Chopping is generally used with circuits where the supply
voltage is considerably higher than the rated voltage of
the stepper motor. The chopping is used to implement a
form of more or less constant current control.

Applying a constant current control to the steppers instead
of a constant voltage allows larger initial voltages and
results in better motor torque and faster stepping rates.

I said that chopping is a form of more or less constant
current control because the mechanism by which the chopping
is implemented usually involves a periodic turn-on time
with the turn off being achieved when the current exceeds
a certain threshold. Thus there can be a certain looseness
in the average current value, but it is quite tolerable.

If your voltage is close to the rated voltage of the steppers,
then chopping will gain you nothing.

Fr. Thomas McGahee


 > -----Original Message-----

> I'm looking for a chopped bridge driver, preferrably a dual, for use >with
low voltage (6V-8.5v) motor supplies.
>
> Everything I've found so far wants at least 10V, but I don't have 10V >to
give!
> --
> Dave's Engineering Page: http://www.dvanhorn.org
>

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