I should really know the answer to this being an EE. However I don't apply that kind of knowledge very often in the consulting world. So let me scratch a little rust off...let me know if I got this right...
You basically have 2 options: series or parallel (whether that be one LED or several in series on parallel strings)
Series is simple, you look at the Vf of each chip, add them up, and this would be the max Vdrop across the series string, then would would need a driver that could supply that level of voltage at the desired current, up to the max current of the lowest-rated LED on the string (which is why you typically do not mix LEDs of different current ratings within a string).
If you run a bunch of single chips in parallel, then the voltage drop across each is the same, thus you would have to match chips with each other according to their Vf, and the current supplied from the driver would be evenly divided across each chip, assuming that each chip has perfectly identical properties at various equivalent temperature points. In this case, the voltage of the driver would need to be match to the Vf of the chips, and the current would be adjusted such that it equalled the sum of the desired current through each chip.
Similarly, if you ran strings of multiple chips in parallel, the sum of the Vf of each chip would have to match on each string, or else you would end up with one string being off balance and pulling more of the current.
Because of this effect, I understand that it's a good idea to put appropriately sized fuses on each string of any parallel array.
Anyways, the sum of Vf's of a string would then be the voltage which your driver would need to be sized for, and the current would then be the sum of the forward current required for each string.
So let's say you have 4 chips, each requiring 10VDC and 2000mA (or 2A for simplicity). No matter how you cut it, you need an 80W driver.
If you put them in one single string: you need 40V and 2A, P=I*V = 80W
If you put them all in parallel, you need 10V and 8A = 80W driver
If you put them in 2 parallel strings of 2 each, you need 20V and 4A, 80W Driver
You can go through a simial excercise for just about any combination of LEDs, whether that is individual or multichip LEDs. The key is that you need a driver that has the current and voltage rating that can handle the quantity and arrangement of LEDs in your specific array.
Someone correct me if I got this wrong LOL. I hope I didn't I would feel pretty dumb!!
