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[on:]

Hi y'all

I'm trying to connect a high power RGB LED to the arduino. The problem is my electric schematics skills, I'm fairly new to this.. I've read some topics on this subject and I think I've got it but I want to ask the pro's to double check :p

The RGB LED:

Forward Voltage
Red: 2,2V - 2,6V
Green & Blue: 3,2v - 3,8V

Forward current:
3x 350 mA

The schematic:

R1: 8,2ohm 3Watt
R2,R3:5,6ohm 3Watt
r4,r5,r6: 1k omh 3watt

q1,q2,q3: 2N2222A

[Reply #1 on:]

So what do you think ? Is this going to work ? or should I keep a fire extinguisher close ?

Thanks in advance,

Ape

[Reply #2 on:]

No the resistors are way too low, you can't drive high current LEDs in this way. You need to drive them with a constant current driver like the LM3402.

[Reply #3 on:]

Actually I think this will work. You may not get accurate equal currents but you can always compensate for that with PWM. I think your resistor and component choices are reasonable.

--
The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, light sensor, potentiometers, pushbuttons

[Reply #4 on:]

Actually I think this will work.

But for how long, using very small resistors to limit the current through an LED is not the most reliable of techniques especially if you want it to work over any sort of temperature range.

[Reply #5 on:]

But for how long, using very small resistors to limit the current through an LED is not the most reliable of techniques especially if you want it to work over any sort of temperature range.

Well that's the thing, who knows what the OP's intentions are? Reliability and temperature independence are concerns one develops with time and experience, and to me it sounds like the OP just wants to blink some lights and the only real concern is whether or not the circuit will start a fire The simple circuit with resistors and transistors can be cooked up on a breadboard in minutes, while a constant-current driver will take quite a bit more effort.

Should the circuit he proposed prove to be too unreliable then for sure, the next step is a constant-current driver, or perhaps a common-collector configuration for the transistors.

--
The Quick Shield: breakout all 28 pins to quick-connect terminals

[Reply #6 on:]

Thanks for the quick reply's  

I'm tying to build a lamp, something that can light a room for a couple of hours. I've downloaded the datasheet for the LM3402 (it's 28 pages long  :o) and I'm going to study it today.

[Reply #7 on:]

Remember that the LED will get very hot and will probably need to be mounted on some kind of heatsink.

Other than that, your schematic looks perfect for this.

[Reply #8 on:]

I've studied the datasheet but it is to much for me. I can't figure out which components to use with the LM3402.

Can I use a darrington array to sink the currency ?