Speed responsive motor control circuit

Abstract

A motor control circuit is provided for an appliance or the like of the type utilizing a speed adjustment device that controls an adjustable centrifugally controlled governor device. The governor includes a switch contact arrangement which is connected in the triggering circuit of a power switching device, a TRIAC for example, for selectively connecting the motor of the appliance to the power source connections. The switch contacts of the governor device open and close as the rotational speed of the motor increases and decreases respectively from the speed selected on the speed adjustment device. A variable impedance element mechanically coupled to and adjusted by the speed adjustment device is also provided in the triggering circuit of the power switching device in series with the governor switch contacts to vary the triggering of the power switching device as the speed setting is varied. Thus, a variable speed versus motor supply voltage characteristic is provided when the governor contacts are closed. A wider range of stable speed control is provided than is obtained with a governor device alone. Low speed cogging and high speed hunting problems are also minimized. The variable impedance element in various embodiments is arranged to provide a variable impedance characteristic over a portion of the speed adjustment device range and a fixed impedance over the remainder of the range.