Optical and temperature feedbacks to control display brightness
AssigneeMicrosemi Corporation
InventorsBruce R. Ferguson, George C. Henry, Roger Holliday
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Abstract
An illumination control circuit allows a user to set a desired brightness level and maintains the desired brightness level over temperature and life of a light source. The illumination control circuit uses a dual feedback loop with both optical and thermal feedbacks. The optical feedback loop controls power to the light source during normal operations. The thermal feedback loop overrides the optical feedback loop when the temperature of the light source becomes excessive.
Claims20
An illumination control circuit comprising:
- an optical sensor configured to detect visible light produced by a light source;
- a thermal sensor configured to indicate temperature of the light source;
- a first feedback loop configured to generate a brightness control signal based on comparing an output of the optical sensor to a predefined brightness setting;
- and
- a second feedback loop configured to override the first feedback loop when the thermal sensor indicates that the temperature of the light source is above a predefined temperature limit.
A backlight system comprising:
- a high voltage circuit configured to generate a substantially AC voltage signal to produce a substantially AC lamp current through a fluorescent lamp for lighting a display panel;
- a controller configured to drive the high voltage circuit in response to a brightness control input;
- and
- a dual feedback loop configured to generate the brightness control input based on lamp brightness and lamp temperature.
A method to control brightness of a lamp and prolong lamp life, the method comprising the acts of:
- detecting visible light produced by the lamp;
- comparing the detected visible light level to a desired brightness level;
- generating a first control signal to adjust a lamp current based on the comparison of the detected visible light level to the desired brightness level;
- detecting operating temperature of the lamp;
- comparing the detected operating temperature to a selected limit;
- and
- overriding the first control signal to reduce the lamp current when the detected operating temperature is above the selected limit.
An illumination control circuit comprising:
- means for monitoring brightness of a light source;
- means for monitoring temperature of the light source;
- means for adjusting power to the light source to achieve a predefined brightness level using an optical feedback loop;
- and
- means for transferring control to a thermal feedback loop to reduce power to the light source if the temperature of the light source is greater than a predefined threshold.
Dependencies are inferred from the claim text.