I did a "back of the napkin" analysis....
Assuming a "raw" PSU voltage of 60 VDC at 130 VAC Mains (very much on
the high side for the USA), which would be RIGHT at "absolute max" for
the LM-317HV:
If the same circuit was fed from a 120 VAC mains, the "raw" DC voltage
would be a 120/130 ratio, or 0.923 x 60 VDC = 55.38 VDC....well within
the LM-317HV's "drop out" spec.
At 110 VAC mains, "raw" VDC would be 110/130, or 0.846 x 60 VDC = 50.77
VDC....now approaching the dropout V for the 317HV.
At 100 VAC mains, the ratio is 100/130, or 0.77 x 60 VDC = 46.15
VDC....oops!
In a separate email, Ike Z. pointed out the STUPIDLY high drop-out
voltage for the 783....but at currents far higher than required for any
reasonable phantom supply.
I am "torn"....neither the 317HV not the 783 are totally perfect. The
dropout behavior of the 317HV seems to be a familiar one, yet the 783
MIGHT be more bullet-proof, especially when using a 65V or higher "raw"
rail.
Siiigh....
Now checking prices....
Mouser has the 783 for $1.60. Digikey has the 317HV for $3.94.
Bri
Matt Syson wrote:
Hi
The HV variant is only just capable in this situation as you would
normally anticipate around 65 Volts when your 'designed' supply is fed
with mains on the high side of it's tolerance. It certainly stands a
better chance than the 'standard' 317. A useful 'dodge' could be to put
a 36 Volt 3 Watt Zener from in to out of the reg and a resistor on the
input to the reg (JLM show a 47 R but perhaps a bit larger would be
better, the normal volts drop across it will be small). Then you could
use a standard part.
Matt S
[email protected] wrote:
There is also a "HV' 317 variant rated for a 60V in/out differential:
http://www.national.com/ds/LM/LM317HV.pdf
Bri
---- Ike Zimbel <[email protected]> wrote:
I think what Matt was talking about was a TL-783
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-20687-5-ND.
best,
Ike
eliya gwetta wrote:
Hi Matt
Yes! I remembered the LM317 not being the right regulator for 48V, a
TL583 would be a drop in replacement or I would have to change other
components in the circuit as well?
On Sat, Jul 4, 2009 at 9:25 PM, Matt Syson
<[email protected] <mailto:[email protected]>>
wrote:
Hi
The JLM circuits are pretty much what you need so you could either
'copy' the circuit and build it yourself or buy the kit.
I am not too impressed at using a LM317 for the phantom 48 rail,
they are only rated to 39 or 40 volt DIFFERENTIAL (input pin to
output pin) , meaning that if you short the output you stand a
good chance of 'blowing it up'. I presume the 47 Ohm resistor is a
lame way of trying not to 'kill' it, hardly a good engineering
solution.
You should substitute it for a TL583 (sorry this number won't come
to me, but there is a similarly packaged regulator that handles
125 Volts).
Matt S
Donald Put wrote:
If you're up to making your own, there are numerous PCBs/kits
available for this type of project. They're set up for dual
voltages and 48VDC for the phantom power. Check out JLM's
offerings on his website:
http://www.jlmaudio.com/JLM%20Power%20Supply.htm
Cheers,
--
Don
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