Lighting control system having a trim circuit
A lighting control system suitable for a surgical lighting device. The lighting control system includes circuitry that compensates for the effects of temperature changes in a lighting device, and that compensates for forward voltage variations among LED lighting modules to provide substantially uniform light output.
1. A lighting control system for a lighting device, the system comprising:
a primary controller;
a plurality of drive controllers electrically connected with the primary controller;
a plurality of drive outputs electrically connected with a drive controller, each drive controller controlling at least one drive output;
a plurality of LED modules, each LED module electrically connected with a drive output and having a plurality of series-connected LEDs, wherein at least one of said plurality of LED modules include:
a trim circuit to compensate for forward voltage variations among said LEDs of the LED module, said trim circuit balancing voltage drop differences across the series-connected LEDs thereby providing substantially uniform lighting for said plurality of LED modules, wherein said trim circuit includes:
a transistor that effectively nullifies the forward voltage variations among said LEDs of the LED module by adjustment of gate voltage of the transistor, said gate voltage of the transistor generated based on the difference between positive input from the transistor drain and a negative input.
2. A lighting control system according to claim 1 , wherein said trim circuit includes a potentiometer to set the negative input.
3. A lighting control system according to claim 1 , wherein at least one of said plurality of LED modules includes:
a temperature sensing device for sensing temperature in the vicinity of the LED module.
4. A lighting control system according to claim 1 , wherein said primary controller monitors a drive current associated with each drive output in order to determine whether one of said plurality of LED modules has an open circuit failure.
5. A lighting control system according to claim 1 , wherein said drive output includes circuitry to determine whether an associated LED module has a short circuit failure.
6. A lighting control system according to claim 1 , wherein said primary controller operates in a maintenance mode wherein said plurality of LED modules operate at a low duty cycle.
7. A lighting control system according to claim 1 , wherein said primary controller operates in a calibration mode allowing tuning of said plurality of LED modules to a LED drive current within a range from a predetermined target drive current.
8. A lighting control system according to claim 1 , wherein said system includes a substrate having a plurality of LED modules located thereon.