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Thread: Bizarre simpledrive II driver problem

  1. #21
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    ... the posted curve shows "manual" switching of an old prototype driver with three parallelized LM338 constant current regulators, so not the really used "pulse trains" for laser-engraving - this initial "slope" could be caused by contact resistance from the mechanical switch, so not typical for this type of driver -- the next days I want to rebuild the old LM338-driver with better signal feeding and digital switching, so can post some more images then ...

    A more actual constant-current driver with OpAmps and MOSFET's gives this waveform when switched with 25 microsecond long pulses with a current of 12 Amps (measured 1.2 Volts across a resistor with 0,1 Ohms):

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    With the last driver I've reduced the negative OFF-spike to some ten Milliamperes and trying to eliminate it totally ...

    Viktor

  2. #22
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    I have a question concerning the Simple Drive V2500 r4 and on turn on I do see some noise and this was the worst I saw just using a diode for protection, I think this is a good reason to use a LASORB and not a switching diode, but my questions is this abnormal ?
    Click image for larger version. 

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    with a LASORB
    Polk SDA SRS, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

  3. #23
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    I do not know what or how you measure, but the typical capture of a signal from load (0.1R + NUBM08) when the driver starts at 20KHz input looks like this
    Click image for larger version. 

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    When I do the same thing but using a switching power supply + my PC and the desk LED lamp is on
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    Your capture looks like you added a ceramic capacitor to the input of the oscilloscope, may be lasorb have at least 0.1uf inside?

  4. #24
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    The scale on one is a signal of 2.89v and the other 0.5v. Maybe its the exact same noise but it looks bigger because the signal is smaller.

  5. #25
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    Bbe, for some reason I cant see your pictures, they did not load.

    I had my scope connected directly at the laser diode with the probe set to 1X
    Polk SDA SRS, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

  6. #26
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    I uploaded them to the forum, they have a standard jpeg extension, this is strange...
    they did not load.
    Do you mean that you measure the voltage on the diode directly and not the current?
    I had my scope connected directly
    What kind of signal do you use for modulation on your capture? What kind of diode? V/div?

  7. #27
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    the volts per division are in the images , the one with the LASORB is a 520nm 50mw laser diode and the other is a 505nm 35mw diode with a switching diode for reverse protection, I had to have the scope in one shot triggered mode to capture the quick start on and the modulation is a 5 volt dc voltage, so no modulation if you will.
    Polk SDA SRS, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

  8. #28
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    Hi Draco,

    BBE's pictures are showing up just fine for me and at least some others on the forum, so I don't know why you wouldn't be able to see them.

    This may not be the relevant to your original question, but for those low current diodes you should be using the Simpledrive v500mw. The zero pot on the v2500 is hard to set so that rise times on your diode are timely. I don't know what it looks like on a scope, but when doing grey-scale adjustments, it looks like this:

    Click image for larger version. 

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    This can be mostly addressed by following some zero adjustment instructions that BBE came up with, but you have to be quite precise with the pot adjustment.

    -David
    "Help, help, I'm being repressed!"

  9. #29
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    I do not know the true I-V characteristics of these diodes, so I'll give specs of PL520 as an example. Why can we see some chaotic voltage surges when power is applied? We measure the voltage at an infinite load resistance, which is not entirely correct and another fact is that the power FETs has some source-drain/source-gate etc parasitic capacitance, and it takes some time to charge it. No electronic start delay will be able to catch this pulse, only a mechanical relay is able to do this (but we will have other issues with relay). It is also possible to use a shunt capacitor with a low ESR, but using a capacitor will result in an increase in the rise/fall time. Are these impulses dangerous? As we know, a laser diode is a device consuming current. Only the reverse voltage (at which the diode has infinite resistance) or a forward voltage exceeding a certain value (at which the forward current exceeds the permissible value) can damage the diode. For the Osram PL520, we should see any signals/spikes with an amplitude above 6 volts (or any reactive/negative voltage) so that we can suspect that they can kill the diode.

  10. #30
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    Hello dkumpula

    I can see your picture but yeah I don't know why I cant see the other two.

    I have never seen the Simpledrive v500mw listed, never knew that existed, I don't remember when I ordered the v2500 that I am using but it has been in use for some time and have never adjusted the Zero setting or the bias.

    knock on simulated wood I have only had one diode fail while on a v2500, could it possibly be an internment fault with the connectors?
    Polk SDA SRS, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

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