LM317 Voltage Regulator R1 & R2

I'm building a strobe and I need max current from my voltage regulator. I have 13.56V DC coming in from the 2000uf caps. I need 12V DC & a max of 1.5A. I haven't been able to find anything that will let my control the voltage and set the max current. I have found current regulating setups, like this:


And Voltage Setups like this:


I used this formula:

R1 = 1.25v / Iout
R1 = 1.25v / 1.5A
R1 = 0.8Ω

Then used:

Vout = 1.25(1+(R2/R1))
(((12/1.25) - 1) / 0.8) = R2
R2 = 10.75Ω

So I grabbed the parts and threw it together an or course everything caught on fire. So I'm guessing the power rating of the resistors are way off? I had 1/8W and looking at the circuit I'll probably need something like 2W? Am I on the right track? or way off? should I just go get some higher wattage resistors and use those?

On another note I may be able to mod my circuit to work on 13.56V right from my cap. But i'm guessing this would be a bad idea no?

 

At 1.5A, the dropout voltage of the LM317 is typically 2.7V (3V spec'ed maximum). This means that to get 12V out, you need at least 15V in.
You might want to look at low dropout (LDO) regulators.

 

Hey guys thanks! I ended up figuring everything out, basically I thought there was some resistor arrangement that would limit the amount of current or something in the second schematic but it seems that's not the case!

 

This has been the subject of many posts here. You can't control voltage and current at the same time with a single active device (unless you include the idea that most voltage regulator chips contain a non-adjustable high current limit circuit).