| 摘要 |
PROBLEM TO BE SOLVED: To stabilize rotational speed of a single-phase induction motor at a low speed, such as a fan motor and the like by a simply structured speed control circuit. SOLUTION: This control circuit is constituted by connecting a single-phase induction motor 2, a diode bridge 3 and a thyristor SCR with an AC power source 1, and connecting a DC circuit of a variable resistor VR and a capacitor C1 in parallel to the thyristor SCR. When the charged voltage of an added capacitor C1, which is added from the middle connected point 4 to an SCR gate through a programmable unijunction transistor PUT exceeds trigger voltage, the SCR is switched on. A rotational speed detector 11 is combined with a motor 2 and DC output voltage is applied into PUT through a constant voltage diode ZD. When charged voltage of the capacitor C1 exceeds trigger voltage sufficient at least for switching on SCR at the stationary time of the motor 2, the PUT is switched on to ignite and switch on the thyristor SCR. |
