Old 04-01-2012, 02:33 AM #1
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Default Theoretical Question

Lets say you had a diode mounted to a heatsink that was 100% efficient in removing excess heat from the diode. What else limits the amount of current that you put through?


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Old 04-01-2012, 02:34 AM #2
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Default Re: Theoretical Question

No heatsink will just be enough in removing the heat from a diode, no matter how efficient. You'll need a fan + heatsink or watercooling if you want to remove heat as a factor.

And the point of diminishing returns limits the output you get from the amount of current you put through.

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Old 04-01-2012, 02:40 AM #3
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Default Re: Theoretical Question

Well the hard limit I suppose is the wires inside the diode melting from to much current
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Old 04-01-2012, 02:48 AM #4
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Default Re: Theoretical Question

Quote:
Originally Posted by mattco2 View Post
Well the hard limit I suppose is the wires inside the diode melting from to much current
But if you had an impossibly good heatsink, wouldn't they not melt?
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Old 04-01-2012, 02:51 AM #5
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Default Re: Theoretical Question

The diode will eventually reach a point where the energy inside the cavity is too great and the semiconductor "chip" will begin to deteriorate. This kind of damage creates "zombie" diodes.

Edit: Even if you surround your diode with an impossibly effective heatsink, the gold plated brass that the semiconductor is attached to (or whatever metal that is) and the semiconductor itself are not perfect heatsinks, so heat will accumulate even if at a slower rate.

Edit again: Come to think of it... what metal is the diode "package" made of? Both "canned" and "uncanned" diodes are magnetic...
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Old 04-01-2012, 02:57 AM #6
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Default Re: Theoretical Question

Ok, so lets say that heat is not a factor. What, besides heat, limits a laser or any other electronic item for that matter?
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Old 04-01-2012, 03:17 AM #7
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Default Re: Theoretical Question

Catastrophic Optical Destruction...

Basically too many photons are flying back and forth in the semiconductor material causing the mirrors to break. That's what causes almost all diodes to die, they're overdriven too much and as a result the mirrors break.
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Old 04-01-2012, 11:58 AM #8
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Default Re: Theoretical Question

Do the bond wires die first or the lasing medium? i guess its diode dependent and if its a instantaneous failure or gradual?
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Old 04-02-2012, 12:24 AM #9
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Default Re: Theoretical Question

I believe it depends on what kind of diode you're talking about.

For some yes it is the die wires just going kaput, others it's just C.O.D.

Usually when a diode C.O.D.'s it's instant, but sometimes there's gradual changes in output where a diode that may have been outputting 1 watt gradually dies and starts to output only say 100 mW.

It's very random from what I understand.
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Old 04-02-2012, 12:29 AM #10
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Default Re: Theoretical Question

I think the facet will break first. Turning them into LED.
Unless you put 10A thru the diode, making a nice firework.
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Old 04-02-2012, 12:30 AM #11
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Default Re: Theoretical Question

The first problem is that there are -always- internal thermal resistances IN the laser diode. No matter what you do to keep the case cool (immerse it in liquid coolant for all i care), the inside still heats up despite the case being at ambient temperature.

COD is probably the mechanism that kills most resonably cooled diodes as it is though, and keeping it at ambient temperature will not prevent it. Perhaps cryogenic cooling could limit the problem, but thats probably beyond the scope of the question.
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