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Power over Ethernet (PoE) basics and beyond

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257 points voxadam | 1 comments | 16 Oct 25 14:09 UTC | HN request time: 0.199s | source
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willis936 ◴[22 Oct 25 02:40 UTC] No.45664343[source]▶
Other stuff engineers should know:

- PoE endpoints should have isolation barriers, factor this into cost and size estimates

- Don't skimp on TVS

- ideal diode full bridge rectifiers are really cool and you should use them (in more power entries than just PoE)

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dynode ◴[22 Oct 25 03:07 UTC] No.45664517[source]▶
Awesome I’m just doing a POE design now.

- Was having a conversation today about isolation and grounding for POE (product has a metal case). Do you have a reference? Or standard?

- TVS ahead of the bridge right?

- Do you have a part recommendation or reference design for ideal diode POE?

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1. eqvinox ◴[22 Oct 25 06:33 UTC] No.45665565[source]▶
> - Was having a conversation today about isolation and grounding for POE (product has a metal case). Do you have a reference? Or standard?

Huh. I'm not the GP poster but interesting question. AFAIK there is no proper ground reference on the LAN cable. I'm not sure I've ever seen a metal case… wait, I do, outdoor wifi APs have metal cases sometimes.

If you find out, report back ;D

> - Do you have a part recommendation or reference design for ideal diode POE?

I've done a PoE device (802.3at, 25W) and just went with TI's reference design; the higher power ones use ideal diodes, sometimes there's multiple circuit variants.

(It's not worth mucking with the PoE design for small-scale builds; the reference design might be a bit more expensive but you get that money back on way less trouble to deal with.)