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Author Topic: 4 pins on my laser diode instead of three? What should I do?  (Read 1405 times)
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I salvaged a laser diode from a broken DVD player. But the laser diode has 4 pins instead of the usual 3. One of them has an arrow pointing out, but none of the others have labels. What should I do?
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From a bit of Googling it seems likely that the device has two lasers (probably IR and Red) and the usual photodiode to allow the drive circuitry to keep the current at optimal level.
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Were they all connected in circuit and to what...? is it possible the extra leads are mounting 'lugs' or that the photo-sensor is un-grounded or the laser for that matter. soldering the laser pellet to a substrate of Be02 or alumina is commonly done. is very effective as a heat conductor as anyone who has had to fix any electronics stuff so mounted knows and anything on the alumina is very well isolated and very well cooled as alumina is a GREAT conductor of heat. Just a few possible explanations.. More.

Doc
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All of the pins have connections to flexible circuitry on the back.
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I wonder it that might have been something of index reader for the index marks on a lightscribe disk. Those disks do have a full set of marks around the inside edge for indexing the disk for printing text with the laser, just looked at a disk to make sure...

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I don't think you connected the grounds, Dave.
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Quote
I wonder it that might have been something of index reader for the index marks on a lightscribe disk
But the index marks can be several centimetres from the read/write head.
There's probably a different sensor altogether for the indices.
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You need to know the specifications to run a laser diode, the operating current has to be kept within fairly tight limits to ensure lasing (and prevent burn-out).  You may have to guess these values if you don't have a part number or other identification - most CD drives of the same write-speed should have similarly spec'd diodes.  It will require a heat-sink I think.
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Ok.
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