| 摘要 |
PURPOSE:To prevent rupture of a semiconductor switching group in a way that an overcurrent is prevented from flowing to the winding of a brushless motor by a method wherein when an air velocity value exceeds a specified value, on on-off means is turned OFF. CONSTITUTION:A thermistor 21 is mounted in a place where an external air force is exerted and a thermistor 22 in a place where no external force is exerted. Since a thermistor self-generating heat produces a difference in a radiation amount according to the presence of an external air force and a thermistor temperature is changed, a difference in a resistance value is produced. By comparing resistors 23 and 24 with a partial voltage by means of a comparator 25, it is decided whether an external air force exceeds a specified value. Since the thermistor 21 is mounted in a place where the external force is exerted, when an external air velocity exceeds a specified value, and when voltage division points V1 and V2 are compared with each other, the resistance value of the thermistor 21 is increased to a value higher than the resistance value of the thermistor 22. Thereby, V1 is higher than V2, an output from the comparator 25 produces 'L', and a relay 30 is brought into an OFF-state through monostable multivibrator 26 for a specified time. |
