24 Dec
2016
24 Dec
'16
12:09 p.m.
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:
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.
Cheers,
--
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?
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