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Power/Alternative Energy  

High PoE made easy

Posted: 03 Sep 2007     Print Version  Bookmark and Share

Keywords:high Power-over-Ethernet  HPoE  power sharing 

The IEEE standards for so-called "high power-over-Ethernet" (HPOE) have yet to be resolved, but most designers expect a 53 VDC source, usable current from each line of about 750 mA, and a total cable resistance of 12.5 ohms. If you design for what will probably be the worst-case scenario, expect 46 VDC (48 V nominal) at 720 mA and 12.5 ohms. At 720 mA, the cable would produce a drop of 9 volts, leaving 37 VDC to work with. In this case, about 26.6 watts would be available at the end of the cable. The typical power stage running from this input would yield a bit over 20 watts. Unfortunately, that's not nearly enough power for some applications. One solution is to use multiple Ethernet lines, but that topology raises the problem of power sharing. Here's how to deal with that issue.

View the PDF document for more information.





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