[qrp-l.org] Fan control for MFJ switching P/S

[qrp_1 at juno.com]

The fan on my MFJ-4225MV switcher runs all the time,
but doesn't really need to.  So I added this simple circuit to make it
come on only when necessary. [[[snip]]]

Nick,
  You and I think totally 180 degrees out of phase !  You modify your
power supply so the fan only comes on when needed.  I have an old Yaesu
FP-757HD power supply here (not a switcher) and thats the way it operated
from the factory.  After replacing pass transistors a couple of times in
it, I modified it so the fan stays on all the time.  SInce I did that, I
have not needed to replace the pass transistors anymore !  But the fan in
my power supply is whisper quiet and I never hear it running anyway. 
Modifications are fun though ! ;^)

73,
Rick McKee, KC8AON, Ohio - www.angelfire.com/electronic2/qrp
Monthly QRP Field Day Group - http://groups.yahoo.com/group/MQFD/
With God all things are possible <><