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

摘要

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 ( 6 ) includes: counter electromotive voltage filter circuits ( 16 _U , 16 _V , 16 _W) for inputting 3-phase counter electromotive voltage induced at the end of each of the stator coils (L_U, L_V, L_W) and switching between a first and a second time constant according to the rotation speed of the rotor (R_O) so as to pass a low-range frequency component corresponding to the time constant; counter electromotive voltage detection comparators ( 17 _U , 17 _V , 17 _W) 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 (P_U, P_V, P_W) as the comparison results; and a motor driver control circuit ( 15 a) for switching/controlling the time constant of the counter electromotive filter circuits ( 16 _U , 16 _V , 16 _W) and controlling the motor driver ( 5 ) according to the counter electromotive voltage polarity signals.