Fault tolerant drive circuit for electrochromic mirror system

  • US 5,424,898 A
  • Filed: 08/08/1994
  • Issued: 06/13/1995
  • Est. Priority Date: 08/16/1991
  • Status: Expired due to Fees
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First Claim
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1. In an electrochromic rearview mirror system for a vehicle having a passenger compartment, said system including at least one exterior electrochromic mirror assembly positioned outside the vehicle passenger compartment, said electrochromic mirror assembly including an electrochromic mirror element and a deicing heater element for removing ice and dew from said electrochromic mirror element during inclement weather, said electrochromic mirror element being responsive to a drive signal that is less than a maximum voltage potential of 1.8 volts to establish the reflectance level of the electrochromic mirror element, said deicing heater element operating at a voltage level of at least approximately 12 volts, a heater supply circuit for supplying one of a vehicle battery voltage and a vehicle ignition voltage to said heater element, and a control system for providing said drive signal to said electrochromic mirror element including at least one electrical conductor to conduct said drive signal to said electrochromic mirror element, comprising:

  • desired reflectance level determining means for producing a signal indicative of a desired reflectance level;

    output drive means responsive to said desired reflectance level signal for producing said drive signal that is applied to said mirror;

    electrical supply means for supplying electrical energy to said output drive means; and

    circuit protection means for sensing a foreign voltage on one of said electrical conductors, said foreign voltage being at least approximately 12 volts, and taking corrective action in response to said foreign voltage that prevents said foreign voltage from being applied to said electrochromic mirror element, in order to protect said electrochromic mirror element during repair or replacement of said exterior electrochromic mirror assembly.

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