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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Other Setups for Surge Testing
In Fig. 11.8, we describe several surge setups commonly seen. The topmost one is the same one we were discussing previously in Figs. 11.4 and 11.5, except that we have made the setup universal, to test either Alt-A or Alt-B (for example a switch or a Midspan). The middle setup is also OK as per IEC 61000-4-5, but may give slightly different (worse/lower) surge survival thresholds compared to the topmost schematic. However both top and middle setups expose the vulnerability of AC disconnect, and that has nothing to do with the setup really. But it is important to test with a PD connected to keep the pass-FET ON. Also, if we use a 40-V Schottky as the AC-disconnect diode, it typically avalanches (behaves as a zener), ...

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