Analys och implementering av EMI-reducerande tekniker i DC/DC-omvandlare

Abstract

As electronic systems become increasingly compact and efficient, the demands on electromagnetic compatibility (EMC) continue to rise. DC-DC converters are a common source of electromagnetic interference (EMI) in many applications, particularly in automotive and industrial environments. This study aims to analyze and implement techniques to reduce conducted EMI in a buck converter. While the requirements defined in the CISPR 25 standard serve as a reference, meeting the standard was not an explicit objective of this work. Through simulations in LTspice and practical measurements in an EMC chamber, several filtering solutions were evaluated, including π-filters, common-mode (CM) and differential mode (DM) filters, as well as complementary techniques such as RC filters, ferrite beads, and increased input capacitance. The results show that the π-filter provided the most consistent attenuation across a wide frequency range (150 kHz–80 MHz), while the CM filter performed better at higher frequencies. The best overall EMI performance was achieved using a combination of a π-filter, increased input capacitance (320 µF), and a ferrite bead. The study also demonstrates that filter placement, grounding quality, and parasitic characteristics of components significantly affect performance. Finally, suggestions for further improvement are discussed, including the implementation of spread spectrum techniques and alternative CM filter designs to achieve improved low-frequency suppression.