CM noise reduction of isolated converter by balancing technique.

Abstract

Common mode (CM) EMI noise in an isolated converter is mainly due to parasitic capacitance occurring within the SMPS. It flows through the transformer coupling capacitance and the parasitic capacitance of switching MOSFETs and rectification diodes. Several techniques have been proposed in the literature to reduce CM noise. The most common techniques are compensation, shielding, and the balancing-shielding technique. In this paper, a new balancing technique is described to reduce the noise of both parasitic capacitances of MOSFETs and transformer inter-winding capacitance. Analysis is presented to demonstrate the efficacy of the compensation method and the resultant reduction in EMI noise. Finally, the practical measurement results obtained from a practical implementation of the new technique in a flyback converter topology, are presented as verification of the benefits of the approach in comparison to the conventional method.