A Soft-Switched Flyback converter with recovery of stored energy in leakage inductance

This paper presents a 500W Soft Switched Flyback converter operating in discontinuous mode. The detailed circuit description, operation, characteristics, circuit equations and simulation results of the Active Clamp Flyback converter are presented here. The clamp capacitor absorbs leakage and a part of magnetizing energy stored in the primary winding of the Flyback transformer. Therefore the leakage voltage spike is reduced to a desired value. The dumped energy in the clamp capacitor is then transferred totally to the source by a LC resonating circuit. For main switch ZVS is achieved at turn OFF and ZCS is achieved at turn ON, as it is operated in discontinuous mode. ZCS is also achieved for the auxiliary switch both at turn ON and OFF. Thus switching loss is reduced and a part of the magnetically stored energy of the transformer, which is absorbed by the clamp capacitor, is sent back to the source, resulting in the efficiency of the converter being increase greatly. Thus, a Soft Switched high power rated Flyback Converter with good efficiency can be designed.