Radiated Emission Due to Common Mode Current in Smps

Shantala Shantala,M L Sudheer

doi:10.35940/ijeat.c6433.049420

Shantala Shantala, M L Sudheer

Open Access

https://doi.org/10.35940/ijeat.c6433.049420

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Abstract

The high frequency switching of semiconductor switches in Switched Mode Power Supplies (SMPS) cause high dV/dt and dI/dt resulting in differential mode (DM) and common mode (CM) conducted and radiated Electromagnetic Interference (EMI). The CM noise current circulating through the ground path is the major contributor for radiated EMI in the frequency range of 30 MHz to 1 GHz which will usually be above the stipulated international standards and are addressed here. The high dV/dt and dI/dt are major sources of EMI producing noise currents which will get coupled to ground through parasitic capacitances. The prominent parasitic capacitors are present in high frequency transformer and the semiconductor’s coupling to ground. They provide path for both DM and CM noise currents. The CM currents flowing in the different prominent parasitic capacitors are obtained by simulation for the four different topologies namely, non-isolated Buck, non-isolated Boost, Flyback and Forward converters. The radiated Emissions are calculated for each of the topologies and are presented. All the four converters are operated at same switching frequencies with same values of parasitic capacitances. The non-isolated Boost converter is found to generate higher radiated emissions due to CM current than the non-isolated buck converter and Forward converter has higher radiated emissions than Flyback converter. The results presented here can be used to decide on the topology of SMPS for a given application when EMI mitigation is a priority

Highlights

Switched Mode Power supplies (SMPS) are widely used in most of the Electronic appliances used for commercial, military and domestic purposes
This paper studies common mode (CM) Electromagnetic Interference (EMI) emitted radiation mechanism in the frequency range of 30 MHz - 1 GHz [8] in 4 different topologies of SMPS
The Electric field strength at a distance of 3 m from Flyback converter due to this CM current circulating in a PCB trace length of 10 cm is calculated from the formula (1) of section IV and is tabulated in Table-II for a frequency range from 30 MHz to 1 GHz

Summary

INTRODUCTION

Switched Mode Power supplies (SMPS) are widely used in most of the Electronic appliances used for commercial, military and domestic purposes. The inter winding and intra winding capacitances of the high frequency transformer and the coupling capacitor between the semiconductor switches and ground are the prominent parasitic capacitors in SMPS. Non-isolated Buck, non-isolated Boost, Flyback and Forward converters are considered here together with their parasitic capacitances and they are simulated in LTSpice software Their switching frequencies, load current and parasitic capacitances are same. The equivalent circuit models of CM radiated emissions are obtained This is simulated and the Fast Fourier Transform (FFT) of the CM circulating current through the ground is obtained. The FFT of CM noise currents in Amps against frequency is obtained This will enable us to find whether the emissions from SMPS are within the stipulated International limits [9-11]

SIMULATION AND RESULTS OF BUCK AND BOOST CONVERTER AND ITS CM RADIATION MODEL

SIMULATION AND RESULTS OF FLYBACK AND FORWARD CONVERTER AND ITS CM RADIATION MODEL

RADIATED COMMON MODE NOISE

CONCLUSIONS