by **Klaas Robers** » Fri Aug 09, 2013 5:48 am

I expect that you routed the LEDs in series, so the resulting current for the RED chain is 40 mA and the current for the Green and the Blue chain is 60 mA. That is the optimal configuration. You need a somewhat higher voltage for the LED chains, see that you have about 10 volts left for the FET. It is not needed that this voltage is stabilised.

The first aproximation is for the 60 mA RED Led:

- the source resistor is 5,6 ohm / 0,6 = 9,3 ohm (try 9,1 ohm)

For the 40 mA Green and Blue LED chains:

- the source resistor is 5,6 ohm / 0,4 = 14 ohm (try 15 ohm)

It should be such that for a voltage increase of 1 volt that the current increases from 1 mA to 60 (or 40) mA.

If your LED configuration is different, please let me know.