Patent ID: 7492113

Claim:
A brushless motor drive control circuit for controlling, through a motor driver, drive of a brushless motor whose rotor is rotated by the flow of a driving current to 3-phase stator coils having one end connected to a common neutral point, comprising: at least one counter electromotive voltage filter circuit for inputting a voltage at the neutral point and a counter electromotive voltage induced at the other end of each phase of the stator coils and switching at least between first and second time constants according to a rotation speed of the rotor to pass a low-range frequency component corresponding to the time constant, at least one counter electromotive voltage detection comparator for comparing the counter electromotive voltage which has passed through said counter electromotive voltage filter circuit and the voltage at said neutral point to output a counter electromotive voltage polarity signal as the comparison result, and a motor driver control circuit responsive to said counter electromotive voltage polarity signal for controlling switching of said time constant of said counter electromotive voltage filter circuit and controlling said motor driver.