LM317 calculator

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Calculate the output voltage of the LM317 linear regulator based on R1 and R2, or find R2 to obtain a desired Vout. Range: 1.25V – 37V.

Vout = 1.25 × (1 + R2/R1) Recommended R1: 240 Ω Current Iadj ≈ 50 µA

Calculation

Suggested E12 values ​​for R2

The E12 series includes: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 Ω (and multiples ×10, ×100, ×1k…)

See also

Frequently asked questions

How do I calculate LM317 output voltage?

Vout = 1.25 × (1 + R2/R1). With R1=240Ω and R2=720Ω: Vout = 5V.

How much heat does the LM317 dissipate?

P = (Vin − Vout) × I. With Vin=12V, Vout=5V, I=500mA: P = 3.5W. Heatsink required.