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From: Steve on 17 Sep 2009 19:56
I need an adjustable constant current source than can be set to
anywhere between 0.5 microAmps and 2 Amps. An output compliance
voltage of say 10 volts should be sufficient. The LT1167 data sheet
has a current source with 2 pA resolution. An earlier version of its
data sheet showed a plot spanning 8 decades up to 10 mA. My dynamic
range is 4 E+6 but needs to go to higher currents. I'm concerned
about offsets, etc restricting the lower range if I tried to construct
a similar instrumentation amplifer from 3 individual op amps using one
capable of high currents such as the OPA548 or LM675

http://cds.linear.com/docs/Datasheet/1167fa.pdf

From: Tim Williams on 17 Sep 2009 21:12
On Sep 17, 6:56 pm, Steve <st...(a)nomail.net> wrote:
> I need an adjustable constant current source than can be set to
> anywhere between 0.5 microAmps and 2 Amps.  An output compliance
> voltage of say 10 volts should be sufficient.

What's wrong with a TIP31? Put an op-amp around it if you need. I'm
willing to bet leakage will be plenty low (as long as you keep it
cool). I've used a 2N4401 current mirror from nanoamps to 10mA, made
a function generator that ran as slow as 1Hz and as fast as 4.5MHz. :-
D

Tim
From: George Herold on 17 Sep 2009 21:37
On Sep 17, 7:56 pm, Steve <st...(a)nomail.net> wrote:
> I need an adjustable constant current source than can be set to
> anywhere between 0.5 microAmps and 2 Amps.  An output compliance
> voltage of say 10 volts should be sufficient.  The LT1167 data sheet
> has a current source with 2 pA resolution.  An earlier version of its
> data sheet showed a plot spanning 8 decades up to 10 mA.  My  dynamic
> range is 4 E+6 but needs to go to higher currents.  I'm concerned
> about offsets, etc restricting the lower range if I tried to construct
> a similar instrumentation amplifer from 3 individual op amps using one
> capable of high currents  such as the OPA548 or LM675
>
> http://cds.linear.com/docs/Datasheet/1167fa.pdf

Hmm 2A at 10V is getting up there. Is it single sided? Then an opamp
driving a transitor might work. The LM675 always seems to have some
wiggies near zero crossing. There's an OPA power opamp I like, not
sure 548 is the right number.

George H.

From: George Herold on 17 Sep 2009 21:37
On Sep 17, 7:56 pm, Steve <st...(a)nomail.net> wrote:
> I need an adjustable constant current source than can be set to
> anywhere between 0.5 microAmps and 2 Amps.  An output compliance
> voltage of say 10 volts should be sufficient.  The LT1167 data sheet
> has a current source with 2 pA resolution.  An earlier version of its
> data sheet showed a plot spanning 8 decades up to 10 mA.  My  dynamic
> range is 4 E+6 but needs to go to higher currents.  I'm concerned
> about offsets, etc restricting the lower range if I tried to construct
> a similar instrumentation amplifer from 3 individual op amps using one
> capable of high currents  such as the OPA548 or LM675
>
> http://cds.linear.com/docs/Datasheet/1167fa.pdf

Hmm 2A at 10V is getting up there. Is it single sided? Then an opamp
driving a transitor might work. The LM675 always seems to have some
wiggies near zero crossing. There's an OPA power opamp I like, not
sure 548 is the right number.

George H.

From: Bill Sloman on 18 Sep 2009 07:41
On Sep 18, 3:37 am, George Herold <ggher...(a)gmail.com> wrote:
> On Sep 17, 7:56 pm, Steve <st...(a)nomail.net> wrote:
>
> > I need an adjustable constant current source than can be set to
> > anywhere between 0.5 microAmps and 2 Amps.  An output compliance
> > voltage of say 10 volts should be sufficient.  The LT1167 data sheet
> > has a current source with 2 pA resolution.  An earlier version of its
> > data sheet showed a plot spanning 8 decades up to 10 mA.  My  dynamic
> > range is 4 E+6 but needs to go to higher currents.  I'm concerned
> > about offsets, etc restricting the lower range if I tried to construct
> > a similar instrumentation amplifer from 3 individual op amps using one
> > capable of high currents  such as the OPA548 or LM675
>
> >http://cds.linear.com/docs/Datasheet/1167fa.pdf
>
> Hmm 2A at 10V is getting up there.  Is it single sided?  Then an opamp
> driving a transitor might work.   The LM675 always seems to have some
> wiggies near zero crossing.  There's an OPA power opamp I like,  not
> sure 548 is the right number.

I like the LM12. It's input bias current is to high - at 1uA max - for
it to be a one-stop solution, but a monolithic dual FET front end
might get it there, if you can find one - Farnell have still got a few
Vishay 2N5912 parts, but only until the stock runs out.

--
Bill Sloman, Nijmegen
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