Darren Gibbs wrote:
> I was thinking that having +50V on the wiring out to the solenoids
> and back all the time was in some sense less safe.

Why?  You circuit and enclosure has to deal with 50V safety issues anyway
whether the 50V is there all the time or part of the time.

> I just wondered if there were other reasons for using NPN.

Yes.  The logic deciding what to switch is ground-referenced, probably 0-5V.
Since the logic is low side, a low side switch is easier to drive.  Think
about what the circuit would look like to drive high side PNP or P channel
FET switches.


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