Integrated Buck-Flyback Converter with Simple Structure and Unity Power Factor

The dead zone in the buck converter can be eliminated by integrating flyback converter with it. However, its input Power Factor (PF) is low when operated with Constant On-Time Control (COTC). In this paper, a Variable On-Time Control (VOTC) strategy is proposed for Integrated Buck-Flyback Converter (IBFC) with simple structure to obtain unity PF. By feed forwarding input and output voltage to change the on-time of both switches, high PF can be achieved. The operating principle of the IBFC is discussed with both types of control schemes and for verifying the effectiveness of VOTC scheme; simulations are carried out by using Saber simulator. Keywords: Constant On-Time Control (COTC), Integrated Buck-Flyback Converter (IBFC), Variable On-Time Control (VOTC) Scheme