Reflectance control of an electrochromic element using a variable duty cycle drive
First Claim
1. A drive circuit for driving an electrochromic element, the drive circuit comprising:
- means for generating a modulated signal having a variable duty cycle defining a low logic state during each cycle and a high logic state during each cycle; and
means for driving said electrochromic element with said modulated signal when said modulated signal is in one or the other of said logic states and shorting said electrochromic element when said modulated signal is in the other of said logic states irrespective of the voltage of said electrochromic element.
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Abstract
An electronic circuit for an electrochromic element. In order to improve the response time of the electrochromic element and reduce the cost and complexity, a modulated signal, such as a pulse width modulated (PWM) signal is coupled to the electrochromic element without signal averaging. In order to compensate for the compressed operating range of the reflectance characteristic under such conditions, the electronic circuit in accordance with the present invention utilizes active loading or alternatively voltage feedback of the electrochromic element to provide a reflectance response characteristic with an uncompressed linear operating range similar to a reflectance characteristic for an electrochromic element with a DC drive circuit.
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Citations
21 Claims
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1. A drive circuit for driving an electrochromic element, the drive circuit comprising:
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means for generating a modulated signal having a variable duty cycle defining a low logic state during each cycle and a high logic state during each cycle; and means for driving said electrochromic element with said modulated signal when said modulated signal is in one or the other of said logic states and shorting said electrochromic element when said modulated signal is in the other of said logic states irrespective of the voltage of said electrochromic element. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 19)
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12. A drive circuit for driving an electrochromic element, the drive circuit comprising:
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means for generating a modulated signal having a variable duty cycle defining a low logic state during each cycle and a high logic state during each cycle; means for monitoring the voltage of said electrochromic element; and means for controlling the electrochromic element as a function of the duty cycle of said modulated signal and the voltage of said electrochromic element during one or the other of low logic state or said high logic state and open circuiting said electrochromic element during the other of said logic states. - View Dependent Claims (13, 14, 15, 16, 17)
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18. A drive circuit for an electrochromic element, the drive circuit comprising:
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an enable switch serially coupled between a DC source and said electrochromic element for applying a predetermined signal to said electrochromic element when said enable switch is enabled and disconnecting said DC voltage from said electrochromic element when said enable switch is disabled; means for controlling said enable switch; a shunt transistor connected in parallel with said electrochromic element; and means for generating a modulated signal, said modulated signal used to drive said shunt transistors. - View Dependent Claims (20)
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21. A drive circuit for driving an electrochromic element, the drive circuit comprising:
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means for generating a modulated signal having a variable duty cycle defining a low logic state during each cycle and a high logic state during each cycle; means for monitoring and averaging the voltage of said electrochromic element; and means for controlling the electrochromic element as a function of the duty cycle of said modulated signal and the average voltage of said electrochromic element.
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Specification