Results 1 to 10 of 10

Thread: thermal shutdown of 445 diode ??

  1. #1
    Join Date
    Dec 2006
    Location
    Netherlands
    Posts
    964

    Default thermal shutdown of 445 diode ??

    the other day I took the 445 diode out of its heatsink to project's its uncolimated beam, however after running for say 20 sec's at full blast it completely turned off.. Thought I lost the diode but it seems to work fine again. Obviously I did not repeat the process. All solder concretions were fine so what could it be? I'm speculating that the lasorb may have acted when the diode's forward voltage went up due to heating of the diode ?????
    Any ideas on this?

  2. #2
    Join Date
    Aug 2010
    Location
    London or Spain depending on the weather
    Posts
    1,381

    Default

    Crikey ! talk about living dangerously !

    Cheers
    Last edited by catalanjo; 09-14-2010 at 03:47. Reason: religion

  3. #3
    Join Date
    Nov 2007
    Location
    Cairns, Australia
    Posts
    1,896

    Default

    I'm not going to explain this very well, I know little on the subject, but I'd say the more likely scenario is your diode got hot enough to "shift" the lasing medium into an inefficient state.

    Thats not the proper way to explain it. Let me try this.

    Diode lasers are just like DPSS lasers. The crystals involved all require specific operating temperatures to work efficiently. If you heat the crystals too much, they require much more power to produce the same amount of light. If your driver doesn't allow it to have the extra power, it'll just appear to be dimming, to the point where it'll be almost 0% efficient.

    Same happens with diodes, if you exceed their operating temperature, the lasing medium will operate less efficiently, requiring more power.

    Gave it a shot, hope it's readable

    Cheers,
    Dan

  4. #4
    Join Date
    Apr 2006
    Location
    Miami, FL
    Posts
    3,580

    Default

    Quote Originally Posted by Zoof View Post
    the other day I took the 445 diode out of its heatsink to project's its uncolimated beam, however after running for say 20 sec's at full blast it completely turned off.. Thought I lost the diode but it seems to work fine again. Obviously I did not repeat the process. All solder concretions were fine so what could it be? I'm speculating that the lasorb may have acted when the diode's forward voltage went up due to heating of the diode ?????
    Any ideas on this?
    my diode did the same thing without a lasorb... its just a design thing I guess?

  5. #5
    Join Date
    Sep 2006
    Location
    Netherlands
    Posts
    1,411

    Default

    I don't think its a protection feature by design.
    If some kind of 'micro clixon' was built in series somewhere, that would protect the diode initially. But when the microclixon would cool down enough to reset, it would instantly set the openloop voltage of the driver over the diode. Especially unwise because the diodes are run in series. That makes a parallel clixon also unlikely.

  6. #6
    Join Date
    May 2009
    Location
    UCSB
    Posts
    681

    Default

    Can anyone confirm/deny that the current through the diode did not change when it went dark?

    Having looked at the diode under a microscope I can say pretty confidently there is no structure added to the die for this purpose, and the effect is unintentional.

    It is more likely to be as Things described, that there just isn't enough gain at high temperatures to get any lasing.

  7. #7
    Join Date
    Apr 2006
    Location
    Miami, FL
    Posts
    3,580

    Default

    well mine released smoke when it went over temp from not being in a heatsink... then like a minute later I tried it again and it was working fine

  8. #8
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,488,805

    Smile

    Released smoke? And it still worked after it cooled off?

    Damn these diodes are tough! Never heard anyone saying that about a long open-can red!

    Adam

  9. #9
    Join Date
    Apr 2006
    Location
    Miami, FL
    Posts
    3,580

    Default

    ya i was trying to look at the raw output not thinking, hey, this thing needs a heatsink... so im like, ooo look at the pretty blue... hey its dimming... hey smoke!

    power off...

    wait wait wait

    reheatsink, reapply power, bam back in business

  10. #10
    Join Date
    Jul 2009
    Posts
    24

    Default

    Definitely not an intentional effect.

    Temperature increase, in essence, causes a threshold current increase, which decreases power output at a given current level (ie, if current stays the same and threshold current increases, then current-above-threshold decreases, and it is current-above-threshold which gives output power).

    As it heats up, power will drop. This is why you get roll-over (decrease in slope) in an L-I curve for a laser diode, instead of a straight light up from threshold with a constant slope.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •