Re: Question re: about current control schematic

I did contact the author of the schematic, Suded Emmanuel. He
confirmed that the base should not go to ground.

However, he states that the emitter and collector are appropriately
positioned in the diagram, and that the circuit has been tested in
that configuration and works fine. Well, at least a smoke test has
speed to recommend itself.

Grant

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> grantfair2001 wrote:
>
> >An article about current control in steppers by Suded Emanuel at:
> >
> >http://www.eio.com/crntctrl.htm
> >
> >has a schematic. When I asked on the Nuts and Volts Forum about using
> >a mosfet instead of the Darlington, I got this reply:
> >
> >"Wow, that schematic appears to have multiple errors. At least two at
> >first glance. It looks like they are trying to do a classic buck
> >regulator. The base of the BDW84 is grounded, which means the PWM chip
> >can't do anything to affect it.
> >
> Yup, the line should be broken. The diode should be grounded, and not
> connected to the base. But, the way they have it drawn, the
transistor is
> STILL hooked up wrong. It looks like they have the emitter and
collector
> interchanged!
>
> > D1 should be grounded, but not the
> >transistor base. Also, looks like the BDW84 is in backwards (collector
> >and emitter reversed). So, be aware of that in any case."
> >
> >I don't know enough about electronics to know if this is true. Any
> >comment from the electronically unimpaired appreciated.
> >
> >
> But, finally, this is a HORRIBLE circuit! It runs the motors as
> unipolar, and makes no provisions for individual control of the
> current in each phase! It will have HORRIBLE performance at
> higher speeds, and will likely blow T1-T4 with any motor larger
> than the ones in floppy drives, since no provision is made at all
> for the inductive energy in the windings. I'd drop it and look for
> a better circuit right away.
>
> Jon