Author Topic: Laser diode identification  (Read 2285 times)

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Offline AlcidePiR2Topic starter

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Laser diode identification
« on: April 18, 2020, 01:21:29 pm »
Dear All,

I made a mistake. I desoldered these laser diode ( from a HP Laser printer board RM1-4756) before noting the pinout.

In any case, this would not have been sufficient to identify the laser diode.

Can any of you can help me on this ?

- identification of the laser diodes ?
- identification of the pinout ?

And as well for the phototransistor  photodiode ?  written 9Z AL ??

Thanks
« Last Edit: April 24, 2020, 04:06:07 pm by AlcidePiR2 »
 

Offline AlcidePiR2Topic starter

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Re: Laser diode identification
« Reply #1 on: April 24, 2020, 04:08:07 pm »
Really ?  Nobody on this one ?

I have searched on my side but I am quite frightened to see the variety of pinouts  for laser diodes.

I see also that many have reverse voltage limit of only 2 V, so I dont want to try too much randomly.

Best Wishes to all. 
 

Online NiHaoMike

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Re: Laser diode identification
« Reply #2 on: April 24, 2020, 04:33:38 pm »
http://repairfaq.org/sam/laserdio.htm#diodct2
Quote
After having played with several CD and CD/RW diodes, I believe that it is possible to determine the pinout to a high degree of confidence without applying any significant power to the laser diode.

All that is needed is a voltmeter (rather a millivoltmeter) and an operating incandescent lamp (tungsten filament like a pocket flashlight). If you direct a light beam to the device under test and measure the voltage between common and each of the other two pins you will find two of the four following possibilities:

    About +500 mV. This is a PD anode.
    About -500 mV. This is a PD cathode.
    About +5 mV. This is a LD anode.
    About -5 mV. This is a LD cathode.

The large difference is due to the fact that the photodiode is a much more efficient converter of light to electricity although both the PD and LD work as photo cells. The above figures depend on the intensity of the light but there will be no mistake: The PD voltage will always be much larger that the LD voltage.
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Offline ChristofferB

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Re: Laser diode identification
« Reply #3 on: April 24, 2020, 04:36:10 pm »
They have no markings at all?

Why dont you look up one of the 4 driver ICs and use its pinout to find what connects to what?

Alternatively make a current limited 2V supply and just try all combinations. (Without shooting your eye out!). Sacrifice one of the diodes. I'm not even sure it would damage it to be reverse connected briefly.

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Offline Gyro

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Re: Laser diode identification
« Reply #4 on: April 24, 2020, 04:59:06 pm »
Note that bare Laser diodes like that are very ESD sensitive. You need to handle them with care.

The 8 pin "photodiode" is actually an IC with active circuitry on it. It looks as if pin1+pin5 and Pin 3+6 are supply and ground (but not clear which polarity).. Pin 2 looks like the output, and pin 4 either a power-on reset or an internal bias supply (capacitor connected to supply or ground).
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Offline AlcidePiR2Topic starter

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Re: Laser diode identification
« Reply #5 on: April 25, 2020, 04:07:32 pm »
http://repairfaq.org/sam/laserdio.htm#diodct2
Quote
After having played with several CD and CD/RW diodes, I believe that it is possible to determine the pinout to a high degree of confidence without applying any significant power to the laser diode.

All that is needed is a voltmeter (rather a millivoltmeter) and an operating incandescent lamp (tungsten filament like a pocket flashlight). If you direct a light beam to the device under test and measure the voltage between common and each of the other two pins you will find two of the four following possibilities:

    About +500 mV. This is a PD anode.
    About -500 mV. This is a PD cathode.
    About +5 mV. This is a LD anode.
    About -5 mV. This is a LD cathode.

The large difference is due to the fact that the photodiode is a much more efficient converter of light to electricity although both the PD and LD work as photo cells. The above figures depend on the intensity of the light but there will be no mistake: The PD voltage will always be much larger that the LD voltage.


Thanks a lot. The web site is very informative. And the method to test very simple and effective.
I used a small  650 nm laser diode to test, at low power, otherwise it saturates both sides.

I could have ~ 300 mV on one side ( thus PD) and only 5 mV on the other ( LD).

Now I can go further and test the polarity.

 

Offline AlcidePiR2Topic starter

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Re: Laser diode identification
« Reply #6 on: April 25, 2020, 04:10:33 pm »
They have no markings at all?

Why dont you look up one of the 4 driver ICs and use its pinout to find what connects to what?


This is of no use.  I dont know  the side it was soldered  on the board. Otherwise I would have just read what is written.
I can do that to check the polarity.
 


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