Best way to power A white LED

[Overclocked]

I would assume is the same as a boost converter, I can't think of the formula of the top of my head though. Doesn't the datasheet suggest a specific inductor?

They do, but they show 2 to 8 LED hooked up in parallel with 2 different inductors. 2,3,4 LEDs are connected in series using a 10uH inductor, and 6 and 8 LEDs are connected in series using a 22uH inductor. However, there is a resistor called "rsense" which changes along with the inductor.

I did calculate how much voltage is being boosted for the number of LEDs. Assuming each LED had a 3.5V voltage drop, I just added it up and found the voltage on Rled (which sets the current for the LED's). I did notice a pattern to it though, If I kept the inductor Constant I can calculate rsense (or atleast get a estimate) by using a linear regression for 6 and 8 LEDs.

What Im also worried about is, will this thing supply enough power to power 5 banks of 3 LEDs in series. Using 3 LEDs, thats 10.5V total (10.8V if you want to include rLED) supplying a current of 20mA (I will be using 30mA, but here it doesnt matter-Hmm, Maybe I should drive them that close to max current, maybe 25mA would do...) So each bank would have their own voltage and current, ie, each bank would have 10.5V across it and consume a current of 20mA. 5 banks consuming 20mA each would give 100mA.

Note, All banks are in parallel with the first. Each banks DOES NOT get it own resistor. All the currents of the banks will be controlled by 1 resistor (ie, Rled). However, If I used seperate resistors for each bank, would the power disipated in each resistor equal the same power if I used 1 resistor? Theoretically, It should be the same. One just has a lower part count.

 

[Overclocked]

For every Controller Made, there is an even better one.
https://focus.ti.com/docs/prod/folders/print/tps61020.html

Ok so it cant provide the nessacry voltage (Can only be adjusted from Vin to 5.5V) but it is capable of providing .5A. I would just have to run all the LEDs in parallel. However, It does run from .9V in which it can run circles around the previous controller selected.

Differences:

The TPS 61020 Can run from .9V, which means it can run on 1 D battery for its entire life.

The package-QFN-10. Its a small block. Looks hard to solder.

Gives formulas to select current and voltage. Voltage is pretty much controlled by 2 resistors. Current is the same. Looking at the data sheet the same inductor can be used, but it does give calcs anyway. They look pretty simple to use.

No Guessing. If I make it so It can supply 100mA @ 3.5V (+/- 10%), I'll know it will work.

More Parts- I want a run for my money, SMD is hard enough so let make it like hell!