VCE sat for BJT

[jinyong]

Why is there a VCE sat for BJTs? Where does it come from?
Can someone explain physically?

 

[Corneo]

Just skimming the surface, the BJT is in saturation when both junctions are forward biased. When that happens, the voltage across the collector with respect to the emitter is very small (~0V). In practice VCE(SAT)~= 0.2 V. Refer to any fine electronics text book (Sedra & Smith, Gray and Meyer, etc) for more information

 

[es1]

Super simplified version: because Ic != Ie (also could be stated as there is charge in the base)
If you would like more details I recommend looking here.
http://ece-www.colorado.edu/~bart/book/book/chapter5/ch5_3.htm#5_3_4

 

[Number2Pencil]

mathematically, when Vce is trying to be a negative voltage it will actually appear as Vce(sat)

don't quote me on it