Analog Angle Article

PoE is getting hot

Every once in a while we see a technology which seems to be getting substantial, genuine momentum and industry support. One which I see is getting it now is Power over Ethernet (PoE).

The existing PoE specification, IEEE 802.3af, is being upgraded via IEEE 802.3at to support larger loads which require substantial current. I'm seeing a lot of PoE support ICs from several vendors, as well as PoE supplies coming into the market (I dislike the abbreviated, short-hand noun “midspan” for “midspan supply” but that nomenclature battle is over, for me).

In addition to the basic voltage and current requirement, PoE brings some interesting additional mandates for source and load protection, adjacent channel interaction, sequencing, and load identification, among other features, This “mundane” stuff makes even supposedly dull power supplies pretty interesting from both a design and application standpoint. Anytime you have an open connector with power on its somewhat-exposed contacts, it's very different than a fully enclosed power-supply subsystem, for sure.

The PoE spec means that suppliers to the market really have to know what they are doing. They have to be able to walk the walk, and not just talk the talk, about power-supply subtleties, perhaps for aspects that they haven't had to deal with previously.

Our industry is always searching for, hoping for, and betting on the next big thing. Will PoE be one of the winners? I don't know, of course; no one does. We so have a legacy of over-hyped “next big things” that have either not gotten off the ground, or which launched and then flamed out (and how is ultra wideband?).

But I think PoE will do well, because it serves as a key enabler to the legitimate objective of having a single, plug-and-go connection for Ethernet-enabled peripherals such as VoIP phones, surveillance cameras, and more. It's a building-block function which, while not glamorous in itself, allows some very nice and efficient applications to happen. Unlike UWB for example, which–despite what its proponents said, is in many ways just another technique for close-distance wireless links but without a clear advantage over existing alternatives (IMO, of course)–PoE really does open up a broad new range of applications and convenience.

Let's check back in 3 to 5 years and see how PoE is doing. All crystal balls need an occasional re-calibration. ♦

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