Electronics > Beginners
Voltage reference not working properly #SOLVED#
StillTrying:
"I just checked the current draw on the -2.5v rail and it is 4mA"
What does the -2.5V supply, as far I know it's just VR29 10k = 0.66mA.
Are you sure the pin out of VR29 is correct on the PCB, the 4.096V 10mA ref. could easily pull the -2.5V ref. up to ~ +0.8V.
I'm running out of ideas on what's wrong with the -2.5V.
iMo:
You must limit the output current of the OP277 with a resistor as we told you (10k-100k for example). You should not wire an output of an opamp powered -V..+V with an input of an opamp powered 0..+V. Did you insert the resistor there? That would be an important point on my checklist.
FotatoPotato:
I have not done that, I'll do it now and see what happens.
StillTrying:
--- Quote from: imo on March 02, 2019, 07:37:56 pm ---You must limit the output current of the OP277 with a resistor as we told you (10k-100k for example). You should not wire an output of an opamp powered -V..+V with an input of an opamp powered 0..+V.
--- End quote ---
I'd agree, but the -5V is now always good at -4.96V. Still a good idea to protect the next op amp's input from -0.3V or more with a series 1k-10k.
iMo:
Put there 100k for a test as it may show something. When all works fine you may start to lower the resistor when necessary.
Hint: It is not a good methodology to wire entire complex system together, power it on and watch various meters and displays :bullshit:. Especially when you mess with a prototype.
Always wire it part by part, module by module while you have to always test the parts or modules individually. Take notes on voltages and currents.
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