Metric for evaluating 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 mitigate the EMI problem. However, until now, a metric to characterize and compare the EMI spectra of power converters is not available in literature. This paper proposes a simple metric to measure and characterize the EMI spectrum of power converters. 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 proposed metric is useful in evaluating and comparing the severity of the EMI noise generated by different implementations of a power converter. Thus, it allows the designer to choose the better implementation option from an EMI noise perspective. The use of the proposed metric is demonstrated through the comparison of the quality of spectra of a power converter with two different switching schemes.