I have developed a product in which
LEDs spectrum is sensed by CCD (
pic microcontrollers. It is being observed that
LED spectrum changes with time. We concluded that it could be due to change in temperature and change in forward current (consequence of change in temperature).
The datasheet of one of the LED is over here. The LED is being driven using NPN transistors. I am using PWM to control the intensity of LED and the maximum current that flows through LED is 12 mA. The datasheet of LED shows change in
intensity with the temperature at constant forward current. The graph which states that in given below and you can find it in the datasheet of the LED.
My question is after starting the system (and starting the LEDs), how to nullify or counter the change in intensity of LED with time. We know there are many products in which LEDs is being used and sensed. I just want to know how industries or experts tackle this type of problems and what are industries best practices to be followed to avoid or counter such effects?
The schematic of my LED circuit is:
NC in the schematics means a zero ohm resistor.
We have tried few experiment with constant current source (LM334) and results were a bit better but still they were not acceptable. I have designed a new PCB with PWM-Controlled constant current source. I will test it in a week and update my question with the results. I liked the answer given by
Misunderstood alot and will try LEDs suggested by him.