Good day! I have the following circuit:
Just looking at the configuration on paper, the voltage at R18's terminal next to D2 would have given me V2 if Vin < V2. I'm not quite sure why my spice simulation is showing 1.683V.
Any insights? Thanks!
Yes. The op-amps 2 input terminals aren't at the same voltage so for some reason the feedback's not working.
Is it a rail-to-rail output op-amp ?
Graham
reason
Hi Graham, according to TI, it's supposed to be rail-to-rail:
I decided to change the opamp, and I'm getting similar results on paper. Thanks!
Is V2 defined as 2.5 volts, somewhere?
The output should go positive enough to supply current through D1 and R14, to ring the right end of R14 up to 2.5 volts. However, that takes (2.5-1.1)/1k= 700uA from the opamp output.
Take a look at the data sheet:
The output current limits with more than the whole supply dropped across the pull up fet before the current gets to
700 mA. Change the 2k resistors to 20k, and it should start working.
That's 700 uA.
Thanks, John! I appreciate the additional insight.
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