LM317 Variable Power Supply Circuit and Calculator

This LM317 adjustable voltage variable power supply circuit and calculator also works for other equivalent voltage regulators in the series. The output voltage range is 1.2 V to 25 V, and the input voltage must be 28 V or more. A basic power supply circuit consists of a 5 kΩ preset for setting the desired voltage, and a pair of capacitors. C1 is needed only if the voltage regulator is more than 6-inches away from filter capacitors. C2 is optional and improves the transient response; however it can be any value from 1 µF to 1000 µF electrolytic type.

Should you decide not to use a preset (R2), and replace that with a fixed resistor, then the calculator below will help you to calculate the value of the fixed resistor required.

Formula

Calculator

In this part of the calculator, enter the desired output voltage required (Vout) in volts. The default example is 5 V, if you wanted to make a 5 V regulator.

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