I've been looking at a LT1084-ADJ regulator to output exactly 12v from an input supply if 12v-36V.

My question is How do i do the math to calculate the output voltage?

It has 1 + (R1/R2) but how to i get the 12v from those figures?

Byt

 

how about reading the datasheet? http://www.linear.com/product/LT1084

 

You are a senior member and that's your response? Classy, but useless.

If I understood it, Why would I come here to ask?

 

http://cds.linear.com/docs/Datasheet/108345fg.pdf page 11 on the right.
VOUT = VREF * (1 + R2/R1) + IADJ * R2. Iadj is negligible, Vref is stated as 1.25V, leave the R1 at 120 ohm and solve for R2. You should come to 1032 ohm.

 

Reading the data sheet is more useful than you think. The device will not output 12 volts with a 12 volt input. There is a minimum difference between the input voltage and the output voltage which is clearly stated.

If you overcome that problem, use the proper fixed resistor and a trim pot to set the output to 12 volts.

 

I admit it is not easy to spot the actual datasheet on that site and not just the basic numbers, but other than that you really need to read the datasheet of any part you want to use. Starting with maximum ratings, tips on how to use the part, test circuits, ending with footprint of that part. Everything you need is in there, you just need to read it.

 

Thanks guys, I get it now!

believe it or not I did actually read the thing, but being a novice, i really wasn't understanding most of what I was reading!

Cheers!