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Types of Drivers

For industrial applications there are basically three types of driver technologies. They all utilize a "translator" to convert the step and direction signals from the indexer into electrical pulses to the motor. The essential difference is in the way they energize the motor winding. The circuit that performs this task is known as the "switch set."

UNIPOLAR

The name unipolar is derived from the fact that current flow is limited to one direction. As such, the switch set of a unipolar drive is fairly simple and inexpensive. The drawback to using a unipolar drive however, is its limited capability to energize all the windings at any one time. As a result, the number of amp turns (torque) is reduced by nearly 40% compared to other driver technologies. Unipolar drivers are good for applications that operate at relatively low step rates.

RESISTANCE LIMITED (R/L)
R/L (Resistance / Limited) drivers are, by today's standards, old technology but still exist in some (low power) applications because they are simple and inexpensive. The drawback to using R/L drivers is that they rely on a "dropping resistor" to get almost 10 times the amount of motor current rating necessary to maintain a useful increase in speed. This process also produces an excessive amount of heat and must rely on a DC power supply for its current source.