I think I've burnt out my diodes, but how?

[charliebruce]

Hi, this is my first post, so hi to everyone. Basically I think I've burnt out my diodes (a Red long open-can and an 803T). Thing is, I don't know why this has happened, and was wondering if anyone has any advice. I've been using a 317T based circuit driving at about 120mA for the blue, and not much more for the Red one. I've tested each change with my test load, (4 4N001s for Red, 6 for Blue), and it has been running fine since Thursday. This evening, I was powering it on, and after a few seconds I noticed my blu one was barely lasing at all. I disconnected it and checked current and voltage, both were fine. Then I hooked it up to my test load, and set up my red diode. It worked fine for a few seconds, then suddenly dimmed to barely-lasing. I checked the battery, about 7.2v, and changed it for a 8.6V wall plug. Same thing happened as the battery. any ideas, or suggestions for the future? By the way, the red one may have been damaged when I resoldered it yesterday, but both had been working fine on that evening, after resoldering. thanks in advance for your advice!

 

[pseudolobster]

It sounds like you've been doing a lot of disconnecting and reconnecting things... Have you been remembering to discharge the capacitor every time before you hook the diode back up? Have you been careful not to overheat things with the soldering iron? Have you been using proper electrostatic discharge procedures?

 

[charliebruce]

I think so, I have a paperclip to hand which I use to short the capacitor, and yes I did use excessive heat, but only on the red one, and it seemed to work fine afterwards, though it may well have been damaged without my knowledge. The blue one was much better treated, and had less than 2 seconds of heat when I soldered it. Is it possible that my battery created a surge not caught by the capacitor? Its a 10uF 25v capacitor in parallel with the LD. As for ESD, when not used, they've been stored in a breadboard, with their wires on the same rails.

 

[rog8811]

I've been using a 317T based circuit driving at about 120mA for the blue,

I blew 2 803T's @120ma.... the 2 803t's I am running @110ma are still going strong. I know others have been driving them much harder but I will stick to 110ma as it seems to be about the safe limit.

As to the red, I can only say that if you are swapping LD's in and out of the circuit you are more likely to get failiures, even though reds seem tougher they can only take so much heating and cooling.

Regards rog8811

 

[styropyro]

Are the diodes installed in Aixiz modules before you soldered leads to them? IF not, the soldering iron could have nuked them because they had no heatsinking.

 

[charliebruce]

Nope, they were in Aixiz modules, but I suspect I blew the red one with excessive heat anyway, reattatching leads. I'm not sure about the blu one, but I suspect it was the repeated switching, or overload of current over long period of time. I'm glad that it was only 2 diodes I burnt out and not my retinas - for a first mistake (or indeed any), diodes are better than eyes!
My last question, rog said that 110mA was the safe limit for 803T's but I heard that lots of people have reached 150mA or so safely? In a proper heatsink (home-lathed Aluminium block) and an Aixiz module, what would the safe limits be, or does it depend too much on the diode to say for sure? Are there any signs that one is overloading a diode, or can you only tell when it's too late?

Thanks to everyone who offered their advice!

 

[NitroxLasers.com]

Check out this interesting post by daguin that talks about various aspects of BluRay diodes: laserpointerforums.com/forums/YaBB.pl?num=1219161671

One thing to keep in mind is that, although with proper heatsinking, 150ma is not too much for an 803t, you need to be sure to keep your duty cycle down to around 30 seconds on / 30 off, as this is around the edge of the diode's capabilities. In addition, both blu ray and red diodes are extremely sensitive to voltage fluctuations, so it's best to always connect these to drivers. I have had a lot of success with rkcstr's diodes, as have many others on the forum. What type of circuit do you have the diodes connected to?