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Thread: Fear of the black cat

  1. #1
    Join Date
    Jul 2008
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    108

    Default Fear of the black cat

    So, I bought a 250mw green laser as the centerpiece of my RGB laser system. It came with the standard TTL driver. I saw a Chinese company selling analog driven lasers and asked them if I could buy just the analog driver. They said: Only an engineer can match the driver to the laser. BUT, they sold me a driver anyway for cheap. So, I yanked the 5W current control resistors for the diode and the TEC driver out of the TTL driver and swapped them out in the new analog driver.

    First thing: @ 5V, the analog driver was cranking the diode to 400mw. So, the electronics themselves were different between the TTL and analog drivers. BUT, the analog driver has a resistor pot to control the upper limit of the +5 control voltage. So, I tuned down the "pot" so the power meter showed 250mw at 5V.

    Question to you all is this: Now that the maximum output of the laser at 5V is the maximum is was initially...does that mean I was successful and transplanting the driver? Or is there something else going on that will bit me in my arse down the road?

    Cheers!

  2. #2
    Join Date
    Jan 2006
    Location
    Charleston, SC
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    2,147,489,073

    Cool

    Yes, there are other things going on (feedback and feedforward control to the pair of TEC's in the head), but whether they'll bite you or not is anyone's guess. If they do bite, it will be in the form of "jellybeaning", or power instability (and non-linearity) when you modulate the laser. If you experience this, you may be able to reduce the effect by tweaking the TEC circuit. This is the "only an Engineer can do it" part that they were talking about, and while you don't need to be an engineer, it *is* difficult to get it right.

    Adam

  3. #3
    Join Date
    Jul 2008
    Posts
    108

    Default

    Quote Originally Posted by buffo View Post
    Yes, there are other things going on (feedback and feedforward control to the pair of TEC's in the head), but whether they'll bite you or not is anyone's guess. If they do bite, it will be in the form of "jellybeaning", or power instability (and non-linearity) when you modulate the laser. If you experience this, you may be able to reduce the effect by tweaking the TEC circuit. This is the "only an Engineer can do it" part that they were talking about, and while you don't need to be an engineer, it *is* difficult to get it right.

    Adam
    Yes, I was concerned about that. That's why I was careful to swap the current resistors on the TEC regulator control line. Also, I broke open the laser and measured the temps of the diode and the hot side of the tec. As the diode heated up to 35c, it locked at that temp and the hot side of the TEC began taking on the load. So, all in all, I feel pretty safe.

    Although, prior to tuning down the +5 current, the laser ran at 500mw (rated at 250mw) for about 20 seconds. WOO WEE...got some serious smoke coming off my target for that duration.

  4. #4
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,489,073

    Default

    Quote Originally Posted by FrankenPC View Post
    Although, prior to tuning down the +5 current, the laser ran at 500mw (rated at 250mw) for about 20 seconds. WOO WEE...got some serious smoke coming off my target for that duration.
    Heh! Nice to know you've got some headroom on that laser then. Keep it running at 250 mw and it should last you a long time.

    Based on your measurements, you may be OK. The proof will be when you modulate the laser. If your power response is more or less linear as you ramp up the blanking voltage, that's a good sign. If you don't see any power fall off when you modulate it rapidly, then you're golden.

    Adam

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