Traditional fuel vehicle has an engine that can charge a 12V battery. The electrical vehicl does not have an engine, but instead is an electric motor and a high voltage power battery. The power battery is generally 400V, and the low-voltage equipments such as entertainment, air conditioning, and so on, cannot directly take power, so DCDC came to play a role of converting the high voltage to the low voltage. The input of DCDC is the high voltage battery, and the output is connected directly with the 12V battery. The DCDC can charge the battery with a constant current when the battery voltage is low. The DCDC can also output a constant voltage when the battery needs a small current. In addition, the DCDC supports CAN communication to make the control and monitor to be easier.