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Topic: Help identify a laser diode (Read 232 times) previous topic - next topic

cloxart

Hello everyone,
I need to change a laser diode but all that is written on it is Q 8C on the bottom (nothing on the side) (picture attached)
anyone have any idea on how to find a suitable replacement?

Thank you!

arduarn

No idea, but it might help if you tell us exactly what device it comes from and maybe post good pictures of the front and the back of the PCB as well.

Paul__B

#2
Nov 19, 2018, 05:19 am Last Edit: Nov 19, 2018, 05:20 am by Paul__B

That's about the size of it.

cloxart

Here are more pictures... it is a temperature sensor

cloxart

attachments not present for some reason... here they are

arduarn


MarkT

#6
Nov 19, 2018, 12:18 pm Last Edit: Nov 19, 2018, 12:19 pm by MarkT
No more information?  The markings on that 8 pin chip would be useful, bit too dark in those photos.

Reverse-engineering the circuit might show how the laser is being driven (constant current usually)
and might show what current value is involved, enabling choice of a compatible laser diode.

Current level is critical for laser diodes, too much and they pop, too little and they will fail to lase
reliably.

You could hook up a power LED in its place with an ammeter in circuit and measure the current?

Although if its PWM modulated that would complicate things. (This can be done to reduce heatsinking
requirements for instance)

Is this basically just a laser pointer for indicating the direction on an IR temperature sensor?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

cloxart

No more informations I am afraid, just that "Q 8C" on the back.

"Is this basically just a laser pointer for indicating the direction on an IR temperature sensor?"

No, the laser diode is used as a sensor itself. ( I suppose measuring the feedback pin when the laser diode is NOT powered on ) and also as a pointer that you activate only when you need to aim the sensor. It is used to measure temperature on metal during welding (between 600 and 700 C) and there are NO other components in there so the only way I can see that working is that the photodiode inside the laser diode package is used as a sensor. That is why I need to get the exact part, in order to be sure that the output is the same.

The two IC are both TLC272CP which are operational amplifiers, that are probably used to amplify the feedback pin signal to a level that is usable to the machine controller.

MarkT

laser diodes are very different from LEDs and normal diodes, no way this thing is a laser diode - xyproblem
again - you guessed wrong, you didn't tell us you guessed something...

Its probably an near IR sensor of some sort, perhaps a standard photodiode, perhaps not.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

cloxart

#9
Nov 19, 2018, 12:45 pm Last Edit: Nov 19, 2018, 12:46 pm by cloxart
MarkT,
When the device is in operation it DOES emit a laser beam for aiming, that is why I am pretty sure it is a laser  diode. the only thing I am "assuming" is the way in which it is used as a sensor

MarkT

#10
Nov 19, 2018, 01:09 pm Last Edit: Nov 19, 2018, 01:09 pm by MarkT
Interesting - a laser diode device is heavily optimized for lasing, with quantum well and waveguide
structure - not the first choice for a photodiode for measurement.

In that case getting the right device is probably crucial as the circuit will have been custom matched
to properties of the diode that even the manufacturer hasn't measured...   Talk to the sensor manufacturer
seems the only course of action.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

cloxart

That is exactly the reason why I need to know the right part number and not a generic replacement...

I tried to contact manufacturer and all they can do is replace the whole unit... I was hoping that someone could make sense of that "Q 8C" number...

arduarn

So who is the manufacturer and what is the exact product?

cloxart

The manufacturer is a small company in italy. the device is the sensor of a temperature controller to be applied on an induction welding machine. I called them and they are not really happy for me to find out all of their precious "secrets". they only offered to replace the whole sensor unit, but the price for that is about £600, while I could repair it for the price of the laser diode... (I am sure that the diode is the problem because I have another unit and swapping the laser diode everything works)

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