What is the significance of AC load line?

The ac load line is a graph that represents all possible combinations of  and  for a given amplifier. Under normal circumstances, the ac and dc load lines for a given amplifier are not identical. A typical ac and dc load line combination is shown in Figure 11-1a. Note that the two lines intersect at the circuit Q-point. The endpoints of the ac load line are defined as shown in Figure 11-1b. As shown, the ac saturation and cutoff points can be defined using circuit Q-point values.

It's Significance

•The ac load line of a given amplifier will not follow the plot of the dc load line.
•This is due to the dc load of an amplifier is different from the ac load. 
•The ac load line is used to tell you the maximum possible output voltage swing for a given common-emitter amplifier.
•In other words, the ac load line will tell you the maximum possible peak-to-peak output voltage (Vpp ) from a given amplifier.
•This maximum Vpp is referred to as the compliance of the amplifier.
(AC Saturation Current  Ic(sat)  ,  AC Cutoff Voltage  VCE(off) ) 


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