Port Protection Diode in PoE: Any TVS Required?
We finally take up one last lingering question that is being asked nowadays, and is getting increasingly debated: Does it make sense to replace the usual output port diode of a PSE with a more expensive TVS, as is practiced by a few, but very large, OEMs today?
The Purpose of the Output Port Diode of the PSE
On page 38 of IEEE 802.3af-2003, the schematics shown in Fig. 11.15 appear. Of key interest here is the diode D1. One of the widespread assumptions about this diode is it is for some sort of reverse polarity protection. Yes, that is true, but only indirectly so. Note that on the same page, the standard actually makes it clear that the primary function of D1 is to present a nonstandard signature ...