Formula:
The LM317 adjustable voltage regulator's output voltage (Vout) is determined by the formula:
Vout = Vref * (1 + R2 / R1) + Iadj * R2
Where:
- Vout: Output Voltage (Volts)
- Vref: Reference Voltage (typically 1.25V for LM317)
- R1: Resistor 1 (Ohms) connected between Vout and Adjust pin
- R2: Resistor 2 (Ohms) connected between Adjust pin and Ground
- Iadj: Adjustment Pin Current (typically 50µA or 0.00005A, often neglected)
For most practical purposes, especially when Iadj is small compared to the current through R1 and R2, the simplified formula is often used:
Vout ≈ Vref * (1 + R2 / R1)