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  Power over Ethernet Isolated Power Supply Delivers 11.5W at 90% Efficiency &mdash DN338
  PDF, 80 Kb, 档案已发布: May 2, 2004
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  Power over Ethernet Isolated Power Supply
  Delivers 11.5W at 90% Efficiency – Design Note 338
  Jesus Rosales
  fewer switches to turn on and off the better. A push-pull
  converter could be used, but the additional complexity
  is not justified at this power level. A single transistor
  forward converter is another option, but requires
  an additional output inductor and rectifier. A flyback
  converter is the simplest choice. Flyback converters
  are thought to be less efficient than forward and pushpull converters, but that changes when the output is
  synchronously rectified (a MOSFET is used instead of
  a diode to rectify the output). When powering IP telephones, wireless access points,
  PDA charging stations and other PDs (Powered Devices)
  from an Ethernet cable, designers have at most 12.95W
  of available power per the IEEE 802.3af standard. Increased demands for power mandate a very efficient
  power converter especially for classВ 3 devices (consuming between 6.49W and 12.95W). The more power lost
  in the converter, the less power available for the PD.
  The voltage available from the PSE (Power Sourcing
  Equipment) ranges from 44V to 57V, but PDs need to
  operate with as much as 20О© of series wire resistance.
  A PD can never draw more than 350mA or 12.95W
  continuously. With the maximum input current of
  350mARMS, the input voltage can droop as much as …

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• Monitor, Control and Protection > Power-over-Ethernet (PoE) Interface Controllers > PoE Powered Device (PD)

其他名称:

LTC4257IDDTRPBF, LTC4257IDD TRPBF