A Metric for Comparing the EMI Spectra of Power Converters

The inherent switching of power devices in a switch mode power supply generates electromagnetic interference (EMI) noise. This noise is dependent on several factors such as component layout, circuit parasitics, and the control techniques implemented. Several methods have been reported in literature to curtail the EMI problem. However, until now, a metric to compare the EMI spectra of power converters is not available in literature. In this paper, a simple metric to measure and characterize the EMI spectrum of a power converter is presented. The proposed technique is based upon the specification and thereby the size of an external passive filter required to meet the given EMI standards. The use of the metric is demonstrated through the comparison of the quality of spectra of two different implementations of an industrial power converter. The metric is also used to compare the spectra of a converter with two different switching schemes