On Sun, Jun 19, 2011 at 12:40 AM, Oli Glaser <oli.glaser@talktalk.net>wrote=
:

>  Because of the bipolar saturation voltage. A FET would be better as a
> pass element, which is why they are used in LDOs.
> It seems you are still seeing the bipolar as a variable resistor. It
> doesn't work like that - better to see it as a voltage controlled
> current source.
>

No no, I'm not. I fully understand that it's a voltage controlled current
source. I just want to observe how the dynamic impedance of the BJT changes=
..


> Try your simulation again, but set the base current to 1uA and plot
> this: d(V(n002))/d(Ic(q1))
> This will give you the dynamic impedance of the collector.
>

Is it the derivative d(V)/d(Ic)? If so, what is the idea behind that?
--=20
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