I'm trying to write up a lab report, but no one seems to be able to give me an answer for what the incremental resistance of a BJT means, or why it's significant so I'm hoping someone here can tell me. In our lab, we first built a DC circuit, pictured below:

First Circuit (DC)

We measured the incremental resistance by calculating Delta(Vy)/Delta(Iy) at different Iy values (10 uA, 100 uA, and 1000 uA).

Then, we built a second circuit, this time with an AC component:

enter image description here

We measured the incremental resistance again, this time with a more complicated formula, and the incremental resistance changed - a good amount, but it was still on the same magnitude as measured before.

I hope I'm not being ignorant by asking, but I truly do not understand the purpose of this laboratory and no one seems to be able to tell me - even the TAs. I'm assuming there must be some theoretical difference in the incremental resistance between AC and DC circuits, but I don't know what the theoretical explanation is. Additionally, I don't know what the significance of the incremental resistance is and/or what the "theoretical" incremental resistance should be for these two circuits. I'm not sure if I provided enough detail, but I'm really just looking for a good explanation of incremental resistance.


1 Answer 1


The problem touches the question: Can there be a difference between both measurements because the "incremental" resistances are not equal? It think, the only differences can only be caused by

(a) thermal properties and/or

(b) capacitive properties of the pn junction.

In this context, the measurement times (first experiment) and the test frequency (second experiment) are important parameters.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.