Spotlight on power over ethernet

One of the biggest advantages of PoE besides having data and connectivity run over a single twisted-pair Ethernet cable (saving a traditional AC power cord) is that it allows centralization of power management. With traditional power systems, each device has its own power supply, which consumes energy even when the device is not in use. With PoE, however, all devices can be powered by a single central power source, which can be turned off or managed when not in use, reducing energy waste.

Because of the centralization, PoE enables also remote management of power. This means that devices can be powered on or off remotely, and their energy consumption can be monitored and centrally managed from one location such as the building management system. This not only increases energy utilization but also provides more control and flexibility over a building's power supply.

PoE also provides a more reliable and secure power supply. Traditional power systems are often prone to power outages and surges of the AC grid, which can damage devices and impact their performance. With PoE, the power supply is centralized and can be supported by an uninterruptible power supply (UPS), providing a more stable power source for connected devices, e.g. for surveillance cameras.

Due to the increased power level per port with the latest IEEE 802.3bt standard, the respective power level of the main power supplies for PoE PSE applications has to increase as well. MOSFETs with a voltage rating between 40 V and 100 V depending on the typical system voltage are used to provide the OR-ing function when combining multiple power stages in PoE power supplies for PSE. However, for synchronous rectification on the secondary side of the power supply before the OR-ing stage, due to the typical PoE voltages of 44 V to 57 V normally 80 V and 100 V OptiMOS™ 6 MOSFETs are considered to keep reliability while keeping highest system efficiency.

On the primary side, superjunction MOSFETs such as Infineon’s CoolMOS™ family enable highest efficiency, cutting-edge performance with high robustness and reliability for converting the AC voltage to DC. The product family 600 V CoolMOS™ P7 SJ MOSFET offers highest efficiency and improved power density due to the significantly reduced QG and EOSS levels, as well as optimized R_DS(on) making it ideal for PoE PSE applications.

The carefully selected integrated gate resistors enable very low ringing tendency, and, due to its outstanding robustness of body diode against hard commutation, it is suitable for hard, as well as so switching topologies, like LLC. In addition, the feature of an excellent ESD capabilty helps to improve the quality in manufacturing. The 600 V CoolMOS™ P7 offers a wide range of R_DS(on)-package combinations, including THD, as well as SMD devices, at an R_DS(on) granularity from 24 mΩ to 600 mΩ and comes along with the most competitive price/performance ratio of all 600 V CoolMOS™ offerings.