Modelling and measurement of high switching frequency conducted EMI

Abstract

High density high switching frequency power converter conducted EMC had been analysed, modelling the noise source and noise path, while providing accurate conducted EMC noise levels comparable to accredited noise measurements up to 100 MHz. The military specified DC-DC converters are generally applicable, spanning from 100 W handheld power managers up to 2 kW DC-DC battery chargers. A Buck topology was used to demonstrate the principles. A general high frequency analyses model was developed and verified. Circuit layout high frequency effects as well as high frequency impedances of the power components were characterised. Thereafter, a lumped element model including the switching devices was created. The software package PowerSim was selected to perform the analyses of the model, presented as a very easy and reliable tool. The common mode effect of electrically non-conductive polymer heatsinks was presented and tested as a remedy to reduce the increased common mode noise levels due to higher switching frequencies.