Protecting the PD from Surges
In a very similar manner, we can test the PD for surges too. The logic is the same actually, because looking in from the cable, the PD looks (coincidentally) very similar to the the PSE. We “see” a bunch of Y-caps, a port cap of 0.1 μF, a TVS, and also a bulk cap—the latter being the input cap of the DC-DC converter that follows. See Fig. 11.11. Just as in the case of a PSE wired in DC disconnect.
FIGURE 11.11 Surge test on a PD.
This leads to an equivalent circuit akin to a PSE with DC disconnect as in