CM Noise Cancellation in Near Unity Power Factor Converter

NUPF (Near Unity Power Factor) converter can improve the low power factor offered by offline SMPS. But, the NUPF also generate EMI which needs to be mitigated to comply with EMC standards. This paper provides an approach to minimize CM (Common Mode) conducted EMI noise by cancellation technique. Here an extra winding PCW (Parasitic capacitance noise Cancellation Winding) in the high-frequency transformer is used to reduce the common mode conducted EMI. By this method, the high-frequency range of CM noise reduction has been achieved and it can reduce the cost of the EMI filter. Experimentation and simulation are carried out with and without PCW for a 30W flyback NUPF and a significant reduction in high-frequency CM conducted EMI is obtained.