Patent ID: 8018749

Claim:
A switch mode power supply apparatus, comprising: a transformer; a source of an input supply voltage; a first switching transistor for periodically coupling said input supply voltage to said transformer to produce an alternating current supply voltage in a first winding of said transformer; a second switching transistor forming a synchronous rectifier coupled to said first winding for rectifying said alternating current supply voltage to produce a rectified output that is coupled to a load, said second switching transistor being conductive, during a portion of a period of said alternating current supply voltage; and a detector responsive to said input supply voltage, during a portion of said period, when said first switching transistor couples said input supply voltage to said transformer, for developing a first control signal coupled to said second switching transistor, said detector being configured to detect a magnitude of said input supply voltage and to alter, in accordance with said magnitude, when, during said period, conduction of said second switching transistor will end in a manner to alter a duration of the conduction of said second switching transistor.