| 摘要 |
PURPOSE:To inexpensively provide a control circuit by detecting the rotating speed of a motor with a magnet and a reed switch, thereby eliminating a tachometer generator. CONSTITUTION:When a motor 2 is rotated, a pulley 28 rotates at the speed proportional to the rotating speed, and a reed switch 32 is switched ON or OFF by a magnet 1. When the switch 32 is OFF, a current flows in the sequence of a diode 42, a capacitor 47 and a resistor 52, thereby charging a capacitor 47. Then, when the switch 32 is ON, a transistor 35 is conducted, and the voltage of the capacitor 47 becomes the emitter potential of the transistor 35. Thus, the cathode voltage of the diode 41 is varied in response to the rotating speed of the motor 2. When the rotating speed, for example, gets high, the cathode voltage is raised, and when it becomes higher than the potential of the divided voltage of the resistors 55, 56, the gate potential of a PUT 34 is raised, thereby reducing the voltage applied to the motor 2, and the speed is restored to the constant value. |
