Electronics > Beginners
Voltage reference not working properly #SOLVED#
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iMo:
Above my hint on an external -5V (hard one, ie an external floating 5V source), and you may pass 20mA via the 431 (125ohm) during the troubleshooting..
The LM431 voltage must be 2.5V +/-0.05V always.
FotatoPotato:
I still have a 2.2k resistor on the 431, If I change it the output voltage changes as well, I'll try it though and update you on the results.
iMo:
And doublecheck (measure!) all 40 resistor's values on your pcb..

BTW, what is the value of R18? I would remove it during the troubleshooting.

Also doublecheck the polarity of the capacitors in your LT1046 -5V generator. I would also try to load it with a resistor to get an idea how much current it gives you actually while having -4.88V on it.

StillTrying:
"I still have a 2.2k resistor on the 431"

I've had to change my previous calculation for R1, I was adding the OPA277's -5V current into the -2.5V.
https://www.eevblog.com/forum/beginners/voltage-reference-not-working-properly/msg2235837/#msg2235837

Now (4.8-2.55)/1.66 = 1.4k or slightly lower for R1.
iMo:

--- Quote from: imo on March 02, 2019, 12:31:33 pm ---..
3. it could be at a specific R29 position the whole stuff starts to oscillate wildly (look at it with o'scope). ..

--- End quote ---
Did you check this?

Read the previous posts and do make a checklist :)
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