ok, I skimmed over the spec and see lots of LM317 calculators (like http://www.whatcircuits.com/lm31... ) on the net that have one resistor held constant (R2) and varies the Vout and the adjustable resistor (R1). What I don't get is what the value of Vin to have the desired Vout.
The Vout equation does not express in terms of Vin at all.
Vout = 1.25(1 + R2/R1)
There has to be a Vin to R1 adjusted to get the desired Vout, no? Or as long as my Vin is within the LM317's spec, I am good?