Phantom Power Unit

[rockgardenlove]

Using this schem:
http://members.nuvox.net/~zt.robgrow...ntompower.html
I've checked it against some other sites on phantom supplies and it looks correct.

Here's my transformer choice:
Hammond 164E24
http://www.hammondmfg.com/162.htm
.1A at 24v
Sounds about right, no? I'm guessing that each mic of mine will draw around 2.5mA, so that should suffice easily for the 5 or so I'm planning.

Here's something I don't get:
http://www.st.com/stonline/books/pdf/docs/2154.pdf
It says it'll provide up to 37v output voltage. I *should* have 48v, even though it won't really make a difference. Just wondering why on the schem it would say it produces 48v?

And for more than one mic I'd do fine just to duplicate the lower half of that schematic a few times, no?

Thanks!

[Enzo]

DO me a favor, add a line explaining what the links are. Your third link is just the data sheet for the 317. If you had said "This data sheet for the LM317 says..." Then I wouldn't have had to download it on my dial-up.

The LM317 doesn't know what voltage it is running at. Unlike the three leg Vregs like 7812, the LM317 does NOT reference to ground. The center leg of the 7812 is grounded. Or lifted by a diode drop maybe. But the 317 doesn't work that way, it is a floating regulator. if you start with it connected to ground, it will only go up so high, but float it, and it can run at most any voltage. Like a 6 foot Xmas tree that only reaches up to 6 feet, if you put it on a 3 foot table, it can reach 9 feet.

There is a maximum voltage differential between input and output of 40 volts, but the thing doesn't connect to ground. So your output can be up to 40 volts below the input, or the input can be as much as 40 volts over the output. However, I would give the poor thing a little more breathing room than 40. 10-20 sounds more friendly.

The LM317 needs a minimum load, don't recall what, so you may beed to add some resistance across the output. I don't think it needs to be a lot of load, just enough to keep it awake. otherwise it wil drift.

Look up high voltage applications for the 317. If the data sheet doesn't cover it, then try the National Semiconductor web site. I bet their "Analog University" covers Vregs. Certainly application help is there.

[rockgardenlove]

Alright, thanks very much, that makes perfect sense.
I'll be sure to note on what my links are in the future too.

It reads that the "minimum load current" is 10mA, so I should just put a resistor across the output that'll present a 10mA load?

Then of course, is that transformer the right one?
And to add more phantom power connections, can I just multiply the bottom half of that schem?

Thanks!

[Enzo]

Very little current draw, so one supply ought to cover the whole collection of inputs.