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Protection circuit for general-purpose digital I/O lines

  • US 7,649,726 B2
  • Filed: 09/08/2004
  • Issued: 01/19/2010
  • Est. Priority Date: 08/16/2004
  • Status: Active Grant
First Claim
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1. An apparatus comprising circuitry for protecting the apparatus from destructive electrical conditions, the apparatus comprising:

  • one or more input/output (I/O) lines;

    a first protection circuit coupled to an I/O line and operable to provide a primary level of protection for the I/O line, the first protection circuit comprising;

    one or more diodes directly connected to the I/O line for voltage clamping, anda current limiting device coupled to the I/O line and to the one or more diodes, wherein the current limiting device is operable to function as a low impedance device in a normal operating range and to function as a controlled power dissipater outside of the normal operating range; and

    a second protection circuit coupled to the first protection circuit and to the I/O line, wherein the second protection circuit is operable to provide a secondary level of protection for the I/O line, wherein the second protection circuit comprises one or more diodes directly connected to the I/O line for voltage clamping;

    wherein the one or more diodes of the first protection circuit are coupled between the current limiting device and the one or more diodes of the second protection circuit;

    wherein the one or more diodes comprised in the first protection circuit have a lower forward voltage drip compared to the one or more diodes comprised in the second protection circuit.

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