Pulse width modulation control sytem for a motor

Abstract

A pulse width modulation (PWM) control system for rotating a spindle motor and a rotatable recording medium at a constant speed. The PWM control system includes a coil phase detecting circuit for detecting a change of stator coil phase based on detecting a rotor magnetic pole and for providing a detecting signal based on the detected phase change; a spindle motor driving circuit for controlling a supply of power to the coils based on the detecting signal; a rotation reference signal generating circuit for generating a rotation reference signal which defines the constant speed of the spindle motor; a real rotation detecting circuit for detecting a real rotation speed of the rotor of the spindle motor and for providing an index signal based on the detection of real rotation; a coil phase selection timing circuit for deciding a selection timing of the coil phase based on the detecting signal and for providing a coil phase selecting signal based on said deciding a selection timing; and a microprocessor for determining a pulse width of a PWM signal based on a phase difference between the rotation reference signal and the index signal, and for providing the PWM control signal with the determined pulse width in synchronization with the deciding of the coil phase selection timing circuit to the spindle motor driving circuit.