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comparator help (super newbie)

I'm trying to understand the basic LM239 comparator. I have read several sites about them, looked at samples, read datasheet, etc, etc and I still am not getting logical results from my simulations.

Here is the test circuit that I made using CircuitMaker, there are 2 version where I switched the reference/input legs

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You will see in those images that the output voltages are either 15.8m (millivolt?) or 21p (I have no idea what that means)

The reference and input voltages are 6v and 3v and I have tried flipping them, I never get output voltage of +9v (my supply to the comparator)

I would really appreciate a tip what I've done wrong. I'm sure it's simple, but 2 hours now and I can't find it.

Thanks for any help, Steve

Reply to
SklettTheNewb
Loading thread data ...

etc

2
15.8m

it's

it

Thank you for the post, that actually did give me the result I wanted. I'm not completely sure why, but I guess that is my next item to investigate ;)

Thanks again!

Reply to
SklettTheNewb 

--
The LM239 has open collector outputs, so R4 needs to go to +V and it
needs to be about 10k.
Reply to
John Fields

Try connecting the other end of R4 to +9V instead of ground.

Look at the internal schematic on the LM339 datasheet. It has an "open-collector" output. It can pull the output pin down to ground, it can't pull up.

Presumably, 21p means pico-volts i.e. 21e-12

Reply to
Andrew Holme

Got it! Circuit is working great now, thank you both for your time, I appreciate it.

-Steve

Reply to
SklettTheNewb

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