Burned voltage regulator? (smoked)

[flubber_butt_2001]

Hi,

I'm currently making the PCB for the 50$ robot from one of the tutorials written by webbot. The tutorial is called "How to build a robot-did you have problems?" I have everything soldered and made now but when i hooked in my 9V battery and 5V battery my voltage regulator started smoking (i think?). Then I decided to check some connections and found that the copper tracing running through the OUT pin of the voltage regulator and the copper tracing running through the GND pin of the voltage regulator has a resistance of about 15kOhm i think? It doesn't beep when I test using the connection tester function on my multimeter but it does give that resistance so I was wondering if I fried something or what should I do. I checked the voltage regulator and there aren't burn marks. Any help would be much appreciated.

Thaniks

[TrickyNekro]

These regulators have thermal shut down if I am right so, you probably won't have a problem...
The regulator heats itself up.... but then closes to protect itself...

If you get no beep you have no short... Check with the Ohm meter what value you get...
That should be more clear ;-)

[flubber_butt_2001]

I'm getting something like 15kOhm's of resistance. Any idea what that means? thanks for all the help

[Admin]

Did you see smoke? Or did it just overheat?

Either way, it means there was a short in your circuit somewhere else after the regulator.

[cyberfish]

They certainly CAN blow up, despite having thermal shutdown, for some reason.

I have blown one up, literally (into 3 pieces).

[TrickyNekro]

Surely they can blow up... if you feed them something like 50V more than the rating or reverse polarize them...

but generally... don't... Although some older ones may don't really have thermal shut down...

But then again... you wouldn't have seen smoke... you could have baked breakfast...

[cyberfish]

I was running mine off a 9V lab supply.

It was just last year, too.

[Admin]

Most voltage regulators don't have thermal shutdown, especially the cheap variety.

Whats the part #?

[cyberfish]

7805, sorry I don't remember the manufacturer, though.

[Admin]

Whats the *exact* part number?

[cyberfish]

I don't even remember the manufacturer .

[Admin]

Well, if its just 7805, there is no thermal shutdown.

If however its a LM7805, there'll be thermal shutdown.

There are plenty others out there . . . I suspect yours didn't have it

[cyberfish]

Oh sorry by 7805 I meant LM7805. I didn't know there's a "just" 7805.

[Soeren]

Hi,


Thermal shutdown is a feature of most regulators, but it will only work (no matter the pricetag on the regulator) if the overload is moderate, as it takes time for the heat to transfer through to the shutdown part of the IC.

[flubber_butt_2001]

I think I found the problem. I did something really dumb and i shrink wrapped the two leads to positive and negative for my 9V connector together, thinking that I would save shrink wrap lol >.<. I figured it out after I was holding the battery and it felt like it was heating up significantly. Do you think it was the battery smoking or was it something else?.

[huevon]

I think I found the problem. I did something really dumb and i shrink wrapped the two leads to positive and negative for my 9V connector together, thinking that I would save shrink wrap lol >.<. I figured it out after I was holding the battery and it felt like it was heating up significantly. Do you think it was the battery smoking or was it something else?.

Power your board again. Be careful not to reverse polarity and do it without the ATmega. After that test it with the voltmeter to see are you getting regulated power (5 - 5.3V). Best way to do it is just connect the COM cable (usualy black) to the metal back of the regulator and with the other one (usualy red) test all middle pins which are innermost to the atmega socket (see attachment). If your regulator is working, then probably was the insulation of you power leads smoking. And because you are already holding the multimeter spend 5 more minutes to check the tracks for shorts and continuity. Doing that will save you future smoke problem. BTW I am curently having problems programming the MCU please share you experience when you are ready http://www.societyofrobots.com/robotforum/index.php?topic=11082.0

[Admin]

Told you there was a short after the regulator

I once had a circuit go up in smoke with a popping sound. I came back a day later without doing anything, and it worked perfectly

(the moral of that story is, if everything works and your multimeter says its ok as huevon said, its probably ok)

Next time, multimeter your circuit before powering it up

[corrado33]

Told you there was a short after the regulator

I once had a circuit go up in smoke with a popping sound. I came back a day later without doing anything, and it worked perfectly

(the moral of that story is, if everything works and your multimeter says its ok as huevon said, its probably ok)

Next time, multimeter your circuit before powering it up

That kinda happened to my programmer.  I heard a popping sound, it didn't work for a while, next day, it worked fine.  I has happy to say the least.

[Soeren]

Hi,

Just wondering... If a similar thing happened to your car, would you drive it the next day if it would start?

I'd dismantle the thing (whether car or circuit) until I was sure I had found the culprit and then fix it before using it, to avoid the possible major disaster that could follow, wiping out a substantial part of the circuit.