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Old 4th Feb 2020, 6:45 pm   #7
John_BS
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Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
Default Re: Another Quad FM4 problem

The derivation of VL is a bit convoluted.

Assuming the op-amp is working OK, you should have Vlow at about 1.9V at ambient temperature. It results from the addition of two currents flowing through R23 (22k): about 45uA from the LM334 and 41uA through R22. If Vlow is wrong, check those resistors and especially the LM334z. A quick n dirty check would be to just replace that current source with another 150k resistor and see if the voltages look about right. If that seems to work, replace the LM334.

John
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