PoE 802.3af injector circuit
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70VDC is over the PoE Vin (57V), even though there will be a load to pull this down you cannot rely on a particular load and risk overvoltage at the PD.

This will not work for GigE; you are not carrying all data pairs through between connectors and you will at most have 10/100. Gigabit Ethernet requires all four pairs.

Finally, I don't know that capacitor (the one below the second diode, see why refdes are important?) is supposed to be doing, but it's connected to the same net on both sides. Hence, it's worthless.

I would recommend that you toss out most of this circuit, and buy a cheap DC/DC converter (boost). Throw a full-bridge rectifier and some caps on the output of your transformer, then use the DC/DC converter to generate a proper 48-56V. Or, better yet, buy a PoE injector, they're really cheap and they will work.