Google Groups no longer supports new Usenet posts or subscriptions. Historical content remains viewable.
Dismiss

High accuracy digitally controlled currant source deign help

1 view
Skip to first unread message

Nir Goren

unread,
Jul 29, 2003, 10:42:20 AM7/29/03
to
Hi,

I need to deign a controlled current source for several tens of uA say about
150uA witch have to be very accurate and vary stable. I'd like to control
this source by some sort of DAC preferably use a 12bit V out DAC witch I
already have on board.

So far searching Analog, Liner ,Maxim, etc.. have gotten me no where.

Pleas help.

Nir goren

BGU uni

VLSI Center


Sir Charles W. Shults III

unread,
Jul 29, 2003, 9:56:50 AM7/29/03
to
Well, if you have a precision resistor you can use as a shunt, your DAC can
provide a voltage that will source the shunt resistor. The resistor will limit
your current, and if it is one megohm, you end up with a microamp per volt.
Now, for feedback, you can measure the voltage drop across the shunt and use
a precision op amp to compare the output voltage and the shunt voltage- this can
be your error signal. A little creative buffering and you can feed that voltage
back to the shunt resistor to correct for the error.
I'm sure that somebody in the group might have a better method, but that
comes to mind right away for me.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip


Nir Goren

unread,
Jul 30, 2003, 4:29:57 AM7/30/03
to
I feel kind of dumb to ask this, but what is a "shunt" ??

"Sir Charles W. Shults III" <aich...@OVEcfl.THISrr.com> wrote in message
news:C2vVa.176582$ic1.4...@twister.tampabay.rr.com...

Sir Charles W. Shults III

unread,
Jul 30, 2003, 3:43:25 AM7/30/03
to
Any path can be a shunt- in this case, you use a resistor. The dictionary
defines it as "a conductor having low resistance in parallel with another device
to divert a fraction of the current" but we can use a high resistance and
measure the voltage drop across it.
Given the resistance and voltage relationships, we can deduce the current
through the resistor by the voltage drop across it.

Laurence Dishman

unread,
Jul 30, 2003, 12:01:06 PM7/30/03
to
"Nir Goren" <ni...@bgumail.bgu.ac.il> wrote in message news:<bg5tko$89m$1...@news.iucc.ac.il>...


Use a PNP transistor with the emitter connected to a precision
resistor which is connected to V+. Connect a Digital to Voltage
Converter between V+ and the base of the transistor.

The Voltage across the resistor will be the same as the DAC voltage.
The current will be V/resistance. This current will be available at
the collector of the transistor.
>
> BGU uni
>
> VLSI Center

0 new messages