Re: gEDA-user: furnace controller I/O port again

["Mark Rages" <markrages@xxxxxxxxx>]

On 11/2/06, Dave McGuire <mcguire@xxxxxxxxxxxxx> wrote:
> On Nov 2, 2006, at 8:15 PM, Bob Paddock wrote:
> >> I'll look into it.  The thing about op amps is that they're cheap and
> >> tiny.
> >
> > Which frequently gets people into trouble when they try to use
> > Op-Amps as Comparators:
> ...
> > TI:
> > Op Amps and Comparators - Don't Confuse Them
> >
> > Operational amplifiers (op amps) and comparators look similar; they
> > even have very similar schematic symbols.
> > This leads a lot of designers to think they are interchangeable.
> > There is a strong temptation to use a spare section
> > of a multiple op amp package as a comparator to save money. This
> > application note will explain why designers should not do this.
> >
> > http://encon.fke.utm.my/nikd/latest/sloa067.pdf
> > Download .pdf (sloa067.pdf, 150 Kbytes)"
>
>    Not to butt in, but...wow, that is a VERY informative
> article...Thanks for sending that URL!
>
>                -Dave

I think the article is overstating things a little bit.

Sure, op-amps make lousy, slow comparators.  But commercially
successful op-amps aren't going to burn up if you let the output go to
a rail!  Some high-spec opamps may have limitations, such as high
current in the input stage if you exceed a certain differential
voltage, but these limitations should be called out in the datasheet.
And expensive, exotic amps aren't the ones being pressed into
comparator duty.

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie


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