Micropower AB is a company that design and produce battery chargers for heavy vehicles. Buck converters are used in some chargers as they provide a regulated output voltage. In buck converter, transistor acts as a switch which is controlled by Pulse Width Modulated signal. The input line voltage is applied to the buck converter through a small input filter capacitor. The charger can induce oscillations on the line current and the input filter capacitor voltage. These oscillations could be critical resulting, the buck converter not to work. This thesis addresses how to reduce or to limit these oscillations by adding a passive filter as an input to the buck converter. The systems are simulated in MATLAB.