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msmukund2000
12-12-2004, 07:41 PM
hi,
i hjave a bipolar stepper
so will it turn if i just give 5V DC directly to its input terminal?
please answer, (it doesnt,what i wanna kno is, should it?)

ashish_bhat
12-12-2004, 10:52 PM
a bipolar stepper has 2 coils, each generating a magnetic field in perpendicular directions. the rotor is a permanent magnet (with many poles). so just giving a DC supply to coil(s) will generate a constant magnetic field. the permanent magnet will not rotate but lock to a position nearly parallel to the magnetic field. you will get "holding torque" which is an important property of a stepper motor.

to make a stepper rotate you have to generate a rotating magnetic field. this is done by switching currents on/off as well as changing their directions so that you get a "stepped" rotating magnetic field. this is usually done using two h-bridges (one for each coil). (L293 / L298 etc.)

on the other hand a uni-polar stepper has 4 coils. two coils generate a magnetic field in one direction but opposite to each other and other two coils generate a magnetic field in their perpendicular direction, opposite to each other. so to make a unipolar stepper turn u only have to switch coils on/off without needing to change current directions. this can be done using four transistors (or transistor arrays like ULN2003/2803)

Ashish