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 Post subject: Re: Op Amp problems
PostPosted: Apr Mon 08, 2019 8:02 pm 
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@OldWireBender, very nice!


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 Post subject: Re: Op Amp problems
PostPosted: Apr Mon 08, 2019 8:22 pm 
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Got it to work both with +12v/0 and =12/0/-12. And got he filtering effect I was looking for and the x10 gain also.
I guess I had something wired wrong and kept making the same mistake. Thanks for all of the comments

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 Post subject: Re: Op Amp problems
PostPosted: Apr Tue 09, 2019 3:15 am 
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Dennis H. wrote:
Got it to work both with +12v/0 and =12/0/-12.


I am curious what schematic you used to get the circuit to work using only a single supply.

As shown in the simulations, when used with a single supply using the original schematic, the circuit is a half wave rectifier.


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 Post subject: Re: Op Amp problems
PostPosted: Apr Tue 09, 2019 2:07 pm 
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Everything you need to know about using a single supply

http://www.ti.com/lit/an/sloa030a/sloa030a.pdf

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 Post subject: Re: Op Amp problems
PostPosted: Apr Tue 09, 2019 6:12 pm 
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flyboy71 wrote:
Everything you need to know about using a single supply

http://www.ti.com/lit/an/sloa030a/sloa030a.pdf

Thanks for your post, but my question was directed at the OP Dennis H. to learn if he actually got the circuit working correctly using one supply.

The original circuit will not work correctly with one supply unless it is modified.

OldWireBender did an admirable job of drawing schematics and simulating 3 different scenarios to demonstrate what is required with a single supply.

I was amazed when reading through this thread of the number of individuals who responded who admitted knowing little about Opamps.

I couldn't understand why anyone would respond to a post in which they knew little about the subject.


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 Post subject: Re: Op Amp problems
PostPosted: Apr Tue 09, 2019 9:44 pm 
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LM386 wrote:
flyboy71 wrote:

I was amazed when reading through this thread of the number of individuals who responded who admitted knowing little about Opamps.
I couldn't understand why anyone would respond to a post in which they knew little about the subject.

I just skimmed back and did not spot anyone making an inappropriate post.....It is not uncommon here to get a bit of banter where someone is simply guessing at the answer while admitting their lack of in-depth knowledge. If we outlawed that, there'd be just about no-one left.

Just for the halibut, how about we try some questions:

1. What's a uA709 and why was it so difficult to work with?

2. Who was Robert (Bob) Widlar?

3. Before CMOS took over everything, what was the key trick to get low input currents on the early op-amps?

4. Why is it often important to have a very high open-loop bandwidth?

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 Post subject: Re: Op Amp problems
PostPosted: Apr Tue 09, 2019 9:47 pm 
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LM386 wrote:
Dennis H. wrote:
Got it to work both with +12v/0 and =12/0/-12.


I am curious what schematic you used to get the circuit to work using only a single supply.

As shown in the simulations, when used with a single supply using the original schematic, the circuit is a half wave rectifier.


I used the original schematic posted in the first post. I just went back out to the "lab" and double checked it. It had no ground reference to the power supply.

I did not check to see where my sine wave was located voltage wise. It may just be a sine wave located above 0V instead of centered on it but what I got is usable for my purposes.

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 Post subject: Re: Op Amp problems
PostPosted: Apr Tue 09, 2019 9:51 pm 
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LM386 wrote:
flyboy71 wrote:
Everything you need to know about using a single supply

http://www.ti.com/lit/an/sloa030a/sloa030a.pdf

Thanks for your post, but my question was directed at the OP Dennis H. to learn if he actually got the circuit working correctly using one supply.

The original circuit will not work correctly with one supply unless it is modified.

OldWireBender did an admirable job of drawing schematics and simulating 3 different scenarios to demonstrate what is required with a single supply.

I was amazed when reading through this thread of the number of individuals who responded who admitted knowing little about Opamps.

I couldn't understand why anyone would respond to a post in which they knew little about the subject.


And I believe his post about single supply pdf link was meant for me. It may have something that I might need to know. Thanks.

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 Post subject: Re: Op Amp problems
PostPosted: Apr Tue 09, 2019 10:04 pm 
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That circuit might appear to work "well enough"---at least for the short term---using a single-ended supply. That solution, however, is what some would call "fragile", meaning that a change in interface or conditions might well stop it from working. Better to do it right from the beginning.

The circuit as-drawn cannot work properly and reliably with a 2-terminal power supply. Any one of many resident pontificators can explain in gory detail why....

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 Post subject: Re: Op Amp problems
PostPosted: Apr Tue 09, 2019 11:13 pm 
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pixellany wrote:
That solution, however, is what some would call "fragile", meaning that a change in interface or conditions might well stop it from working.

As shown by the simulations, with a single supply, unless modified, the original circuit can never work correctly.

The output can never go negative and the original circuit will always be acting as a half wave rectifier and not faithfully amplifiying the original input signal.


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 Post subject: Re: Op Amp problems
PostPosted: Apr Tue 09, 2019 11:18 pm 
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pixellany wrote:
I just skimmed back and did not spot anyone making an inappropriate post...


I did the same earlier and I agree with you Pix. The circuit diagram posted was incomplete and we had no idea of that the OP was trying to achieve. I admit that I have done little work with op amps in 30 years since I graduated college. Does that make it wrong for me to try to help someone? (even though I did not offer advice other than saying it should have a gain of 10).


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 Post subject: Re: Op Amp problems
PostPosted: Apr Tue 09, 2019 11:29 pm 
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Quote:
As shown by the simulations, with a single supply, unless modified, the original circuit can never work correctly
.
Forget the simulations--- it's Op-Amps 101...

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 Post subject: Re: Op Amp problems
PostPosted: Apr Tue 09, 2019 11:36 pm 
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pixellany wrote:
Quote:
As shown by the simulations, with a single supply, unless modified, the original circuit can never work correctly
.
Forget the simulations--- it's Op-Amps 101...

I've forgotten the simulations. Perhaps you were away the day that this topic was taken up in Op-Amps 101.

I was hoping that you can demonstrate the output waveform from the original circuit using a single supply when a small sinewave is applied to the non-inverting input.

I think you will discover that only the positive going portion of the input waveform is being amplified resulting in the output resembling that of a half wave rectifier.

pixellany wrote:
That circuit might appear to work "well enough"---at least for the short term---using a single-ended supply. That solution, however, is what some would call "fragile", meaning that a change in interface or conditions might well stop it from working.
I would suggest that the original schematic using a single supply is not "fragile" and is also not the correct or intended operation of the original circuit.

The waveforms below demonstrate the outputs from the original schematic when using a single supply and dual supply.

The green trace is the output that would occur if using the original schematic with a single supply and will never be an accurate representation of the input waveform.

The red waveform is the correct output that would occur if using a dual supply.

The original circuit can be modified to perform correctly using a single supply as suggested by a number of those who responded.


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 Post subject: Re: Op Amp problems
PostPosted: Apr Wed 10, 2019 4:14 am 
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Wow!!---That's a lot of reaction to my simple comment.
It seems that we're in agreement that the circuit would not work correctly as drawn...

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 Post subject: Re: Op Amp problems
PostPosted: Apr Wed 10, 2019 1:05 pm 
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flyboy71 wrote:
Everything you need to know about using a single supply

http://www.ti.com/lit/an/sloa030a/sloa030a.pdf


Rather than re-write my Masters thesis I posted an application note to be helpful. Sorry my apologies. My 25 years as an analog design engineer working with single and dual supply op-amps in high reliability military applications obviously disqualifies me to speak about this matter. Ill go back under my rock now and let the experts handle this matter.

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 Post subject: Re: Op Amp problems
PostPosted: Apr Wed 10, 2019 1:19 pm 
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Huh?--who said you did anything wrong??

My comments about "fragile" solutions, and "Op-Amps 101" were obviously misinterpreted...

A "fragile" solution is one that might work under certain conditions, but which which can generally be expected to fail in different conditions. The OPs comment that the "circuit did what he needed" is a perfect example---change the conditions a bit, and he would have had a different outcome.

And--I said: "forget the simulations, it's OpAmps 101". In context that simply meant that no simulations were required to prove that the circuit would not work properly.

Whenever we get into this kind of discussion, I think we are all right---each in our own special way.....;)

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 Post subject: Re: Op Amp problems
PostPosted: Apr Wed 10, 2019 2:00 pm 
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pixellany: Thank you for diplomatically clarifying your comments.

flyboy71: The article that you submitted was a valuable contribution and I have saved it along with other technical articles in my dedicated technical .PDF folder.


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 Post subject: Re: Op Amp problems
PostPosted: Apr Wed 10, 2019 2:06 pm 
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flyboy71 wrote:
flyboy71 wrote:
Everything you need to know about using a single supply

http://www.ti.com/lit/an/sloa030a/sloa030a.pdf


Rather than re-write my Masters thesis I posted an application note to be helpful. Sorry my apologies. My 25 years as an analog design engineer working with single and dual supply op-amps in high reliability military applications obviously disqualifies me to speak about this matter. Ill go back under my rock now and let the experts handle this matter.


That was an excellent post that should have helped the OP out. It certainly is better for the OP to read through that paper rather then have us take stabs at what he is doing, what he intends to do and how he is building his circuit.
Often it is better to give someone the tools to figure it out themselves and learn.


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 Post subject: Re: Op Amp problems
PostPosted: Apr Wed 10, 2019 3:08 pm 
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No offense taken on my part. My comment was more light hearted than it was interpreted. Everyone's contribution is valuable especially simulation. Had I had time to simulate I would have posted also. Hopefully all of this is useful to the OP.

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 Post subject: Re: Op Amp problems
PostPosted: Apr Wed 10, 2019 4:59 pm 
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We have come a long way since this OP_Amp was offered as the advanced State of the art..


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