I've seen in Sedra&Smith or here that the collector of a NPN-BJT is much bigger than the emitter why is that so?

The only thing what comes in my mind about it, is that when forward biased the base-collector "diode" has a lower voltage drop compared to the base-emitter "diode" given the same current.

On the other hand when we would make it the opposite, e.g. emitter bigger than collector the bjt would be better suited as a switch no? Since we could have $v_{ve} = 0$ and still $v_C/v_E > 0$.

Of course bjt's are not always a used as switch's, but are are my calculations correct in essence?

PS: This is my first question, is there something like math jax? Any math formatting tools?

 

I always thought they were about the same size. Isn't it the base that is much smaller?

 

the collector of a NPN-BJT is much bigger than the emitter why is that so?

I don't feel like examining the whole Power Point Presentation, but there are drawings of real transistors in the first 20 pages which contradict your belief.

 

Actually already the forth slide supports my claim. Perhaps I should clarify that when I was talking about the collector being bigger I especially meant the crossover area between collector/base being bigger. Actually this coincides with the overall volume of the according region in the examples I've seen, and also the one showed in the slides, since the outer n-region/collector often somewhat surrounds the base, who itself surrounds the emitter.

I just stumbled about his Quora question, that has some nice answers to my question.

I'd still like to know if my assumptions regarding the bjt used as a switch are correct in essence.

 

I have sometimes been wondering about circuits where transistors work with C and E swapped or abnormal currents flowing out of the base instead of the base used more like a control gate with negible current.

 

Actually already the forth slide supports my claim.

I read that differently. The left drawing shows equal areas for the emitter and collector, but it's a cross section, so it doesn't prove anything.

I'd still like to know if my assumptions regarding the bjt used as a switch are correct in essence.

Apparently the right person hasn't discovered your Thread, yet.