I have a couple of moving heads like this They have a QCL (Quad color led chip) Theres a total of 10w. Most of the time I don't use the colors, I just use the white quadrant, which I presume is 10w. If I want a bright white I can turn on the R G & B quadrants as well but it gives a rather sickly white with weird colored edges.
I was thinking of replacing the QCL led with a single 10w White led. Obviously each color, R,G,B,W is controlled by a separate dmx driver.
I'm just wondering would it be a very bad idea to join all these drivers together and solder them onto a single chip? I'm concerned about the output from one going into the the others. I can programatically be fairly certain to make sure that all the drivers are set to the same output at all times though but I can never be 100% sure!
What do you think?
Also on a side note, these lighting fixtures are rarely on for more than a few minutes at a time so well below their max in terms of overheating, would it be better to take the output from one of these RGBW channels and just use that with a transister to maybe drive a 20w or 15w white led chip?
2 Answers
You can't in general connect multiple drivers to a single LED, they are likely to damage each other.
Why don't you replace it with four white LEDs, each connected to a single driver? That way it should be electrically good and you can adjust the brightness by an extra 6dB.
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\$\begingroup\$ Hmmm, I'd be very surprised if I can replace my RGBW chip with a WWWW one, I can't see any reason they'd exist! All the leds are part of the same chip. \$\endgroup\$– jasonCommented Jan 22, 2016 at 10:36
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\$\begingroup\$ Yes, there's no reason to have 4 independently-pinned white LEDs in a single package, so I doubt that exists. But since single-white-LED packages do exist, could you replace the RGBW package with 4 packages, each one a discrete white LED, as William suggested? \$\endgroup\$ Commented Jan 22, 2016 at 14:15
Even if you protected yourself in software such that only one driver was on at a time, I would be concerned about the circuit.
Unless your drivers have the ability for their outputs to go a high-impedance state when they are off, you'll need to add some extra hardware to your circuit to prevent the drivers from driving each other.
This might be as simple as adding in some MOSFETS (assuming you have available GPIOs).
An alternative solution would be to add a diode in series with the output of the driver (of course, this will be cause less power to go to the LED, and your diode will need to be chosen so that it can withstand the heat dissipation).
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\$\begingroup\$ So if I use diodes I'll end up with less than 10w coming out so I'd lose power? That would be annoying! I don't have an GPIO as such, it's not my own system, I imagine I have 20v, 5v GND and whatever voltage is coming from the drivers at my disposal. It might be possible to swap out the drivers for higher current ones to compensate for using diodes maybe? Or could I take the signal from one RGBW channel and use it as a signal to drive a completely different circuit? \$\endgroup\$– jasonCommented Jan 22, 2016 at 2:20
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1\$\begingroup\$ If the drivers are the Constant Current type then a series diode on each channel will not cause any drop in LED power - the drivers will compensate. \$\endgroup\$– brhansCommented Jan 22, 2016 at 3:14
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\$\begingroup\$ Ok thanks, I can try with the diodes and compare it to the other unit for brightness. \$\endgroup\$– jasonCommented Jan 22, 2016 at 10:38