Method and apparatus for controlling an electrochromic device

Abstract

A method and apparatus for controlling a charge/discharge voltage applied to an EC device to ensure that an appropriate voltage drop across the EC device is maintained during charge and/or discharge modes of operation. The appropriate voltage drop is determined with respect to a temperature measurement proximate the EC device. The charge level of the device is monitored using a coulomb counter circuit having a topology designed to minimize interference in the operation of the EC device.

1 . Apparatus for controlling a charge state of an electrochromic (EC) device, comprising: 
 a controllable voltage source, for providing a charging voltage to said EC device;    a temperature sensor, for providing an indicium of a temperature proximate said EC device; and    a controller, for determining, in response to said temperature indicium, an appropriate voltage to be applied to said EC device by said controllable voltage source, said determined voltage defining a rate of charge.    
     
     
         2 . The apparatus of  claim 1 , further comprising: 
 a charge counter, for counting charge quanta imparted to said EC device;    said controller causing said controllable voltage source to stop producing said changing voltage when said charge quanta imparted to said EC device reaches a desired level.    
     
     
         3 . The apparatus of  claim 2 , further comprising: 
 a polarity reversal circuit, for selectively applying said voltage produced by said controllable voltage source to said EC device as one of a charge current and a discharge voltage.    
     
     
         4 . The apparatus of  claim 2 , wherein said charge counter comprises: 
 a current mirror, for producing a reference current proportional to said current produced by said controllable voltage source; and    a switch, selectively coupling said reference current to a capacitor, for repeatedly causing said capacitor to be charged to a first threshold level and discharged to a second threshold level by said reference current;    wherein a pulse is provided to said controller each time said capacitor is charged to said first threshold level and each time said capacitor is discharged to said second threshold level.    
     
     
         5 . The apparatus of claim. 4 , further comprising: 
 a counter, said counter being incremented in response to pulses provided during a charge mode and decremented in response to pulses provided during a discharge mode, said count being indicative of a present charge level of said EC device.    
     
     
         6 . The apparatus of  claim 5 , wherein said charge level of said EC device Q EC  is approximately defined by the following equation:  
       C REF *2(V H −V L )*COUNT  
       where: 
 C REF  is the capacitance of the reference capacitor;  
 COUNT is the presently stored counter value;  
 V H  is the first threshold level; and  
 V L  is the second threshold level.  
 
     
     
         7 . The apparatus of  claim 1 , wherein: 
 said controllable voltage source provides a charging voltage across said EC device; and    said appropriate voltage to be produced by said controllable voltage source comprises a charging voltage bounded by a minimum charge voltage and a maximum charge voltage, said minimum and maximum charging voltages being temperature dependent.    
     
     
         8 . The apparatus of  claim 7 , wherein said maximum charge level is selected to avoid browning or bubbling of said EC device.  
     
     
         9 . The apparatus of  claim 7 , wherein said minimum charge level is selected to provide a minimum rate of chromatic change within said EC device.  
     
     
         10 . Apparatus for controlling a charge state of an electrochromic (EC) device, said electrochromic device receiving a charging current said apparatus comprising: 
 a reference impedance, coupled to receive a reference current proportional to said charging current, said reference impedance having a known impedance relationship with said electrochromic device;    a window comparator, coupled to said reference impedance, for comparing a voltage level of said reference impedance to upper and lower threshold levels and producing an output signal indicative of said comparison; and    a controller, coupled to said window comparator, for determining a charge level of said EC device using said window comparator output signal.    
     
     
         11 . The apparatus of  claim 10 , further comprising: 
 a temperature sensor, for determining a temperature proximate said electrochromic device;    said controller, in response to said determined temperature, determining an appropriate charging voltage for said EC device and adapting said charging voltage to said appropriate charging voltage.    
     
     
         12 . The apparatus of  claim 8 , wherein said appropriate charge voltage is bounded by a minimum charge voltage and a maximum charge voltage, said minimum and maximum charging voltages being temperature dependent.  
     
     
         13 . In eyewear having a lens portion optically cooperating with an electrochromic material, apparatus for controlling a charge state of said electrochromic material, comprising: 
 a controllable current source, for providing a current to said electrochromic device;    a charge counter, for counting charge quanta imparted to said electrochromic device;    a temperature sensor, for providing an indicium of a temperature proximate said electrochromic device; and    a controller, for determining, in response to said temperature indicium,, an appropriate voltage to be produced by said controllable current source;    said controller causing said current source to stop producing said current when said charge quanta imparted to said electrochromic device reaches a desired level.    
     
     
         14 . The apparatus of  claim 13 , further comprising: 
 a polarity reversal circuit, for selectively applying said current produced by said controllable current source to said electrochromic device as one of a charge current and a discharge current.    
     
     
         15 . The apparatus of  claim 13 , wherein said charge counter comprises: 
 a current mirror, for producing a reference current proportional to said current produced by said controllable current source; and    a switch, selectively coupling said reference current to a capacitor, for repeatedly causing said capacitor to be charged to a first threshold level and discharged to a second threshold level by said reference current;    wherein a pulse is provided to said controller each time said capacitor is charged to said first threshold level and each time said capacitor is discharged to said second threshold level.    
     
     
         16 . The apparatus of  claim 15 , further comprising: 
 a counter, said counter being incremented in response to pulses provided during a charge mode and decremented in response to pulses provided during a discharge mode, said count being indicative of a present charge level of said electrochromic device.    
     
     
         17 . The apparatus of  claim 15 , wherein said charge level of said electrochromic device Q EC  is approximately defined by the following equation:  
       C REF *2(V H −V L )*COUNT  
       where: 
 C REF  is the capacitance of the reference capacitor;  
 COUNT is the presently stored counter value;  
 V H  is the first threshold level; and  
 V L  is the second threshold level.  
 
     
     
         18 . The apparatus of  claim 13 , wherein: 
 said controllable current source induces a charging voltage across said electrochromic device; and    said appropriate current~to be produced by said controllable current source comprises a current that produces a charging voltage bounded by a minimum charging voltage and a maximum charging voltage, said minimum and maximum charging voltages being temperature dependent.    
     
     
         19 . Apparatus for controlling a charge state of an electrochromic device, comprising: 
 a controllable voltage source, for providing a charging voltage to said electrochromic device;    a charge counter, for counting charge quanta imparted to said electrochromic device;    a temperature sensor, for providing an indicium of a temperature proximate said electrochromic device; and    a controller, for determining, in response to said temperature indicium, an appropriate voltage to be applied to EC device by said controllable current source;    said controller causing said current source to stop producing said current when said charge quanta imparted to said electrochromic device reaches a desired level.    
     
     
         20 . The apparatus of  claim 19 , further comprising: 
 a polarity reversal circuit, for selectively applying said voltage produced by said controllable voltage source to said electrochromic device as one of a charge current and a discharge current.    
     
     
         21 . The apparatus of  claim 19 , wherein said charge counter comprises: 
 a current mirror, for producing a reference current proportional to said current produced by said controllable current source; and    a switch, selectively coupling said reference current to a capacitor, for repeatedly causing said capacitor to be charged to a first threshold level and discharged to a second threshold level by said reference current;    wherein a pulse is provided to said controller each time said capacitor is charged to said first threshold level and each time said capacitor is discharged to said second threshold level.    
     
     
         22 . The apparatus of  claim 21 , further comprising: 
 a counter, said counter being incremented in response to pulses provided during a charge mode and decremented in response to pulses provided during a discharge mode, said count being indicative of a present charge level of said electrochromic device.    
     
     
         23 . The apparatus of  claim 22 , wherein said charge level of said electrochromic device Q EC  is approximately defined by the following equation:  
       C REF *2(V H −V L )*COUNT  
       where: 
 C REF  is the capacitance of the reference capacitor;  
 COUNT is the presently stored counter value;  
 V H  is the first threshold level; and  
 V L  is the second threshold level.  
 
     
     
         24 . A method for maintaining charge delivered to an electrochromic device at a predetermined level as the temperature proximate said device varies, wherein said charge is induced by an applied voltage, said method comprising the steps of: 
 (a) sensing the temperature proximate said device; and    (b) adjusting said applied voltage in accordance with the temperature sensed in step (a) so as to maintain said charge at said predetermined level.    
     
     
         25 . The method of  claim 24 , wherein said device is an electrochromic lens.  
     
     
         26 . The method of  claim 24 , wherein the polarity of said applied voltage is adapted to selectively increase and decrease said charge.  
     
     
         27 . The method of  claim 24 , wherein said applied voltage is bounded by a minimum charging voltage and a maximum charging voltage, said minimum and maximum charging voltages being temperature dependent.  
     
     
         28 . A method for maintaining charge delivered to an electrochromic device at a predetermined level as the temperature proximate said device varies, wherein said charge is induced by an applied current, said method comprising the steps of: 
 (a) sensing the temperature proximate said device; and    (b) adjusting said applied current in accordance with the temperature sensed in step (a) so as to maintain said charge at said predetermined level.    
     
     
         29 . The method of  claim 28 , wherein said device is an electrochromic lens.  
     
     
         30 . The method of  claim 28 , wherein the polarity of said applied current is adapted to selectively increase and decrease said charge.  
     
     
         31 . The method of  claim 28 , wherein said applied current is bounded by a minimum charging voltage and a maximum charging voltage, said minimum and maximum charging voltages being temperature dependent.  
     
     
         32 . A method for adapting the charge level of an electro-optic device, comprising the steps of: 
 (a) sensing the temperature proximate said device; and    (b) simultaneously adjusting a rate of charge and a maximum charging voltage in accordance with the sensed temperature to achieve a desired charge level in said electro-optic device.    
     
     
         33 . The method of  claim 32 , wherein said electro-optic device comprises an electrochromic device.  
     
     
         34 . The method of  claim 32 , wherein said electro-optic device optically cooperates with one of a lens, a vehicle windshield and a window pane.  
     
     
         35 . The method of  claim 32 , wherein said method is performed by a controller within an eyewear housing, said eyewear housing including a lens that optically cooperates with said electro-optic device and a power source for providing said charging voltage.  
     
     
         36 . The method of  claim 35 , wherein said power source comprises one of a battery, a fuel cell and a solar cell.  
     
     
         37 . A method, comprising the step of: simultaneously controlling, according to a temperature proximate an electrochromic (EC) device, a total charge applied to the EC device and a rate at which the charge is applied to the EC device.  
     
     
         38 . The method of  claim 37 , further comprising the step of: 
 adapting said applied charge to a determination that a desired charge level has been reached.