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Is all PoE 48 V DC?

We are building a PoE power supply at 48 V DC. Do the 12 V loads decrease the 48 V to 12 V?

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2 Answers 2

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Power over Ethernet is standardized in IEEE 802.3 as 47 to 57 V DC. If you are using general purpose PoE drivers, they will most likely only work in that range - overwise the manufacturers cannot really call it PoE.

You can build your own supply (also referred to as PoE injector) that generates PoE at 48 V, but the loads will not automatically regulate it down to 12 V. You will need a regulator circuit in between to do so.

Basically: main supply -> PoE supply (48 V) -> regulator (e.g. buck converter) to 12 V -> load (12 V).

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No, only the standard PoE is 48V, +/- some tolerance.

There are non-standard "PoE" injectors which may use any voltage they want and will forcibly inject supply voltage without negotiating it first, and thus equipment not compatible with this can get damaged.

What your device requires or supports is up to the device, but if it is a non-standard PoE device, it may not support 48V and can't negotiate/request supply from PSE.

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