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Low-Power Design Enables PoE Networking

Feb. 14, 2013 by William Wong in alt.embedded

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Power consumption is on everyone’s specification checklist these days. Minimal power consumption means longer use between charges for smart phones, tablets, and laptops. It also means not having to liquid-cool thousands of cores in high-performance computing (HPC) systems. And, it means that devices can be wired and powered using different technologies like Power-over-Ethernet (PoE).

PoE has been around for more than a decade. It’s well known in the network industry, but it has been primarily used for network devices like wireless access points and Voice over Internet Protocol (VoIP) telephones. It greatly simplifies wiring since deployment no longer requires a power outlet.

PoE requires a 48-V source that’s typically found in the Ethernet hub or switch. It’s possible to add a power injector inline with a connection, but that tends to be used as a stopgap measure or when only a single PoE device is needed.

Managing PoE »

Discuss this Blog Entry 2

arthur
on Feb 25, 2013

A 5 port ethernet hub is available for $15. A wall transformer is available for $7. The cheapest power over ethernet injector is $18. Ethernet hubs? Be prepared to spend hundreds. About the only real application I can see for POE is telephones. You have ethernet there but no power? Where is this? What do you have there that does not use power and needs ethernet? Great idea, lousy economics.

Bill Wong
on Mar 20, 2013

Actually there are a number of industrial applications where this makes sense. Power outlets are fine in an office setting but rare in a large warehouse unless you explicitly put them there. Likewise, external devices, dongles, etc. are not a good idea in these environments. This approach allows everything to fit into a compact box.

Another area where this approach works is embedded devices from UAVs to trains. Running an extra cable costs money.

This solution does not make sense for most PC/104 applications but where it does it is a very good approach.

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Bill Wong covers Digital, Embedded, Systems and Software topics at Electronic Design. He writes a number of columns, including Lab Bench and alt.embedded, plus Bill's Workbench hands-on column....
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