LM317T Power supply issues.

Thread Starter

Anubhav Sharma

Joined Mar 21, 2016
68
Hi every one, This is for the first time am posting thread here and i really hope to get a solution here.
I am trying to make LM317 Power supply for the first time. I designed a diagram on stimulation software and it goes well.
The major problem is when ever i adjust POT, it gets burnt and not showing any effect on output volts. I have already wasted 12 POTs.

Please take a look at schematics attached. I really dont know where am wrong. I am not an experienced person in electronics.
I am using 12-0-12 / 2 Amp transformer, bridge rectifier ( diode version ), 10 K POT ( B 10K SHARP ).

Output volts - 37v. When the pot is at zero mark, circuit still shows 37V but pot got burnt.

Please help me with this problem. Thanks in advance.

Power Supply_1024x719.gif
 

panic mode

Joined Oct 10, 2011
1,787
you need to be more specific - WHERE is your meter connected when you read that? are you sure your transformer is ok (no leak, connected ok)?
 

Alec_t

Joined Sep 17, 2013
10,582
Your pot is wired as a rheostat. If it is set for a low resistance value then 37V (or less) will drive a lot of current through it via R1 if the circuit can't stabilise quickly. Lots of current = lots of heat.
DMMs don't read correctly on the AC range if the voltage has a large DC component (37V here).
 
Last edited:

donpetru

Joined Nov 14, 2008
185
1. Make sure the potentiometer is 5k or 10k.
2. Connect a 10K - 0.5W resistor in parallel with capacitor C3.
3. LM317 has TO-220 package ? If so, then numbering pins from schematic is OK.
 

Marcus2012

Joined Feb 22, 2015
382
Hey :)

Try exchanging your R1 for 330 Ohm. This will then set your whole pot range at attainable values (currently your maximum output voltage is 58V!) LM317 Calculator. With a 330 ohm as R1 you would have 1.25 - 39V range. Also the LM317 needs a minimum current draw to operate properly and this is in the region of 10-20mA so you can just use a LED with current limiting resistor (set at maximum input voltage) rather than just a dummy load resistor. Finally check that the regulator itself is still ok because a shot regulator usually does not function at all and Vo is only Vin - dropout voltage, this can be checked with continuity across input and output, if there is continuity the regulator is shot.
 

Thread Starter

Anubhav Sharma

Joined Mar 21, 2016
68
you need to be more specific - WHERE is your meter connected when you read that? are you sure your transformer is ok (no leak, connected ok)?
I have checked readings at V IN + Gnd, Vout + Gnd and final out put after cap. all same.
I have also tried 3 different LM317 and also tried 12-0-12 2amp, 15-0-15 500mA, Pot burnt in all conditions.

Please suggest.
 

Thread Starter

Anubhav Sharma

Joined Mar 21, 2016
68
Your pot is wired as a rheostat. If it is set for a low resistance value then 37V (or less) will drive a lot of current through it via R1 if the circuit can't stabilise quickly. Lots of current = lots of heat.
DMMs don't read correctly on the AC range if the voltage has a large DC component (37V here).
I have checked none of resistor and cap is over heated, connected heat sink on LM317 but its cool any ways.

Can you please explain that, as am hobbyist and have least knowledge about circuits, still this circuit is a challenge for me, I mean where am wrong? What should i do to make a clean power supply?
Thanks.
 

Thread Starter

Anubhav Sharma

Joined Mar 21, 2016
68
1. Make sure the potentiometer is 5k or 10k.
2. Connect a 10K - 0.5W resistor in parallel with capacitor C3.
3. LM317 has TO-220 package ? If so, then numbering pins from schematic is OK.
Yes sir, i am using 10 K POT its a volume Pot. (B 10K Sharp).
I will connect a resistor in parallel and will update result.
Whats TO-220 package? I am using LM317T also checked data sheet.
Transformer is of 2 amps can this be a issue?
 

Thread Starter

Anubhav Sharma

Joined Mar 21, 2016
68
Hey :)

Try exchanging your R1 for 330 Ohm. This will then set your whole pot range at attainable values (currently your maximum output voltage is 58V!) LM317 Calculator. With a 330 ohm as R1 you would have 1.25 - 39V range. Also the LM317 needs a minimum current draw to operate properly and this is in the region of 10-20mA so you can just use a LED with current limiting resistor (set at maximum input voltage) rather than just a dummy load resistor. Finally check that the regulator itself is still ok because a shot regulator usually does not function at all and Vo is only Vin - dropout voltage, this can be checked with continuity across input and output, if there is continuity the regulator is shot.
Sure ill update circuit and will reply.
Thanks
 
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