High precision, good accuracy Current Source Schematic

[_maxim_]

Sorry for delay, just don't get to everything anymore.
Beware of that "smartfortress virus" it's out again ...

So happy to be an "old" Linux user who uses windows only for playing chess...

Okay - your scheme is so good it doesn't need much change i think.

All I did was three things:

1. make Vref variable to give 0-300ma adjustment range with 10 ohm R1.

To that end, Added Radj a ten turn pot with locking dial. That let's you set current by a ten turn dial with good resolution.
http://search.digikey.com/us/en/products/3590S-2-502L/3590S-2-502L-ND/1088592
http://search.digikey.com/us/en/products/H-22-6A/H-22-6A-ND/499307?wt.z_cat_cid=Dxn_US_US2011_Catlink

Added a buffer voltage follower amp A2 to Radj. 500 and 2500 ohm divider on output make his output 0-3 volts for 0-2.5 in. If you use instead ADR3430, omit those resistors.
A2 can be another AD8603, or half an AD8607 with other half replacing your 8603
http://www.analog.com/en/all-operat...plifiers-op-amps/ad8607/products/product.html

The buffer keeps the resistance of your potentiometer from appearimg in series with Mr8276's internal 40K resistors.

That's ok for me.

2. Added provision for "Criss-Cross" jumpers at inputs of Mr AD8276.
That let's you use either NPN or PNP driver.
Install horizontal jumpers for NPN like your 2N1711 or one of Yungman's Mosfets
Install diagonal jumpers for PNP like my TIP125.

Simply so smart!

3. Showed three dots instead of drive transistor.
Make two sets of holes on you board, one set for TIP and another for your 2N1711.
That way you can use either NPN or PNP or MOSFET driver, emitter up for PNP and emitter down for NPN.

Yes, I see.


http://s232.photobucket.com/albums/ee289/oldjimh/?action=view&current=ForMaxim1001.jpg

NOW while typing i realized that you may not need infinite adjustment.
If not, consider this:
Omit buffer and Radj, go back to 2.5 volt Vref.
Make your R1 measuring resistor be three 25 ohm resistors and a switch that let's you select one, or two or three of them in parallel. That'll give you 100, 200 or 300 ma.

And in keeping with Detecive Columbo's "One Last Thing";;

Yungman's sketch in post 10 had a capacitor to stabilize things. Always a good idea.
That additional stage behind Mr8276 increases his open loop gain , but only if we use PNP driver.
Sooo we should add a zero ohm resistor (jumper) between top of driver transistor
and Vsupply , to be replaced with just a couple ohms to reduce loop gain in case PNP exhibits instability.
Can add that to sketch.

What's your thoughts so far?

This circuit is a wonderful solution!
I will keep you informed about progress.

i see size is a matter. That ten turn pot is big.

BTW while you're experimenting, try that LM317 circuit from post 14

1.25V/.1amp = 12.5 ohms

Right. I will try also the LM317' solution: easy and compact.