EMI filter design and compatibility measurements for buck type DC/DC converters

The suppression of electromagnetic interference (EMI) in switched-mode power supplies is of great importance for commercial and military areas where electronic systems are used. The biggest side-effect of the proliferation of switched sources is the EMI noise which is produced by them. It becomes a problem that high frequency noise is transmitted to other devices in the system, reducing the performance of sensitive analog or digital signal circuits. For this reason, input filters are applied to switched-mode power supplies. The use of an input filter has two main purposes: one is to suppress noise and ripple from the power supply, and the other is to reduce the interference signal at the switching frequency for other devices using the same power. In this study, a high efficiency switched DC/DC Buck converter operating at 150 kHz switching frequency is investigated. An input filter has been applied to the DC/DC Buck converter and it is aimed to operate harmoniously despite the EMI problems occurring in the power lines. In this study, common mode and differential mode EMI suppression filters are designed and simulated in accordance with CE 102 test in MIL-STD-461G standards. The designed filters are optimized in LTspice program to get the best results. The DC/DC Buck converter was brought to 3 different voltage levels as 12V, 5V and 3.3V, and graphics were obtained through the simulation program. Emission measurements and tests on transmission lines at 3 different voltage levels were carried out by putting the design into circuit. Results with and without filter were compared.