> -----Original Message----- > From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Adrian > Graham > Sent: 24 December 2016 12:09 > To: General Discussion: On-Topic and Off-Topic Posts > <cctalk@classiccmp.org> > Subject: Re: ICL7611 op-amp (was: Motorola MC14081B) > > On 24/12/2016 04:34, "Glen Slick" <glen.sl...@gmail.com> wrote: > > > On Fri, Dec 23, 2016 at 7:48 PM, Brent Hilpert <hilp...@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? >
