@altenbach wrote:

Assuming the function s well behaved, you can place all terms to the right and use **Newton-Raphson** to find the value of I where the term is zero.

Basically find "I" where:

{right side equation} - I = 0

Given all other constants. repeat for all possible V's. Graph I vs V.

Now create a fit model model that uses this to solve for I given a V and all other parameters)

Do you know how the function is approximately supposed to look like? What is the value for VT?

*(Also watch your terminology. You problem is not the transcendental equation but the fact that you cannot solve for I. Fitting typical transcendental functions (e.g. y=e^x) is no problem.)*

You're totally right, I was confused and using that terminology was misleading. My mistake. Thanks for letting me know and thanks for taking the time.