# Can Ideality factor (n) be determined from Vce and Ic with constant Ib

1. Dec 6, 2013

### Matt_Michael

Hello, I am performing a lab report which required a NPN BJT transistor (2N3904), recording values of Ic as Vce was swept from 0-10v. These trials were done for 5 different constant base voltages of 2 µA, 4 µA, 6 µA, 8 µA, and 10 µA.

The just of the lab was simulating the transistor in PSPICE and then verifying the parameters used through experimentation. The lab write up asks me to calculate an ideality factor (n) using Vbe for the two lowest base currents (Ib = 2 µA and Ib = 4 µA) for a collector-emitter voltage of 5v.

I accomplished this in the prelab by running two separate PSPICE trials for the two different Ib values with Vce set to a constant 5v. I was able to get values of Vbe from the output file. By assuming Is was the same for both trials, I solved the diode equation for Is and set the two equations together. Imputting the values from each trial to there respective side of the equation, I was able to solve for n. I got a value of 1.00577. This task seemed like an odd request to me because we specify a value for n in the simulation model, but my value seemed like it could be plausible as it was a dimensionless number between 1 and 2.

Is anyone able to give any insight on how I could calculate an experimental value for n? I have a rough understanding of what n is, and was able to find an equation here, listed as equation (5.4.4): http://ecee.colorado.edu/~bart/ecen3320/newbook/chapter5/ch5_4.htm
The task also specifies to assume T=300k.

Unlike the prelab, I did not record values for Vbe vs Vce. Do I need to go back and record these or do I have I way around it?

If anyones interested, the lab write up can be found here: http://www.ele.uri.edu/courses/ele339/supplemental/Lab 5 BJT Modeling.pdf