>Vce(sat) - collector-emitter saturation voltage should
>not be significantly higher for a darlington compared to
>regular NPN transistor, since darlingtons have the same
>single transistor as power stage. The saturation voltage
>will depend mostly on the base and collector current and
>Hfe.

Not quite right. Vbe(sat) for a darlington is typically about 0.6V higher
for a darlington than a single transistor, unless the collector of the first
transistor is brought out separately. Think about the way a typical 3 lead
darlington is connected - the Vce(sat) of the output device will be Vce(sat)
of the first transistor plus Vbe(sat) of the second transistor - because if
the voltage was any lower then there is not enough voltage to drive the base
of the second transistor.

The only way around this is to bring the first transistor collector out
separately, and supply it from a voltage higher than the second transistor
Vbe(sat) plus first transistor Vce(sat). This then means the second
transistor Vce(sat) is not dependant on any characteristics of its own
Vbe(sat) or the first transistor Vce(sat).

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