LED Ring Light Circuit Design

[mlewus]

I have a question about the LED Ring Light project from the January February 2013 issue.

The MIC3289 is used as a programmable current source which is what you would expect to drive a series of LEDs. Normally one would expect one current source for each string of LEDs. But in this project there are six LED strings that are driven in parallel. Unless the LEDs are identical, you would expect the current, and therefore the brightness, to vary between the six parallel strings. That is, the output of the MIC3289 would not be equally shared between the six strings.

In a production environment you could "bin" the LEDs for forward voltage vs. current to get an acceptable match. But if you build this project from the printed circuit board (not the kit) using distributor sourced parts, you are not likely to get matched LEDs.

Has anyone built this project, and if so, have you noticed different brightness between the six LED strings? And, did you build from the kit or from your own parts?

Thanks in advance for any help you can offer.