Analysis and design of self-oscillating flyback converter

The self-oscillating flyback converter is a popular circuit for cost-sensitive applications due to its simplicity and low component count. It is widely employed in mobile phone chargers and as the stand-by power source in off-line power supplies for data-processing equipment. However, the optimization of this circuit is almost exclusively performed by a cut-and-dry approach since its operation is generally not well understood. This paper presents a detailed steady-state analysis of the self-oscillating flyback converter along with its small-signal model. Design guidelines of the control circuit and loop compensation are presented and verified on an offline, stand-by, 5 V/2 A power supply.