Design Considerations of Soft-Switched Buck PFC Converter With Constant On-Time (COT) Control

In contrast to the conventional boost power factor correction (PFC) converter, the buck PFC converter can achieve high efficiency in the entire universal input voltage range. A critical conduction mode (CRM) soft-switched buck PFC converter with constant on-time control is presented in this paper. The design methodology and criteria for zero-voltage switching range, high efficiency and low harmonics of the CRM buck ac-dc converter are achieved. A 100-W prototype built up according to the proposed design criteria shows that the input current harmonics meet the IEC61000-3-2 (Class D) standard and the efficiency is higher than 0.965 during the universal input range.