[TowerTalk] BCD relay driver ideas needed

[Dan Zimmerman N3OX]

>
> Has anyone already been down this road, so I won't have to reinvent the
> wheel?  Is there a way to use traditional PNP transistor source drivers,
> but with 5 volts on the base and 12 volts on the collector?


I'm using a bunch of 2N4401 NPN transistors ('bout the same as a 2N2222) and
some P channel MOSFETS to do exactly what you're suggesting (circuit to the
left).  I think the MOSFETS are IRFU5305's but there are lots of suitable
(and severe overkill) parts out there.

http://n3ox.net/projects/stepperswitch/schematic_lg.jpg

It says "to motor phases" but I'm using identical circuits that I built into
my RCS-8V to run the relays.  A nice upgrade would be to replace the NPN
transistor with an optoisolator.



73
Dan