V G wrote:
>> When fully on, a Bipolar has a voltage drop - Vce(sat)
>
> So what does the base control exactly? If the current through the base
> controls the current through the collector, and I =3D V/R, is it also
> controlling the resistance? Or is it controlling the voltage drop?

A BJT is a current multiplier.  The base controls how much current the
collector *can* allow to flow.  If the external circuit does not supply tha=
t
much current, then the transistor will be "saturated" and look like a fixed
voltage drop to rough first order approximation.  In power switching
applications, a BJT is deliberately operated in saturation to minimize the
on-state voltage drop.


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