This thesis aims to propose a design-oriented method for an Active EMI Filter (AEF) in DC-DC converters. The STEVAL-L3751V12 evaluation board, developed by STMicroelectronics, will be considered the reference platform for this work. The board embeds the DC-DC Buck controller L3751, and it implements a voltage–mode controller synchronous Buck converter. In order to mitigate the ElectroMagnetic Interference (EMI) generated by the converter, the board includes a passive π-type EMI filter. First, the design criteria for the filter are established to achieve the required EMI attenuation without compromising the converter stability. Next, one filtering capacitor of the passive EMI filter is replaced with an AEF.