[sdiy] In search of a reasonably precise comparator output

Lloyd Abbott lloydabbott94 at gmail.com
Wed Jun 20 17:30:30 CEST 2018

What rails do you have available ? Have you considered a comparator IC
(e.g. LM339) rather than using general purpose op-amps ?

If you have 0V, +5V and +15V rails, with an LM339 you can reference the
comparator input side to the 0V and +15V rails and have the output side
referenced to 0V and +5V. The datasheet has an example circuit using one
pullup resistor and one cap per comparator.

On Wed, Jun 20, 2018 at 4:05 PM, Guy McCusker <guy.mccusker at gmail.com>

> Hello,
> I am "designing" (i.e. cobbling together) a circuit in which I need a
> comparator whose output is fairly accurately 0V or 5V.
> I can think of many ways to do this. Some are very stable (at least on
> paper) but appallingly complicated, which is bad because I need at
> least 7 of these;  some are very simple but rely on careful trimming
> of the saturation voltage of an op amp, which I would rather not do
> for reasons of reproducibility.
> It is 100% likely that someone on this list has a very simple and
> solid way to do this, so rather than reinvent the wheel I thought I'd
> ask... how would you do it?
> (What I really want, in fact, is to take an input voltage X and output
> X if X<=5, or X-5, if X>5.)
> Guy.
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