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Dim Diode

Galdor

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Aug 31, 2008
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Okay, I built the LM317 based driver which I found on these forums.
I harvested my diode from a spare HP Burner and hooked it up to the
driver. The diode lit up very bright and I only ran it for about a
second or two since I don't have my module yet. Being a noob at this
I pushed it of course and tried another test. It lit up bright again but
then went very dim. It still lights up but is very dim when on. Did I blow
out my Diode or is it a problem with the driver? Any help would be appreciated.

Thanks
 





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Aug 13, 2008
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A blown diode will still have it's LED working. That is what you may be seeing. It is much harder to blow the LED itself but can happen. When the crystals blow you are left with only the LED. Sounds like bad news for you unless it is just lasing very dim. Does it shine a dot on a wall 1 foot away?
 

Galdor

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It did. Now it gives of a dim red glow, definitely not visible at any distance.
Is there a way to test the LD? Sounds like I may have killed it. :-[
 

tomcat

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its not got a led in it.... and deff not crystals...

a diode is 2 silicon plates with a expanded junction between the 2 and a tuned quantum tunnel through the middle "blown diode" is where you melt the area and the cavity optics by subjecting them to too much power without adequate cooling (or just too much electrons racing through no matter what the mount temp is) and ruin the tunnel and cavity optics or just saturate it until the junctions n/p plates have a dense electron hole in them it still emits like aled becuase the junction still works but the "laser" part of the cavity nolinger works so you dont get stimulated emission and therefore high powers you just get the initial emission of the silicon junction...

basily yes you blew it go get another and be more careful next time :p even jayrob / senkat / daguin get it wrong at one point

take it as a learning curve and next time be more careful :p
 

Galdor

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Thanks for the info. I did find the problem I think. When I assembled my circuit I misswired my pot and in
a way that bypassed it so that the driver was operating at max output. Unfortunately I didn't notice it untill after I blew my LD.
Definitely a learning experience. I will definitely be more carefull next time.

Thanks again.
 
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Science wise, you have the classic symptoms of COD, catastrophic optical damage. Basically, too much power screws up the mirrors on the ends of the active region (maybe melted, maybe not, but definitely damaged). Without the mirrors, you have no cavity and very little or no gain/lasing action, which means little to no stimulated emission. Without stimulated emission, you have only spontaneous emission, which means your LD turned into an LED, and there's no good way for you to fix it. Now it's a test dummy-load for your future drivers to make sure the current is right. We've all done it, and I'm sure you'll do it again, probably much sooner than you would prefer to.



tomcat-
I applaud you trying to help out sportcoupe, because yes, there are no optical crystals in a red laser diode, and there is no LED in it. It is simply a laser diode, nothing more or less. However, you are not quite right in some ways. One, laser diodes are not made of silicon. There are several reason for this, and if someone wants a better explanation I can try to give it. But suffice to say that it doesn't work: you figure out how to make a laser directly out of silicon, and you'll be a rich person. Laser diodes in use today are made out of III-V semiconductors. Two, well, your description of a laser diode structure isn't quite right. There's no physical gap in the middle, it's not plates. It's a stack of thin films, one right on top of the other. It gets more complicated, but if anyone is interested I could oblige with more of what it really is like.

Also, some capitalization and punctuation would go a long way. I'm not one to normally complain, and maybe it's just me on this one, but I found your post almost impossible to read.
 
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Sigh, I guess you can't believe everything you read on the internet then. I stand very corrected now and more educated. I've only been a member here less then a month if that cuts me a little slack? ;) In other words, I'm just a big newb.
 

tomcat

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ah cool learn something every day

and im dyslexic, if it was not for spellcheck you would not read one word never mind a sentence
 

Galdor

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So if I read you correct pullbangdead then I can use my once LD now LED as a test device.
I assume that means that even though the Diode is no longer a laser it will still draw
current about the same as a good LD? If that is the case I suppose it is not a complete
loss. Any more info anyone would like to provide would be great! Thanks!
 
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sportcoupe - No problem, we all start somewhere. People have always helped me in my education, I jsut try to do the same.

tomcat - No problem again, glad you learned something, I try to do that everyday (and it isn't too hard when still in school like I am). Rereading my post later, I didn't meant o come off harsh or anything, no harm intended, and you seem to be too offended. :)

Galdor - Well, that's the beauty of constant-current drivers like the LM317 - In theory, it will give you the current you set it to no matter what the load is, as long as the voltage of your supply (batteries) is enough (meaning greater than the combination of the load/LD and the driver). And with a laser diode, yes, the voltage characteristic should remain the same even if you're not getting stimulated emission. It probably changes some, but really it's generally close enough that it works well: the driver gives its current no matter what, and the voltage of the dead diode still is close enough to make sure the driver will work with a live diode and your chosen battery supply. So basically, yes, it's a good test load since it's still giving you some light.
 

Galdor

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Well, I finally corrected my circuit. I have no idea how I managed to get
it soooo messed up but it was not even close to being right. Guess that's
what I get for attempting it while running low on sleep! That being
the case I just desoldered everything and did it over from scratch. I used
the now dead LD as a test and it seems to be working properly. When I
turn my POT all the way out the diode gets very dim and my DMM reads about
1.4 volts. If I crank it up a bit the diode gets brighter and I get about 2.6 volts.
Thanks for all your help and advice. Now I just need to find me another old
DVD burner to destroy! :)
 

Ryo

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Hey Galdor..
Could you measure the breakdown voltage of your blown diode? Just wondering if the value would be the same as a non blown one.. Hopefully your DMM has a diode measurement mode.
 
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Galdor said:
Well, I finally corrected my circuit. I have no idea how I managed to get
it soooo messed up but it was not even close to being right. Guess that's
what I get for attempting it while running low on sleep! That being
the case I just desoldered everything and did it over from scratch. I used
the now dead LD as a test and it seems to be working properly. When I
turn my POT all the way out the diode gets very dim and my DMM reads about
1.4 volts. If I crank it up a bit the diode gets brighter and I get about 2.6 volts.
Thanks for all your help and advice. Now I just need to find me another old
DVD burner to destroy! :)

During your testing, you will be concerned about the current delivered to the LD.
Place the DMM leads in series with your test load to measure mA. You may have to place the test lead
positive in the other hole labeled mA on your meter.
 

Galdor

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Ryo, I would be happy to post that info if you could tell me how to get that measurement.
My DMM does have a diode test feature.

Thanks, moond0ggie. I will give that a shot. Can I just use my blown LD as the test load for measuring
that or should I build the test load circuit for the DDL driver?
 

Ryo

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Galdor said:
Ryo, I would be happy to post that info if you could tell me how to get that measurement.
My DMM does have a diode test feature.

Thanks, moond0ggie. I will give that a shot. Can I just use my blown LD as the test load for measuring
that or should I build the test load circuit for the DDL driver?

It's pretty easy.. just set the DMM to diode  (some DMM share capacitance and diode measurement in the same section so you might have to press a button to measure it.  For example a Fluke meter would require you to push the blue button until you see Voltage as the unit of measurements instead of F)  Any case if everything is right, then all you have to do is put the red on the positive side of the LD, and the black side to the negative/ground of the LD.  It will give you a voltage reading.  

Note if you ever have it backwards, it will typically show OL (overload) which basically doesn't damage anything.  Useful if you don't know which side of a diode is suppose to be positive.

Another note, this typically will power up the LD but make it look like a LED since it only drives in a small limited amount of current (typically 1 mA for Fluke meters).. at least it did for me on my LD's.

A example: I hooked up a KES-400A and measured 1.7V for the red LD.
Another example: I measured a 1N4745 diode (zener diode) and it measured 0.72 V for it's breakdown voltage.
 




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