Driving multiple LEDs in parallel/series ?

I think I've got this down pretty good but let's go over it once more to be sure.

Let's say I'm driving 4 XMLs with a buck driver with a 1V drop. I want each of em to run @ 3A. From the datasheet, I can gather that they will be dropping about 3.35V each...

If I were to run them in series, off a 3A driver, this would require at least 14.4v in ?

If I were to run them in parallel, it would require a 12A driver, but could be run off 4.35v of input ?

And the most important question, could I run a 6A driver, with 8Vin or so, running 2 parallel banks of 2 diodes in series ?

I know this is not laser related at all... and would probably belong more on CPF than on here... but I hardly post there and it smells bad over there...

I would never put LED's in parallel. If one fails then the other will get double amount of current in case you have put two in parallel.

All the commercial spot lamps or bulbs with multiple LEDs are connected in series.

Unless your LEDs are very well matched and you're confident that they have the same lifetime, it is bad to run them in parallel without separate drivers per LED. Even in series it isn't so hot, but at least if the connection breaks it won't cause extra current to flow through the other LEDs, burning them out like Christmas bulb strings.

To add to what was said before: you can put some fault protection for each parallel chain as depicted in this application note (figure 4).

I don't really have a problem with 2 of them getting the axe if one goes... I mean they're <10$ LEDs... and I'm trying to pack a high powered build in as tight a package as possible, and the less Vin I need, the shorter my battery tube has to be...

I'm still kinda looking for an answer to my questions.

I haven't yet decided exactly what I'm gonna run... I just want to know if I have the correct understanding.

cilegray said:

Let's say I'm driving 4 XMLs with a buck driver with a 1V drop. I want each of em to run @ 3A. From the datasheet, I can gather that they will be dropping about 3.35V each...

If I were to run them in series, off a 3A driver, this would require at least 14.4v in ?

If I were to run them in parallel, it would require a 12A driver, but could be run off 4.35v of input ?

And the most important question, could I run a 6A driver, with 8Vin or so, running 2 parallel banks of 2 diodes in series ?

Click to expand...

The two parallel banks of two are fine . . .

if they all have a good heatsink.

Try to match the voltage of each string.

I have run four LED's like this with no problems.

LarryDFW