Abstract: While the converter works at light load‚the output filter inductor current will go negative through MOSFET in synchronous rectifier and the circulating current will be formed．In order to solve this problem‚the detection method of light load condition of converter used by UC3842is proposed in this paper‚meanwhile‚the technique has also been studied which is used to make the inductor current cannot be flow negatively by switching off the MOSFET while converter works at light load．The theory analysis and experiment have proved that the proposed method is effect‚the converter efficiency has also been improved a lot at light load． 

Key words: forward converter, synchronous rectifier, switching mode power supply