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Thread: Diode in laser Head

  1. #1
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    Question Diode in laser Head

    The protection diode on the CNI 473 that I am replacing the pump diode on has been physically broken in two (by me not by a fault). It is located just outside the laser head and is in parallel with the pump diode.
    The only markings that I can still make out are 5T , does anybody know if this is a schottky or zener and which one will it be?
    Any help appreciated.

    Jim
    Attached Thumbnails Attached Thumbnails diode in head.JPG  

    Last edited by JimBo; 02-20-2007 at 11:47. Reason: include picture

  2. #2
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    Jim Its very likely just a diode ie 1N4148 put in reverse across the LD to protect against current in the wrong direction. I had some 808nm diodes from SDL that had them bonded next to the LD chip. It helps protect from nurks who hook em up wrong. You may wanna put in something a little more beefy i.e. a 1N4001 that can handle a bit more juice tho. the lowly 1N4148 can take some nasty treatment before death.

    Rob

  3. #3
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    I was wondering if it was for over voltage rather than polarity.
    The driver puts out 4.45v to the LD without the protection diode which seems a little high.

    Jim

  4. #4
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    the volts are (mostly) of little significance. An LD driver is a constant current supply - the diode by its nature will regulate the volts to what ever it needs if that makes sense (im trying to simplify). I think Im right (and stand to be corrected if im not) that Ion laser tubes do this also. The PSU need to be in the right ball park but the current regulation is the more important characteristic.
    As long as it provides no more than the max current and keeps nasty spikes and the like at bay it will work.
    If you wanna test this daisy chain some silicon diodes together 3 or 4 will do this will give you around 2 volts drop. Turn the current down on the driver and power it up. Then, while monitoring the current, turn up the driver and measure the volts on load. Im sure it will not be 4.45v.

    Rob

  5. #5
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    I must admit I forgot that it is CC rather than voltage

    Jim

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