Power Electronics
IEEE802.3bt: How Serving New Markets Is Shaping The New Standard

IEEE802.3bt: How Serving New Markets Is Shaping The New Standard

Dave Abramson from Texas Instruments answers a reader question about what markets are driving the need for >25.5W PoE and a new IEEE 802.3 standard.

Bio: Dave Abramson is a design engineer for linear power products at Texas Instruments and serves on the IEEE 802.3 committee. He graduated from Georgia Tech with a Ph.D. in electrical engineering. Although his experience has been concentrated on protection circuits and Power-over-Ethernet (PoE), he also has experience in mixed-signal and system design.

Question: What markets are driving the need for >25.5W PoE and a new IEEE 802.3 standard?  Are there technical challenges for these markets not covered in the existing standard?

Many markets are driving the need for a new IEEE 802.3 standard. A few examples:

Pending task force approval, the 4-pair PoE (4PPoE) study group began discussing technical challenges that will need to be solved. One interesting topic discussed at the IEEE 802.3 Interim Session that was  recently held in York, UK was the requirements of PoE lighting and how they affect the future standard for 4PPoE. 

Before I get into the requirements of PoE lighting and the interesting questions they raise, let me provide a little background.  The two main advantages of 4PPoE discussed in the Call for Interest (CFI) held in March 2013 are the ability to deliver more power than the current standard and increased efficiency.  These two advantages both play a big role in opening up many new markets to PoE.  Building automation and LED lighting is a great example for illustrating how these new markets will help to shape the new 4PPoE standard.

One requirement for LED lighting to address is efficiency, but not in the way you might expect.  In fact, it is standby power regulations for lighting that are prompting some discussion.  Current regulations state that an LED lighting device cannot consume more than 1W in standby mode, but the level is lowering to 0.5W in 2016.  What makes this requirement more difficult to meet than you might think is that it is measured from the AC mains supply. Meaning, the inefficiencies of all the power supplies between the AC mains and the lighting device are included.

The requirement for lower standby power led to a discussion about lowering the maintain power signature (MPS) specifications in the new 4PPoE standard.  The current standard allows for a minimum power of approximately 500mW (10mA at 50V) if a DC current is used to maintain the connection or approximately 100mW if a pulsed current is used.  Some of the ideas discussed in York include lowering the 10mA current level specification and lowering the duty cycle of the pulsed MPS signal.  One thing to keep in mind is that the low current levels used for MPS will be divided between 2 pair sets.  This is critical to remember as the PSE is already tasked with sensing a very small current. 

I write content twice a month on TI’s e2e Power House blog to share discussions from the IEEE committee and get feedback from people who actually use PoE technology. Most recently, I wrote on the issue of backwards compatibility.

To follow and contribute to the development of the new IEEE 802.3 standard, email subscribe to the Power House blog here: www.ti.com/IEEE802

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