[sdiy] Mind blown -- TL074 saturated outputs different

David G Dixon dixon at mail.ubc.ca
Wed Nov 28 21:50:52 CET 2018


> > I need three of these
> > comparators, and their sole function is to act as a 3-bit AD to 
> > control some digital switches.
> 
> But why do you need precise output voltages from the comparators then?
> 
> And if you need quad comparators, why not use the good old 
> LM339 instead of abusing a TL074 for that purpose?

What I want to do is easier (in principle) with an opamp that swings
positive and negative.  I'm using the output state of the comparators to
provide the threshold voltages to the next comparator in the chain.  In this
way, I can get a reasonably precise 3-bit AD converter.  My input CV is -5V
to +5V, and the AD switches state every 1.25V (-3.75V, -2.50V, -1.25V,
0.00V, +1.25V, +2.50V, +3.75V).  The 2-bit version I used in my 5-channel
scanner worked perfectly with just divided raw opamp output, but the 3-bit
version for my 9-channel scanner is a bit more finicky because the levels
need to be just a bit more precise.

However, I will get it working this afternoon.




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