So far I just remember it's named after Mr.Early and not much else (I know I'll learn it later). In hybrid-pi model it's added as a fairly high resistance on order of x100k's across the collector/emitter, so I usually leave it out. So far since I've known the name, I never noticed it explicitly on a datasheet. What should I look for ?

In what cases should you really be adding it? I suppose if you have a similar sized load across Vce. In simple AC models, when does leaving it out, make your answer the most off ?

 

The EARLY effect can be visualized by inspecting the output characteristics Ic=f(Vce) for Ib=const or (alternatively) Vbe=const. You will notice that in the active region the slope of the curves is not zero but positive. This slope is identical with a finite (but relatively) large differential (dynamic) output resistance rce=1/h22=d(Vce)/d(Ic).
When you construct a tangent to all the curves they meet (more or less) in a common point on the negative Vce axis. This voltage defines the (fictive) EARLY voltage which cannot be measured (because it is not a measurable voltage).

Comment: Surprisingly, in some textbooks the EARLY voltage is defined for Ib=const. and in some other sources for Vbe=const. However, both definitions do not give the same EARLY voltage because the slope of both sets is different.
Up to now, I did not succeed to find an explanation which of both definitions is "correct" resp. valid.

Question to all forum members: Is there a definite answer if VA is defined for Ib=const or Vbe=const ?

 

Yeah I remember it being derived off the non-zero slope of collector curves, and then they just plot back to the x- intercept to get Va

I only know the basic model for DC biasing, when does stuff like EE get added to a DC model ?

 

when does stuff like EE get added to a DC model ?

It is included in the standard Spice model of the BJT.

 

So what's the DC Early Eff, still just a res. across Vce ?? So far I really do only know the Vbe, beta*Ib BJT DC model

 

So what's the DC Early Eff, still just a res. across Vce ?? So far I really do only know the Vbe, beta*Ib BJT DC model

According to Wikipedia:

 

Ok thanks you put to much work into helping newbs like me

I remember seeing Bf and Bf0 and wondering, so I'll learn and remember that stuff soon too. I really have to learn more on PN junctions too. I've tried watching a few uni-lectures on that, so it's really time to start on that too.