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Adjustable linear regulator

LM317 Working Principle

Learn how LM317 works with an illustrated explanation and practical readings.

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LM317 at a glance

Follow the labeled connections and functional stages

LM317 working principle: illustrated functional stages, basic circuit and connections
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How it works

3 stages · Explore one step at a time

Step 1 / 3

Create the reference

The regulator maintains approximately 1.25 V from OUTPUT to ADJUST. Unlike a 7805, the adjustment terminal is not tied directly to ground.

Step 2 / 3

Set output with two resistors

R1 runs from OUTPUT to ADJUST; R2 runs from ADJUST to the return. Their ratio sets the output, with a small additional term from adjustment-pin current.

Step 3 / 3

Keep the loop within its limits

The source must provide headroom and the load must draw sufficient current. Input-to-output voltage and current become heat in the pass stage.

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