SPEED AND TORQUE CONTROL FOR FRACTIONAL HORSEPOWER MOTORS HAVING VARIABLE DUTY CYCLE SUPPLY

摘要

"SPEED AND TORQUE CONTROL FOR FRACTIONAL HORSEPOWER MOTORS HAVING VARIABLE DUTY CYCLE SUPPLY" Power control circuitry for supplying pulses of power from a power source to a fractional horsepower motor with a plurality of power pulses applied to the motor during each half cycle of the power source waveform for more uniform speed and torque characteristics of the motor at low speeds. A timing capacitor in a motor speed control portion of the circuitry has a constant sum of resistances in the charge and discharge paths for fixed frequency of power pulses applied to the motor. The timing capacitor is electrically connected to a wiper arm of a variable resistor located in both the charge and discharge paths such that resistance may be shifted between the paths to vary the duty cycle of the pulses over a wide range. A pulse generating portion of the circuitry includes a threshold comparator and a trigger comparator to respectively monitor the voltage on the timing capacitor for high or low conditions and cause a bi-stable circuit to change output states upon the occurrence of either condition to generate a train of pulses. The bistable circuit is adapted to control the conductive states of transistors in series connection between the motor and the power source to apply repetitive constant-freguency, variable duty cycle pulses of power from the power source to the motor in accordance with the train of pulses. Related methods are also disclosed.