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Stepper Fundamentals Slide 19

One way to reduce the time constant while maintaining the same peak current is shown here. By placing a resistor in series with the motor winding and increasing the drive voltage, the same motor current can be achieved, however the time constant, which is L over R, is decreased. This drive technique, called L over nR, was very common in early line printer applications that needed a faster response from the stepper motor. Going back to the example motor, if the supply is increased to 25V and an external 20Ω resistance is added, a 1A current is still available, but the rise time is significantly reduced.

PTM Published on: 2011-12-14