Can somebody please explain to me what is VBE(SAT) as it relates to BJTs ? How and when does the base-emitter BE junction enter into saturation?

Thanks!

 

Like a conventional diode the Base-Emitter junction becomes saturated when the voltage difference between the base and the emitter is greater than about 0.7V. It is very difficult to further increase the voltage across the junction because the current increases exponentially for small increases in Vbe. That's the how. The why is related to the behavior of a p-n junction according to the diode equation. If you try to force more than Vbe(sat) across the junction then the device will conduct enough current to destroy itself. That is the principal reason for the base resistor in switching circuits: to limit the base current.

 

That's very helpful. Thanks very much.