UPDATE(12/29/2017):
Project is finished and works as expected. I thought I'd do one final update on the first post for people searching in the future.
I've created a zip file containing a full design: schematic, BOM (including links), gerber files, and some pictures. Download from my dropbox:
5VPrecisionVoltageReferencev0.6.7zHere is an EasyEDA.com link to the the schematic and PCB layout:
https://EasyEDA.com/TerryJMyers/Precision_Voltage_Reference_v06ORIGINAL POST:
I was going to buy one of Dough Malones 10V references (
http://www.voltagestandard.com/-.html), probably still will, but I thought I'd try my hand at designing my own. I found an old article he wrote (
http://www.nutsvolts.com/magazine/article/build_a_01_accurate_voltage_reference) and used it as a basis for my own. I choose an LT1021 5V 5ppm, non-trimmable IC. 9V battery powered from a TL431. I substituted some components based on my current component stock to reduce how much I had to buy. My plan is to build the board and age it for a month, then characterize its voltage at 20C, 25C, and 30C using a decent DMM (6.5+ digits, hopefully 7.5). This IC has a basic accuracy of 1%, but a temp coef of 5ppm, so I really don't care what the voltage is, I will just measure it after a months of aging.
I'm using the following box:
https://www.aliexpress.com/item/dark-grey-szomk-wall-box-plastic-enclosure-for-electronics-case-4-pcs-125-67-40mm-split/32444149094.html?spm=a2g0s.9042311.0.0.odh0Dd, again because I have a few of these lying around. I'm mounting the PCB to the top of this box so that the Banana plugs, switch, and LED come out the top. The battery holder is mounted to the bottom, so it will be hanging down under the lid. The LT1021 will be mounted to the top of the board just a few mm shy of the top of the case. There shouldn't be any air flow.
What do you like? What do you not like? What did I do wrong? Any suggestions on improving design? Thanks!
Link to the EasyEda page:
https://easyeda.com/terryjmyers/Precision_Voltage_Reference-0ee0deb5ce994b2780e0ad7feb90c282