I’m attempting to design a small board that splits 802.3af and provides both data and 5v power to an MCU on the same board.

I can find plenty of ICs with reference schematics for the splitter part - but they all expect an RJ45 port, which I understand contains something called “magnetics”. So far as I can tell, this is both about isolation and impedance matching.

My intended application is for outside, where I’d expect just using a reel of solid core cable. Personally, I find it annoying having to crimp a plug, so use an IDC and then a short patch for that.

What I’d really like is somehow to avoid either the plug or IDC + patch, so there could be 8 punchdown connectors directly on the board. Presumably then you’d have to replicate these mysterious (to me) magnetics on board.

I’m struggling though to find anything like this.

Here’s a picture I found of the internals of a PoE splitter; essentially, I’d like to understand what would be needed to replace the RJ45 port with a punchdown connector.

enter image description here


1 Answer 1


It's not uncommon to have the magnetics external to the RJ-45 socket, especially in cheaper devices — Just like in this case, where I'm certain the magnetics are inside the TMSEMI package closeby.

That board looks like it's only for 10/100 Mbps Ethernet; so I'm sure you could get by with nearly any PCB-mount punchdown connector there (preferrably rated cat 5 or better for 100MbE).


Keep the magnetics package, and 'just' replace the RJ-45 socket with your punchdown connector of choice.


Looking around, the magnetics part seems to be second sourced version of Pulse Electronics H2019NL/HX2019NL, a 100MbE, 15W PoE-specific part. Quite widely available too!

  • \$\begingroup\$ Wow that was quick, thanks Richard. I didn't even bother to look up that IC - I assumed it was part of the active PoE negotation. I see now from the datasheet: cdiweb.com/datasheets/pulse/H327.pdf. As a followup up, could you help out with the search terms for the punchdown part? Googling only seems to find little boards with that and the RJ45 port. I have found something called 'gas tight IDC' mouser.co.uk/new/avx/avx-gas-tight-wtb-idc - but can't find one with 8 connections. \$\endgroup\$ Jul 11, 2019 at 14:53
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    \$\begingroup\$ By a quick search, I found that Mouser carries Stewart SS-51000-003 and SS-51000-004. Surprisingly cheaply too! Those are specifically made for Ethernet, and already come pre-painted with the correct wire colors. Haven't looked much farther yet. \$\endgroup\$ Jul 11, 2019 at 14:57
  • \$\begingroup\$ Ah I see - so I have the right thing, it's just one is expected to mount 2x4 on the PCB, rather than some single 1x8 part. \$\endgroup\$ Jul 11, 2019 at 14:59
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    \$\begingroup\$ Oh the part you linked is for 8 connections, just in pairs. \$\endgroup\$ Jul 11, 2019 at 15:08
  • \$\begingroup\$ Yup! It's indeed made for all four pairs. This might kind of limit the compactness of your thing compared to having two sets of two pairs, however. But you can always just saw/snap it in two if you're not making too many of those. :D \$\endgroup\$ Jul 11, 2019 at 15:15

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