Re: Allegro 3967 chip driver board

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "caudlet" <info@t...> wrote:

> --- 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

I had considdered a similar idea with the A3977, but ther is no way
to get feedback into the chip to tell the logic when to chop the
output. normally, it is connected to the motor and senses the motor
and chops the current at the proper points. when you drive MOSFET's
or Darlingtons, you loose the motor feedback and only see those chips.

But, I think many of us wish that Allegro would make the logic chip
to drive user selected transistors.

And I too wish Allegro would offer thru hole chips and not just smt
packages for these chips.

Dave