Optimal Dual Constant Switching Frequency Control for CRM Buck-Buck/Boost PFC Converter

Due to the dead zone in the average input current, the Buck power factor correction (PFC) converter is difficult to meet the design requirements in many applications. In order to solve the demerit, the Buck-Buck/Boost PFC converter has been proposed. However, the traditional critical conduction mode (CRM) Buck-Buck/Boost PFC converter adopts constant on-time (COT) control. Operating with COT, the switching frequency varies greatly during a line cycle. This complicates the design of the electromagnetic interference (EMI) filter. In this paper, an optimal dual constant switching frequency (DCF) control for CRM Buck-Buck/Boost converter is proposed. The switching frequency of the converter with DCF is fixed in Buck mode and Buck/Boost mode separately in a line cycle, and the PF can be improved by optimizing the switching frequency. The experimental results from a prototype of 120-W are given to verify the effectiveness of the proposed method.