| 摘要 |
PROBLEM TO BE SOLVED: To provide a sensorless driving circuit of a brushless DC motor which enables the stable driving of the brushless DC motor even if a load is suddenly changed and a power supply voltage is suddenly changed in a low speed and high load operation. SOLUTION: The level of a commutation command is switched from HIGH to LOW in an intermediate zone between 1st and 2nd current increase regions after the command is generated. By this switching, an analog switch AS1 is turned off. A voltage value (instantaneous output) of a current detection circuit 4 immediately before the turning-off is held in a sampling circuit 5, amplified approximately 1.6 times by an amplification circuit 6 and outputted to a target value control circuit 8 through a priority circuit 9. As the target value control circuit 8 keeps a commutation target voltage higher than a commutation target wave peak value at every commutation command, the commutation command is prohibited. A commutation target voltage outputted from the target value control circuit 8 is outputted to a commutation command circuit 10. If a voltage value outputted from the current detection circuit 4 reaches a value certain times of the output voltage value of the sampling circuit 5, the commutation command circuit 10 outputs one-shot pulse to a numerical circuit 13 and the commutation of a brushless DC motor 51 is practiced by a distribution circuit 14 and an inverter circuit 3. |
