Sunday, August 26, 2018

DIY Open Source LM399 10V Voltage Reference

while working on a project i needed a really stable voltage reference so i made my self  LM399 based 0.5 ppm/ C 10V refernce.
LM399 is nice shunt reference chip , Although initial accuracy is only 2% but accurancy does not matter , what matter is stability. Because i have recently calibrated Agilent 34465A 6.5 digit multimeter , i can easily find out absolute value. 

With 0.5 ppm/C and 10V range , its translate to 5uV /C. At this range of temperature stability it is way beyond what my Agilent 34465A can measure.



Schematic
Schmeatic is directly from the LM399 Datasheet, Reference Chip, Opamp LT1001 and 10PPM Tempco resistors for gain setting.  and few capacitor and connectors




PCB
It is a quick project so PCB is quite simple , Just LM399, Opamp and few other component. 


Hard foam cover sat down in slots around LM399

2 Hour voltage Plot
12 Hour Plot
1 Hour Plot

PCB source and bill of material  is available in my github account 



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