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Detecting legacy powered device in power over ethernet system

  • US 7,856,561 B2
  • Filed: 10/19/2005
  • Issued: 12/21/2010
  • Est. Priority Date: 01/25/2005
  • Status: Active Grant
First Claim
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1. A system for providing power to a powered device (PD) in a Power over Ethernet (PoE) system, comprising:

  • a PD probing circuit for supplying the PD with a first detection current followed by a second detection current smaller than the first detection current, and determining a first response voltage developed in response to the first detection current, and a second response voltage developed in response to the second detection current, anda control circuit for detecting a legacy PD that uses capacitance as a detection signature, the control circuit detecting the legacy PD when a detection resistance value defined by a difference between the first response voltage and the second response voltage, is less than a pre-defined minimum resistance value or negative,the legacy PD being a device that could be powered by a power supply device in the PoE system.

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