This thesis is performed in collaboration with Kraftpowercon AB in Surte, Sweden. Focus has been on to identify the powerlosses in one of Kraftpowercons Halfbridge DC-DC converters. First theoretical calculations are made, the calculations is verified with measurements of six different operation modes. In a later stage, methods like soft switching and synchronous rectifying are proposed to increase the efficiency for the converter. To achieve softswitching for the Halfbridge, the LLC resonant converter topologies are implemented and examined.