Tuesday, November 13, 2018

DIY Open Source LM399 10V Voltage Reference, Second Revision

This is second version of my simple LM399 based reference board, when i made my last version i received quite few small feedback form eevblog forum member, so i have made few improvements in second reversion accumulating those suggestions.

Fist improvements is , Reverse probity protection, Now you can see in left corner a P-channel Mosfet and a resistor forming reverse polarity protection. Now it can save its self from damage caused by reverse polarity.
With reverse polarity protection comes this little red power led indicating supply to the board.
one major change is , now there is this 1k 10 Turn pot with 10PPM Opamp gain setting registers  with help of this pot now it is possible to adjust output voltage from reference to exactly 10.00000V. And it can be easily jumpered if not needed
There are few minor change in the PCB as well slots cut around actual reference chip is now wider, so now it is little bit easier to fit insulation foam cap, there are few minor changes on silk screen indicates input voltage, input and output voltage polarity.

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Plot over 17 Hours 30 Minute , Temperature Ranging from 14 to 27 Degree C 


  1. Very nice, need one for my lab. Can build it if pcb available. How much/where? Thanks.


  2. Hi,

    Very nice design.
    I will probably order one on eBay shortly.

    Would be handy to have addition voltage like 1v and 0.1v on the same board.


  3. Very nice and clean looking board, as is your frequency counter mod and other projects on this site. I just ordered your LM399 reference on ebay. I'm kind of amazed you don't have more comments here, your projects are much better looking than most I've seen online.