How to set the LM317 voltage

 

To set the output voltage of the LM317 adjustable voltage regulator, you use two resistors in a voltage divider configuration between the output and adjust pin.

 

 

LM317 Output Voltage Formula

 

To set the output voltage of the LM317, you use the following formula:

 

Vout = 1.25V × (1 + R2 / R1) + Iadj × R2

 

Where:

- Vout = Output Voltage

- R1 and R2 = External resistors

- Iadj = Adjustment pin current (typically very small and often neglected)

 

 

Common Resistor Values

 

 R1 (Ω)  R2 (Ω)  Approx. VOUT (V)

-----------------------------------------------

 240         0            1.25                

 240         720          5                   

 240         1440         10                  

 240         1920         11.25               

 

Tip: Always add a 0.1 µF capacitor from the adjust pin to ground for improved ripple rejection.

 

Important Notes

- Use precision resistors (1% or better) for accurate output.

- Use heat sinks if output current exceeds 500mA.

- Add input and output capacitors (typically 0.1 µF on input, 1 µF on output) for stability.

For video tutorial: