Drive circuit for an electrochromic cell.

摘要

A continuously variable rearview mirror system (10) includes a reflective element (28) having a reflectance condition that varies as a function of the amplitude of a signal applied to the element. Forward and rearward facing light sensors (12,14) receive light independent of the reflectance condition of the mirror and produce an ambient light signal and a signal indicative of light directed into the reflective element. A control circuit (13) includes a difference amplifier (20) that is responsive to the ambient and rearward light signals for producing an output signal that is a function of the arithmetic difference between the ambient and rearward light signals multiplied by the gain of the difference amplifier. The control circuit produces a family of constant-reflectance curves which model an ideal response over all relevant ambient light levels. Offset circuits are provided to allow the relationship between the output signal from the control circuit and the drive signal applied to the reflectance element to be preselected to accommodate various types of reflectance elements and to fine-tune the response of the drive signal applied to the reflectance element.