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Topic: Weird behavior on RGB leds. (Read 888 times) previous topic - next topic

ThomasH

I have 4 common anode rgb leds wired in parallel into a TLC5940 but they are acting weird.

Red and green works fine on their respective channels.
Blue won't light up when driven by the tlc, but if i ground the pin all 4 blue leds light up.

Ive tested all the channels on the tlc. and its not the drivers fault.

If i try to connect the blue wire to the greens channel while green is on. the green will shut off.
But i can wire red and green in one channel without problems.
If i wire red and blue together the red gets very dim. but doesn't shut off.

So im kinda stumped here. in my head this should be working just great. and it was. This happened after i changed one of the leds which was wired in the wrong way.
Tried to replace the led that was wired incorrectly and still no luck. blue will only turn on if grounded directly in gnd without any limiting ressistor.

Any thoughts?

Grumpy_Mike

Blue LEDs need more voltage to turn them on than the other colours. Wiring LEDs in parallel like you are doing seldom works as you have found.
What voltage are you running the chip at, is it 5V? That should be enough but 3v3 will not be.

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