Brushless motor drive control circuit and brushless motor device using the same

Abstract

There is provided a brushless motor drive control circuit capable of assuring an S/N ratio of a predetermined counter electromotive voltage and suppressing lowering of efficiency of a brushless motor at a high-speed rotation. More specifically, the brushless motor drive control circuit includes: counter electromotive voltage filter circuits for inputting 3-phase counter electromotive voltage induced at the end of each of the stator coils and switching between a first and a second time constant according to the rotation speed of the rotor so as to pass a low-range frequency component corresponding to the time constant; counter electromotive voltage detection comparators for inputting the counter electromotive voltage which has passed through the counter electromotive voltage filter circuit and comparing it with voltage at a neutral point so as to output counter electromotive voltage polarity signals as the comparison results; and a motor driver control circuit for switching/controlling the time constant of the counter electromotive filter circuits and controlling the motor driver according to the counter electromotive voltage polarity signals.