PoE negotiation can be simplified to a few components.  Although I
imagine that PoE chips are cheaper now than when I designed that
solution.  I don't recall all the details, but it involved two zeners,
a transistor, and a few passives.  I think the tradeoff was that it
only requested the full power - requesting power for smaller loads was
slightly more complicated.

-Adam

On Sun, Apr 11, 2010 at 10:21 AM, Olin Lathrop
<olin_piclist@embedinc.com> wrote:
> 'William Chops" Westfield ' <westfw@mac.com wrote:
>> I for one would very much like to see a PoE (Power over Ethernet)
>> circuit(s) capable of supplying 0.5 to 2W isolated power.
>
> That is easily available. =A0I fail to see the problem. =A0For example,
> Coilcraft makes POE transformers for three different power ranges, the
> lowest being 3W if I remember right.
>
> No matter what you do with the switcher though, you still have to do the =
POE
> negotiation. =A0There are chips from various vendors, including TI and
> National for that. =A0One National chip I saw used recently included the
> swither controller and the POE negotiation in the same chip.
>
>
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