[sdiy] Unused opamps in multi-opamp ic / Re: triangle core VCO comparators

[Simon Brouwer]

Hi Rick, 

It probably depends on the opamp. For example, the LM324 has input range down to
negative rail, and looking at the functional diagram given in its datasheet, I
don't see how the "NO!" circuit could give any problem at all.

However, with opamps that have an input range that doesn't include negative
rail, I can imagine this could give unpredictable results.

Best regards
Simon

> On 25 February 2016 at 21:27 Rick Jansen <rick.jansen at xs4all.nl> wrote:
> 
> 
> 4.2.1 in that article has an interesting section on what to do with unused
> opamps in a multi-opamp ic...  Comments? (Apparently I did it wrong, a few
> times..)
> 
> rick
> 
> > On 25 Feb 2016, at 21:15, Rick Jansen <rick.jansen at xs4all.nl> wrote:
> > 
> > This month's (March/April) NL Elektor has an article on the difference
> > between actual comparators and opamps. True comparators are (much) faster,
> > and can reach rail voltages, and so not rely on the amplification factor of
> > the opamp. Also, the output stage of many opamps is not suited for
> > comparator functions, and can even damage them.
> > 
> > The end of the article refers this document:
> > http://encon.fke.utm.my/nikd/latest/sloa067.pdf
> > 
> > Bruce Carter : opamps and comparators , don't confuse them.
> > 
> > R.
> > 
> >> On 18 Feb 2016, at 01:48, Chris McDowell <declareupdate at gmail.com> wrote:
> >> 
> >> howdy, 
> >> 
> >> I'm wondering about the choice of comparator for triangle core VCOs. I've
> >> seen it done a few ways, like Thomas Henry's discrete comparator, or the
> >> LM311 in J3RK's (STROH Modular) VCOs on Muffs, and my own builds just use
> >> TL07x and work -pretty much- great. But I'm wondering what the experiences
> >> and preferences are of you here on the list. Fast op amp? Real comparator?
> >> Doesn't matter? I'm aware that it only matters as much as HF-Tracking
> >> matters, but I'm interested in opinions anyway. 
> >> 
> >> Cheers!
> >> Chris
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