laser diode: undocument temperature protection

Jean-Pierre Coulon

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Aug 24, 2018, 3:49:58 AM8/24/18

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I am working with a laser diode like:
http://dilas.com/assets/media/products/DILAS_MF_808nm-400um.pdf and sometimes
the output power goes to zero for a couple of minutes.

Could there be an undocumented temperature protection in this laser diode?
Anybody having the same trouble?

Regards,
--
Jean-Pierre Coulon

Phil Hobbs

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Aug 24, 2018, 12:56:38 PM8/24/18

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I'd be very surprised if it didn't have overtemp protection.
Thermoelectric coolers are vulnerable to runaway if the heat sinking is
inadequate--at some current the sign of the loop gain changes, so that
turning the current up further makes the cold plate get hotter rather
than colder.

Once that happens, you have to turn the TEC off to keep it from turning
to lava.

Cheers

Phil Hobbs

(Who's designing a similar sort of gizmo as we speak.)

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Jean-Pierre Coulon

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Aug 26, 2018, 5:46:10 AM8/26/18

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On Fri, 24 Aug 2018, Phil Hobbs wrote:

> I'd be very surprised if it didn't have overtemp protection.
> Thermoelectric coolers are vulnerable to runaway if the heat sinking is
> inadequate--at some current the sign of the loop gain changes, so that
> turning the current up further makes the cold plate get hotter rather
> than colder.
>
> Once that happens, you have to turn the TEC off to keep it from turning
> to lava.

They have no TEC and they have a hole for you to put a PT100 or a NTC but
we put none.

I understand what you mean because we also use other smaller models in
DIL14 package with a TEC and a NTC included in this package.

So I was thinking of some weird mechanical alteration with the heat.

Bye,

Jean-Pierre Coulon

Phil Hobbs

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Aug 26, 2018, 2:59:57 PM8/26/18

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Don't think so. Of course the laser threshold is a fairly strong
function of temperature, so if it's running in automatic power control
mode, the supervisor might well turn it off to avoid overcurrent damage.

Any idea how hot it runs?

Cheers

Phil Hobbs

Jean-Pierre Coulon

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Aug 27, 2018, 9:41:16 AM8/27/18

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On Sun, 26 Aug 2018, Phil Hobbs wrote:

> Don't think so. Of course the laser threshold is a fairly strong function of
> temperature, so if it's running in automatic power control mode, the
> supervisor might well turn it off to avoid overcurrent damage.

As I said, there is no supervisor at all.

> Any idea how hot it runs?

About 5 °C above the room temperature. And blowing it with a fan prolonges
the working time.

Bye,
--
Jean-Pierre Coulon

Phil Hobbs

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Aug 27, 2018, 10:50:34 AM8/27/18

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Five degrees at 50 watts dissipation? That's quite the heatsink!

Jean-Pierre Coulon

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Aug 28, 2018, 3:53:44 AM8/28/18

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On Mon, 27 Aug 2018, Phil Hobbs wrote:

> Five degrees at 50 watts dissipation? That's quite the heatsink!

We have a big heatsink!

Bye,
--
Jean-Pierre Coulon

Jean-Pierre Coulon

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Aug 28, 2018, 9:59:46 AM8/28/18

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If no one else has the same problem I think we can close this topic. :-)

--
Jean-Pierre Coulon