Re: Question re: about current control schematic

Jon-

Sorry, last message got sent prematurely. I am willing to look for
other circuits - any suggestions? I am interested in more current than
what some chips like the LM298 (2 amps, I think) can provide.

And since I have the parts for this circuit, I might as well make one,
more because I have invested the time on the PCB layout. I do have a
use for chopped current control for a unipolar motor although I
understand some of the shortcomings of this circuit which you outline.
I don't know why it will be terrible at high speeds, can you explain?

I am confused about the use of diodes to deal with the current in
coils which are turned off. I understand the need to put a diode
accross a relay coil because of this. In the configuration shown will
a diode between ground and the other end of each coil do what is
needed? I have seen other arrangements (I think) but have not
understood the reasons for one approach over another.

Thanks again!

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.

Jon wrote:

> 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