Portable, battery powered 2-channel (full 10ma/channel!) phantom power unit

This web page documents the development of this design.  This is a shipping commercial product; pricing approx $250, inquire for details.

Board is 2-layer 3.1" x 3.0"
Design timeframe: Early 2005 to mid 2006
Last webpage update: May 19, 2007

Top View:
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Bottom View:
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This product is a spinoff of the high-performance phantom power circuit designed for the 4 channel design. The combination of very low noise and high efficiency is unmatched by any other portable phantom power unit.  This will run a pair of Earthworks microphones for hours!



Good phantom power is surprisingly hard to do.  The basic choices to make 48V from a battery are a switchedcap array or a dc/dc converter.  Switchedcap generation is very low noise but not efficient, generally doesn't produce a lot of power, and requires additional design complexity to keep the output voltage steady as the battery voltage drops.  dc/dc converters are noisy, even "low noise" ones, and few can boost all the way to 48V.

A good deal of trial and error with several different designs and constant checking on the Audio Precision 2522 was required to produce this design.  I cannot go into any technical details, sorry.

A simple PIC microcontroller reads the battery / DC input levels and drives the indicator LED, controls inrush current to the huge caps, and regulates 48V generation.  The on/off switch also serves to drain the caps quickly when powered off.  A diode-OR arrangement is used to combine power from the two batteries and protect against reverse polarity.