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Thread: Stan_Ham diode driver (analog)

  1. #11
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    Now that i think of it.....
    Why would softstart be something we wan't?

    It is better for the diode?
    what about the DVD burners where diode's are used in and what about modulating the dioded like we do?
    thats alot of fullpower ON OFF ON OFF.. so softstart there.

    Would it really hurt a fast semiconductor/diode?

  2. #12
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    Anthony
    Steve is right and a softstart would prevent the diode being damaged by transients on the power supply as its turned on not as it is modulated. I have thought about this in the past but have not got round to implementing it and this circuit has worked for me with no probs in my RGB for 2 years. Ok I know that does not mean it cant have a problem....


    Rob
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  3. #13
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    Would that be the first place you would suspect if you had a faiure?

  4. #14
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    Quote Originally Posted by stanwax View Post
    Anthony
    Steve is right and a softstart would prevent the diode being damaged by transients on the power supply as its turned on not as it is modulated. I have thought about this in the past but have not got round to implementing it and this circuit has worked for me with no probs in my RGB for 2 years. Ok I know that does not mean it cant have a problem....


    Rob
    Rob,

    i can understand that a softstart is nicer on the diode when used in an non modulated form.

    We use the modulation to turn on the laser.
    Wen i power on the driver, the diode is off until i start modulating.
    The powerled/caps etc are al powered on before modulation.

    maybe i don't understand the concept entirely. :-)
    i'm no electrocs expert like you guys

  5. #15
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    The modulation takes place when the supply line is (hopefully) in a steady state, but during the power up nanoseconds spikes on the power supply line can provide the killer dose of electrickery that the diode cannot stand. So the modulation, no matter how fast does not (or should not) provide a spike but the PSU start could.

    Rob
    If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
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    Laserists do it by the nanometre.

    Stanwax Laser is a Corporate Member of Ilda

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  6. #16
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    Quote Originally Posted by stanwax View Post
    The modulation takes place when the supply line is (hopefully) in a steady state, but during the power up nanoseconds spikes on the power supply line can provide the killer dose of electrickery that the diode cannot stand. So the modulation, no matter how fast does not (or should not) provide a spike but the PSU start could.

    Rob
    ok,

    So C1 and C2 cant handle the nanosecond spike because they act to slow?

    Maybe we could improve the driver as a combined PL efford.
    Could be a nice solution for alot of people.
    maybe something good comes out of the TEC controller topic.

    having a nice tec controller and a nice diode driver should be a dream com true for alot of DIY people.

  7. #17
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    I will get round to doing something about this but its not been that important in my list of jobs .
    There are several ways to do it but slow ramp up of the diode current from cold start plus good input protection on the PSU connectio is the way to go.

    Rob
    If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
    -----------------------------------------------------------------------------------------------
    Laserists do it by the nanometre.

    Stanwax Laser is a Corporate Member of Ilda

    Stanwax Laser main distributor of First Contact in UK - like us on Facebook http://www.facebook.com/FirstContactPolymerCleaner
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  8. #18
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    I used a dual version of this Cct of Robs on my twin red/pbs set up on my ALC68. It worked a treat
    Easy to set up as well.
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  9. #19
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    die4drive has slow start. you could take a look at it as an example of how to do it I suppose. I have wondered how slow start effects modulation speeds.

  10. #20
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    Gary
    As far as Im aware what you need to do is apply the slow start to the first diode turn on, therein afterwards the modulation should not be affected - or at least that should be the aim of the design. The Roithner EU38 has a real slow start on it and you can see the laser ramp up over about a second and a half but this has no modulation....
    I guess what you need is to ensure the diode is held hard off during the power phase and remains in this state until the power has settled. Probably only needs a short time - maybe 100ms would be way more than needed so a couple of seconds should be belt n braces.
    Like I said I will get round to looking into this but its at about 489th in the queue at present

    Rob
    If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
    -----------------------------------------------------------------------------------------------
    Laserists do it by the nanometre.

    Stanwax Laser is a Corporate Member of Ilda

    Stanwax Laser main distributor of First Contact in UK - like us on Facebook http://www.facebook.com/FirstContactPolymerCleaner
    www.photoniccleaning.co.uk

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