Just thanked you all as I appreciate the input, as I will be pleased to get this little project off my plate.
So the project has two relatively independet parts:the first is finding a suitable LED and mountig it in place. The second is biulding / buying an adjustable current source to drive the LED.
Yes I should work it this way. I will get the LED sorted first then maybe that can refine my driver options.
When I can, I will put in a Cree XPG and a Cree MLE and see how they look, using a lab power supply to drive them, I have these LEDs lying around somewhere, both Warm White IIRC. Might be able to unglue/remove any lenses?
If I can get one of them looking good I will try to find a driver.
As far as RGB, not today, all they want is a direct replacement, maybe I can give them an option down the track.
Though maybe if I can score a microscope I will put something like this in, sounds nice.
Be careful of the LED module you use, it has to have a single die in it, as the optics in the microscope will be very carefully set so they take light from a small portion of the incandescent lamp filament, and use this to make the collimated beam to illuminate. Your LED must have the emitting surface of the die in exactly the same spot and it must have a single LED dice in it, otherwise you will have very uneven and colour changing illumination across the visible viewing area.
Yes this could be tricky, this is where I am out of my depth. I will have to experiment.
Isn't that a bit of overkill?
You have 12V and access to a 10K pot, why not just roll your own simple 1 transistor job to drive the LED, a 3W LED shouldn't take much.
How many LEDs per unit?
Does it have to dim to completely off?
I would probably avoid PWM just in case they put a video camera on the microscope as this would create stroboscopic effects.
The microscopes currently have a 3 legged 10k dimmer + mains on/off switch. This I have to use, but it should slot in easily if I use an analogue controlled LED driver. I guess it has to dim as well as the halogen did. Which I don't know. I will do a mock up and see if they like it.
Yes I could bring the mains down to say 5V and do it like that. Though I still have to use feedback, maybe a linear reg? I would prefer to do it in PWM though, as I could then use the same device in my stalled mppt solar charger project.
Any chip suggestions? I was playing with an LT3740 in LTSpice. I really only need one switching FET but one that also has a bootstrapped hi side driver was what I was looking at for the mppt.
Still looking through the microscopy website, seems to be a good resource, thanks.