LM317 basic adj regulator help

Thread Starter

Al Vince

Joined Feb 24, 2015
27
For the life of me I cannot seem to get this simple circuit to work... I have created similar circuits in the past without any issues. I simply want to bring in 13v and output to an adjustable 2-12 volts. Seems simple right.

I have tried multiple LM317s, multiple resistors, multiple pots, multiple breadboards... no matter what I do the volts out will only adjust between 10-12volts. Any help would be appreciated. I initially had the setup with the capacitors, but removed them to trouble shoot my issue.

My layout with LM317, 240 resistor, 5k pot... LM317-issue.jpg

Reference... variable voltage power supply.png
 

ScottWang

Joined Aug 23, 2012
6,831
Th pins of LM317 shows in the circuit was wrong, if count the pins of LM317 from left are 1,2,3 then the 1--adj, 2-- Vout, 3-- Vin, so you have to recheck the circuit, the pins should be like this way, Vin=3, Adj=1, Vout=2, please check this.
 

Thread Starter

Al Vince

Joined Feb 24, 2015
27
Th pins of LM317 shows in the circuit was wrong, if count the pins of LM317 from left are 1,2,3 then the 1--adj, 2-- Vout, 3-- Vin, so you have to recheck the circuit, the pins should be like this way, Vin=3, Adj=1, Vout=2, please check this.
Yes I noticed half of the diagrams online don't show the correct pin numbers... if you check the photo, I got the right pins connected to the rights components... I think anyways.
 

ScottWang

Joined Aug 23, 2012
6,831
Is the front of lm317 facing the camera?
Another problem is that the LM317 needs 3V drop voltage between Vin and Vout, so when you want a 12V output then you should input 15V.
 

Thread Starter

Al Vince

Joined Feb 24, 2015
27
Is the front of lm317 facing the camera?
Another problem is that the LM317 needs 3V drop voltage between Vin and Vout, so when you want a 12V output then you should input 15V.
Yes that is the front of the LM317... even if I set the Vin to 15V then I get a range of 13V-14V. I have spent all day on this simple circuit. I have rechecked. The photo shows a different resistor, but even with a 240 I get the same results. I don't know how many diagrams I have downloaded, and printed out for reference.

This is driving me crazy haha. I have built power regulators before.
 
If you have an ohm meter then remove the trimmer pot and check the resistance between the terminals that you are using.
As someone else mentioned, you stated that the fixed resistor that you are using is 240 Ω, but the picture shows a 560 Ω.
That would throw off the LM317 resistor formula if you were using 240.
 
Rechecked... this time I added the caps... still, with about 13Vin.... I get a range of about 11V-12V

Al, I hate to ask, but have you considered that your LM317 may be defective? Do you have others that you can try?
I once burned one and it was nearly a dead short.
 

Thread Starter

Al Vince

Joined Feb 24, 2015
27
If you have an ohm meter then remove the trimmer pot and check the resistance between the terminals that you are using.
As someone else mentioned, you stated that the fixed resistor that you are using is 240 Ω, but the picture shows a 560 Ω.
That would throw off the LM317 resistor formula if you were using 240.
In the new photo I have the 240 installed... removed the pot and checked the resistance between the two pot connectors... I got -7.5 on the 20k voltmeter setting. I am guessing that is 7500? Not sure if the negative symbol means anything.
 
Al said "In the new photo I have the 240 installed... removed the pot and checked the resistance between the two pot connectors... I got -7.5 on the 20k voltmeter setting. I am guessing that is 7500? Not sure if the negative symbol means anything"

You can't check resistance on the voltage setting. What brand and model of meter do you have? I might be able to help you with the dial settings
so that you can measure resistance.
 
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