/lm317 — LM317 Voltage Regulator
Set the output of an LM317 adjustable regulator from its two resistors, or solve R2 for the voltage you want. R1 is usually 220–240 Ω.
Output voltage
Vout = 1.25 V × (1 + R2 / R1). Keep at least ~10 mA through R1 (the device needs a minimum load), and Vin must sit ≥ ~3 V above Vout.