Help with high power RGB LED circuit

I'm trying to construct the circuit at the bottom of this post and am confused about one thing. The datasheet for the RGB LED states that the maximum voltage rating for the different LEDs are as follows: R=2.6V, G=3.8V, B=3.6V. How do I supply different voltages to these LEDs without destroying them?

The different voltages refers to the forward voltage at which the LED turns on (Vf). The different colours have different turn on voltages.

As long as you have reasonable resistors in series with the LEDs (R1, R2 and R3 in the diagram) the voltage won't matter, it will be the amount of current that needs to be controlled.

There is an explanation about how to estimate resistors for RGB here


If these are high power LEDs then you will need a constant current supply for each of them rather than the current limiting resistor you have shown.
See threads:-
and the threads off these links.
To calculate the resistance value use:-
If the resistor value is less than about 50R you need to start to think about constant current.

Mike, you might want to know that

To calculate the resistance value use:-

Leads to a page which says:

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Thanks I didn't know that. Try this one:-

you may want to use a constant current driver to feed the leds rather then wasting power with resistors .
i think you could use something like this RGB LED Ampflifier / / Driver (Constant Current) 350mA/Ch it is a Constant Current RGB LED Amplifier but i believe it will work with the output of an arduino feeding the input pins (you may have to bypas the 3 diodes before the opto-coupler but it outputs a constant current that will work with common annode 350mA LEDs and it already has all the transistors/mofsets built in along with an opto-coupler to isolate your arduino
i have one in my kitchen so if i get a chance i will test it out with my arduino

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