OP- Amp Circuit 4

[KSue]

Can anyone explain this circuit to me?

Why is the feedback resistor at the non-inverting input?

 

[sreid]

The opamp is being used as a schmit trigger.

 

[OperaHouse]

You are probably familiar with negative feedback. This circuit has positive feedback. Positive feedback prevents the switching from jittering on slow changing signals.

 

[IRstuff]

Looks to me that the hysteresis is backwards from normal though. The threshold appears to be closer to the input signal state rather than farther. The feedback resistor value is not specified, so...

The fact that the OP is calling a comparator an op amp is likewise mysterious. Did you read the datasheet? See page 8 of

http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS005706.PDF

This circuit appears to be a mixture of two hysteresis reference circuits at the bottom of the page.

TTFN
faq731-376

 

[KSue]

The datasheet was helpful. It appears to have the official name Non-Inverting Comparator with Hysteresis.

Thanx All.

 

[IRstuff]

Yes, I was mistaken about the way the hysteresis was working. Not enough caffeine yet.

TTFN
faq731-376