How to Build a Variable Linear Voltage Regulator with LM317

How to Build a Variable Linear Voltage Regulator with LM317


A variable linear voltage regulator like the LM317 is a useful circuit for generating a stable and adjustable DC output voltage from a higher voltage DC source. With just a few external components, the LM317 can be configured as a variable voltage regulator with adjustable output between 1.25V to 37V.

Here's what I'll cover in this guide on how to build a variable linear voltage regulator with the LM317:

How the LM317 Works

The LM317 is a 3-terminal adjustable linear voltage regulator. It works by comparing a fraction of the output voltage against a stable reference voltage of 1.25V. Based on the difference, it adjusts the pass element to maintain a constant output voltage.

The key features of the LM317 are:

Internally, the LM317 contains the following key components:

By adding just two external resistors, we can configure the LM317 as an adjustable voltage regulator.

Parts Needed

To build a variable voltage regulator with the LM317, you'll need the following parts:

Optionally, you can add:

LM317 Variable Voltage Regulator Circuit

Here is the basic circuit diagram for a variable voltage regulator using the LM317:

LM317 Variable Voltage Regulator

Let's go through each component:

The key formula for the LM317 is:

Vout = 1.25V * (1 + R2/R1) + Iadj * R2


This allows the output voltage to be adjustable from 1.25V to about 37V.

Construction Tips

Here are some tips for constructing the circuit:

Testing and Adjustment

After constructing the circuit, test it as follows:

That's it! You now have a working variable linear voltage regulator.

Example Applications

Some examples of how this LM317 regulator can be used:

With some additional components, the LM317 can provide a wide range of useful and stable DC voltages.


So that's how to build a simple variable linear voltage regulator using the LM317 IC! Let me know if you have any other questions.