Design and implementation of digital controlled boost PFC converter under boundary conduction mode

The use of power factor correction (PFC) converters is widely discussed and considered for most off-line power supplies. For low power applications, boost PFC converters operated in discontinuous conduction mode (DCM) or boundary conduction mode (BCM) mode are usually employed. The main advantage of BCM mode is the reduction of reversal recovery loss of diode and simple control, especially at the high-line light-load condition. In this paper, a digital-controlled method for boost PFC operating under boundary conduction mode without input voltage sensing is proposed. The digital PI controller voltage is used to determine the constant on-time period and the comparator block inside the DSP controller is employed to detect the zero-crossing of inductor current for turning on the main switch. Therefore, the size and cost are reduced significantly. A 200W boost PFC prototype is implemented and tested to verify the feasibility of the proposed control scheme.