DIY V2 Open Source LM399 10V Calibration Reference Board

[@pault6533]

The LM399 device is already temperature stabilized and thermally insulated, so the foam is unnecessary. The buffer circuit is where you may find a greater variation with temperature. Using temperature stable high accuracy resistors is a good plan, perhaps using a temperature controlled box for a stable voltage divider.

[@maciekkawalkqcwski8616]

I made one of the version 2 boards . It would be much easier to have multiple series resistors vs multiple parallel resistors. You can add a few low ppm resistors as needed (Keithley uses this approach in older meters to get 2V reference. ). Also the zener diod could be pulled up from the output via 1.5...3K resistor for better current stability. Keep the current pull up from main power via but change it to 200K resistor to make sure it starts. Thanks for the board design. The pot is best to have it in the 100 ohm or lower range as the 100uV position requires ~ 0.2 Ohm adjustment per 100uV . I bought 12 Lm 399 from LT and they the voltage spread was between 7.025V to 7.064V . Not sure if that is Normal but that should narrow the resistor values a little. The LM unit I tested was 7.0355V and to get 10V i needed 8,06Kom + 1.5Kohm on the feedback from output and 22K +499+ pot ~180 on the lower end of feedback. Still hard to adjust the last digit.

[@Aga-Bubamara]

open source.. whoouuuuu.. schematic simplex shown on every data sheet.. whauuu ... open source by linear technology... freee .. amazing

[@conodigrom]

I'm a bit concerned about the pot.. It's to fine tune the 10V, but what if it gets bumped into during shipping or while you are operating the board?

[@mailchaduarygaurav]

There is bit of silicon glue put onto pot to prevent accidental changes.