ABSTRACT

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 with traditional constant on-time (COT) control. This makes the electromagnetic interference (EMI) spectra appear great differences and complicates the design of EMI filter. An optimal switching frequency variation range (OFR) control strategy is proposed in this project. The optimal harmonics amounts for the lowest switching frequency variation range without and with a limited PF are both figured out. In addition, a lower output voltage ripple is obtained. A prototype has been built and tested in the lab to demonstrate the validity of the theoretical analysis.