48VDC to 5VDC converter

I'd like to convert phantom power to 5VDC. I need a minimum of 25-30 mA. I assume most phantom power sources can output at least 5mA for 240 mW of power, which would allow for 100 mW of loss in the circuit. Anyone know of a circuit to do this? The simpler, cheaper and smaller the better, and transformerless if possible.

Thanks

There may be some circuits made specially for telecommunication purposes. Telephones runs off 48VDC.

Jakob E.

Like Jakob suggested there are many circuit meant for 48V use. Have a look at the switcher sections of the maxim-ic, national and ti sites.

Best regards,

Mikkel C. Simonsen

I am unsure what you need 5 volts at that high current for.

You are treading on thin ice.
Phantom power normally is limited to 10ma max. As the 6.81K resistors
in the voltage feed line are the main limiting factor.

Switchers will draw a hell of lot more current than that.
the spikes in current draw and getting one quiet enough
will drive you crazy. Do not go there.

Go here if you must.

http://www.cadmics.com/e100.htm
With the manual in PDF below.
http://www.cadmics.com/pdf_files/e100_manual.pdf

This mic broke the mold. As they did not use discrete circuits.
They wanted op-amps in there. But they needed more current than phantom could deliver. So they trickle charged 2 - 9V NiMh batteries
with the phantom power. The batteries were charged in 16 hours.

To get the circuit to work for you see schematic on page 4 of manual.
R13 and R14 go to microphone XLR conn. pins 2 and 3
Connection C on bottom goes to XLR conn. pin 1
Remove all circuits to the left of R11 and R12 including R11,R12.
For +5V you will need to add a regulator from V9 and V0 to your circuit.
remove V18, Q2, R3,R9,SW3A (a section only) and you only need
one 9V NiMh batter from B2 to B1 (B2 is pos.)
Short JP1 pins 1 and 2 this will now only drain the batteries
when the phantom power is applied. I.E. when the mic is unplugged Q3 is
not biased on and power does not flow from the battery Through Q1 to your circuit.

Hope this helps.

[quote author="adrianh"]I am unsure what you need 5 volts at that high current for.
[/quote]

I've got a hair up my ass about building a mic, and thought it might be nice to suck from the power already available rather than build a dedicated power supply. CAD's method looks interesting and feasible, but I hate to be dependent on a battery that might fail or not be charged at an inopportune moment, though NiMH's are certainly more dependable than others available in the past.

Thanks for the responses, and especially adrainh for taking the time to post your thoughtful response. I appreciate it.

Brauner uses a DC/DC converter for the heater voltage in their phantom-powered tube microphone..

Doc build the mic.
Use external power not phantom. Like the classic tubes ones did.
It is way easier.
You may want to use a lot higher than 5V as the voltage
that you have limits the swing of your audio signal and your
dynamic range. The computer audio guys today only have
+3 volts to use and the audio quality suffers because of that.
Use at 12 to 24 volts if you can.

Yes Gryaf I think Geffel and Bruner may have had phantom powered tube mics with DC/DC inside the mic. My hat is off to them for doing the impossible. I am not going to attempt it.

AT also has a phantom powered tube mic. I think the trick is they use tubes that were designed for hearing aids. ie low plate and low heater.

Any examples of this kind of tubes?

http://www.wps.com/archives/tube-datasheets/Datasheets/Raytheon-SP-7073-360-20M/2.JPG

Raytheon developed the tube for use in missle systems in WWII. very small. For a picture check out:
http://www.radiolaguy.com/Showcase/submini.htm