Re: Allegro 3967 chip driver board

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Charles Knight <charles@i...>
wrote:

> >
> >
> >I double checked Allegro's site.
> >
> >these are limited to tiny steppers with a current draw of 750 mA.
> >
>
> Well, I had the thought that I might be able to take the outputs,

and

> use them to drive some transistors...multi stage, if you will

forgive

> the rather crude description. The output is, after all, defined by

the

> load supply...up to 30V, but 5V would provide just the right

signals for

> a transistorized second stage.

> Would this work, or am I just barking up the wrong tree? Basically

I

> want to use it as a stepper translator only.
>
> -- Chuck Knight

Chuck: In looking at the data sheet you may have a problem. The
chip has built in H bridges for each coil. That will not give you
the right set of logic signals to drive an external bridge (or even
unipolar configurations. By the time you add enough circuitry to
translate the outputs so you can drive FETS in a bipolar arrangment
you can add a few more parts and build a descreet motor drive. If
you plan on using more than about 35V you will also have to deal with
turning on the high side FETS using a charge pump scheme. This chip
does not appear to be the solution for a low cost micro stepping
motor driver unless you can find some really low current (< 750 ma )
motors. I would probably make a cute science fair project....

Tom