Patent ID: 7206208

Claim:
A synchronous rectifying control circuit, suitable for utilizing in a forward topology of rectifying circuit and controlling a first current switch and a second current switch provided on both ends of an output winding of a transformer, comprising: a forward synchronous rectifying driven unit, receiving a synchronous control voltage signal from the drain pin of the second current switch, and producing a first gate switch signal to control on and off of the first current switch; a signal-producing unit acting as a frequency divider, dividing an original frequency of the first gate switch signal into a half frequency, and producing a first charge switch signal and an inversed signal as a second charge signal of the half frequency; a first charge and discharge control circuit and a second charge and discharge control circuit, producing a charge current of the first charge switch signal and the second charge switch signal respectively during a charge period in order to provide charging respectively to a first capacitor and a second capacitor steadily, the first charge and discharge control circuit and a second charge and discharge control circuit are also producing a discharge current for discharging the first capacitor and the second capacitor steadily during a discharge period, potential of the first capacitor and the second capacitor are compared respectively with a first reference potential in order to produce respectively a first and a second discharge switch signals; a fly wheeling synchronous rectifying driven unit, inputting the first discharge switch signal and the second discharge signal in order to produce a pause period signal, wherein the pause period starts when potential discharge of the first and second capacitor are equaled to the first reference potential during a discharging period, and the pause period ends when a next charge period of the first and second charge switch signals starts, the fly wheeling synchronous rectifying driven unit inputs the first gate switch signal and the pause period signal so that a second gate switch signal of the fly wheeling synchronous rectifying is produced, the second gate switch signal is utilized to control the second current switch so that the second current switch will only be switched on during a non-pause period and when the first current switch is on an off status; and a power supply unit, providing source voltage, and outputting the first reference potential and a second reference potential.