IEEE 802.3bt was the need of this technology because of the increase in the number of Ethernet-connected devices and their need for power.As Power over Ethernet (PoE) continues to grow in popularity, so does the demand for applications with a higher power. The current standard, IEEE 802.3at, allows for maximum power at the powered device (PD) of 25.5 W, while the upcoming standard will allow the maximum power of up to 90 W.
What’s New?
This will increase the limit of PoE because it will use all four pairs of the wires which are in it. It will be very useful for pan-tilt-zoom cameras, VoIP Phones, LED Lights and the list is countless.
This not only enables the new higher power level but also provides better efficiency for the current PoE power level. The power loss in the cable is cut in about half. For example, an IEEE 802.3at PSE (power sourcing equipment) is required to supply a minimum of 30 W to ensure that the PD will receive 25.5 W. In the IEEE 802.3at standard, as much as 4.5 W is lost in the CAT5 cable.
Powering the same 25.5 W with the IEEE 802.3bt standard will cut the loss to less than 2.25 W. This increases the power-delivery efficiency from ~85% to ~92%. When you consider the number of PoE-powered devices in the world, this translates to the very large reduction in power, and in many cases up to a 7% lower carbon footprint for areas that are powered by fossil fuel.The new standard will define two more types of PSEs and PDs—Types 3 and 4. These additions will increase the maximum PoE power by delivering more power through two or more pairs of Ethernet cables.A new physical-layer classification, autoclaves, will help the PSE determine the actual maximum power drawn by the connected PD. Type 3 and 4 PSEs will identify the PD and set the power accordingly to the maximum PD power, resulting in a better power-delivery system.To maintain a PSE power, a PD must generate a power signature while the lights are off and data communication remains active. The new standard will reduce the time duration and the Maintain Power Signature (MPS) duty cycle to reduce the average standby power/current, benefiting applications such as LED lighting due to the high number of ports.The IEEE 802.3at standard required ~0.13 W to be consumed by a PD,” explains Heath. “If the PD fell below this power level, the PSE would turn off power completely. The new IEEE 802.3bt standard allows a much lower power for the standby level. Only ~0.02 W is required to maintain a power connection. This allows PoE to power ‘green’ applications with agency requirements for low standby power.
Jason Holder
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