source and drain connected to any one of a voltage output line or ground line connected to the drive secondary winding and its gate connected to the first switch.