Destroyed diodes - help

Seeder98 · Feb 27, 2015

Hi,

can someone help me here please ?

I had 4 red laser diodes form DVD readers/burners. I used exacly this LM317 driver http://laserpointerforums.com/attac...dification-lm317-drivers-driver-250ma-out.jpg connected to 7.5V 1.5A power supply.

I set the driver to produce around 60mA. All 4 diodes were OK. The problem was all 4 diodes after 20sec just reduced their brightness for around 10%. After 2 diodes i thought the diodes just getting damaged from heat. But i tried to hold the third and fourth diode in hand without heatsink and they weren't even heating ! (i mean not as much as it can burn the diode). And same thing happened.

This issue is permanent for the diodes and it happened to me also with more powerful IR diode.

I'm now afraid to try my 500mW diode, which i want to use for CNC plotter.

Any ideas ?

Thanks a lot !

I created a similar thread 1 month ago. This problem is little bit different. Now i'm sure it's not a fault of LM317.

Cyparagon · Feb 27, 2015

Set it to 60mA how? 60mA might be too much for a reader diode. When running a dead diode, what is the voltage across ADJ and OUT pins? Don't run diodes without a heat sink in the future.

Seeder98 · Feb 27, 2015

Cyparagon said:
Set it to 60mA how? 60mA might be too much for a reader diode. When running a dead diode, what is the voltage across ADJ and OUT pins? Don't run diodes without a heat sink in the future.

Well, i had connected Amp meter between diode and driver and played with trimer.

As i sad, it happened to me also with more powerful IR diode (300mW).

I tested voltage across ADJ and OUT. It's 1.23V. I noticed diode during this test died completely.

Ofcourse, i just wanted to know if it's not fault of heatsink, which wasn't sinking perfectly.

Maybe i dont fully understand how diodes works but how can diode die without heatink ?

Cyparagon · Feb 28, 2015

Can and will.

Seeder98 · Mar 2, 2015

So...no ideas ?

Aleksa · Mar 2, 2015

DVD burners have diodes that output almost 200mW ,readers on the other hand output 10-20mW. I suggest you do more research on how diodes work. If you have a LM317 driver,monitor the current,don't go over 400mA for 650nm and 300mA for 780-808nm. That way it will always work,if it dies again,its your fault,you are doing something wrong. :beer:

Seeder98 · Mar 2, 2015

Aleksa said:
DVD burners have diodes that output almost 200mW ,readers on the other hand output 10-20mW. I suggest you do more research on how diodes work. If you have a LM317 driver,monitor the current,don't go over 400mA for 650nm and 300mA for 780-808nm. That way it will always work,if it dies again,its your fault,you are doing something wrong. :beer:

I know...it is my fault

. I'm doing something wrong, but what ?

Well, in LM317 driver i have 2x10Ohms resistors + trimer. That means max. current is 250mA. And DVD burner diodes are still dying.

- Diodes are not heeting much.
- Current is under 250mA.
- Voltage on diode 2-3.8V (depending on diode)
- Voltage LM317 ADJ-OUT is still 1.25V

Aleksa · Mar 2, 2015

Always put diodes in a heat sink. It doesn't matter that you don't feel it instantly,but they are heating up,a specially at 250mA. Big IR diodes run on 20c,if you go beyond that temperature they loose power and die. Laser diodes are very sensitive optoelectronic components. I see that you are a young fellow,i must advise you to take safety while playing with lasers. Even lasers at " low " power are dangerous. I hope that you have safety goggles

alessnilsen · Mar 2, 2015

I always use 400mA for my red laser and it still working great. What model of DVD burner/reader are you using? You need to put it in a heatsink if you want it to last.

For known red ones (like the LPC-815) I use 400mA, for IR ones I use 150mA, for unknown red diodes I use 350mA. For your tests, 250mA is OK. I also don't recommend using a trimpot with the driver, it probably will overheat and make the current unstable enough to kill the LD. Check too the pinout of the LM317, check all the connections.

Good luck! :yh:

hakzaw1 · Mar 3, 2015

Seeder98 said:
I know...it is my fault . I'm doing something wrong, but what ?

Pics would help
so would your location into your profile page.

did you ask??
"
Ofcourse, i just wanted to know if it's not fault of heatsink, which wasn't sinking perfectly.

Maybe i dont fully understand how diodes works but how can diode die without heatink ?"

you mean 'but how can diode LIVE without a heatsink (ing).

below see what happens if you dont do good heat sinkings--:shhh:

back to the search my friend- its all there- use it.

***********

EDIT- whatever you do keep doing it with cheap sled diodes...AS the solution to your dilema is NOT to buy expensive diodes- WAIT---

Seeder98 · Mar 3, 2015

Aleksa said:
Always put diodes in a heat sink. It doesn't matter that you don't feel it instantly,but they are heating up,a specially at 250mA. Big IR diodes run on 20c,if you go beyond that temperature they loose power and die. Laser diodes are very sensitive optoelectronic components. I see that you are a young fellow,i must advise you to take safety while playing with lasers. Even lasers at " low " power are dangerous. I hope that you have safety goggles

So, you think it's a thermal issue. Well, even heatsink with thermal conductive paste and active cooling isn't helping. I know a lot of people, who think its a thermal issue. But how can i fix that if the diode isn't heating during dying (measured with thermometer nad without heatsink max. 35 degrees on DVD burner diode).

Seeder98 · Mar 3, 2015

alessnilsen said:
I always use 400mA for my red laser and it still working great. What model of DVD burner/reader are you using? You need to put it in a heatsink if you want it to last.

For known red ones (like the LPC-815) I use 400mA, for IR ones I use 150mA, for unknown red diodes I use 350mA. For your tests, 250mA is OK. I also don't recommend using a trimpot with the driver, it probably will overheat and make the current unstable enough to kill the LD. Check too the pinout of the LM317, check all the connections.

Good luck! :yh:

I'm not normally turning diodes on without heatsink, it was just a try.

I don't know exact model. I can only say it was diode from 22x DVD-RW (22x is a writing speed).

Great idea with a trimpot, thanks !

Aleksa · Mar 3, 2015

Do i need to post the exact same photo hakzaw did? We have killed so many diodes during tests,so we know what are we talking about. Trial and error my friend

How about a photo of your setup? And a photo of your DMM. You must think this trough.
Diode requires somewhere between 2.2-3v and lest say 300mA to be at the safe side.
If you have a cheap dmm,expect a lot of error in the reading. Use a 1om resistor and measure the voltage across. I=U/R so 1mV=1mA. If a diode is working on 300mA and it is on a heat sink,there is no way for it to die unless you are doing something wrong.

Eudaimonium · Mar 3, 2015

Seeder98 said:
Well, i had connected Amp meter between diode and driver and played with trimer.

This is your problem.

NEVER interrupt a connection between the driver and the diode.

A very tiny opening of the connection results in the output capacitor suddenly being charged, and when connection is re-established, it empties into the diode, killing it.

Also, that schematic is all wrong and I have no idea why do people still use it. Where do you dig up this schematic?

Anyhow, use this:

To measure the output current, use a dummy load:

Seeder98 · Mar 3, 2015

hakzaw1 said:
Pics would help
QUOTE]

I know, this pics won't help much. But here they are
- Screenshot by Lightshot
- Screenshot by Lightshot
- Screenshot by Lightshot

Eudaimonium · Mar 3, 2015

Oh no, that's a breadboard connection.

Like I said in my post above, the connection to the diode must be permanent - solder it to the driver, don't use breadboards or alligator clips or whatever else is non-permanent.

That is the true problem IMHO, heatsinking is not an issue, never was, not with 60mA and not while the diode is in Aixiz module.

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