| 摘要 |
PROBLEM TO BE SOLVED: To realize a sensorless brushless DC motor without using a CPU. SOLUTION: The rotary mechanism section 3 of a brushless DC motor comprises three drive coils W1-W3 arranged at an interval of 120 deg., and a pole rotor R being rotated upon conduction of the drive coils wherein the pole rotor R is rotated by conducting three drive coils sequentially. When the pole rotor R is located above one coil (e.g. W1), counter-electromotive forces induced in two other coils (W2, W3) are detected and pulse signals (L1+, L1-; L2+, L2-; L3+, L3-) including the 0 level of respective counter-electromotive forces at the center are obtained. The pulse signal serves as the switching signal of a circuit 6 for driving the drive coils wherein the width of the pulse signal is substantially constant regardless of the revolutions of the motor and when the load increases, the pulse width enlarges to increase torque. |
