Design considerations of a self-biased current driven SR in DCM flyback DC/DC converter

In this paper, different kinds of driving methods for synchronous rectifier (SR) are compared, and a self-biased current driven circuit for SR is proposed. The circuit uses a current transformer (CT) to generate driving signal, as well as provide the driving power. With a capacitor to produce bias voltage, this circuit can be used without considering the location of SR and the output voltage of converter. Furthermore, a speed-up capacitor is added to fasten the turn-on speed, thus high frequency application is possible. Experiments based on a 120W flyback prototype have been done to verify the theoretical analysis. The efficiency of the prototype is improved by 2% with proposed SR driving method, compared with Schottky diode rectifier at full load.

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