Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers



Laser Pointer Store

my hl6388mg just died

deadshadow

New member
Joined
Feb 21, 2016
Messages
475
Points
0
hello everyone today one of my 1st builds i ever made when i started this hobby died-zombified, althought it was an old build it had very low hours runtime(im guessing somewhere 5 hours).

today i turned it on and noticed it wasn't that bright and after checking the batteries i unfocused the lens and i noticed what is going on from the output shape.after checking it on the lpm it produces something less than 10mw

the diode was running at 410ma while the datasheet suggests max 430ma,so it was set lower than the datasheet.

i played with it on my psu and pushed it at 1.1A and nothing changed(managed to get an output of 30mw at 900ma :p)

here is the output shape at this moment,those diodes look like are very sensitive and maybe static electricity killed it as those are case negative.



not a big lose i just wanted to share it and have it logged in the forum for anyone that will search for this diode in the future :beer:
 

Attachments

Last edited:

paul1598419

Well-known member
Joined
Sep 20, 2013
Messages
14,600
Points
113
Yes, it appears to have LEDed on you. The driver should be fine, so a new diode and you'll be ready to go. If you'd rather, use an LPC-836 or 840. They are case negative and should output close to 400 mW at 410 mA. They are dirt cheap too.
 

deadshadow

New member
Joined
Feb 21, 2016
Messages
475
Points
0
Yes, it appears to have LEDed on you. The driver should be fine, so a new diode and you'll be ready to go. If you'd rather, use an LPC-836 or 840. They are case negative and should output close to 400 mW at 410 mA. They are dirt cheap too.
that diode was 638nm,i already have a red 650nm build(lpc 836 or 840,not sure)
and its not a big lose as for 638nm im using my tec cooled p73 build ;)
 

paul1598419

Well-known member
Joined
Sep 20, 2013
Messages
14,600
Points
113
Interesting, Chris. What kind of host are you using for the P73? It would be difficult to TEC cool a HH effectively, is the reason I ask. I see it is a HH in your sig. How are you powering the TEC and removing all that extra heat to the air?
 

Benm

Well-known member
Joined
Aug 16, 2007
Messages
8,115
Points
113
Too bad it died, but you should realize you are actually overdriving that laser diode:

The datasheet specifies a couple of things, like
- absolute maximum optical output 250 mW
- maximum current 430 mA

The point is that -neither- of these values are to be exceeded. If the diode is 'typical', it takes only 340 mA to reach that 250 mW output power, and any current above that is operating it out of spec (because you exceed the 250 mW optical absolute maximum) even if it's -far- below 430 mA (say just 350 or so).

Also these maximums are at a case temperature of 25 celcius, which may or may not be realistic depending on your host size/construction and ambient temperature.

Surely static electricty or something could have fried your diode, but as a general warning i'd also say that operating it beyond limits may just be the cause. I know almost everyone pushes laser diodes beyond their maximums here, often with good results, but you need to accept that this -can- destroy a perfectly good diode quite quickly.

Obviously there is the thing of getting the maximum power out of a diode, but if you want your laser to last a long time respect the maximums - in the rest of electronic design it's common to keep pretty far away from the absolute maximums on any component.

You would not run a 400 mW rated resistor at 350 mW, you'd use a larger one or run it at lower power by other means. Unless you're making chinese phone chargers where you run it a full watt and just wait for it to melt its way out of the plastic case :D
 

paul1598419

Well-known member
Joined
Sep 20, 2013
Messages
14,600
Points
113
I don't see anywhere that OP exceeded the 250 mW rating of this diode. Only that he did not exceed the maximum current rating. I agree that it is more likely it failed for reasons other than ESD, as it was in a build with driver and fairly well isolated from static discharge, but other than not allowing it to wander higher than 25* C, I doubt he did anything wrong.
 

RedCowboy

Well-known member
LPF Site Supporter
Joined
Jul 10, 2015
Messages
7,460
Points
113
Time for a new diode.
 
Last edited:

Benm

Well-known member
Joined
Aug 16, 2007
Messages
8,115
Points
113
I don't see anywhere that OP exceeded the 250 mW rating of this diode. Only that he did not exceed the maximum current rating.
That's a mistake people often make: The datasheet says absolute maximum rating of 250 mW optical output, which -typically- occurs at 340 mA. If you have a diode that is a bit less efficient than average you can increase the current above 340 mA as long as you make use the output power doesnt exceed 250 mW. On the other hand, if you have a more than averagely efficient diode you could already be exceeding the abs max optical power output at 340 mA.

The only way to know is to measure the output power.

People often interpret datasheets like 'if i stay below the absolute maximum current it will be fine', but that's just not correct - you need to stay below the abs max optical power output as well.

And sure, you get away with exceeding that often enough, but it is one explanation of why laser diodes often don't last the number of hours stated in the datasheet, even if there is no ESD or other problem involved.
 

paul1598419

Well-known member
Joined
Sep 20, 2013
Messages
14,600
Points
113
So, your assumption is that he "might" have exceeded the maximum optical output power even though he did not exceed the maximum current rating. That is a mighty big IF. The optical power is a function of the lens assembly used, so even if he measured the output, it might not reflect what the diode was actually putting out. He would need to measure the power of the diode without a lens to be sure.
 
Last edited:

Benm

Well-known member
Joined
Aug 16, 2007
Messages
8,115
Points
113
Afaik the manufacturers refer to raw output for the maximum ratings, so not taking into account any losses from lenses at all.

This would be hard to measure for most people but it's still part of the specification and absolute maximums for laser diodes regardless.

If you have no means to measure the true output power you can stick with the typical current stated in the datasheet to achieve that (340 mA), but don't ever assume the absolute maximum current (430 mA) is something to aim for. That would be the current required to get the worst diodes of the batch to meet the stated optical power output, and most diodes will output far too much if you stick with that figure as a drive current.
 

deadshadow

New member
Joined
Feb 21, 2016
Messages
475
Points
0
Too bad it died, but you should realize you are actually overdriving that laser diode:

The datasheet specifies a couple of things, like
- absolute maximum optical output 250 mW
- maximum current 430 mA

The point is that -neither- of these values are to be exceeded. If the diode is 'typical', it takes only 340 mA to reach that 250 mW output power, and any current above that is operating it out of spec (because you exceed the 250 mW optical absolute maximum) even if it's -far- below 430 mA (say just 350 or so).

Also these maximums are at a case temperature of 25 celcius, which may or may not be realistic depending on your host size/construction and ambient temperature.

Surely static electricty or something could have fried your diode, but as a general warning i'd also say that operating it beyond limits may just be the cause. I know almost everyone pushes laser diodes beyond their maximums here, often with good results, but you need to accept that this -can- destroy a perfectly good diode quite quickly.

Obviously there is the thing of getting the maximum power out of a diode, but if you want your laser to last a long time respect the maximums - in the rest of electronic design it's common to keep pretty far away from the absolute maximums on any component.

You would not run a 400 mW rated resistor at 350 mW, you'd use a larger one or run it at lower power by other means. Unless you're making chinese phone chargers where you run it a full watt and just wait for it to melt its way out of the plastic case :D
the datasheet states max 430ma and i was running it at 410ma,i do have mesured the output in the past and it wasn't passing the 250mw(with g2) but i was using it with a 3 element 638nm lens with 160-170mw output.
the temperature might be a reason also but those diodes aren't hot at all.
what im trying to say is i never exceeded the maximum values of the datasheet while esd or temperature could be a small or big reason for death.

Interesting, Chris. What kind of host are you using for the P73? It would be difficult to TEC cool a HH effectively, is the reason I ask. I see it is a HH in your sig. How are you powering the TEC and removing all that extra heat to the air?
i had made a thread in the past with this build(although with not that many pics) here is the thread : https://laserpointerforums.com/f50/my-handheld-tec-cooled-ml501p73-almost-finished-101861.html
it has a heatsink fan and cycles well the airflow from the heatsink.it also has infinite runtime with the tec on or even off as in that state the heatsink from the tec is quiet big and absorbs the heat from the diode too.
tec is giving a nice boost in output.you can see it on the thread too :) i even pushed it up to 1500+mw if you check the comments
i
 
Last edited:

paul1598419

Well-known member
Joined
Sep 20, 2013
Messages
14,600
Points
113
Thanks, Chris. The reason I missed this thread was because I was in the hospital for a month at that time and was not able to get around well even after getting out. I see it took basically what I thought it would to keep this diode at a low enough temperature to run it constantly.
 

Benm

Well-known member
Joined
Aug 16, 2007
Messages
8,115
Points
113
That's a bit odd with the power output: You should expect 250 mW at around 340 mA for the average diode in the batch, though the one you used might just have been less efficient than average and required a bit more current (which is fine in itself).

One issue is how to actually measure the output of the diode though: The datasheet figure is for the just the diode, no lens at all. This makes measuring the power very impractical, but otherwise you'd have to know how much is lost in the optics.

Another problem could be that the optics reflect a certain amount of light back into the diode, though i wouldn't expect that to be a big problem when using optics with the proper AR coatings for the wavelength.
 

TinLethax

Member
Joined
Jul 19, 2018
Messages
97
Points
8
hello everyone today one of my 1st builds i ever made when i started this hobby died-zombified, althought it was an old build it had very low hours runtime(im guessing somewhere 5 hours).

today i turned it on and noticed it wasn't that bright and after checking the batteries i unfocused the lens and i noticed what is going on from the output shape.after checking it on the lpm it produces something less than 10mw

the diode was running at 410ma while the datasheet suggests max 430ma,so it was set lower than the datasheet.

i played with it on my psu and pushed it at 1.1A and nothing changed(managed to get an output of 30mw at 900ma :p)

here is the output shape at this moment,those diodes look like are very sensitive and maybe static electricity killed it as those are case negative.



not a big lose i just wanted to share it and have it logged in the forum for anyone that will search for this diode in the future :beer:
I also just killed my LPC-840 from the too much current .I tried to push up but maybe the ESD damaged the diode (maximum current before I will disconnect the diode is 270mA).
 

paul1598419

Well-known member
Joined
Sep 20, 2013
Messages
14,600
Points
113
The LPC-840 can take 370 mA and even higher. The best way to do it is to use a high quality driver with it. I have one that is running on 400 mA with a continuous ground adjustable buck driver from lazeerer. It has worked well for several years. I pull it out every few days just to see it again. Nice tight beam at 385 mW.

Actually, the data sheet doesn't say the current can be 430 mA. What it does say is the 840 are rated at 50 mW higher than the 836s are at 370 mA. It is not the same thing. I have one running at 400 mA, but the data sheet still puts the max current at 370 mA.
 
Last edited:




Top