Realizing what confuses me the most, I will make this more straight-forward. Say that a transistor works in the forward active region and it receives an ac input signal at its base.
Is there a chance that the change in the base voltage will decrease Vbe and force the transistor into the cut-off region? Is there any chance this might happen before first entering the saturation region?
I'm soon taking an exam on transistors and I've just started my revision. After having a look at the conditions for each region of operation and some example problems, there is something I don't understand or that maybe I don't remember very well.
The condition for an npn bjt to be on is that the base emitter voltage is above 0.7 volts. From what I remember this is not an accurate value but let's say it is around there.
When we analyse the small signal model of a circuit , the values we calculate are superimposed on the dc values, right? So, when we apply an ac signal to the base of the bjt, the base emitter voltage changes.
So, my questions are : Is there a chance that the ac input signal will take the bjt in the cut off region?
If yes, how do we check it?
If yes, when deciding on the swing of the output voltage are we more worried about entering saturation or cut-off region? I mean, which comes first as the swing increases? Does it depend on the operation point?