LM317 Current Regulator Calculator

Constant Current Output from LM317

Input Fields

Resistor value

R

Ω

Resistor used to set constant current

CalculateReset

Calculate automaticallyIf enabled, the result will update automatically when you change any value.

Your Results

Output Current

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LM317 Current Regulation Formula

$$I = \frac{V_{ref}}{R}$$

Where:

• $$I$$ = output current (A)
• $$V_{ref}$$ = reference voltage ≈ 1.25 V
• $$R$$ = resistor between output and adjust pin (Ω)

This configuration uses LM317 as a constant current source. The resistor value sets the output current directly.

Calculation Example

Given:

• $$R$$ = 3.9 Ω

Calculation:

1. $$I = \frac{1.25}{3.9} ≈ 0.32~A$$

LM317 can be configured as a simple and effective constant current regulator by connecting a resistor between the output and adjust pin. This setup is especially popular in LED driver circuits, battery charging applications, and situations where current limiting is critical. The output current is determined entirely by the resistor value, with minimal component count and reliable performance.