Patent ID: 7420340

Claim:
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, comprising: 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 clamp circuit that limits a level of the reference voltage generated by the reference voltage circuit; a comparator that has a speed voltage corresponding to an actual rotational speed of the motor and the reference 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, the clamp circuit limiting the level of the reference voltage to be applied to the comparator to within a common-mode input voltage range of the comparator while the control signal generator generates and outputs the control signal for controlling the amount of current flowing through the drive coil based on the comparing results of the comparator.