100V MOSFETs for power-over-Ethernet

September 23, 2015 // By Graham Prophet
The DMN10H120SFG MOSFET (Diodes Inc.) has been designed as a switch for IEEE 802.3 compliant 48V Power-over-Ethernet (PoE) systems. This switch enables the delivery of power through the Ethernet cable to end-applications such as wireless access points, VoIP phones, point-of-sale terminals, call systems, IP security cameras and building management devices.

In power-sourcing equipment such as LAN routers and midspans, this 100V N-channel MOSFET switches power to the CAT5 (or CAT6) network cable. End-user protection is provided as PoE operates between 44V to 57V, which meets the 60V Safety Extra Low Voltage (SELV) rating, removing the need for rigorous isolation and certification of end-equipment while also easing system maintenance. I ²R losses are minimised when operating at these voltage levels and this helps maximize power delivery to the end-equipment and improve efficiency.

With a 100V BVDSS rating the DMN10H120SFG MOSFET provides headroom for 48V PoE operation. The DMN10H120SFG also offers an extended safe-operating-area (SOA) that can withstand the power dissipation due to short-circuit fault conditions, such as an Ethernet cable breaking, until the PSE controller detects the fault and switches off. During this fault condition the MOSFET goes into linear mode and needs to dissipate 30W for at least 20 msec, which is achieved even with a +60°C elevated operating temperature.

Diodes; www.diodes.com