All-Fixed Switching Frequency Control of CRM Boost PFC Converter Based on Variable Inductor in a Wide Input Voltage Range

Critical conduction mode (CRM) boost power factor correction (PFC) converter is widely used in low-to-medium power applications for its advantages of high power factor (PF), zero-current turn-on of the switch and no reverse recovery in diode. Nevertheless, the switching frequency varies continually with the input voltage phase angle under the traditional constant on-time (COT) control. This makes complicates the design of inductors and electromagnetic interference (EMI) filters. An all-fixed switching frequency control based on variable inductor (AFFVI) is proposed in this paper. This strategy controls the variable inductor through DSP to achieve a constant switching frequency over wide input voltage range. In addition, a lower output voltage ripple and a higher efficiency is obtained. A 120 W prototype has been built and tested in the lab to verify the analysis.