LAN Transformer & Power Inductor
Wire-Wound Magnetics

A LAN transformer is a magnetic component required in the Ethernet physical layer, sitting between the PHY chip and the RJ45 connector. It does three jobs: removes any DC path so ground potential differences between the two ends are isolated, suppresses common-mode noise to cut EMI, and matches the 100 Ω differential impedance of Ethernet. Any device with an RJ45 port needs one.

Four. Ethernet uses four twisted pairs and each pair needs its own transformer winding. The Moritek MAT series is a discrete single-port design, so you can lay the parts out to suit your board rather than working around the pinout of an integrated module.

An integrated module packs the transformer and common-mode choke into one body — bulky, and it constrains your routing. A discrete single-port design places each part individually, freeing up the layout and even allowing double-sided placement for higher port density. It is also automatically wound, so part-to-part consistency beats hand-wound toroidal cores.

Yes. Both windings in the MAT series are centre-tapped (1CT:1CT), and the line-side centre tap serves as the PoE injection point, letting data and power share the same twisted pairs.

It comes down to data rate and board space. For 10/100/1000BASE-T, 150–200 µH is typical; for 2.5G / 5GBASE-T, 180 µH; for 10GBASE-T, use the 120 µH part whose insertion loss is specified out to 500 MHz. Choose the 3232 package (3.2×3.2 mm) when space is tight, or 4532 (4.5×3.2 mm) for a wider choice of inductance values.

Molding presses the alloy powder around the coil as a single piece — there is no separate core part and no air gap. That gives a closed magnetic path with low flux leakage and no air-gap noise, a gentler inductance roll-off at high current (better DC bias behaviour), and greater mechanical strength than assembled cores.

Isat is the saturation current — the current at which inductance has dropped 30% — and it sets the instantaneous peak the circuit can handle. Irms is the temperature-rise current, measured at a 40 °C rise, and it sets the continuous operating limit. Check both when selecting a part and design to whichever is lower.