Re: micro wire-edm project (and software solution)

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler" <eexgs@n...>
wrote:

>
>
> > A current sense resistor has to be able to handle the total current.
> > diodes are cheap in comparison. They have a high voltage drop which
> > is not always a good thing, but can make monitoring the current easy.
> > But, did I mention they are cheap ?
> >
>
> I am still a little confused as the voltage drop over a diode will be
> its forward voltage and that is not normally very large. The voltage
> drop will not be proportional to current and as you would still need
> to limit the current you could use the current limiting resister.
>
> > Many of the low end RC EDM machines use them as the sense voltage
> source.
>
> So they are not using them as a voltage references?
>
> I will probably measure gap voltage anyway to be quite honest and if I
> were to use a shunt it could be a tiny value, at the low intended
> currents it would not need to be all that big or expensive.
>
> Graham
>

ummm..... I have to check the schematics. I know of at least two
very widly known circuits that use diodes between the part and ground
and connect an op-amp or comparator across it.


Dave