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passive POE adapter for alix poe1a2

passive POE adapter for alix poe1a2
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Price: $3.50
Availability: In Stock
Model: poe1a2
Manufacturer: PC Engines
Average Rating: Not Rated

 

Status active
Part numbers poe1a2 = POE adapter, RoHS compliant
Use with ac18veur 
ac18vuk
Spec Passive POE (Power Over Ethernet) adapter, uses unused pairs of 100baseT network cable to transmit power to remote device.
Pinout DC jack center positive, 2.1 mm pin. RJ45 pins 4,5 = positive, RJ45 pins 7,8 = negative.
Issues • Passive POE does not comply with the IEEE 802.3af specification. 
• To minimize cable losses, feed the highest allowed voltage, e.g. 18V. Demarc Technology has a nice POE voltage drop calculator- select 1 pair for correct results. Keep in mind that WRAP input power is fairly constant over input voltage - when the input voltage drops, the current goes up. Power = voltage * current. 
• To avoid ground loops, ground should be referenced on the receiving end only, that is use a 2 prong (non grounded) AC adapter.
Why not active POE ? • Cost - 802.3af compliant solutions require a high component count, and compliant switches are too expensive for small installations such as CPE. 
• Board space - DC-DC isolation transformer takes a lot of space. 
• Efficiency - DC-DC converter is required for 802.3af. Typical solution is a flyback inverter, maybe 70% efficiency. Unless you have a very long cable run, passive POE will be more efficient overall.
Manufacturer PC Engines
Origin Taiwan
Schematics PDF
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