| 摘要 |
PURPOSE:To prevent the damage of a motor by detecting the decrease in the motor speed due to an overload by the decrease in counterelectromotive force of the motor and stopping the supply of voltage to the motor. CONSTITUTION:The output voltage V2 of an operational amplifier 10 is varied in response to the input voltage V1, and the base currents of transistors 17, 18 will thereby vary. When the motor M becomes an overload state so that the rotating speed is decelerated, the counterelectromotive force (e) becomes low and the current IC increases. Thus, the emitter voltage VE of the transistor 17 is raised, and the output voltage V2 of the amplifier 10 is lowered, thereby interrupting the transistor 13. When the transistor 13 becomes OFF, the drive circuit 19 becomes in OFF state, and the current IC becomes zero. Thus, a protecting operation having good responsiveness can be obtained. |
