Speed control means for AC motor

A speed control means for an AC motor comprising:

• a bi-directional rectifier adapted to be connected in series with an AC motor and a power source;
• a control circuit connected in parallel with said bi-directional rectifier and having a variable resistance element and a capacitor connected in series, the side of said capacitor opposite the side connected to said variable resistance element being adapted to be connected to one side of said motor;
• an unbalanced switching circuit connected between the gate terminal of said bi-directional rectifier and the junction between said variable resistance element and said capacitor and having different absolute values of positive and negative switching voltages;
• a fixed resistance and a first diode connected in series and being adapted to be connected in parallel with said power source, the anode of said first diode being adapted to be connected to the other side of said AC motor;
• and
• a second diode havng the cathode thereof connected to the junction between said fixed resistance and said first diode and the anode connected to the junction between said variable resistance element and said capacitor, whereby when the speed of rotation of the motor tends to increase, the time during which said bi-directional control rectifier is conductive is reduced, whereas when the speed of rotation of the motor tends to decrease, the time during which said bi-directional control rectifier is conductive is increased, thereby to keep the rotary speed of said motor constant.