OK, so this is changing the subject, but in most cases, I fail to see the need for fancy current control for single, relatively low powered LEDs. I can't count how many bazillions of LEDs I have connected to 5, 6, 12 or whatever volts and just used a limiting resistor. Keeping in mind that:
- LEDs, especially cheap Chinese ones, often do not operate within the specified range, much less are they uniform.
- Using a light meter, I have found almost no difference between running an LED (rated for 20ma max) at 20ma or running it about 12-13ma. After about 12-13ma, the light meter registers almost no increase in brightness. Therefore, I give myself a nice safety margin and calculate my resistor to target around 12-13ma.
Now, these 10watt RGB chips are of course a step above the little 5 and 3mm. According the datasheet, the red should have a voltage drop of 6-7 volts, and the green and blue a drop of 9-10 volts, and all 3 have a max current of 350ma. I have tested 9 of these chips so far, and have found the red has a voltage drop of 6.22-6.35 volts, green 10.1-10.8, and blue 9.5-10.2. So none of them are really in spec. I have targeted my resistor values to drive them at around 260-280ma, and my measurements have confirmed my values to be in the desired range.
I hacked 4 of these 10watt RGB floods as described 3 years ago, and they survived 2 whole seasons of a Christmas light show so far without problems. Now I am hacking 5 more.
And now, all that being said--- Some of these LED current driver chips are much cheaper than I realized. With a cost similar to the high wattage resistors. So now you've got me rethinking my approach if I build more of these in the future.
If I didn't make this clear before, this is a budget build. I scored a deal on the lights (usually $15 ea) for $8 ea and I don't wanna spend a fortune or a lot of time modifying them. As it is, the cable and connectors cost me as much as the lights.