A Constant Current Output Technique Applied to Primary-Side Controlled Quasi-Resonant Flyback Converters

Flyback converters have been widely used in low power applications due to simple structure and low cost. Quasi-resonant flyback converters with valley switching technique provide less turn-on losses compared with continuous-conduction mode and discontinuous-conduction mode, resulting in better efficiency and lower device temperature. In this thesis, we will illustrate the theory of the flyback converter and propose a constant current output technique applied to primary-side controlled quasi-resonant flyback converters. An output current estimator is presented, and simulation results have verified the feasibility of the proposed circuit.