Ethernet & LAN Transformers

Yes. In practice these names, along with Ethernet magnetics, LAN magnetics and network magnetics, describe the same signal magnetics for copper Ethernet ports. Keep three part types apart: discrete transformers on this page, RJ45 jacks with integrated magnetics, and PoE power transformers, which sit in the DC-DC stage and do a different job.

Start with the PHY reference design. It states the data rate, the line driver type and how the PHY-side center tap is connected, and it often lists recommended OCL, turns ratio and loss limits for Ethernet PHY magnetics. Compare those limits with the Ethernet transformer datasheet, then match ports, PoE current, package and temperature.

It depends on the PHY. Current-mode line drivers usually need the PHY-side center tap fed from a supply, while voltage-mode drivers usually take a decoupling capacitor to ground. Cable-side center taps go to the Bob Smith termination or to the PoE path. Follow the PHY reference design and the Ethernet transformer pinout, and ask our FAE team to check the schematic if the two disagree.

Not by default. 2.5GBASE-T and 5GBASE-T signalling occupy a wider band than 1000BASE-T, so return loss, insertion loss and crosstalk must be specified over that range. Choose a part listed for 2.5G/5G, or a 10GBASE-T transformer if the PHY may later run 10G, and confirm the limits in its datasheet.

Work out the current each pair carries for your PoE class and for the PSE or PD side, then choose a part whose PoE rating covers it, noting whether the figure is per channel or total. The DC bias used in an OCL test is not a PoE rating. The LAN transformer only passes the DC current through its center taps; converting that power is the job of a separate PoE power transformer.

Discrete magnetics let you place the transformer, choose the RJ45 separately and route the common mode path your way, at the cost of board area. An RJ45 jack with integrated magnetics saves space and BOM lines. Neither is always better for signal quality or cost, so decide from PCB space, PoE, EMC and assembly. Never add a second transformer to a jack that already contains magnetics.

Yes. Send the original part number and its datasheet. Our FAE team compares footprint, pin functions, center taps, turns ratio, PoE rating and isolation, then lists the differences you need to validate. A LAN transformer replacement is confirmed by that review and by sample testing, never by pin count and pitch alone.

VOOHU is a LAN transformer manufacturer with its own magnetics factory in Mianyang, China. For a known part, send the part number, quantity and destination. Samples are available for evaluation and selected parts are free of charge; our FAE team confirms the options. Pricing and lead time are confirmed per part and order, and the first reply comes within 1 business day.