Abstract: A bi-directional DC-DC converter and an on-board charger with the bi-directional DC-DC converter integrated into it are disclosed for converting a first voltage to a second voltage. The bi-directional DC-DC converter includes a transformer for magnetically coupling a primary circuit receiving the first voltage on a primary side with a rectification circuit on a secondary side. Further, a high voltage power source is connected to the rectification circuit for supplying a high voltage to one or more high voltage loads and a low voltage power source is connected to the high voltage power source through a secondary circuit for supplying a second voltage to one or more low voltage loads. The bi-directional DC-DC converter functions in both stationary condition and running condition of a powered device.