Author Topic: limitation of opamp in the single supply differential mode  (Read 5833 times)

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Offline ebastler

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Re: limitation of opamp in the single supply differential mode
« Reply #25 on: April 12, 2019, 04:38:14 pm »
No, I never ever feel insulted by the technical talking or challenging the information. we learn from discussion. but please check you wasted how many hours to investigate someone else posts and make angry comments like that just because maybe the topic or content is repetitive or information is not enough.

Generally, engineers never support each other and they have the habit to ruin each other work, [...]

Your approach is a bit strange, if I may say so. Instead of two posts complaining about Ian's reference to your old thread, you could simply have said "Yes, it's the same design challenge" or "No, this is about a different requirement".

And how do you know that Ian "wasted how many hours" to find that old post of yours? He might simply have remembered you. I can see how that could happen... ;)

Finally, if you come here asking for help with your design, you have to be prepared for criticism. If there was nothing wrong with your design, why would you have asked for help in the first place? So I don't understand the second paragraph of your quoted post.
 

Online Ian.M

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Re: limitation of opamp in the single supply differential mode
« Reply #26 on: April 12, 2019, 04:55:00 pm »
For the record: I didn't go looking for O.P's old topic on my own, StillTrying posted the link to it, and it took me no more than 10 minutes to skim through it for an overview of O.P's problem.

Doctors mistakes kill patients one at a time.  Engineers mistakes kill people by the plane, train or bridge full.
« Last Edit: April 12, 2019, 04:56:32 pm by Ian.M »
 

Offline StillTrying

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Re: limitation of opamp in the single supply differential mode
« Reply #27 on: April 12, 2019, 04:58:16 pm »
Thank you, Mr. Sherlock Holmes, for being a detector of my posts

If it wasn't for me remembering and eventually finding the old thread none of us would have much idea of what you're trying to do!
Getting a clean <mV signal AC coupled off a noisy +12V is certainly going to be V hard.

Years ago when I did similar I did it like below, the high side switch is a minor problem, but the single supply opamp is simple - no differential or AC coupling caps needed. It's so long ago I can't remember what I used for the high side switch or the opamp, probably a CA3130, or something.


And how do you know that Ian "wasted how many hours" to find that old post of yours? He might simply have remembered you. I can see how that could happen... ;)

LOL. I well remembered the other thread, but was to busy with other things to find it (there's 2!) and choose a good post to link to.
« Last Edit: April 12, 2019, 05:04:06 pm by StillTrying »
.  That took much longer than I thought it would.
 

Offline VanitarNordicTopic starter

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Re: limitation of opamp in the single supply differential mode
« Reply #28 on: April 12, 2019, 05:22:05 pm »
Quote
So I don't understand the second paragraph of your quoted post.

if you don't have a technical point, please stay out of this. I did not ask you to teach ethical points. That was my comment just for Ian.
« Last Edit: April 12, 2019, 05:26:31 pm by VanitarNordic »
 

Offline VanitarNordicTopic starter

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Re: limitation of opamp in the single supply differential mode
« Reply #29 on: April 12, 2019, 05:28:50 pm »
I already got the technical answer and solved the problem. Thanks for all technical contributions
 

Offline ebastler

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Re: limitation of opamp in the single supply differential mode
« Reply #30 on: April 12, 2019, 05:49:35 pm »
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So I don't understand the second paragraph of your quoted post.
if you don't have a technical point, please stay out of this. I did not ask you to teach ethical points. That was my comment just for Ian.

Sorry, but you made a very general, sweeping, moral statement about the bad behavior patterns of engineers "in general". That's what moved the discussion into the realm of "ethics" for me, if you want to use that term.

I already got the technical answer and solved the problem. Thanks for all technical contributions

Fair enough. See you next year!  ;)
 

Offline VanitarNordicTopic starter

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Re: limitation of opamp in the single supply differential mode
« Reply #31 on: April 12, 2019, 06:00:30 pm »
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Fair enough. See you next year!  ;)

You don't reply in that case and stay out of this. you have made no contribution here. if you want to continue to your moral things, do it, but I'll not reply anymore.
 

Offline Zero999

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Re: limitation of opamp in the single supply differential mode
« Reply #32 on: April 12, 2019, 07:57:16 pm »
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Anyway, back on topic. The op-amp should be run off the 12V rail. An AC coupled differential amplifier could be used.

so you confirm my word that when the sensor is VCC referenced (+12V), then the opamp should be at least 12V and a 3.3V opamp cannot do the best job
I was a bit confused when I made that statement.

If the peak to peak value of the ripple on the 12V supply plus the input signal you're trying to measure is under the op-amp's input voltage range than it should be fine.

In other words, assume the op-amp is run off 3.3V and will work with its inputs down to -0.3V and up to 3.6V (300mV beyond either rail is pretty common for most rail to rail op-amps), then it should work, as long as the ripple on the 12V plus your signal is under3.9V peak to peak. There should also be protection diodes between the op-amp inputs and its positive power supply rail, assuming it doesn't have them built-in.
 

Offline mikerj

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Re: limitation of opamp in the single supply differential mode
« Reply #33 on: April 12, 2019, 08:41:13 pm »
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Fair enough. See you next year!  ;)

You don't reply in that case and stay out of this. you have made no contribution here. if you want to continue to your moral things, do it, but I'll not reply anymore.

You seem like a real piece of work.  You are the one that came here asking for help remember?
 


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