Cannot Simulate an Op Amp buffer

[nlsmith]

I am simply trying to use an op amp as a buffer (or unity gain voltage follower).  I connect the input signal to Non-Inverting input output fed back to Inverting input. And of course I am supplying +/-12V at the rails.  When I attempt this with multisim the output is always 0.   If I set it up in the standard inverting amplifier configuration with gain set by two resistors(Rinput = Rfeedback) then I see the expected results but this is not the configuration I want to use. 

I have tried it with several different op amp models to the same effect.  I have been building buffers like this for years now and I can simulate this exact configuration with altium's Xspice with good results.  But altims spice tools are otherwise user abusive and I don't like using them. 

So their must be a trick involved to make this basic principle simulate correctly.  Does anybody know it?

Thanks

-Nick-

[kittmaster]

can you post your schematic so we can review it?

[nlsmith]

The configuration looks like this.   buffer amp


In addition the rails are supplied with +/- 5V respectively.  The load is a 10K resistor to ground.

[nlsmith]

Sorry that last link is broken.  Try this one.

[digitalguy]

I think what Kittmaster was saying is that it would be nice to see your actual Multisim simulation file so people could see what was actually happening. I took the venerable 741 op amp and built the attached buffer, which works fine.

[nlsmith]

Interesting,  your model does indeed work.  When I replace the 741 with AD8051 (high speed rail to rail amplifier) your model breaks too. 

I don't know how you were able to attach you sim file to the post otherwise I would have.
I have options to...

quote
insert smiley
insert line
insert link
insert image

How did you attach you simulation file?

[digitalguy]

When you submit a post, look at the bottom of the page and you will see a place for adding attachments. It's below the "box" where you actually post your message.

Hope this helps

[OStep]

nlsmith,

Somehow, in the underlying netlist, the subcircuit name in the instance call of the op-amp got out of sync with the actual name of the subcircuit. To fix this, you can just replace the op-amp component with the same component from the database.

However we would be interested to know about a possible reproduce scenario as this is not normal behaviour. Would you be able to briefly describe the actions you took to end up with this circuit?

Thanks,

Message Edited by MaxNI on 05-21-2008 12:55 PM

[nlsmith]

I just reproduced the same problem as follows

Place --> Component --> Analog --> OPAMP --> AD8051AR --> OK

route wires

simulate

voila... Garbage out.

Also to satisfy your curiosity I did try a replace to the same end result.  So my library is out of sync and how it occured I do not know, but it sounds like a re-install is in my future.
The good news is that I can copy your LM741 model into my project with good result (it does not exist in my library).  So it will work well enough to get me through what I am actually trying to simulate.


Thanks for the help guys.

-Nick-