Patent ID: 6900604

Claim:
A drive control system for a multi-phase and sensor-less motor for driving the motor by switching a current of a field coil in each phase of the motor depending on a rotational phase of the motor, comprising: a power feeding circuit feeding electrical power, for a predetermined period, to a selected field coil when the selected field coil is in a phase other than a detection phase to induce a voltage in another field coil; an induced voltage detecting circuit detecting the induced voltage on said another field coil during the detection phase; a magnetic pole position detecting circuit detecting a magnetic pole position of a rotor based on an amplitude of said induced voltage; a driving circuit determining a power supply phase for drive of the motor based on the magnetic pole position, and executing power supply for drive depending on the power supply phase; a control circuit alternately conducting detection of the magnetic pole and power supply for drive of the motor by said driving circuit when a rotating speed of the motor is less than a predetermined speed; and a back electromotive force detecting circuit detecting a back electromotive force on said field coil so as to determine the power supply phase when the rotating speed of the motor is greater than said predetermined speed, with drive of the motor being executed based on a detection result of the back electromotive force detecting circuit.