A driving device is electrically connected with an AC power and a brushless DC motor for a fan. The driving device includes a rectifier unit, a filter unit, a switch power conversion unit and a control unit. The rectifier unit receives the AC power and rectifies the AC power. The filter unit, electrically connected with the rectifier unit, filters the rectified AC power and generates a DC power. The switch power conversion unit, electrically connected with the filter unit and the brushless DC motor, receives the DC power and outputs a driving power to the brushless DC motor. The control unit is electrically connected with the switch power conversion unit and the brushless DC motor.