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Design for 48v 802.3af PoE injector

I am wondering if this little guy will work or if it will fry my router. Router is a UniFi AC Pro requiring 802.3af Gigabit PoE. I don't have one laying around so I came up with this. Its a voltage doubler providing (tested) 70v dc unloaded to the output lines on the ethernet cable from the 24 volt ac input. I do not have the 24 watt resistor to verify the 0.5amp requirements of the design and without over/under volt protection I don't want to just plug it in all willy nilly without verifying that it should theoretically function. I am not a EE student, this is just a hobby so be nice with the reply's please.

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This site has a built in schematic editor, please use it to redraw your schematic with component values so we can properly analyze it. (Your schematic is well-drawn, but the values and reference designators are missing).

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.

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  • \$\begingroup\$ Thank you, Turns out the device was fried to begin with (found) this was all to see if it was working. I will use the schematic editor in future designs I was unaware of it. I used 50v 2200uf electrolytic caps and 1n4001 diodes and 104 caps for the rest. Using 10 watt sandbar resistor I was able to test the load voltage at 52v. And for the Gigabit having used all 4 pairs I was unaware.. Should there be switching and feedback protection as well on the used power lines? little over my head and for sure purchase over make... but again, found :) \$\endgroup\$ – Kavin Erd Apr 23 '18 at 0:43

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