[sdiy] comparator feedback resistor

[Michael Ruberto]

most schematics I see with comparators do not have a feedback resistor, but 
sometimes they do. one I am looking at now uses a TL07X and has a resistor 
of 2.2M between the + input and the output. now from what I have read it 
seems that the resistor is there for either hysteresis or to improve 
reaction speed. since one text claims one explanation and the 2nd text the 
other explanation could somebody please tell me which is correct? or are 
they both true? I guess I need a better explanation.

also, if it's an advantage to include this feedback resistor how do you go 
about calculating the proper value for it?

Thanks!

~Mike

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