Methods for identifying causes of EMI emissions from switched mode power applications

A typical switched mode power application (SMPA), such as a power supply, motor driver, or regulator, may have multiple converters switching at different frequencies and may produce an array of broad-banded EMI emissions. This paper presents a method for identifying SNTA components that are the causes of these emissions by correlating the spectral bands of an emission with real-time events occurring on the SNTA. The identified components' spectral impedance characteristics are studied next, giving insights into the component's in-circuit behaviors. These insights are then used to develop various countermeasures intended to control these EMI emissions.