LM317 Voltage Regulator Calculator

LM317 Voltage Regulator Calculator. The LM317 is a popular adjustable voltage regulator IC used in power supply circuits to deliver a stable output voltage set by two resistors. Enter your Resistance R1 and Resistance R2 values into the LM317 Voltage Regulator Calculator to find the Output Voltage, along with power dissipation and regulation factor. Optionally, enter a Target Output Voltage to calculate the exact R2 value needed to achieve it. Also try the Boost Converter Calculator.

LM317 Voltage Regulator Calculator inputs
Ω

Recommended value is 240Ω (range: 100Ω - 1000Ω)

Ω

Variable resistor to adjust output voltage

V

Enter desired voltage to calculate required R2

Results

Output Voltage

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Required R2 for Target

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Power Dissipation

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Regulation Factor

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What is an LM317 voltage regulator?

The LM317 is an adjustable three-terminal positive voltage regulator that can supply more than 1.5 amperes over an output voltage range of 1.25V to 37V. It requires only two external resistors to set the output voltage. See also our Power Dissipation — LM7805 / 78xx Regulator.

How does the LM317 calculator work?

The calculator uses the formula Vout = 1.25 × (1 + R2/R1) + (IADJ × R2) to determine output voltage. You can enter R1 and R2 values to get output voltage, or enter target voltage to find required R2.

What is the recommended value for R1?

The recommended value for R1 is 240Ω, but it can range from 100Ω to 1000Ω. A 240Ω resistor ensures optimal load regulation and minimizes the adjustment current error.

What is the maximum input voltage for LM317?

The LM317 can accept input voltages from 3V to 40V DC. The minimum input-output differential voltage should be at least 1.5V for proper regulation.

How do I calculate the required R2 for a specific output voltage?

Use the formula R2 = R1 × ((Vout/1.25) - 1). For example, for 5V output with R1=240Ω: R2 = 240 × ((5/1.25) - 1) = 720Ω.

What are common applications of LM317?

LM317 is used in power supplies, battery chargers, current regulators, LED drivers, and adjustable voltage references. It's popular for DIY electronics projects requiring variable voltage output.

How much power does the LM317 dissipate?

Power dissipation equals (Vin - Vout) × Iout. For example, with 12V input, 5V output, and 1A load: P = (12-5) × 1 = 7W. Proper heat sinking is essential for higher power applications. You might also find our Flyback Converter Calculator useful.