Aaron said:
Crap! What is a better (newer) technique for achieving the same
functionality of an SCS? What I am trying to do is use a momentary switch
to turn on a system that can time itself out (power itself down).
Thanks,
Aaron
As someone else mentioned, the SCS is a 4-layer device, it is really
an SCR with the anode gate also available; i think GE may still make
them.
In any event, they can easily be made with two transistors: an NPN and
a PNP; connect collector of one to base of the other (two symmetrical
connections); the NPN emitter becomes the "cathode", the PNP emitter
becomes the "anode", the NPN base becomes the cathode gate (SCR gate),
and the PNP base becomes the anode gate - which is like a PUT gate.
Note PNPs tend to have a larger B-E breakdown, allowing a larger
stand-off voltage for PUT type applications.
You can use small signal transistors, power transistors, or a mix as
you see fit and depending on tha application requirements.
If you need very sensitive gate requirements, Zetex has very high beta
transistors (300 minimum on PNP and 500 minimum on NPN if i remember
corretly) that could be used. Do not use a darlington, as thsy cannot be
saturated.