modified 11 years ago

Comparator -- fixed

00:36:10

The - input is set at less than 3v. Shouldn't the op amp output go low when the input is less than three?

published 11 years ago

jstynen

11 years ago

A comparator circuit has no negative feedback..?

jstynen

11 years ago

Need to open my eyes :)

hurz

11 years ago

OpAmp Quick Help: Measure the voltage from input+ to input- and multiply this delta with 100000. This is the voltage the opamp tries to output, if it can and its not above its output limits. Hope this helps. BTW, positive feedback is only used if you want a hysteresis and a schmitt trigger behavior. I guess you are looking for an inverting amp, just swap plus and minus input.

hurz

11 years ago

right, and a comparator does not has feedback at all.

thebugger

11 years ago

So just remove the 1Mohm resistor and you're good to go.

antilogues

11 years ago

Thanks for the help. I saw this design on the internet and i was using a lm339 to implement it. The hysteresis was strange and i didn't really understand it; however the circuit didn't work on my board w/o it. I just uploaded another simpler comparator based on the way I'm more familiar w building, and built w a 324. Thank you.

faceblast

11 years ago

339 needs a pullup resistor on the output, they don't simulate very well in EC

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