Driving string of RGB LEDs over distance


I need to drive 40 x RGB LEDs spaced at 25cm intervals over a distance of 10mts.

Initial thoughts are to make a small PCB for each LED and use 3 Infineon BCR401R constant current LED drivers for each to ensure even brightness along the cable run.

Hook-up wire for daisy chaining the PCBs will probably be solid AWG24. Space is quite tight - the PCBs need to fit in a channel which is only

10mm wide.

The LEDs will be driven in PWM mode (for colour mixing) using a micro and NPN bipolar/P channel FET switching the high side of 5, 9V or 12V.

Any suggestions or "gotchas" please?

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I did some experiments with Kingbright 5mm RGB-Leds. It is not a good idea to use drivers, because you need to adjust each LED to the same white colour with all segments on. First use 2x47R for the 2 blue chips for a total of

50mA from 5V. then the green needs around 12mA, use ~120R and finally the red needs less current, 9mA with ~330R. Adjust the resistors for each Led individually, but keep the 50mA for the blue, as they are the weakest. Best to do this with a duty cycle of 50%, to avoid overheating. compare the color in a breadboard. The resistors can be of the 100mW axial ones, use shrinktube to cover them and make different lengths for each connection to avoid shorts. No PCB needed, which will only break. AWG 24 is to small, use it only for the gn and red and take AWG20 for gnd and blue. Do not use higher current for the red or gn, since you will overheat the chip and get the blue too weak.
ciao Ban
Apricale, Italy
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