Patent ID: 7466093

Claim:
A motor drive unit for driving a sensorless motor having a multiplicity of stator coils and a drive switching circuit for supplying drive current to said stator coils, said motor drive unit adapted to control the drive switching circuit by a drive signal, said drive unit comprising: a sequence circuit for providing said drive switching circuit with a rotor-position detecting signal for controlling said drive switching circuit such that, prior to starting up said sensorless motor, said multiple stator coils are supplied with rotor position detecting drive voltages that vary the middle point voltage of the respective stator coils but will not rotate said sensorless motor; and a matching-pattern detection circuit adapted to compare said middle point voltage of said multiple stator coils obtained under said applied rotor-position detection drive voltages with the detection reference voltage established on the basis of said rotor-position detection drive voltages, and determine whether or not the result of said comparison matches any one of predetermined detection logic patterns, wherein when they do match in said comparison, said motor drive unit generates a startup logic in accord with the rotor position specified by the matching detection logic pattern, but when they do not match in said comparison, said motor drive unit varies the detection reference voltage and causes said sequence circuit to generate a further rotor-position detecting signal to repeat detection of said rotor position.