US Patent 7564204 Motor speed control circuit

A motor speed control circuit which controls a rotational speed of a motor by controlling an amount of current flowing through a drive coil of the motor. The control circuit comprises a reference voltage circuit that generates a reference voltage corresponding to a speed-specifying signal inputted to specify the rotational speed of the motor; a speed voltage circuit that generates a speed voltage corresponding to an actual rotational speed of the motor; a clamp circuit that limits the level of the speed voltage generated by the speed voltage circuit; a comparator that has the reference voltage generated by the reference voltage circuit and the speed voltage limited in level by the clamp circuit applied thereto and compares the two; and a control signal generator that generates and outputs a control signal for controlling the amount of current flowing through the drive coil based on the comparing result of the comparator.