Bipolar and Unipolar Drives for Stepper Motors: A Comparison

A stepper motor is a type of brushless DC motor comprised of connected coils called “phases.” These electromechanical devices are generally driven in open loop without a feedback sensor, with current applied on the phases without knowing the rotor position. The rotor moves into alignment by means of the stator’s magnetic flux, generated by the current flowing in the phases. At each pulse, the current can be supplied to the next phase, allowing incremental rotational movements, or steps.