A Comprehensive Loss Analysis of Quasi Resonant Flyback Converter for Design Purpose

For universal input AC/DC applications, the hard switched flyback converter efficiency is relatively low and ranges between 75% and 85%. With quasi resonant switching method, the efficiency can be improved up to 90%. Although the efficiency improvement is significant, the total losses are large and they dominate the design of the converter due to the thermal considerations involving the reliability and the life of the power supply. Besides, it is hard to find a practical guide in order to estimate critical component power losses during design stage. For these reasons, a comprehensive power loss analysis is investigated for a quasi resonant flyback converter (QRFB) in this paper. For those purposes, a design procedure based on thermal considerations is presented, crucial loss items are illustrated on a basic schema and detailed calculations are done for 40 W universal power supply. Additionally, two methods are presented for transformer total loss measurement with a laboratory test setup. Evaluation of the results is also discussed at the end of the paper.