Voltage Regulator Calculator / Stack of Circuits

Calculation of resistors for the voltage regulator

The LM317 voltage regulator requires two external resistors: $R_{1}$ and $R_{2}$ . They allow you to adjust the output voltage.

Circuit with LED and resistor

This calculator will help you calculate the voltage value for a specific pair of resistors or select a pair of resistors to get the desired voltage. The calculator is suitable for calculating the values of the LM317 controller and some other ICs, such as the LM338 or LM350.

The LM317 is an adjustable voltage regulator that can deliver a current of more than 1.5 A. The output voltage can range from 1.2 V to 37 V, and the input voltage can range from 3 V to 40 V. This regulator is very easy to use and requires only two external resistors to adjust the output voltage.

The output voltage $V_{out}$ depends on the values of external resistors $R_{1}$ and $R_{2}$ by the following formula:

V_{out} = 1,25 V * (1 + \frac{R_{2}}{R_{1}})

The recommended value of the $R_{1}$ resistor is 240 ohms, but you can also use a different value in the range from 100 ohms to 1000 ohms. To calculate the output voltage of the LM317, enter the value $R_{1}$ and the desired voltage $V_{out}$ in the calculator. For example, if $R_{1}$ is 240 ohms and the desired voltage is 5 V, then the required resistance of resistor $R_{2}$ will be 720 ohms.