Effect of common mode transients on front end rectifiers in offline SMPS

Abstract

This paper presents the effect of common mode (CM) transient on a typical front-end rectifier of offline power electronic equipment like switched mode power supply (SMPS) and near unity power factor (NUPF) converters. They undergo mode conversion to differential mode (DM) transients. The magnitude, rise time and fall time of such DM transients depend on the coupling capacitance to ground, rise time and position of occurrence of CM transients on AC mains voltage. This DM transient may damage sensitive components and may cause malfunctioning of the ICs used in the SMPS/NUPF circuitry. It will also cause interference in their output voltages. Connecting RC snubbers across the diode bridge can mitigate them. Simulation results, mathematical analysis and experimental results presented here are in close conformity.