Design and Implementation of Self-Oscillating Flyback Converter With Efficiency Enhancement Mechanisms

This paper presents a self-oscillating flyback converter with efficiency enhancement mechanisms using lossless snubber and the energy recovery winding. The conventional self-oscillating flyback converter with resistor-capacitor-diode snubber has the issues of low conversion efficiency and high no-load power loss. Furthermore, in order to fulfill the 95 Vp-p voltage limitation of the IEC62684 Common-Mode (CM) Standard, the parasitic capacitor of a transformer between the primary and secondary windings has to be reduced, which leads to large leakage inductance for the transformer. However, the larger leakage inductance stores more energy to cause the high voltage spike on the main switch during the turnoff transition period. Therefore, the lossless snubber is employed to suppress the voltage spike and increase the conversion efficiency. In order to increase more conversion efficiency, the energy recovery winding is employed to recycle the energy discharged from the gate-source capacitor of the main switch. Furthermore, the burst-mode control mechanism is utilized to reduce the power consumption at the no-load and light-load conditions. Finally, a prototype circuit of the 7.5-W self-oscillating flyback converter with efficiency enhancement mechanisms is built to verify the performance feasibility, such as the CM voltage, the voltage stress on the switch, the conversion efficiency, and the no-load power loss.