Single‐stage QR AC–DC converter based on buck–boost and flyback circuits

In this study, a single‐stage quasi‐resonant (QR) AC–DC converter based on buck–boost and flyback circuits is proposed. The forestage buck–boost circuit works in discontinuous conduction mode to achieve a high‐input power factor (PF), and the backstage flyback converter, working in QR mode, is responsible for energy transfer. The QR switch mode can improve the efficiency of the converter by decreasing the switch turn‐on losses. The single‐stage topology can reduce the cost and raise the reliability of the system. The detailed design process is described in this study, and a 50 W prototype was developed that has a maximum PF higher than 0.99 and a maximum efficiency of 90.91% in nominal working conditions.