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Stepper Fundamentals Slide 12

The simplest topology is to drive the motor with the rated voltage and simply switch the coils in sequence, as shown in the full step or half step sequences. The figure here represents such a drive topology. The circuit has been simplified with the single transistor representing one of transistors of a unipolar drive or the composite of two transistors in the bridge of a bipolar drive. When the phase is energized the current will increase exponentially until it reaches a value that is equal to the supply voltage divided by the motor resistance, Rc. The time constant of the exponential is L divided by R which gives rise to the name L over R drive. This drive configuration is very simple, requires no additional components beyond those required to control the current sequence and operates from a single supply voltage. However, it exhibits relatively low performance in terms of the speed torque profile. One of the reasons the performance is limited is due to the inductive properties of the coils that limit the rate of change of current.

PTM Published on: 2011-12-14