stablised high intensity white light source for fibre optics

[sobrie33]

Hi,
Im a currently trying to build the above titled project. So far i have designed the filtering section and power supply. However i am having difficulty with the feedback section of my circuit. I need to place a fibre optic at the end of the bulb and have this connected to a photodiode. By doing this i will be able to control the light intensity, i.e keep it stable by using a voltage controlled resistor of some sort.
My main objective will be to provide more voltage to the 12v bulb if it's intensity starts to drop. I will be running 2A of current through the circuit and this is why i choose to use a voltage regulator as my power supply.
I would really appreciate it if someone could share their views on this matter and help me design the best possible circuit.
Layout: Mains input ->Filtering->Voltage regulator->Bulb->Fibre optic->
^ |
|<-<-<-<-<-<-<-<-<-<-<-<-
Thanks.[/img]

 

[Klaus]

Are you trying to compensate for long term light loss due the ageing of the bulb or for short term light fluctuations due to input power fluctuations?
For short term a very stable power source would be simpler than adding feedback. If not possible to stabilise the source you could add, after the photo diode output, a comparator and a reference voltage. The output of the comparator controls the input voltage regulator. Make sure the reference does not fluctuate, it should have an independant supply source from the lamp.