Hi. ! I have read that a port of a PoE switch has a 44VDC - 57VDC output voltage. I have a microntroller that works on 5VDC. My question is, if I use one of the ports as the supply for the microcontroller, will it deal any damage to it or does it depend on any other factors such as current rating? Thank you
If you want to power anything from a 802.3af or at POE switch, it takes more than an electrical connection to do it.
The POE switch port provides 48V at a very low current at the connection time, and there is a negotiation sequence between the device and the switch to enable additional current.
The arduino POE Ethernet shield uses a SilverTone module to do the negotiation and provide a switch mode controller to reduce the POE line voltage to (I think) 12V which is then regulated using the on-board LDO for 5V.
There are other SilverTel modules that provide 5V or 3.3V (at a lower total power output).
Designing a POE device controller from scratch is non-trivial, if you are really interesting in doing this, drop another note and I will provide some links to chipsets you might consider. The Silvertel modules are going to be a better idea unless you are planning on making 100's or 1000's of a device (and maybe even still at that quantity).
