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
