Variability of EMI Measurement for Switched Mode Power Supplies EMI in the 2-1000 kHz Range

The paper presents a study of the influence of the measurement setup to the variability and uncertainty of conducted emissions of Switched Mode Power Supplies (SMPS) in the 2-1000 kHz frequency range. The range was selected to cover supraharmonics and the most relevant RF conducted emissions. Tests were carried out on a 220 VAC/ 12 VDC SMPS fed by a Line Impedance Stabilization Network and varying the loading conditions. The most significant aspects are resolution bandwidth (which is still currently not completely standardized), the stability of the mains fundamental frequency and the dependency of the mechanisms of emission from the thermal transients inside the SMPS, as well as for the applied load. Short-and long-Term variability are thus analyzed to verify the minimum conditions for thermal stabilization.