Try to disconnect the potentiometer from ground. This will probably solve the potentiometer melting problem. See my previous post. One more time..

 

Try to disconnect the potentiometer from ground. This will probably solve the potentiometer melting problem. See my previous post. One more time..

You are correct, i connected adjuster pin of LM317 to wiper and other leg to ground(left most when knob is on our side), it worked but i tried this with low volts ( 9v). But what if high volt and current is flowing ( 32v / 2amps) ?

Let me try, i already wasted so many regulator and pots, lets try with one more.
Ill update soon.

Thanks for the advice.

 

i connected adjuster pin of LM317 to wiper and other leg to ground

Try NOT to have the GROUND connected to the potentiometer. Just use two pins from the potentiometer. One pins on the SIDE (it doesnt matter which one, just the rotation direction will change) and the MIDDLE pin.

 

Try NOT to have the GROUND connected to the potentiometer. Just use two pins from the potentiometer. One pins on the SIDE (it doesnt matter which one, just the rotation direction will change) and the MIDDLE pin.

So i should connect wiper pin to adjust pin and any side pin to v out on regulator and turn pot into variable resistor.
Am i right?

 

Hi Again,
Tested circuit with 7.5 volts input and am getting 6.74 volts max and 1.26 volts to the minimum side. And nothing burns.

Hi,

Well that sounds much better, but what resistor are you using to ground in place of the pot? We need to use a resistor so that there is no question about what the value of that resistance is, and also check it to make sure it is the right value. A 220 ohm resistor will produce 2.5v at the output.

1.26 sounds promising though, and that would mean you still have the pot and it is adjusted way down. But using a 220 ohm resistor will verify once and for all that the LM317 is either working or not working. Try that next, it's easy enough, then take it one little step at a time to get higher.

 

Hi,

Well that sounds much better, but what resistor are you using to ground in place of the pot? We need to use a resistor so that there is no question about what the value of that resistance is, and also check it to make sure it is the right value. A 220 ohm resistor will produce 2.5v at the output.

1.26 sounds promising though, and that would mean you still have the pot and it is adjusted way down. But using a 220 ohm resistor will verify once and for all that the LM317 is either working or not working. Try that next, it's easy enough, then take it one little step at a time to get higher.

Ok thanks ill do so and will update.

 

So i should connect wiper pin to adjust pin and any side pin to v out on regulator and turn pot into variable resistor.
Am i right?

yes try this..

 

What are the output voltages you need?
What are the specs of the pot, ie the max. power?
Typically it is less than 0.1W.

With output voltage near 40V the power is about 0.16W with a 10kohm pot.

As has been told before, put a resistor in series with the pot. For example 4k7 resistor and 4k7 pot, but then the minimum output is about 25V.

If you want have a stabil and variabel output voltage, the one end of the potentiometer must be grounded.

 

Hi,

Well that sounds much better, but what resistor are you using to ground in place of the pot? We need to use a resistor so that there is no question about what the value of that resistance is, and also check it to make sure it is the right value. A 220 ohm resistor will produce 2.5v at the output.

1.26 sounds promising though, and that would mean you still have the pot and it is adjusted way down. But using a 220 ohm resistor will verify once and for all that the LM317 is either working or not working. Try that next, it's easy enough, then take it one little step at a time to get higher.

Hi again, Tested circuit by replacing pot with 220 (exactly 215 as per ohm meter) ohm resistor. and it gives 2.48v stable while input voltage is 8.5v. LM317 is fine i guess.

 

What are the output voltages you need?
What are the specs of the pot, ie the max. power?
Typically it is less than 0.1W.

With output voltage near 40V the power is about 0.16W with a 10kohm pot.

As has been told before, put a resistor in series with the pot. For example 4k7 resistor and 4k7 pot, but then the minimum output is about 25V.

If you want have a stabil and variabel output voltage, the one end of the potentiometer must be grounded.

Hi, As this is a variable power supply i need max between 30 to 36v as maximum output. I am using B10K pot normal one( its not 1watt pot that only i know).
So if i leave ground led blank, this will not give stable response. I also have 47K pot but not 4.7K actually where i live its hard to get specific value components, i can get commonly used components.

Should i try this with 22k or 47K pot ot 10 k will be ok. with equal series resistor.

 

Hi, As this is a variable power supply i need max between 30 to 36v as maximum output. I am using B10K pot normal one( its not 1watt pot that only i know).
So if i leave ground led blank, this will not give stable response. I also have 47K pot but not 4.7K actually where i live its hard to get specific value components, i can get commonly used components.

Should i try this with 22k or 47K pot ot 10 k will be ok. with equal series resistor.

The pot should have a lower value, even 10kohm is too high.
The output voltage is ~ 1.25x(1+R2/R1), which gives R2~ 6kohm for Vout = 35V, if R1 = 220 ohm
You should use at least a 0.5W potentiometer.

 

Just one check.
Output of the bridge - Cathodes are positive and Anodes are negative. Correctly drawn in your circuit. By any chance are you connecting them reverse? I am assuming you have used a different supply for 7.5V, right?

 

Just one check.
Output of the bridge - Cathodes are positive and Anodes are negative. Correctly drawn in your circuit. By any chance are you connecting them reverse? I am assuming you have used a different supply for 7.5V, right?

I have used battery supply for 7.5v. Cathodes and Anodes are connected properly i checked thrice. I used bridge for transformer supply only, i dont think that bridge is required for battery supply.

 

Hi again, Tested circuit by replacing pot with 220 (exactly 215 as per ohm meter) ohm resistor. and it gives 2.48v stable while input voltage is 8.5v. LM317 is fine i guess.

Hi,

Sounds very good. It appears that the LM317 is working.

Now you can start to increase the output, but with a resistor again only this time of a different value.

To start, increase the input to say 20 volts and make sure the output stays at 2.48 volts or close to it.

Next, for 220 ohm we got 2.48v output, so for every 220 ohm resistance increase we increase the output by 1.24 volts. This means using a 1.1k resistor will give us 7.44 volts output, with the proper input. So next replace the lower 220 ohm with a 1.1k and increase the input voltage to around 10 volts. Verify that you get around 7.5 volts output. If you dont have 1.1k, then use 1k, and look for around 6.9 volts output.

Then you can increase more, say to 2.2k and look for 13.64 volts output. You have to increase the input to at least 15 volts for this test, but dont go too high.

All we are doing is using an incremental test method. We test until we either get to the right max output or something goes wrong.

 

Hi,

Sounds very good. It appears that the LM317 is working.

Now you can start to increase the output, but with a resistor again only this time of a different value.

To start, increase the input to say 20 volts and make sure the output stays at 2.48 volts or close to it.

Next, for 220 ohm we got 2.48v output, so for every 220 ohm resistance increase we increase the output by 1.24 volts. This means using a 1.1k resistor will give us 7.44 volts output, with the proper input. So next replace the lower 220 ohm with a 1.1k and increase the input voltage to around 10 volts. Verify that you get around 7.5 volts output. If you dont have 1.1k, then use 1k, and look for around 6.9 volts output.

Then you can increase more, say to 2.2k and look for 13.64 volts output. You have to increase the input to at least 15 volts for this test, but dont go too high.

All we are doing is using an incremental test method. We test until we either get to the right max output or something goes wrong.

Thanks, am goint to work on it now.
1 question: Can there be a problem with bridge rectifier?
I mean i checked IN4007 (x4) bridge which i was using and its showing 23v DC BUT its also showing 50v AC in meter. Now i replaced that with another bridge (Module version). Its showing 26V DC and 0 v AC.

 

Should i try this with 22k or 47K pot ot 10 k will be ok. with equal series resistor.

You really should read and understand the data sheet.

 

Can there be a problem with bridge rectifier?
I mean i checked IN4007 (x4) bridge which i was using and its showing 23v DC BUT its also showing 50v AC in meter. Now i replaced that with another bridge (Module version). Its showing 26V DC and 0 v AC.

One of the reasons I suspected was a negative voltage to LM317, since they were going bad regularly. LM317 cant stand a negative voltage input.
Is it the same meter? Then it is likely that there could be problems with the diode(s). Because, most meters, will show higher value in AC mode when measuring DC voltage. Try posting a picture of your setup with the meter.
Mr Al - Sorry to have interrupted you from a step by step approach.

 

One of the reasons I suspected was a negative voltage to LM317, since they were going bad regularly. LM317 cant stand a negative voltage input.
Is it the same meter? Then it is likely that there could be problems with the diode(s). Because, most meters, will show higher value in AC mode when measuring DC voltage. Try posting a picture of your setup with the meter.
Mr Al - Sorry to have interrupted you from a step by step approach.

Thats fine on behalf of Mr Al because am working on step by step approach and on other bread board am testing rectifiers.

Yes its the same meter, mostly DC volts shows almost double in AC volts, i have tested with batteries even. i have tested diode bridge rectifier using multi meter, appears fine as per instructions on youtube.

What i want to ask is if all DC volts shows AC volts also, so why Module version of bridge rectifier not showing AC volts (0.00v)? Is it fine or better or its bad?

If LM317 cant stand negative voltage then ho should i rectify that?

 

Hi,

Sounds very good. It appears that the LM317 is working.

Now you can start to increase the output, but with a resistor again only this time of a different value.

To start, increase the input to say 20 volts and make sure the output stays at 2.48 volts or close to it.

Next, for 220 ohm we got 2.48v output, so for every 220 ohm resistance increase we increase the output by 1.24 volts. This means using a 1.1k resistor will give us 7.44 volts output, with the proper input. So next replace the lower 220 ohm with a 1.1k and increase the input voltage to around 10 volts. Verify that you get around 7.5 volts output. If you dont have 1.1k, then use 1k, and look for around 6.9 volts output.

Then you can increase more, say to 2.2k and look for 13.64 volts output. You have to increase the input to at least 15 volts for this test, but dont go too high.

All we are doing is using an incremental test method. We test until we either get to the right max output or something goes wrong.

Ok, so the test results.

Let me start step by step please.

9v Battery input:

Initially i started with 220 ohms resistor in place of pot and as i told you before the output was 2.48v. After that i replaced 220ohms resistor with 1K, at this time the output was exactly 7v, and then i replaced resistor with 2.2K and the output was 8.7v and that the max i could get with 9v i believe.
Unfortunately i was not having any other DC or low volt power source, so i switched to transformer supply. This time half wave rectifier i connected -12v and +12v to two IN4007 and their negative were connected together. I connected 2200uf cap and at this point voltage was 18v.
Then i connected Lm317 ( Adj pin to 220 ohm resistor ) the out put was 15.8v. I replaced resistor with 1K again the output was 16.4v, the out with 2.2K resistor was 16.9v.
Then i connected POT in place of resistor as variable resistor with one pin ground and wiper pin to adj, it worked well and showed readings from 1.2v to 16.9/17v. NO BURNS.

So finally i switched to the original supply that is -ve 12v and +ve 12v step by step i measured volts. I connected bridge rectifier, at this time the voltage was 26v and then i connected 2200uf CAP, voltage raises to 34v. ( I really dont know why? ) then connected those 3 resistors step by step and out put was 26v, 28v, 28.9v.
Then i connected POT and guess what? POT BURNS. LM317 was safe but on second attempt it damaged, anyhow there was no short sign no continuity between pins, it was only showing almost same volt on output as input.

Now what should i do?
I think its -12v that damages pot, because i tried pot without ground also ( wiper pin to adj pin and right most pin to output. It didnot burn but was not responding while turning. ( Suggested by member to try this way).

Please suggest.
thanks

 

Was this the original diode bridge? As shown, is it properly / completely connected?

Trying to make head and tails of it.