# LM317 voltage regulator short circuit

It worked as expected, but then I tried connecting a TDA2005 audio amplifier. I connected the LM317 to my audio amplifier as a power supply and because I am new to electronics I had some problems with my amplifier. Trying to fix the problems, I probably shorted my circuit accidentally (not sure about it). My LM317 potentiometer burned down with pretty bad smoke.

I was wondering whether could this happen because of shorting the output of the LM317.

• I don't think so - if you really short-circuited Vout, the LM317 may burn down, not the potentiometer. There's not such a large current there. You may have touched something else accidentally?
– user17592
Commented Jan 31, 2015 at 9:47
• well I am also not sure about shor circuiting LM317 itself, because i soldered it with my beginners skills, not sure about circuit itself, but i was testing it before with my multimeter, and it was ok, so not sure what could go wrong, can still feel the smell of burned circuit because it was such an unexpected thing :D Commented Jan 31, 2015 at 9:54
• Thank you for your answers, cant upvote, because of i'm new to forum and have no reputation. Commented Jan 31, 2015 at 10:12

My LM317 potentiometer burned down with pretty bad smoke. ... I was wondering whether could this happen because of shorting the output of the LM317.

No, for shorting output to ground.
Yes for shorting LM317 input to output.

If you short the LM317 input to output you will apply 28V across R1 and R2 in series. You get the maximum power in R2 when R1 = R2 = 240 Ohms. At that point P(R1+R2) = V^2/R = 28^2/480 = 1.6 Watts.
Dissipation in R2 = 0.8 Watts Voltage across R2 = 14 Volts.

If R2 is a low wattage rated pot (much less than 1 Watt) this could destroy it.

Usually when R1=R2 the LM317 acts to place 1.25V across R1 and 1.25V across R2 and dissipation in the resistors is much lower. Shorting the LM317 removes the protection that it usually provides.

Any action which stops the LM317 acting to control output voltage and which allows higher voltages to appear across the pot or part of it may cause such problems.

Yes, there are a couple of ways that could have happened.

If you had the pot turned down to get a low output voltage (say 50 or 100 ohms) and shorted output Vout to ADJ that would do it.

If the wiper of the pot was grounded and turned up all the way, and shorted the output to the free end of the element, that could also have a similar effect.

these circuit is good for about 1A load (maximum), I cannot use these for an amplifier

but for a pre-amplifier .Furthermore, in actual use, Input should not be more than 25V,

20V is good enough. But if you needed more current output for your regulator *317, then

you should boost the regulator with a power transistor. Only then, it can be used for your

desired amplifier.Use adequate heatsink on both electronic components. Be sure to use

proper insulating spacer, bolt and nut, and mica insulator for your project.