[volt-nuts] LM399 selection test PCB

Ian Johnston ian at ianjohnston.com
Wed Nov 25 17:29:14 EST 2015

Hi all,

Thought you guys might be interested in a small PCB I made in order I 
could test, select & check pre-age (if there is such a thing!) my LM399's.

10 channel.
Each channel has it's own chopper op-amp (self bias the LM399),
2ppm/degC tempco resistors throughout,
2x2 sockets for the LM399's (same footprint).
Test points for each channel.
Jumper link on the power rail to disable each channel individually 
(op-amp and heater power).
Holes around each LM399 footprint to help isolate any thermal stress.


So far it's working out great.......i've already discovered one of my 
LM399AH's (sitting in ch.4 in the photo) is somehow unstable. It's 
output jumps around by about 10uV's. Need to investigate........

The idea is that I can test, select and pre-age LM399AH's before 
soldering them into my target PCB's. I understand that soldering 
can/will reset any aging.......but I figured it might help.

I did a pre-test on those Ebay LM399's I bought and they seem to work 
ok.......still to properly evaluate.....but I do notice that the new 
ones's I bought from Digikey are all giving over 7Vdc, the Ebay ones all 
well under 7Vdc.



/"because it feels good to make stuff"/

[Sent by MDaemon Mail Server at IanJohnston.com]

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