| 摘要 |
PURPOSE:To improve the safety of a motor by a method wherein a protective capacitor which is connected in parallel to an internal motor protective circuit and has a capacity which is not fully discharged during the cut-off period of a speed control transistor is provided. CONSTITUTION:During the H-level period T1 of a pulse signal (c), as a speed control transistor 12 is closed, the state is equivalent to a state wherein speed control is not performed. During the L-level period of the pulse signal (c), even if the speed control transistor 12 is open, a voltage not lower than a certain value is applied between both the terminals of an internal motor protective circuit 3 by the existence of a protective capacitor 20. As a result, a capacitor 8 is not discharged significantly unless a transistor 9 is closed. Therefore, as the terminal voltage Vc of the capacitor 8 is elevated if a locking phenomenon is created during the L-level period of the pulse signal (c), an H-level exciting current cut-off command signal (b) is transmitted from a comparator 11 to cut off an exciting current, so that the motor can be protected. |
