48V Phantom from 2 AA batteries

[riggler]

Been looking for a schematic for the little Shure FP23 preamps. I want to find out how they're getting 48V phantom from 2 AA's. Runtime is approximately 5 hours, including the preamp itself on top of the phantom draw.

 

[sahib]

If you can share the schematics perhaps we can comment on it,  but I would assume by using low power opamps for the audio and pwm drivers to boost for phantom.

 

[Gus]

maybe this?
http://www.national.com/pf/LM/LMR64010.html#Overview

 

[JohnRoberts]

The interesting thing is that few mics need the full 48V of phantom supply voltage and much of that power is wasted in the 6.81k phantom buildout resistors.  While not trivial, hypothetically we could provide a current source (from less than +48V) in parallel with a 6.81k resistors, tied to some lower nominal voltage and realize improved efficiency and battery life.

Since there are too many applications that draw current from phantom supplies to simply anticipate all of them this might be better addressed application by application, if interested in saving power. Otherwise battery life may be disappointing. On the positive side most microphones only draw a small fraction of the available phantom current so life will be decent. 

JR 

 

[gemini86]

in most generic SDC china mics, the dump the 48V down to 12v with zeners, run the amp off that, then pump the 12v back up to 48+ with a simple oscillator/multiplier circuit.

 

[Andy Peters]

maybe this?
http://www.national.com/pf/LM/LMR64010.html#Overview

Or TPS61081 with a doubler on the output.

-a

 

[Andy Peters]

maybe this?
http://www.national.com/pf/LM/LMR64010.html#Overview

The doubler trick should work with that National part. Might be fun to build up and see.

-a

 

[riggler]

Going to try a doubler on the National part!