GA Shawn, 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? 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. Or just use the buck/boost as
your primary regulator and forget the 317. The buck
boost will have to be capable of handling quite a bit of
power so choose it with that in mind.
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. A
regulator or voltage divider would need to be
incorporated to supply the 317/337. 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. They arent very practical however. It would need
to pass about 10 times the current you'd expect to pull
from the supply in order to be stiff enough to work. I
used this approach a long time ago and don't recommend
it, except in vy low current applications (ma range).
Even there a 3 termial regulator is as easy and is
Another option might be to add a
zener in the ground leg of the regulator between the
adjusting pot and ground. The idea would be to prevent
the 317 from seeing the full 56 volts. So the zener
would have to be rated at more than 16 volts. Havent
tried this approach so dontknow how effective it would
In any of these, a heat sink will
be needed, e.g dropping 16 volts at 1A = 16 Watts.
Good luck, it's an interesting project.
Back to the bench, Winter's too valuable to waste.
I love this radio stuff !
----- Original Message
December 07, 2013 2:23 PM
I have a LM317adj. TO220 regulator-1.5A, 40v
max., I mean to use. --Coming off my 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? Thanks for any help. Shawn Reed,