Curve fitting of three curves to single equation


I have extracted data from image and do some curve fitting. I tried manually Engauge Digitizer software to extract numeric data from image Files three curve’s data .csv files. Now I can have three curve fitting from each csv file. Each curve are temperature dependent

Vce25 = a25Ic + b25log(Ic) + c25 —(1) @ temperature Tvj=25C
Vce125 = a125Ic + b125log(Ic) + c125 —(2) @ temperature Tvj=125C
Vce150 = a150Ic + b150log(Ic) + c150 —(3) @ temperature Tvj=150C

Vce,Tc,Tvj are variables & a,b,c are constants how to find them?

I want to combine these three curves, coefficients can be made temperature-dependent to a single equation { Vce = f(Ic,Tvj) }. How to do thisi in R?


All these three curves is basically just one curve: Vce = Tvj( alc + blog(lc) +c) Where Tvj = 25, 125 or 150. More information is needed to solve this equation.


In the image you can see three curves, each curve is dependent on temperature. The equation in the question are my assumption for best fit for individual curves, but i need to estimate Vce at any given Ic and Tvj(eg: at Ic=200, Tvj=50C Vce=?).