Driving system for fan and method of driving fan

A driving system for a fan that enables an increase in motor current that may be supplied to excitation windings at the time of a maximum static pressure without increasing the rotational speed excessively at the time of an amount of maximum air flow is provided. The fan driving system includes a drive signal generating circuit that generates drive signals, a motor driving circuit that supplies a motor current to the motor in accordance with the drive signals, a current detecting circuit (resistance) that detects the motor current, and a drive signal changing circuit. The drive signal changing circuit changes the drive signals generated by the drive signal generating circuit to restrict an increase in the motor current when the motor current becomes larger than a threshold.