Controlling a very large number of LED's

Other Hardware LEDs and Multiplexing
1

Hello all,
I am trying to figure out the best way to power/control a very large amount of LED's. 1 set of LED's would be 900 total. I only need to be able to fade them all up and down together. I do not need any individual control. I want to be able to run this off of 12V. The LED's have a forward voltage of 3.2 and a forward current of 20mA. I used the LED wizard here (http://led.linear1.org/led.wiz) and it is telling me to use sets of 3 LED's with a 120 Ohm resistor. Would this be the best way of doing it and would I be able to use a transistor to PWM them?

Thanks,
-Korki

2

Yes three in seriese would be good.
A FET would be better to control them than a transistor.
You might have to split them up into batches controlled by an FET each.

3

Any chance you could use a higher voltage supply?
Say, 24V? Then you could have more LEDs in each string (6 or 7) vs 3, and cut the # of strings needed in half.
Say 150 strings of 6, each drawing 20mA max.
Then have 3 N-channel MOSFETs sinking 1A each to turn 50 strings on/off each.