Analysis on ringing effect of auxiliary winding in primary side regulated flyback converter

The ringing effect in auxiliary winding of transformer, which may cause faulty estimation in primary side regulated flyback converter, is detailed discussed in this paper for the first time. It has been found that: (a) Ringing of auxiliary winding occurs after main switch turns off and is derived from oscillation of the current in primary winding´s leakage inductance; (b) This ringing is delivered through the leakage inductance of auxiliary winding. Basis on these discussions, several schemes have been proposed for the design of converter and transformer in order to suppress this ringing effect. Simulation results and experimental results of a singlestage 16-W primary side regulated flyback converter with active power factor correction are given to validate proposed discussion.