GA Shawn,Â nearly everyone on
the list will have better ideas than I do, but heres
some food for thought.
Does your PS have lower
voltages available?Â If so use something closer to
20 or 30 volts if you can. With semiconductor
projects you'll seldom need more than 20 volts.
I think the best option is to
use a buck-boost regulator and set the output to
30-40 volts, then use your 317.Â Or justÂ use the
buck/boost as your primary regulator and forget the
317.Â Â The buck boost will have to be capable of
handling quite a bit of power so choose it with that
One possibility is to use a
series pass transistor (1 or more) to handle the
full voltage, while providing more current capacity
than the 317.Â A regulator or voltage divider would
need to be incorporated to supply the 317/337.Â
This would take somw fiddling to make it work. There
are lots of 315 circuits and calculators on the web.
Another possibility is to use
a resistive divider to make the voltage drop for the
317.Â They arent very practical however.Â Â It would
need toÂ pass about 10 times the current you'd
expect to pull from the supply inÂ order to be
stiff enough to work.Â Â I used this approachÂ a
long time ago and don't recommend it, except in vy
low current applications (ma range).Â Even there a
3 termial regulator is asÂ easy and is superior.
Another option might be to add
a zener in the ground leg of the regulator between
the adjusting pot and ground.Â The idea would be to
prevent the 317 from seeing the full 56 volts.Â So
the zener would have to be rated at more than 16
volts.Â Havent tried this approach so dontknow how
effective it would be.
In any of these, a heat sink
will be needed,Â e.g dropping 16 volts at 1A = 16
Watts.Â Â Good luck, it's an interesting project.
Back to the bench, Winter's too valuable to waste.
I love this radio stuff !
72Â Â WA0ITP
----- Original Message
December 07, 2013 2:23 PM
Â Â Â Â Â I have a LM317adj. TO220 regulator-1.5A,
40v max., I mean to use. --Coming off myÂ PS
transformer I have several voltages, one of them
being 56vdc, unused. I would like to drop this to
40v output, and then use a 10-turn pot. to vary the
voltage down to the min. 1.5vdc.The 56v has been
filtered. What is a preferred method to drop this
voltage? I imagine a heat sink may be needed,
also?Â Thanks for any help. Shawn Reed, kf7yff