Pulse Offers Off-the-Shelf PoE Transformers

Pulse®, a Technitrol company, has announced a series of high efficiency, small footprint, off-the-shelf power transformers for powered device (PD) side Power over Ethernet (PoE) products that meet IEEE standard 802.3af. These parts have been tested and approved for use with many of the most popular PoE ICs and are available in standard output voltages from 3.3 Volts (V) to 12V.

The PoE series consists of twenty-two powered device (PD) side PoE transformers for 3 Watt (W), 7W and 13W output power levels. The Pulse transformers have 50 percent lower leakage than previous PoE power transformers, reducing the need for inefficient snubber circuits and increasing overall power supply efficiency.

The PoE standard allows the PD to request one of three levels or classes of power: 3W/Class 1, 7W/Class 2, and 13W/Class 3. Pulse has designed 3.3V, 5.0V, and 12.0V output voltage transformers at each of the three power levels. Three sizes of power transformers and three output voltage levels for each power class allow designers to select the smallest and most efficient package for the class of PoE device they are designing and to use standard, off-the-shelf components.

The Pulse PoE series transformers are designed for continuous mode flyback topologies operating between 200 and 400 kilohertz (kHz). This topology has been chosen by all the major power IC vendors because it is the least expensive and produces 90%+ efficiency. The 1,500Vrms isolation between primary and secondary windings meets the isolation voltage specification for PoE applications as defined in the IEEE 802.3af standard. Each transformer has a primary side auxiliary winding to supply input power to the power IC, further reducing power loss.

These Pulse PoE series transformers maximize the usage of available height and minimize PCB footprint. The footprint of the 13W/Class 3 output transformers is 40% smaller than competitive packages. Industry standard footprints provide the opportunity to develop a second source, if required. The footprints are 13.2mm x 10.7mm for the EP7 (8-pin SMT, 3W/Class 1), 15.2mm x 12.7mm for the EP10 (10-pin SMT, 7W/Class 2), and 17.8mm x 12.7mm for the EP13 (10-pin SMT, 13W/Class 3) transformer.

"The IEEE 802.3af specification standardizes the requirements for delivering power to electronic devices over Cat5 Ethernet cables, making standard, off-the-shelf PoE transformers possible. Each transformer has been tested and approved by a power supply IC company offering a PoE solution. This simplifies the design and layout of a power supply using these transformers," said Geoff Wildman, Pulse Power Division Product Line Manager.

Parts in this series are available in tape and reel, with prices starting at $0.69 per unit for a 100,000 units.