> An SCR is like a locking relay:  Once you turn it on, it's on.

Yeah... it was my dad suggesting it :)  And he was thinking of AC... I
remember the conversation.

> I'd suggest a power MOSFET or even a small relay.

Yeah, MOS is what I was thinking originally but it seems that most of these
transistor/relay circuits are BJT.

> There is no such diode in the TIP120, sorry.

http://www.fairchildsemi.com/ds/TI/TIP120.pdf

That's the datasheet for a TIP120.  There is a diode, however it appears to
be in the wrong direction to shunt current from a collapsing field in a
relay coil that would be above this device (connected at C).  When base
current disappears, both the BJTs go off, but nothing can flow to ground
through that diode... no?

Shrug!

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics