Derivative of I-V curve

[g1lai]

It could be a simple question, but my brain stops running ...

I have I-V test data, and try to derive the 1st derivative (dV/dI) and/or followed by smoothing. Is there any build-in function to do this?

Thanks a lot.

[TomGutman]

The Lambert W solution is nothing more, nor less, than a rearrangement of the equation in the article. It applies and will be accurate under exactly the same conditions as the articles equation.

There is one possible gotcha, which I haven't looked into. The W function is not single valued. For positive arguments, it is. But for negative arguments there are two solutions to the defining equation. I have implemented the solution that is just the extension of the solution for positive values. But there is a second branch, and if the arguments are negative it is possible for that to the the desired solution. I don't think this to be the case, as the exponent should be positive, but as I said, I haven't checked this out.
__________________
� � � � Tom Gutman

[ptc-1368288]

Oh ! you are right about Lambert W.
Attached: all what we have Mathcad 11.2a

Caution: open the work sheet, scroll down in one shot, wait until the last plot appears, now you can browse the sheet. This work sheet has tendency to crash Mathcad on progressive scrolling.

jmG

[ptc-1368288]

On 7/11/2009 9:38:33 PM, g1lai wrote:
>Thanks Jim S. If get insight
>of physics, we will see that
>A0 (or n in eq 1 of the
>attached paper) is a variable
>that can be determined from
>I-V data analysis. The
>exponential relationship b/w I
>and V is nice for MathCAD
>analysis. However, we may have
>to deal with the more
>complicated equation, i.e.
>eq(1).
___________________________

Interesting, it remembers a project done with a more involved model ... 2 prallel rsistors, 3 series resistors (from recollection). The final XFR function is of much different form, in fact it ended as a continued fraction. Sorry, but no recollection about the thread, surely in my box ?

What I mean above is what you suggest:

>However, we may have
>to deal with the more
>complicated equation, i.e. eq(1).

... well, even more complicated !

jmG