Prev: PicKit 2 WARNING (problem solved)
Next: Kindle/Sony? (was: MIT rad lab series)
From: Nico Coesel on 18 Sep 2009 17:03
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

Is it for testing where manual adjustment is allowed? If yes, you can
use a transistor controlled by a potmeter.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
"If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------
From: George Herold on 18 Sep 2009 19:53
On Sep 18, 9:19 am, Steve <st...(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
>
>
>
> <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
> >>http://cds.linear.com/docs/Datasheet/1167fa.pdf
> >Is it single sided?  - Hide quoted text -
>
> - Show quoted text -

How much money can you spend? I like the lm395? 'npn' power
transistor. It's got thermal shutdowns if you over drive it so it's
hard to kill. 2A at 10V leaves 5V to drop on the current sense
resistor. So 2 ohms might work... at the low end you've got to set
the voltage to a microvolt to get your 0.5ua spec. That might be
doable?

George H.
From: George Herold on 18 Sep 2009 20:04
On Sep 18, 11:58 am, John Larkin
<jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> On Fri, 18 Sep 2009 09:19:28 -0400, Steve <st...(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
> ><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
>
> >>>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- Hide quoted text -
>
> - Show quoted text -

Yeah, I if you can float the load, then tie the sense resistor to
ground. If not you have to tie it to the positive rail. And then use
the positve rail as the voltage reference...(can be a pain.) If you
want it to be voltage programable then the easist is to use ground as
the reference.

Switchable resistors as John L. suggests are a good solution to the
resolution issue.
George H.
From: George Herold on 18 Sep 2009 20:14
On Sep 18, 1:41 pm, John Larkin
<jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> On Fri, 18 Sep 2009 12:39:56 -0400, Steve <st...(a)nomail.net> wrote:
> >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....
>
> Fig 2 is insane. It must be drawn wrong. Most EDN "design idea"
> schematics are.
>
> John

OK, I was going to use one opamp and one transistor. That does look
crazy. Every once in a while I find something that works in the EDN
archives. but hardly anything from this decade.

George h.
From: Phil Hobbs on 18 Sep 2009 20:51
Jim Thompson wrote:
> On Fri, 18 Sep 2009 10:41:36 -0700, John Larkin
> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:
>
>> On Fri, 18 Sep 2009 12:39:56 -0400, Steve <steve(a)nomail.net> wrote:
>>
>>> 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
>>
>> Fig 2 is insane. It must be drawn wrong. Most EDN "design idea"
>> schematics are.
>>
>>
>> John
>>
>
> Nowadays EDN is so short of contributors that most "designs" come from
> third world countries ;-)
>
> ...Jim Thompson

Now _that_ is a riot. Two instrumentation amps, and all it's measuring
is the offset voltage of the buffer. It does null that out reasonably
well, but not as well as an op amp and a feedback resistor....

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4 5
Prev: PicKit 2 WARNING (problem solved)
Next: Kindle/Sony? (was: MIT rad lab series)