LM317 Resistor Voltage Calculator – Precision Regulator Design
The LM317 is an iconic adjustable positive voltage regulator capable of delivering over 1.5A with output ranging from 1.25V to 37V. Its simplicity relies on just two external resistors (R1 and R2) to set the output voltage. The standard formula Vout = 1.25V × (1 + R2/R1) provides excellent precision when using 1% resistors. For instance, with R1=240Ω and R2=2.2kΩ, Vout ≈ 12.7V — ideal for powering audio amplifiers or microcontrollers. To select R2 for a target 5V output, R2 = R1 × (5/1.25 -1) = 240 × 3 = 720Ω (use 680Ω or 750Ω E24 series). Always add input/output decoupling capacitors (0.1μF minimum) to prevent oscillations. Power dissipated in R2 is P = Vout² / R2; for 12V and 2.2kΩ, P≈65mW — use 1/4W resistor. This calculator supports bulk upload for fast prototyping across multiple voltage rails, making it ideal for power supply design.