LM317 getting hot in <10sec.. Short in diode wiring?

I have had some lm317's get super hot because of mis-wired resistors. Be absolutely sure that all resistors (especially if in parallel) are setup and wired correctly if overheating that should happen is occurring.

awlego said:

I have had some lm317's get super hot because of mis-wired resistors. Be absolutely sure that all resistors (especially if in parallel) are setup and wired correctly if overheating that should happen is occurring.

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Here is the source of all your problems, simply following the schematics you were given without asking questions.

As I already said ... you only need one single resistor. Why complicate your lives?

OP, you can probably find 3.3 ohm resistor any any general electronics you have busted around you.

3.3 is a common resistor, but if you can't find it, remember Rtotal^-1= R1^-1+R2^-1+...+Rn^-1

Hmm, that's kinda hard to read....

1/Rtotal = 1/R1 + 1/R2 +...+1/Rn


If you are just paralleling 2 resistors, you can use the shortcut product over sums (R1*R2)/(R1+R2)

Assuming correct wiring, heat is probably from a source voltage that is way higher than the voltage that the load drops.

I don't think the resistor setup is wrong as is. I've done the math. 10/3. The lm317 isn't bad like it was when I had the larger resistors plus schotty diode plus capacitor crammed into casing. Plus now I insulated it better. no problem. Is there a way of looking closely for a detail on the LD that will tell me for sure if it's blown? I mean I still can focus a beam on the wall. THe projection still has a line (from 5ft it's about 4 inches long) going though the center of the dot.

lam0r said:

I don't think the resistor setup is wrong as is. I've done the math. 10/3. The lm317 isn't bad like it was when I had the larger resistors plus schotty diode plus capacitor crammed into casing. Plus now I insulated it better. no problem. Is there a way of looking closely for a detail on the LD that will tell me for sure if it's blown? I mean I still can focus a beam on the wall. THe projection still has a line (from 5ft it's about 4 inches long) going though the center of the dot.

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Look at the projected light?
Does it show signs of destructive interefence in your vision, percepted as fuzzines of the ligh (instead of flat equal pattern of LED) ?

Your diode is most likely toast.
Check the current going into it - if you use resistors like you decribed, it should put out ~380mA.
If from cold start (all components on room temperature) does not give very strong light, it's dead.

what is the correct way of wiring resistors in parallel? I don't see how I could've messed that up

I just hanged to another completely dead diode and I get 8-15mA for some reason

LM317T's do get hot. Even with a large heatsink, mine get up to ~60 celsius running at 400mA. Any extra voltage is thrown away as heat, that's just how they work. That's okay though, they have built-in thermal protection and they'll start to pulse their output if they get over something like 120 degrees celsius. I think they're rated up to 150 degrees celsius, which is enough to cause serious burns. I wouldn't be too concerned about your regulator getting hot, that's normal. I've had them desolder themselves without dying.

It looks like you're probably doing everything correctly, but I'm wondering though, maybe those are "short open can" diodes, which LED at around 350mA... Any way you could take a macro shot of the diode itself?

yeah.. I figure so.

I now have everyhthing working except for the LOC brightness. current reads 382mA.

just bought 5 replacement diodes

I have an LM317 running a 445nm diode at 1.25A with 3x 18650's powering it. Yes, may not be the smartest thing to do, and no, I don't really have an additional heatsink attached to it, only a very small piece of aluminum, but even that I get to work and the diode is fine.

I only read half the thread, so if I am saying something already said or solved, I'm sorry. But in general, you want to put something over the LM317 to have it not touch the case. This was a problem I had to figure out on my own case build. To solve it, it is good to wrap it up in kapton tape like this: DealExtreme: $2.88 High Temperature Tape (10mm / 300-C) . Also, I used to solder things freestanding like that, but it is better if you cut a small piece of perf board w/ copper joints and make your circuit on there - much stronger joints and connections, cleaner, more professional. Also, I think someone mentioned it, but your pot would have to be rated for medium to high wattage if i'm correct. This is why I use a 4.3 ohm 1/2W resistor or else 3ohm 1W resistors rather than pots. Pots are bulky and are un-needed if you know what current you want. Lastly, what I don't like about those O-like cases are that they aren't easily adjustable with a nice top like the aixiz modules are. I would suggest ordering a set of 10 aixiz modules from aixiz or else even o-like sells similar for cheaper in 10 packs. Yes, they might not heatsink the diode as much, but come up with your own heatsink - either out of washers, if you can find access to a lathe, or else buy from a member on the forums. Most people make heatsinks for aixiz size, and they come out very nice (though I pride in making my own on - even out of washers can come out nice). If you enjoy this hobby, you will use all 10 of the aixiz modules and more, eventually.

Well, good luck with your builds. I know starting off I broke a lot of diodes (like 10). In total, I've broken maybe 10 more since then, my highest value being a 445nm diode (at least it wasn't a 12x blu-ray or something). Bottom line though, don't give up. I saw you ordered 5 replacements, and well, you're lucky they've gotten so cheap. They used to be $20+, and I only 17 and started a few years ago

Mine is very adjustable. I'm not sure which olike your'e talking about. mine has adjustable focus and it seems to work great with a little teflon in the threads

solder a penny to it =]

Make sure it's a < 1983 penny though, so it's actually copper.

If you find a copper 1983 penny, don't solder it, as it's rare (1983 is when they switched to zinc).

i found a 1969 penny, i swear it cost more to make a penny than its actually worth

lamor, to check to see if laser is lasing and not just emitting light, look for the weird speckly pattern in the light. Speckle = destructive interference. Just red light = LED'd.