| 摘要 |
PURPOSE:To prevent the production of unpleasant noise due to the vibration of a load at the time of switching a speed based on a requested speed of the load by reducing the variation in the drive voltage and reducing the variation in the torque of a transistor motor. CONSTITUTION:When a speed shift switch 17 is set to a terminal m' to shift the low speed to middle speed during low speed by setting the switch 17 to a terminal l' in case that a blower is driven by a transistor motor 10, the compared voltage to a comparator 20 is gradually raised by a delay circuit 30. In this manner, the duty of a switching signal outputted from the comparator 10 is gradually varied. Accordingly, the drive voltage supplied from a switching power source circuit 14 to the motor 10 gradually increases. The switch 17 for shifting from the middle speed operation to the high speed operation is set to a terminal h', the operation is similarly performed. |
