Quick setup guide: LM317 and LM337 Adjustable Regulators¶

A voltage regulator will 'step down' an input supply voltage to a level appropriate for a particular circuit. For example, the LM317 can be used to regulate a 10V supply rail used by a motor driver, where a 12V power supply is used.

The LM317 is a popular adjustable voltage regulator that can output a voltage between 1.25-37V at 1.5A. The LM337 is a negative equivalent that can output a voltage between -1.25V to -37V. Both devices require two resistors to change the output voltage, and an output filter capacitor.

LM317¶ R1 and R2 adjust the output voltage. Select R1 and R2 using the following equation, or the table below:
Vout = 1.25(1+(R2/R1))
 Voltage R1 R2 Error Use 3.3V 1.2k 1.8k 3% 3.3V IC 5V 270 820 2% 5V IC 6V 180 680 Servos 9V 560 3.3k 2% 12V 510 4.3k 1% 15V 62 680 1% 24V 560 10k 1%

A useful calculator: http://electronics.stevenvh.net/lm317/

Vin must be between 3 to 40V larger than Vout.

C1 should be a 1uF Electrolytic Capacitor with a rated voltage higher than the input voltage.
C2 is recommended if the power supply is more than 6" from the input
Pin numbering is for TO-220 package

LM337¶ R1 and R2 adjust the output voltage. Select R1 and R2 using the following equation:
-Vout = -1.25(1+(R2/R1))

C1 should be a 1uF Electrolytic Capacitor with a rated voltage higher than the input voltage.
C2 is recommended if the power supply is more than 6" from the input
Pin numbering is for TO-220 package