Adjustable Voltage Regulator Resistor Divider Calculator

Calculate R2 for an adjustable voltage regulator (LM317, LM350, etc.) given desired output voltage and R1.

Inputs

Desired Output Voltage (V)

R1 (Ω)

Typical: 240Ω for LM317

Reference Voltage (V)

LM317 Vref = 1.25V

Results

R2 Required

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Actual Vout

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Formula: Vout = Vref × (1 + R2/R1)
R2 = R1 × (Vout/Vref − 1)