Coilcraft Guide to Magnetics for Power over Ethernet (PoE)

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Coilcraft Guide to Magnetics for Power over Ethernet (PoE) details the operation of the magnetic components used in PoE. PoE is a method where twisted-pair Ethernet cables of up to 100m are used to deliver power to remote powered devices (PDs). The PDs include wireless and BLUETOOTH® access points, IP security cameras, VoIP phones, network routers and repeaters, LED lighting, PDA charging systems, and controllers. PoE helps eliminate the time, required space, and expense of installing a separate line voltage power outlet. PoE also allows for power management and control of many devices from a central location. PoE operates in the 36V to 57V lower voltage telecom range and up to 73V, typically over Cat5 Ethernet cables. This gives PoE a safety advantage over standard line voltage (110/220V) power outlets.

Usage

How are Magnetic Components used in PoE?
In the signal path, center-tapped 1:1 transformers are used for injecting current, and common mode chokes are used to filter out EMI.
Signal path isolation transformers for both the transmit and receive sections are incorporated into a single package in Coilcraft HPX2126L
Common mode chokes for both transmit and receive sections are also incorporated into a single package in Coilcraft HPF2187L

Connections

Schematic - Coilcraft Guide to Magnetics for Power over Ethernet (PoE)

Schematics: Typical Connections for PoE Signal Path Magnetics
Pairs of these components may also be used to achieve higher (double) power levels.

Coilcraft ETH1–230L (802.3at) and ETH1–460L (802.3at) PoE magnetics integrate signal path transformers and common mode chokes into a single package for the most compact design in applications up to 120W.

For power-sourcing equipment (PSEs) or midspans, off–the–shelf magnetics are available for providing isolation, voltage transformation, and power injection. End users MUST have a transformer to provide functional isolation at the PD. Functional insulation is used to provide at least 1500V_rms isolation between the transformer's primary and secondary. Many Coilcraft off-the-shelf power transformers exist for PDs to provide isolation and standard voltages at a multitude of power levels.