Mixed Mode EMI Noise Level Measurement in SMPS

Abstract

Fast switching in SMPS generate large amount of Electromagnetic Interference (EMI).The proposed method to determine Common Mode (CM) and Differential Mode (DM) noise of a low power Switched Mode Power Supply (SMPS) using two-probe approach i.e. using one current probe as an injecting probe and other current probe as receiving probe Common Mode (CM) noise is measured between power line and ground. Differential Mode (DM) noise is measured between each power lines. EMI radiated emissions occur in the range of 150 KHz-30MHz. EMI filter is usually needed in the input of the Switch Mode Power Supply (SMPS) to attenuate the noise. The proposed approach allows measurement of noise level in Switched Mode Power Supply without interleaving its normal operation. With proper set up calibration, the proposed approach can be used to measure the noise level with reasonable accuracy. The noise level is measure from the frequency of 1MHz-3MHz using signal generator the signal is induced in the injected probe and using receiving probe noise level is measured in db using spectrum analyser.