ICL7611 op-amp (was: Motorola MC14081B)

[Dave Wade]

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Adrian
> Graham
> Sent: 24 December 2016 12:09
> To: General Discussion: On-Topic and Off-Topic Posts
> <cctalk at classiccmp.org>
> Subject: Re: ICL7611 op-amp (was: Motorola MC14081B)
> 
> On 24/12/2016 04:34, "Glen Slick" <glen.slick at gmail.com> wrote:
> 
> > On Fri, Dec 23, 2016 at 7:48 PM, Brent Hilpert <hilpert at cs.ubc.ca>
wrote:
> >>
> >> The op amp is configured as a schmitt trigger or comparator with
> hysteresis:
> >>         There is no negative feedback so it is operating at full gain
> >> and functions like a comparator.
> >>         However there is positive feedback via R412 (*1), this adds
> >> hysteresis to the trip point(s).
> >>         (Brief hackneyed, not rigorous, theory of op: As the input
> >> differential varies past the trip point, the output pulls the + input
> >>         further above or below the point at which it just tripped, so
> >> the inputs now have to 'overcome' a greater differential
> >>         to trip as the input differential varies in the opposite
> >> direction.)
> >>
> >
> > A recent EEVblog video has some whiteboard explanation of using
> > positive feedback for hysteresis if anyone is curious...
> >
> > EEVblog #941 - Schmitt Trigger Tutorial
> > https://youtu.be/Ht48vv0rQYk?t=13m43s
> 
> Ah cool, I was watching some of Dave's tutorials yesterday but in one of
> them he lost me completely towards the end, talking about Virtual Ground
> on op-amps.

That's how op-amps are typically used in linear mode. If you 

1. Have a split rail PSU
2. Ground the +ve input
3. Connect the output back to the inverting input,

You get a unity gain circuit.  Add resistors and you can adjust the gain as
required. 

Dave


> 
> Cheers,
> 
> --
> Adrian/Witchy
> Binary Dinosaurs creator/curator
> Www.binarydinosaurs.co.uk - the UK's biggest private home computer
> collection?
>