Patent ID: 7116562
Filing Date: 2006-10-03
Classification: H02M,Y02B

Abstract:
1. A fly-back type synchronous rectifying switching power supply device comprising a primary winding of a transformer and a main switch element connected to each other in series between input terminals and which has a control circuit for subjecting the main switch element to PWM control within a fixed period, a synchronous rectifying element connected to a secondary winding of the transformer in series between output terminals, and driving means for turning on the synchronous rectifying element complementarily with the switching element, a different power supply source charged by a pulse voltage occurring at the secondary winding of the transformer through a switching operation of the main switch element, and interrupting means disposed between the gate and source of the synchronous rectifying element and which turns off the synchronous rectifying element, wherein an off-timing at which the interrupting means turns off the synchronous rectifying element is set to a timing which corresponds to a fixed time set by current from the different power source after the switch element is turned on and is within a range which is as near as a fixed driving period of the switch element.