A heat dissipation system for an electronic device comprises a base, a fan, a pulse width modulation speed control circuit controlling the speed of the fan, a converter outputting a voltage signal, a selection switch connected to the motor, and a control element provided on the base, connected to the switch and to the converter. When the control element is operated, the switch selectively enables the motor be connected to the output of the pulse width modulation speed control circuit or to the output of the converter, and when the motor is electrically connected to the converter, the control element can modify the output voltage of the converter.