Digital electrochromic mirror system

  • US 6,089,721 A
  • Filed: 04/02/1997
  • Issued: 07/18/2000
  • Est. Priority Date: 04/02/1997
  • Status: Expired due to Term
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First Claim
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1. A vehicular electrochromic rearview mirror system, comprising:

  • at least one electrochromic rearview mirror assembly comprising an electrochromic reflective element, wherein said electrochromic reflective element assumes a partial reflectance level in response to a signal applied thereto;

    a drive circuit applying a drive signal to said electrochromic reflective element establishing a partial reflectance level thereof, said drive circuit including a digital controller and a variable source, said variable source controllably repetitively interrupting current through said variable source in response to said digital controller thereby providing a voltage reduced from a particular voltage level, said drive signal comprising said voltage reduced from said particular level; and

    wherein said variable source comprises an electronic switch, wherein said electronic switch is alternatingly driven and not driven according to a duty cycle by said digital controller, and wherein said drive circuit monitors voltage across said electrochromic reflective element and varies said duty cycle at least in part as a function of the voltage across said electrochromic cell.

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