The LM317, and its high current version, LM338 are popular voltage regulators which can accept an input voltage of 3-40 Volts DC, and provide an output voltage from 1.2 to 37 Volts DC.
The output voltage is set using two resistors
(R1 and R2) whose values chosen according to this equation:
VOUT = 1.25 * ( 1 + R2/R1 )
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