Input current distortion of CCM boost PFC converters operated in DCM

Power factor correction (PFC) converters for the higher power range are commonly designed for continuous conduction mode (CCM). Nevertheless, operation in the discontinuous conduction mode (DCM) occurs for light load in a zone, close to the crossover of the line voltage. This zone will gradually expand with decreasing load to finally encompass the entire line cycle. Whereas in CCM the parasitic capacitances of the switches only cause switching losses, in DCM they are a source of converter instability, resulting in significant input current distortion. In this paper, this source of input current distortion is analyzed and a solution is proposed. Experimental results are obtained using a digitally controlled boost PFC converter, designed to operate in CCM for 1 kW.