AC/DC critical conduction mode buck-boost converter with unity power factor

The buck-boost converter operating in critical conduction mode (CRM) is commonly utilized in various applications because of many advantages like protection against short circuit, minimum component count, low operating duct-cycle, and low voltage on MOSFETs. However, its input power factor (PF) is not high while operating in constant ontime control. To attain unity PF for universal input voltage range, a new control scheme of variable on-time control (VOTC) is proposed in this paper. The VOTC can be implemented by modulating the turn-on time of the buck-boost switch. The working principle and performance comparison of the converter is discussed with both types of control scheme. The input PF the converter is high in case of VOTC than the COTC. Simulation results are presented to verify the effectiveness of the proposed control strategy).