23 Dec
2016
23 Dec
'16
8:34 p.m.
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