On 18/06/2011 01:44, V G wrote:
> I'm pretending that R2 is the battery, gradually increasing its impedance=
 as
> it's state of charge increases. The voltage across the battery never seem=
s
> to hit 4.0V.

Because of the bipolar saturation voltage. A FET would be better as a=20
pass element, which is why they are used in LDOs.
It seems you are still seeing the bipolar as a variable resistor. It=20
doesn't work like that - better to see it as a voltage controlled=20
current source.
Try your simulation again, but set the base current to 1uA and plot=20
this: d(V(n002))/d(Ic(q1))
This will give you the dynamic impedance of the collector.



--=20
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