transistor base nomenclature Vbb vs. Vb vs. Vin

Thread Starter


Joined May 23, 2012
The attached NPN Common Collector circuit has Vbb = 15V.

Just a few trivial questions.

I suppose Vbb stands for the base bias voltage?

Is Vbb = Vin?

Why isnt the Collector voltage mentioned in the circuit problem? Is it only because the common collector circuit function is not dependent on the voltage at the collector?

Is the active mode of operation not applicable to the common collector design?

Please advise



Joined Mar 14, 2008
Vbb is the collector voltage as well as the voltage to bias the base. Calling it Vbb is somewhat confusing.

Vin is the AC signal voltage, which is independent of Vbb.

Certainly the common collector (emitter follower) configuration can operate in the active mode region.


Joined Nov 30, 2010
So many questions in one post!
1) Vbb is the supply voltage. (It is usually labeled as Vcc.)
2) the collector voltage is mentioned, It is +15 DC volts.
3) That transistor is in an active mode but I don't know exactly what you mean. That circuit is an analog voltage follower, as in, "not saturated".

Edit: simultaneous post with crutschow