Conduction current in a bipolar transistor

[Justin Herrmann]

The current flow is a normal current, since it involves electrons.  The
electrons go one way, but current is defined in the other way.  The
barrier voltage at the collector-base junction sweeps the free electrons
that are flowing from the emitter to the base into the collector.  The
collector current is defined as flowing into the collector.

A transistor whose base-emitter junction is forward biased and whose
collector-base junction is reversed biased is in the active mode.  A
transistor where both junctions are reverse biased is in cutoff mode, and
if both junctions are forward biased, it's in saturation mode.

					-Justin Herrmann-

On Thu, 19 Oct 2000, Heiko van der Linden wrote:

> Hi All,
> 
> This may sound like a stupid question but I would really like to know the answer.
> 
> I was talking with a friend about bipolar transistors and how they work. This went ok for a while but
> after some talking we got into a problem: what kind of current flows through the collector during normal
> operation ?
> I understand that the majority carriers come from the emitter into the base. And then they feel the electric
> field coming from the collector and are swept over the reverse biased base collector junction.
> This sounds all very intuitive (the charge carriers are attracted by the oppositely charged collector)
> but the base collector junction is reverse biased. So the current that flows is not a "normal" current.
> What I would like to know is: what's the conduction mechanism of this current ? Is it an avalanche type 
> of conduction or something else ? And what's this type of conduction called ?
> I couldn't find a website that explained this aspect of transistors. Some of them say it's a transistor
> current etc. So that's not much use either when you want to understand what is really happening in
> those little black and silver cans....
> 
> Thanks,
> Heiko
>