Stepping motor excitation circuitry

Abstract

Circuitry for driving stepping motor coils through a sequence of discrete steps, each winding of the stepping motor having drive circuitry which includes a first, low power circuit, having a regulated power supply, for supplying a substantially constant voltage and a second, high power circuit having a transistor constant current circuit, the substantially constant voltage being supplied to the base thereof. The second circuit can use a substantially unregulated power supply, the voltage of which may vary considerably. Such second circuit, however, supplies a substantially constant current pulse to its associated stepping motor winding even if the unregulated power supply voltage varies over a relatively wide range. The same circuitry configuration is used for each winding so that the current pulses supplied to each winding are substantially the same even if the winding resistances differ from winding to winding. Such circuitry is extremely effective when used for positioning the read/write heads of a disk storage device in a data processing system wherein rapid and accurate positioning of such heads relative to the disk surface is required. The heads can be controlled to move in a manner which permits them to be stopped at a desired position substantially at zero velocity so that little or no oscillation thereof occurs.