Enter your R1 and R2 resistor values into the LM317 Voltage Regulator Calculator to find the output voltage your circuit will produce, along with power dissipation and regulation factor. Got a specific voltage in mind? Drop it into the Target Output Voltage field and get the exact R2 value you need.
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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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.
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.
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.
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.
Use the formula R2 = R1 × ((Vout/1.25) - 1). For example, for 5V output with R1=240Ω: R2 = 240 × ((5/1.25) - 1) = 720Ω.
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.
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.