Electrochromic element driver with negative output resistance

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.

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.