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Thread: thermal shutdown of 445 diode ??

  1. #1
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    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
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    Crikey ! talk about living dangerously !

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

  3. #3
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    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

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    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
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    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.

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    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
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    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

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    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
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    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
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    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.

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