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i am an electrical engineering student and have been tasked in creating a quite interesting project. Basically , the whole PCB with the microcontroller and all other parts is already designed, however me and my fellow colleagues are stuck with choosing/finding a proper Led driver IC. Here is the problem : We need to power a 20 W led as show in Picture 1. In the attached photos we can see the characteristics of the led. It need 300/350 mA of CC , with its voltage varying differently for the corresponding color. Now, we know that a CC source adjusts its output voltage depending on the load. However , the whole PCB needs to be powered by a 12V CV source. My question is this, is there such an IC which will take 12 Volts as an input voltage , and convert it to a constant current of 350 mA with its output voltage matching the led characteristics ? . Currently we only have considered the ZXLD383 (https://www.diodes.com/assets/Datasheets/ZXLD383.pdf) , but its input voltage is too small. Does anyone know a proper IC for this job ? Any tips are welcomed, thank you in advance.

Picture 1

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A current mode boost converter looks likely at least for the 30W part, the 20W part red has an inconveniently low voltage and would really want a buck/boost stage (Do look at the output numbers for those two choices, it is not clear that the 30W part is actually significantly better then the 20W).

There will be external inductors, and probably fets and I might be very tempted to do one boost converter to say 36V or so, and then do a current mode buck per colour (Less mosfets, and buck regulators are more standard then boost ones).

I would be thinking that both TI & linear tech probably have something workable.

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  • \$\begingroup\$ Hmm, i was initially trying to avoid using higher voltage, and then stepping it down, however, it actually sounds quite interesting. For example, maybe stepping up the voltage up to 30 Volts , and then probably using a much simpler LM317 configured as a constant current mode ? , still would need to ask the profs whether we are allowed to do this ( they initially wanted for us to figure out / find out a solution for the original problem with using 12 Volts) , thank you btw. \$\endgroup\$ – Tommy D Jan 16 '19 at 12:28
  • \$\begingroup\$ 12V into a boost converter to get 36V or so on the board, then buck down to regulate the current, at 300mA per colour you could be burning quite a lot of power in those LM317s, hence the preference for a buck mode LED driver. \$\endgroup\$ – Dan Mills Jan 16 '19 at 12:45
  • \$\begingroup\$ I just got permission to do whatever is needed to finish , so boosting the voltage, then messing around with the constant current and stuff should work, thanks for the advice . \$\endgroup\$ – Tommy D Jan 16 '19 at 16:52

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