Illumination device and age compensation method
First Claim
1. A method for controlling an illumination device comprising a photodetector and a plurality of LED chains, wherein the method comprises:
- applying drive currents to the plurality of LED chains substantially continuously to produce illumination;
measuring a photocurrent induced on the photodetector in response to the illumination produced by each LED chain, one LED chain at a time, and received by the photodetector;
measuring a forward voltage developed across the photodetector by applying a non-operative drive current to the photodetector;
determining, for each LED chain, an expected photocurrent value corresponding to the forward voltage measured across the photodetector and the drive current currently applied to the LED chain by applying one or more interpolation techniques to a table of stored calibration values correlating forward voltage and photocurrent to drive current at a plurality of different temperatures; and
adjusting, for each LED chain, the drive current currently applied to the LED chain if a difference exists between the expected photocurrent value and the measured photocurrent.
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Accused Products
Abstract
An illumination device and method is provided herein for controlling individual light emitting diodes (LEDs) in an LED illumination device, so that a desired luminous flux and a desired chromaticity of the device can be maintained over time as the LEDs age. According to one embodiment, the method comprises applying drive currents to a plurality of LED chains substantially continuously to produce illumination, measuring a photocurrent induced on the photodetector in response to the illumination produced by each LED chain, one LED chain at a time, and received by the photodetector, and measuring a forward voltage developed across the photodetector by applying a non-operative drive current to the photodetector. For each LED chain, the method may further comprise determining an expected photocurrent value corresponding to the forward voltage measured across the photodetector and the drive current currently applied to the LED chain by applying one or more interpolation techniques to a table of stored calibration values correlating forward voltage and photocurrent to drive current at a plurality of different temperatures, and adjusting the drive current currently applied to the LED chain if a difference exists between the expected photocurrent value and the measured photocurrent.
274 Citations
20 Claims
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1. A method for controlling an illumination device comprising a photodetector and a plurality of LED chains, wherein the method comprises:
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applying drive currents to the plurality of LED chains substantially continuously to produce illumination; measuring a photocurrent induced on the photodetector in response to the illumination produced by each LED chain, one LED chain at a time, and received by the photodetector; measuring a forward voltage developed across the photodetector by applying a non-operative drive current to the photodetector; determining, for each LED chain, an expected photocurrent value corresponding to the forward voltage measured across the photodetector and the drive current currently applied to the LED chain by applying one or more interpolation techniques to a table of stored calibration values correlating forward voltage and photocurrent to drive current at a plurality of different temperatures; and adjusting, for each LED chain, the drive current currently applied to the LED chain if a difference exists between the expected photocurrent value and the measured photocurrent. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An illumination device, comprising:
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a plurality of light emitting diode (LED) chains configured to produce illumination for the illumination device; an LED driver and receiver circuit configured for applying drive currents to the plurality of LED chains substantially continuously to produce the illumination; a photodetector configured to detect the illumination produced by the plurality of LED chains; a storage medium configured for storing a table of calibration values correlating forward voltages and photocurrents that were previously measured from the photodetector to drive currents that were previously applied to each of the LED chains at a plurality of different temperatures during calibration of the illumination device; and a control circuit coupled to the LED driver and receiver circuit, the photodetector and the storage medium, wherein the control circuit is configured for determining an expected photocurrent value for each LED chain from the stored table of calibration values using a current measurement of temperature and the drive currents currently applied to each LED chain. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification