A novel control scheme of DCM boost PFC converter

Discontinuous current mode (DCM) boost power factor correction (PFC) converter features zero-current turn-on for the switch, no reverse recovery in diode, constant frequency operation. However, when the duty cycle is constant in a line cycle, the input current contains rich 3rd harmonic which has a phase difference of π with fundamental component. The harmonic results in not only low PF but also larger peak and rms current values of the main power components, which leads to higher conduction and switching turn-off loss. A variable duty cycle control is proposed in this paper so as to enable that the input current contains only 3rd harmonic which is in phase with fundamental component while remaining the same PF at a certain input voltage, comparing with 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 can be increased and the peak and rms current value is therefore decreased. The proposed method also achieves the output voltage ripple or the output storage capacitance reduction. The experimental results from a prototype of 120W are given to verify the effectiveness of the proposed method.