Abstract— The electromagnetic interference (EMI) conducted by a DC/DC buck converter was experimentally investigated in this study. The research focused on the influence of the duty cycle and the selection of switching devices—metal-oxide-semiconductor field-effect transistor (MOSFET) or insulated-gate bipolar transistor (IGBT)—on both common-mode (CM) and differential-mode (DM) emissions. Measurements were conducted in accordance with the EN 55022 conducted emission standard, covering the frequency range from 150 kHz to 30 MHz, using a Line Impedance Stabilization Network (LISN) and a spectrum analyzer. The results reveal that DM emissions dominate the conducted spectrum, exceeding the Class B limit in a narrow frequency band at lower frequencies, while CM emissions generally remain within the limits across most of the measured range. Overall, lower duty cycles lead to higher CM and DM emission levels, whereas higher duty cycles result in a significant reduction in total noise. A comparison of the switching devices shows that the MOSFET-based converter generates more CM noise due to its rapid switching, while the IGBT-based converter maintains lower CM noise but exhibits slightly higher DM emissions under certain conditions. In conclusion, the converter is close to meeting EN 55022 Class B standard and requires only minor adjustments at low frequencies to achieve full compliance. These findings provide valuable insights into the impact of control parameters and semiconductor selection on conducted EMI, contributing to the design of DC/DC converters that are both efficient and compliant with electromagnetic compatibility (EMC) regulations.