A Novel Control Scheme of DCM Boost PFC Converter

The discontinuous current mode boost power factor (PF) correction converter features a zero-current turn-on for the switch, no reverse recovery in diode, and constant frequency operations. However, when the duty cycle is constant in a line cycle, the input current contains rich third harmonic which has a phase difference of π with respect to the fundamental component. The harmonic results in not only a lower PF but also larger peak and RMS current values of the main power components, which lead to a higher conduction and switching turn-off loss. In this paper, a variable duty cycle control scheme is proposed to make the input current contain only third harmonic which is in phase with fundamental component, while remaining the same PF at a certain input voltage as that of constant duty cycle control. A method of fitting the duty cycle is further proposed for simplifying the circuit implementation. The efficiency is improved as the critical inductance increases and the peak and RMS current values consequently decrease. The proposed method also achieves an output voltage ripple or the output storage capacitance reduction. The experimental results from a prototype of 120 W are given to verify the effectiveness of the proposed method.