LM317 Voltage Calculator

All misc tools

Calculate output voltage for LM317 adjustable voltage regulator circuits.

Circuit Resistors

Resistor R1 (Ω)

Typically 240Ω or 120Ω

Resistor R2 (Ω)

Adjusts the output voltage

Input Voltage (Vin)

Regulator Output

Vout6.51V

Dropout Voltage5.49 V

Min Input Req8.01 V

About this calculator

Overview

LM317 is an adjustable linear voltage regulator. Output voltage set by two resistors. Input must be 3V higher than output. Essential for DIY power supplies and voltage regulation.

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Pro Tips

R1 typically 240Ω (sets reference current).
Input voltage must exceed output by 3V minimum.
Add capacitors for stability (0.1μF input, 1μF output).
Heat sink required for high current/voltage drop.

Fun Facts

"LM317 output range: 1.25V to 37V."
"Maximum current: 1.5A (TO-220 package)."
"Introduced by National Semiconductor (1970)."
"Thermal shutdown protects against overheating."

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