DCM boost PFC converter with high input PF

Discontinuous current mode (DCM) boost power factor correction (PFC) converter features zero-current turn-on for the switch, no reverse recovery in diode and constant frequency operation, however, the input power factor (PF) is relatively low when the duty cycle is constant in a half line cycle. This paper derives the expressions of the input current and PF of DCM boost PFC converter, and based on which, a variable duty cycle control is proposed so as to improve the PF to nearly unity in the whole input voltage range. A method of fitting the duty cycle is further proposed for simplifying the circuit implementation. Besides a higher PF, the proposed variable duty cycle control achieves a lower output voltage ripple and a higher efficiency over the constant duty cycle control. The experimental results from a 120 W universal input prototype are given to verify the effectiveness of the proposed method.