Patent ID: 6888728
Filing Date: 2005-05-03
Classification: H02M,Y02B

Abstract:
1. A switching power supply unit comprising: a transformer; a switching circuit provided on the primary side of the transformer; a synchronous rectifier circuit provided on the secondary side of the transformer and having at least a rectifier transistor; a rectifier-transistor driving circuit provided on the secondary side of the transformer and forming a first control signal synchronous with a switching operation of the switching circuit; and a timing generating circuit which receives the first control signal for forming a second control signal which exceeds a threshold voltage of the rectifier transistor at a timing substantially equal to the timing that one edge of the first control signal is generated based on the first control signal and which falls below the threshold voltage of the rectifier transistor at a timing earlier by predetermined time than the timing the other edge of the first control signal is generated, and for supplying the resulting second control signal to the control electrode of the rectifier transistor.