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From: Steve on 18 Sep 2009 09:19
Yes, it is single ended. And it is DC.

Being able to set the current level by an external voltage would be a
nice feature but not necessary.

On Thu, 17 Sep 2009 18:37:03 -0700 (PDT), George Herold
<ggherold(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

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


>Is it single sided?

From: Steve on 18 Sep 2009 10:32
The design that shows use of a follower to buffer the bias current to
provide 8 decades is actually Figure 4 of Design Note 182 at :
http://cds.linear.com/docs/Design%20Note/dn182f.pdf

On Thu, 17 Sep 2009 19:56:25 -0400, Steve <steve(a)nomail.net> wrote:

>I need an adjustable constant current source than can be set to
>anywhere between 0.5 microAmps and 2 Amps.
>...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.

From: Spehro Pefhany on 18 Sep 2009 11:43
On Thu, 17 Sep 2009 19:56:25 -0400, Steve <steve(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

Something like that circuit, with a MOSFET follower (and probably some
compensation), ought to work, assuming you're talking about 0.5uA
resolution, not generating an accurate 0.5uA current. If it's the
latter, I think you'll have a great deal of trouble covering that
range. If your sense resistor is 1 ohm (4W at 2A) then you'll only
have 500nV at 0.5uA, and the offset of the LT1167 is 40uV (A version)
which represents 40uA. 500nV is possible, but will be noisy and you
might have to wait something like half an hour after running at 2A for
the bulk of the thermal gradients to go bye-bye. Best avoided if
possible.

If you can put switches in there, two 2000:1 circuits (or three 200:1
circuits) are a lot easier than one attempting to cover 4E6:1.

From: John Larkin on 18 Sep 2009 11:58
On Fri, 18 Sep 2009 09:19:28 -0400, Steve <steve(a)nomail.net> wrote:

>Yes, it is single ended. And it is DC.
>
>Being able to set the current level by an external voltage would be a
>nice feature but not necessary.
>
>On Thu, 17 Sep 2009 18:37:03 -0700 (PDT), George Herold
><ggherold(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
>
>>> http://cds.linear.com/docs/Datasheet/1167fa.pdf
>
>
>>Is it single sided?

For a unipolar current source, it's silly to float the sense resistor
on top of the load, then work hard to take out the resulting errors.
It's more reasonable to nail one end of the sense resistor to a supply
rail.

But floating the sense resistor does sell a lot of high-performance
instrumentation amps.

Something like this, maybe:

ftp://jjlarkin.lmi.net/Isrc.JPG

To get your huge dynamic range, you'll need chopper opamps and maybe a
trim or two, or switch Rs to give two or three ranges.

John

From: Steve on 18 Sep 2009 12:39
I should have mentioned that more than one range is fine. I do need
to generate 0.5 microamps accurately.

EDN has a Design Idea from 5/14/09 showing transistors for higher
current. with some errors in connections of IC2
http://www.edn.com/article/CA6656306.html?talk_back_header_id=6598899#talkback

Yes, John it is written by a mfr of instrumentation amps.

On Fri, 18 Sep 2009 08:58:42 -0700, John Larkin
<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:

>But floating the sense resistor does sell a lot of high-performance
>instrumentation amps.

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