Using OP484 as Comparator

[J. Tarrako]

Hello all,

I wanted to use one spare op of an OP484 as a comparator. I was wondering about what should care about when using it with positive feedback to have some hysteresis.

I know that the inputs of the 484 can’t be at a different voltage due to their diodes. As long as I use resistors in the inputs of enough value to limit the current to not stress it (for example, 10k, with inputs and supply at 13V), the OP484 will work OK as a comparator? Is there any other problems I should be aware of? I will use it to compare two DC signals.

 

[Laplace]

An op-amp makes a poor comparator, yet it will compare two voltages. Have you read Analog Devices Application Note AN-849 "Using Op Amps as Comparators"?

 

[KrisBlueNZ]

Thanks for the pointer Laplace! Good information there.

Here's a direct link: http://www.analog.com/static/imported-files/application_notes/AN-849.pdf

 

[J. Tarrako]

Thanks! I will read it very carefully... I guess:

"
In addition, op amps are often available in
packages of two or four—if you need three op amps and a
comparator, it seems pointless to buy four op amps, not use one
of them, and then buy a separate comparator.
However, the best advice on using an op amp as comparator is
very simple—don’t! "

Mostly answer my question, but let's see how bad of an idea it is...