Electrochromic element driver with negative output resistance

• US 6,222,177 B1
• Filed: 01/19/1999
• Issued: 04/24/2001
• Est. Priority Date: 01/19/1999
• Status: Expired due to Term

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Tonar, William L., Anderson, John S., Turnbull, Robert R., Bechtel, Jon H., Poe, G. Bruce
• Primary Examiner(s): Evans, F. L.
• Application Number:
  US09/233,270
• Time in Patent Office: 826 Days
• Field of Search: 250/214.AL, 250/214.B, 359/603, 359/604, 359/265
• US Class Current: 250/214.00B
• CPC Class Codes: G02F 1/163 Operation of electrochromic cells, e.g. electrodeposition cells; Circuit arrangements therefor
• CPC Class Codes: G02F 2203/21 Thermal instability, i.e. DC drift, of an optical modulator; Arrangements or methods for the reduction thereof

Abstract

An electrochromic element driver has a feedback loop that imparts a negative output resistance wherein the drive voltage across the electrochromic element varies in response to changes in current draw by the electrochromic element. The amount of current drawn by the electrochromic element varies as a function of temperature. At high temperatures, the drive voltage increases, enabling the electrochromic element to darken uniformly at high temperatures. At lower temperatures, the drive voltage decreases, improving the useful life of the electrochromic element. Transitions between the opaque and non-opaque states are achieved quickly, and steady state currents are lower than in many conventional implementations, decreasing power consumption.

Claims

1. A control arrangement for controlling an electrochromic element, the control arrangement comprising:

a drive circuit, configured and arranged to selectively apply a drive voltage across the electrochromic element in response to at least one of a glare signal and an ambient light level, the drive circuit being characterized by a negative output resistance;

a feedback arrangement, integral with the drive circuit and configured and arranged to vary the drive voltage as a function of current draw in the electrochromic element; and

at least one light sensor arrangement, configured and arranged to detect the ambient light level and to provide an indication thereof to the drive circuit

whereby the drive voltage will increase at higher element temperatures and decrease at lower element temperatures.

2. A control arrangement, according to claim 1, wherein the feedback arrangement is configured and arranged to detect the ambient temperature using at least one of a thermistor and a direct current response.

3. A control arrangement, according to claim 1, wherein the electrochromic element comprises at least one of a mirror and a window.

4. A control arrangement, according to claim 1, wherein the glare signal is one of a pulse width modulated signal and a digital signal.

5. A control arrangement, according to claim 4, wherein a reflectance level of the electrochromic element is varied as a function of a duty cycle of the pulse width modulated signal.

6. A control arrangement for controlling an electrochromic element, the control arrangement comprising:

a drive circuit, configured and arranged to selectively apply a drive voltage across the electrochromic element in response to at least one of a glare signal and an ambient light level, the drive circuit being characterized by a negative output resistance;

a feedback arrangement, integral with the drive circuit and arranged to increase the drive voltage across the electrochromic element in response to an increase in current draw by the electrochromic element and further arranged to decrease drive voltage across the electrochromic element in response to a decrease in current draw by the electrochromic element; and

at least one light sensor arrangement, configured and arranged to detect the ambient light level and to provide an indication thereof to the drive circuit.

7. A control arrangement, according to claim 6, wherein the feedback arrangement comprises:

a microcontroller having at least first and second outputs;

a first transistor arrangement, coupled to the first output of the microcontroller and configured to enter a conducting mode in response to assertion of the first output;

a second transistor arrangement, coupled to the first transistor arrangement and configured to reduce a base voltage of the first transistor arrangement in response to an output voltage at the electrochromic element exceeding the sum of an emitter voltage of the second transistor arrangement and the base voltage; and

a third transistor arrangement, responsive to the first and second transistor arrangements and configured to control the output voltage at the electrochromic element.

8. A control arrangement, according to claim 7, further comprising a fourth transistor arrangement, configured and arranged to selectively short the electrochromic element.

9. A control arrangement for controlling an electrochromic element, the control arrangement comprising:

a drive circuit, configured and arranged to selectively apply a drive voltage across the electrochromic element in response to at least one of a glare signal and an ambient light level, the drive circuit being characterized by a negative output resistance;

a feedback arrangement, integral with the drive circuit and configured and arranged to vary the drive voltage as a function of current draw in the electrochromic element, the feedback arrangement comprising;

a microcontroller having at least first and second outputs,

a first transistor arrangement, coupled to the first output of the microcontroller and configured to enter a conducting mode in response to assertion of the first output,

a second transistor arrangement, coupled to the first transistor arrangement and configured to reduce a base voltage of the first transistor arrangement in response to an output voltage at the electrochromic element exceeding the sum of an emitter voltage of the second transistor arrangement and the base voltage,

a third transistor arrangement, responsive to the first and second transistor arrangements and configured to control the output voltage at the electrochromic element, and

a fourth transistor arrangement, configured and arranged to selectively short the electrochromic element; and

at least one light sensor arrangement, configured and arranged to detect the ambient light level and to provide an indication thereof to the drive circuit.