PoE RJ45 ethernet connector clarification


Joined Mar 15, 2020
PoE runs on different pins depending on the standard being followed. Take a look at this PoE Pinout for example. I suspect the design for that RJ45 connector is using transformers between the pins and the board to drive the PoE. For example, if you energized pin 10/11, it'd provide power to the pin 1/2 in the socket. Or the other way around too, if there was power on 1/2, it'd energize 10 and 11. Pins 1,6,7,12,13-19 are tapped to the center of the transformer so they'd see half the voltage that's on the transformers. 17-20 are used for driving the LEDs.

Here's an example of another RJ45 POE jack, except it's only got transformers sitting on pins 1,2,3,and 6. if we look at the above pinout page at the chart near the bottom, we can see that's following 802.3af using shared data/power pins, while your example is configured to support 802.3af using spare pins (802.3at mentioned in the datasheet of your example is basically 802.3af with more power).
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Thread Starter


Joined Oct 12, 2018
Thank you the link to the MTJ-88SX1-FSP-PG-LG-M7Y works.

I understand now. Thanks!

The connector only needs 8 pins for the Ethernet cable. The cable itself delivers power through spare pair or data pair to a few of the 8 pins.

The PoE special pins in the connector I posted is from a connection of the center-tap of the transformers included inside of the RJ45 connector itself.