Conducted emission analysis of DC-DC converters and proper selection of pre-filtering stage

At low frequencies, DC-DC converter is one of the noisiest components that can adversely affect conducted emission (CE) measurements. Since DC-DC converter does the switching at a frequency that is proportional to the load, there is a strong component of interference signal in a certain frequency band that depends upon the load. It not only includes the fundamental frequency but also its harmonics. The dynamic range of the amplitude and frequency of this interference signal is important to analyze for the design of proper pre-filtering stage. In this paper, we shall present the experimental measurements of conducted emissions for DC-DC converter with and without using the filter and would show the importance of proper filter design to bring the conducted emissions within the envelope of MILSTD-461F. The measurements indicate that without filter there is a strong interference signal at the fundamental frequency and its harmonics which are well above the threshold value. As the properly designed filter is inserted, the conducted emissions fall within the envelope of MIL STD-461F.