LM317 is a widely used adjustable positive linear voltage regulator.
LM337 is a negative supplement to LM317 which regulates voltages below the reference level.
The LM317 datasheet specifies an adjustable
three-terminal positive voltage regulator capable of supplying more than 1.5 A over the output voltage range of 1.25 V to 37 V. Exceptionally easy to use and setting the output voltage requires only two external resistors. Furthermore, both line and load adjustments are better than standard fixed regulators.