24th October 2018      
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Power over Ethernet

  
The IEEE802.3af committee are currently working on a draft standard to supply power over existing Ethernet cabling using RJ45 connectors and 2 or 4 pair cable. The standard will permit the supply of power, typically 48v, using either the Ethernet pair (Tx/Rx) or the currently unused pair of cables in the 10/100BaseT Clauses. The project undertaken was to supply two demonstrator units, Power Sourcing Equipment in the Mid-Span, to supply intelligent power sensing for a Powered Device using upto 13W. The power sensing system was required to ensure that 'Bob Smith' terminations (100/150R) could be correctly detected and the line to remain unpowered. The power supply system was current limited during start-up and contained overload sensing as well as under and over voltage sensing.

Additionally the PSE contained a Phase Lock Loop system to detect and recover a differential incoming clock, from the Powered Devices. A clock source would be selected as Master for the PLL by a strict order of precedence. When the PLL had achieved lock, a clock signal was transmitted by the PSE to all the Powered Devices by differential line drivers. This system was able to support a full Ethernet span of 100m.
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Qutec Systems Ltd.
Registered Office: The Old Church, Verulam Road St. Albans, Herts. AL3 4DH
Registration No. 1807115