What am I doing wrong with the lm317?

Thread Starter

No one of consequence

Joined Jan 3, 2023
7
Hello. I have a very frustrating problem. Im using the lm317 voltage regulator to add adjustability to a fixed output power supply.

I have used the lm317 numerous times over the years and never had or seen this problem. I have used regulators from 3 different sources, checked and rechecked all the connections and placement of the components. I have checked the continuity of the breadboard, and nothing.

15vdc is applied at the input. The output is showing .25v and the adjuster is showing .17v.
if I short circuit the unit bypassing the regulator all together every thing works as it should, just no variability. Im not using the filter or ripple capacitors because the voltage in is already regulated.

here is a photo of what I’m working with. In it you will see clearly how it is wired, a circuit diagram and pinout I found online and a wiring diagram of my unit I drew.

what am I doing wrong? Please help. Thank you.69E3BA9B-325C-42D9-83D6-B8419BCEF7EA.jpeg
 

panic mode

Joined Oct 10, 2011
2,795
do not see values on the components but connections seem to match the schematics and IC pinout except that there are no capacitors. capacitors are needed for stability to prevent oscillation. they can also absorb some of the transients.

the real question is what if that thing used as a load? doorbell? (without bell)

at any rate inductive load characteristic is the most likely the root of the problem. do not drive inductive loads without surge suppression - specially in DC circuits. add in parallel to that load a diode that is reverse biased. without diode circuit may work - ONCE. but as soon as you turn it off, that inductor is going to fry the heck out of the LM317. also what is the Ohmic resistance of the load? are you sure this is not overloading the regulator?

to test your voltage regulator always try low hanging fruits first to see that circuit works. this means use some resistive load. then when you get comfortable with it, try other things. inductors and capacitors are able to store energy. that energy can spell doom if not managed.
 

Thread Starter

No one of consequence

Joined Jan 3, 2023
7
do not see values on the components but connections seem to match the schematics and IC pinout except that there are no capacitors. capacitors are needed for stability to prevent oscillation. they can also absorb some of the transients.

the real question is what if that thing used as a load? doorbell? (without bell)

at any rate inductive load characteristic is the most likely the root of the problem. do not drive inductive loads without surge suppression - specially in DC circuits. add in parallel to that load a diode that is reverse biased. without diode circuit may work - ONCE. but as soon as you turn it off, that inductor is going to fry the heck out of the LM317. also what is the Ohmic resistance of the load? are you sure this is not overloading the regulator?

to test your voltage regulator always try low hanging fruits first to see that circuit works. this means use some resistive load. then when you get comfortable with it, try other things. inductors and capacitors are able to store energy. that energy can spell doom if not managed.
It is like a door bell. It is a tattoo machine. The lm317 is a common regulator for tattoo machine power supplies, never had this problem before. I did not use capacitors because the input voltage is already regulated. Thank you for your reply.
 

WBahn

Joined Mar 31, 2012
30,239
Don't connect you load yet.

Put the input and output capacitors on it.

Replace your pot with a fixed 1 kΩ resistor.

Check to see that the output voltage is ~6.5 V.

If it is, verify that your pot is hooked up correctly. Set it to a measured value of 1 kΩ and replace your fixed resistor with it and verify that you get about the same input voltage.

When you get it working without a load, be sure to put anti-kickback protection on your load, otherwise your regulator might not last very long.
 

dl324

Joined Mar 30, 2015
16,989
15vdc is applied at the input. The output is showing .25v and the adjuster is showing .17v.
The voltage difference between the output and adjust terminal should be 1.25V.
if I short circuit the unit bypassing the regulator all together every thing works as it should, just no variability. Im not using the filter or ripple capacitors because the voltage in is already regulated.
Add the capacitors anyway. There's a reason why they're shown in typical circuits. I've used them without capacitors before for quick and dirty breadboards, but it can cause problems that would be difficult to diagnose without the proper equipment.

What is the value of the current set resistor (I can't read it from the picture)? The schematic shows 240 ohms which isn't guaranteed to work without additional load on the regulator. The datasheet should specify a minimum current of 10mA for the regulator to function. That won't explain the symptoms you described.
 

WBahn

Joined Mar 31, 2012
30,239
But the minimum load that dl324 points out should be honored. An easy way to meet this requirement is to make your reference resistor 120 Ω (or just use 100 Ω if that's what you've got). This will give you a fixed quiescent current regardless of output voltage. It also let's you use a smaller variable resistor, though it does increase the power dissipation in that resistor by about a factor of two.

If your actual load has some minimum value that it will always be above, you can subtract that from the 10 mA needed and resize your reference and variable resistors accordingly.
 

WBahn

Joined Mar 31, 2012
30,239
I added capacitors, still only 1/4 volt at the output.
Fine. That's one thing taken off the table. Let's take some more things off the table. Have you done the things I suggested?

Don't connect you load yet.

Put the input and output capacitors on it.

Replace your pot with a fixed 1 kΩ resistor.

Check to see that the output voltage is ~6.5 V.

If it is, verify that your pot is hooked up correctly. Set it to a measured value of 1 kΩ and replace your fixed resistor with it and verify that you get about the same input voltage.

When you get it working without a load, be sure to put anti-kickback protection on your load, otherwise your regulator might not last very long.
I would recommend either changing your reference resistor to 100 Ω to 120 Ω or putting about a 1 kΩ fixed resistor on the output to satisfy the minimum load current. Again, taking possibilities off the table.
 

MrAl

Joined Jun 17, 2014
11,565
Hello. I have a very frustrating problem. Im using the lm317 voltage regulator to add adjustability to a fixed output power supply.

I have used the lm317 numerous times over the years and never had or seen this problem. I have used regulators from 3 different sources, checked and rechecked all the connections and placement of the components. I have checked the continuity of the breadboard, and nothing.

15vdc is applied at the input. The output is showing .25v and the adjuster is showing .17v.
if I short circuit the unit bypassing the regulator all together every thing works as it should, just no variability. Im not using the filter or ripple capacitors because the voltage in is already regulated.

here is a photo of what I’m working with. In it you will see clearly how it is wired, a circuit diagram and pinout I found online and a wiring diagram of my unit I drew.

what am I doing wrong? Please help. Thank you.View attachment 284405
Hi,

It can only be a few things wrong, but first you should test it with no load if you have not done that already.

Some common issues:
Pins mixed up.
Bad connection.
Load draws too much current (test with no load).
Input voltage too high or too load.
Device burnt out, possibly from a previous test that burnt it out but was not noticed yet.
Device came burnt out.
Fake part.
Breadboard not wired right, or pins not making good contact on plug board with socket pins stretched out too much from previous use.
Potentiometer arm is not connected properly.
Part of the pot is open (this could reduce the output to a very low value, the adjust pin has to be able to source at least some current to ground).

I've seen pins mixed up on professionally made boards.

You could do a simple test by shorting the adjust pin to ground and see if you measure around 1.25 volts output with maybe 10 volts input and no load. That will test the device itself. If that dont work, the part is defective.
 

dl324

Joined Mar 30, 2015
16,989
You're also likely abusing the breadboard. They're designed for #22 wire (0.0253" diameter). TO-220 leads can be 0.027-0.037".
1672845758794.png
I've been twisting them 90 degrees so they're 0.014-0.022".
 

MisterBill2

Joined Jan 23, 2018
18,941
In that setup it is not likely that the capacitors are able to solve the problem. The application note tells me that they must be close to the IC with adequate connections.
Everybody requesting capacitors is right!! Solder them right to the IC leads about 1/4 inch away from the case. You do need to solder very quickly and then wait until it is cool to apply the power. Then it should work.
 

DickCappels

Joined Aug 21, 2008
10,226
My gut feeling is that although you really don't know what's happening with at least a bypass capacitor on the input the symptoms reported do not seem to be related to a lack of capacitors. It seems that the input or output is not connected.
 
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