| 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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