Sinrace Power Supply Technology (Shenzhen) Co., Ltd.

The main source of Electromagnetic Interference (EMI) emissions in power converters used for Telecom application comes from the high switching frequency of DC voltages. Power converters are generally operating in a periodic steady state, interested converter waveforms are typically periodic functions of time. Indeed the EMI emissions are a critical factor, which, can harm the system and degrade the satisfaction of Electromagnetic Compatibility (EMC). However, the most of design engineers use randomly various basic EMI reduction techniques. It is meaningful to quantify and analyze them before taking any solution measures. In fact, the diagnostic research of power converters is still under exploring. This article presents simplified equivalent circuit model used to predict the influence of common mode (CM) current noise in switching mode power supply. At the base of analysis, proposed equivalent circuit model contains essential couplings, parasitic elements, and sources occurred in the common mode current path. This circuit composed of input cables; equivalent voltage source and the intentional parameters of the converter is examined theoretically. A comparative analysis between practical results and the proposed model highlight good matching. At last, effective EMI suppressing techniques has been realized on an AC/DC converter prototype in order to validate the proposed model.