Re: Electronics gurus please help

I apologize for the quality, but I uploaded a JPEG of this schematic
to the files section as "Unipolar Stepper Driver.jpg" with
description of "PIC Driven Unipolar Stepper Driver"

Hope you can read it.

It uses the PWM output of the PIC to set the comparator threshold for
the current limit. When the voltage across the sense resistor
exceeds this threshold the comparator signals an interrupt on the PIC
at which point the interrupt code turns off the outputs for about
25uS. It then turns the ouputs back on and the cycle repeats. The
proper output state is stored in a variable to make this easy.

If anyone is interested I can provide more details. I am only saying
this circuit is simple and it does work. As I recall I can only get
about 300 RPM out of a Vexta PH264 using this circuit, but that was
adequate for my needs at the time.

Scott

--- In CAD_CAM_EDM_DRO@y..., "Ian W. Wright" <Ian@i...> wrote:
> Hi Scott,
>
> This sounds like an interesting way of doing things - how about
putting your
> circuit in the files section?
>
> Best wishes,
> Ian
> --
>
> Ian W. Wright
> Sheffield, UK
>
>
> The following added for automatic email harvesters!
> abuse@w... abuse@p... abuse@b... abuse@y...
> UCE@F... abuse@t... abuse@f...
>
> ----- Original Message -----
> From: "Scott M. Thomas" <scott@d...>
> To: <CAD_CAM_EDM_DRO@y...>
> Sent: Wednesday, September 11, 2002 8:54 PM
> Subject: RE: [CAD_CAM_EDM_DRO] Re: Electronics gurus please help
>
>
> > Hmmm. I suppose you could use 6 if you want to. I built one
using a PIC
> > and chopped the input to the 4 "end" transistors, worked very
well. I
> also
> > used a common current sense resistor, so this simplified it even
further.
> >
> > I'll have to check out the voltage doubling effect, hadn't
thought of
> that.
> > But this shouldn't have a huge effect on things depending upon
the power
> > supply voltage.
> >
> > Thanks
> >
> > Scott
> >
> >
> > -----Original Message-----
> > From: mariss92705 [mailto:mariss92705@y...]
> > Sent: Wednesday, September 11, 2002 3:38 PM
> > To: CAD_CAM_EDM_DRO@y...
> > Subject: [CAD_CAM_EDM_DRO] Re: Electronics gurus please help
> >
> >
> > Scott,
> >
> > If it were an R/L drive you would be correct. The center-tap of
the
> > motor coil would go to the + supply thru a large current limit
> > resistor and the winding ends would have the transistors.
> >
> > Since a unipolar chopping drive was mentioned, 6 transistors are
> > required; the current limit resistor is replaced with a
transistor to
> > which pulse width modulation (chopping) is applied. The end
> > transistors still would behave the same.
> >
> > A center-tapped (6-wire motor) winding is a 2:1 step-up
transformer.
> > because the center tap goes to the + supply, pulling one end wire
to
> > ground causes 2 times the supply voltage to appear on the other
end.
> >
> > Mariss
> >
> > --- In CAD_CAM_EDM_DRO@y..., "Scott M. Thomas" <scott@d...> wrote:
> > > I count 4 mosfets not 6 for a unipolar drive, did I miss
> > something? And,
> > > because there are half the parts and no high side drivers
involved,
> > I would
> > > say that a unipolar drive is much simpler. I also don't
understand
> > why the
> > > voltages would be different.
> > >
> > > Scott
> > >
> > > -----Original Message-----
> > > From: mariss92705 [mailto:mariss92705@y...]
> > > Sent: Wednesday, September 11, 2002 12:59 PM
> > > To: CAD_CAM_EDM_DRO@y...
> > > Subject: [CAD_CAM_EDM_DRO] Re: Electronics gurus please help
> > >
> > >
> > > Hi,
> > >
> > > It takes 6 power transistors and 6 high speed rectifiers to
build a
> > > unipolar "chopper", it takes 8 power transistors and 8 high
speed
> > > rectifiers to make a bipolar (full bridge) one.
> > >
> > > The power rectifiers are not across the power transistors in the
> > > unipolar drive. If MOSFETs are used in a bipolar drive, the
> > > rectifiers are included in the transistors.
> > >
> > > The power transistors "see" twice the power supply voltage in a
> > > unipolar drive. In a bipolar drive, the maximum voltage "seen"
by
> > the
> > > power transistors is equal to the supply voltage.
> > >
> > > The performance of a unipolar drive is about equal to a bipolar
> > drive
> > > running a motor in a half-winding connection.
> > >
> > > A bipolar drive is prefered because it is simpler (when MOSFETs
are
> > > used) and the circuit voltages are lower.
> > >
> > > Mariss
> > >
> > > --- In CAD_CAM_EDM_DRO@y..., Vajk Fekete <vajk.fekete@o...>
wrote:
> > > >
> > > > question1: is a chopper unipolar driver much worse than a
chopper
> > > bipolar drive?
> > > >
> > >
> > >
> > >
> > > Addresses:
> > > FAQ: http://www.ktmarketing.com/faq.html
> > > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> > >
> > > OFF Topic POSTS: General Machining
> > > If you wish to post on unlimited OT subjects goto:
> > > aol://5863:126/rec.crafts.metalworking or go thru Google.com to
> > reach it if
> > > you have trouble.
> > > http://www.metalworking.com/news_servers.html
> > >
> > > http://groups.yahoo.com/group/jobshophomeshop I consider this
as
> > a sister
> > > site to the CCED group, as many of the same members are there,
for
> > OT
> > > subjects, that are not allowed on the CCED list.
> > >
> > > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY
POSTING
> > THEM.
> > > DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> > >
> > > Post messages: CAD_CAM_EDM_DRO@y...
> > > Subscribe: CAD_CAM_EDM_DRO-subscribe@y...
> > > Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@y...
> > > List owner: CAD_CAM_EDM_DRO-owner@y..., wanliker@a...
> > > Moderator: jmelson@a... timg@k... [Moderator]
> > > URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
> > > bill,
> > > List Mom
> > > List Owner
> > >
> > >
> > >
> > > Your use of Yahoo! Groups is subject to
> > http://docs.yahoo.com/info/terms/
> >
> >
> > Addresses:
> > FAQ: http://www.ktmarketing.com/faq.html
> > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> >
> > OFF Topic POSTS: General Machining
> > If you wish to post on unlimited OT subjects goto:
> > aol://5863:126/rec.crafts.metalworking or go thru Google.com to
reach it
> if
> > you have trouble.
> > http://www.metalworking.com/news_servers.html
> >
> > http://groups.yahoo.com/group/jobshophomeshop I consider this
as a
> sister
> > site to the CCED group, as many of the same members are there,
for OT
> > subjects, that are not allowed on the CCED list.
> >
> > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY
POSTING THEM.
> > DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> >
> > Post messages: CAD_CAM_EDM_DRO@y...
> > Subscribe: CAD_CAM_EDM_DRO-subscribe@y...
> > Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@y...
> > List owner: CAD_CAM_EDM_DRO-owner@y..., wanliker@a...
> > Moderator: jmelson@a... timg@k... [Moderator]
> > URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
> > bill,
> > List Mom
> > List Owner
> >
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
> >
> > Addresses:
> > FAQ: http://www.ktmarketing.com/faq.html
> > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> >
> > OFF Topic POSTS: General Machining
> > If you wish to post on unlimited OT subjects goto:
> aol://5863:126/rec.crafts.metalworking or go thru Google.com to
reach it if
> you have trouble.
> > http://www.metalworking.com/news_servers.html
> >
> > http://groups.yahoo.com/group/jobshophomeshop I consider this
as a
> sister site to the CCED group, as many of the same members are
there, for OT
> subjects, that are not allowed on the CCED list.
> >
> > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY
POSTING THEM.
> DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> >
> > Post messages: CAD_CAM_EDM_DRO@y...
> > Subscribe: CAD_CAM_EDM_DRO-subscribe@y...
> > Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@y...
> > List owner: CAD_CAM_EDM_DRO-owner@y..., wanliker@a...
> > Moderator: jmelson@a... timg@k... [Moderator]
> > URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
> > bill,
> > List Mom
> > List Owner
> >
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
> >
> >