Speed control for d. c. motors

Claim 1

A speed control apparatus for a D. C. motor comprising, in combination, a D. C. motor whose speed is desired to be controlled, and means for controlling the speed of said D. C. motor, said speed control means comprising: Oscillator means comprising first and second transistors and a capacitor for producing a square wave oscillating signal; Means coupling said first and second transistors for effecting opposite respective conductive states thereof during operation; A third transistor connected in series with said D. C. motor and a source of supply, means connecting said second transistor to said third transistor such that conduction of said second transistor effects conduction of said third transistor; said oscillator means including: First circuit means including the base emitter path of said first transistor and an adjustable resistance element for charging said capacitor, said first circuit means being connected across said source of supply for charging said capacitor immediately upon the activation of said supply, said first transistor being rendered conductive during charging of said capacitor and being rendered non-conductive when said capacitor is charged; Second circuit means including the collector emitter path of said second transistor and an adjustable resistance element for discharging said capacitor; and Wherein the mark-space ratio of said oscillator means is controlled by varying said adjustable resistance elements.