Why is my LM317 current limiter circuit not working?

bokeb's picture

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Joined: Jul 09, 2021

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Why is my LM317 current limiter circuit not working?
July 9, 2021 - 11:21am

Noob here, but attempting to build a current limiter with a LM317 for use with a power supply to give constant current.

I have placed an extra potentiometer (the white one) to simulate changing load conditions - but when I adjust it, I am getting changing amperage - which if the LM317 was working correctly, I'm pretty sure it should not.

For testing purposes, I have not placed the R1 resistor, or connected the third leg of the R2 potentiometer (don't think either of those are needed?)

What am I doing wrong?

circuit1.jpg

circuit2.jpg

circuit3.jpg

circuit4.jpg

LM317 current limiter.jpeg

 

Sourav Gupta's picture

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Joined: Feb 12, 2018

Replies: 628

You need the R1. Moving the potentiometer to the end will short the Adjust leg with output.