[asterisk-users] Why Aastra uses 48V whereas other IP Phones use much less, i.e. 5-12V

[Julien Goodwin]

On Tue, Nov 21, 2006 at 08:57:44PM -0500, Zeeshan Zakaria arranged a set of bits into the following:
> Why Aastra phones use more electricity, i.e. 48VDC whereas other phones use
> much less, e.g. Grandstream and Linksys both use only 5VDC. I first thought it
> was because of PoE, but the ones with 5VDC also run fine on PoE. What is the
> difference in power consumption then?
The difference due to the different voltages would be < 1w. Many of the
commercial phones (Aastra, Polycom, Cisco) use 48 volt power supplies
as it lets them have a single power circuit for wall-warts and PoE
(Standard PoE is 48 volts).

Basic electrical theory (for DC) is that power == Watts, and Watts =
Volts * Amps, so the only real difference between a 5v input and a 48v
is that the 48v will use less current (although it might go through more
DC-DC convertors those are highly efficient these days)

Thanks,
Julien
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