Active bridge optimises Power-over-Ethernet device supplies

July 26, 2016 // By Graham Prophet
Fairchild says its GreenBridge delivers thermal, efficiency and size advantages superior to diodes for Power-over-Ethernet (POE) powered devices (Pds).

GreenBridge is an active bridge, quad MOSFET technology (a synchronously-switched FET in place of each diode): the latest addition is FDMQ8205, aimed at security cameras, wireless access points, LED lighting and other PDs. GreenBridge promises optimum Rdson performance, extremely small form factor and superior thermal performance.

 

Advanced GreenBridge technology is compliant with the IEEE 802.3at standard as little as 10% of the power dissipation of Schottky diodes, reducing or eliminating heat sinks.

“Dealing with heat has always been a critical design challenge, but even more so with these new generations of IoT devices that require 25.5W or more. The MOSFET technology in GreenBridge devices help designers eliminate excessive heat and achieve key system design goals, including higher efficiency, ensuring standards compliance and decreasing overall size and reducing costs,” Fairchild adds.

 

Low conduction losses of this GreenBridge series are another important advantage as power and voltage must be maximized for the limited input power of POE systems. Rdson performance is rated to deliver 47% lower conduction losses than alternative devices due to the power conversion efficiency of its Fairchild’s PowerTrench MOSFET technology.

The small size of GreenBridge devices also makes them ideal for new POE-based devices that need to be smaller than previous generations. At 4.5 x 5 mm, the GreenBridge devices incorporate four MOSFETs in an MLP package connected in a full bridge. GreenBridge devices do not require an external driver, saving additional PCB space.

 

Fairchild; fairchildsemi.com/greenbridge and www.fairchildsemi.com