Industrial Application - Power Over Ethernet
Power over Ethernet (PoE) is the delivery of DC power along with data over short distances of Ethernet
unshielded, twisted-pair cables and has evolved from proprietary solutions to inclusion in the IEEE802.3af
standard of 2003, and again in IEEE802.3at of 2009 for PoE+. Ethernet data transmission requires two of the
four available pairs in standard Cat5e/6 cabling. PoE can deliver power either over the remaining two spare
pairs, over the data transmission lines by using signal transformers, or via both methods together for
maximum wattage (PoE+). Via PoE, DC power is delivered to devices that are located near Ethernet cables, but
where additional standard AC lines are either not possible or not convenient.
Today, PoE solutions exist that may or may not follow the IEEE802.3 standards regarding PoE. IEEE
standards safeguard older technology (Ethernet-connected) devices that may not be expecting power by
requiring handshaking and verification before providing power, and also protect against shorts and
accidental polarity reversal. The standard describes how PoE injects power via Power Sourcing Equipment
(PSE) and how downstream devices tap the power with a Powered Device (PD) Controller located at the
device. PoE-powered devices are usually VoIP (Internet) phones, wireless access points, web cameras, and
any other device that can use 13, 25.5, or 51 Watts of DC power over Cat5, Cat5e, or Cat6 cable. PoE
capability can be embedded in a product or a product can be adapted with external PoE equipment.
Power Over Ethernet Block Diagram
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This design is for reference only. The design, as well as the products suggested, has not been
tested for compatibility or interoperability.
Application Notes and Resources
