Re: Question re: about current control schematic

Oops . . .

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "grantfair2001"
<grant.fair@s...> wrote:

> 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.

Suded later emailed me back to say you are right Jon, about the
emitter and collector needing to be reversed.

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