Tutorial

Applet Tutorial

First, familliarize with the current components by clicking the buttons on the top of the applet. The buttons turn 'on' or 'off' the corresponding carrier flows.
Second, use the arrow-control at the bottom of the applet to control the input voltage. As the voltage varies, we are looking only the forward active region (Emitter-junction = forward-bias; Collector-junction = reverse-bias) of operation for the BJT. As you vary the input signal voltage, the DC operating point (the magenta-colored dot) moves in the active region of the BJT output characteristics.
As you vary the input signal voltage, and as the transistor goes between the upper limit (of this applet, closer to the saturation region) and the lower limit (close to the transistor cut off), take a note of how much the Emitter junction voltage, Vbe, varies. Does it vary between 6.6V and 7.5 Volt for this BJT while the DC operating point scans almost the entire active region ? This is why most text books assume that Vbe = 0.7V.
more to come.