powering 2 DC lasers off of single power source

Discussion in 'The Projects Forum' started by jdub765, Oct 1, 2009.

  1. jdub765

    Thread Starter Member

    Mar 5, 2009
    15
    0
    I'm trying to power two of these green lasers:
    http://cgi.ebay.com/532nm-Green-Las...in_0?hash=item2301a1f6e5&_trksid=p3286.c0.m14
    off of one power source. Eventually, it'll be a 12v -> 3v converter, but for now, I'm using two AA batteries.

    Powering a single laser is no problem, but if I hook up the second laser in parallel while the first one is hooked up, the first one shuts off and neither works.

    How can I get this to work?
     
    Last edited: Oct 1, 2009
  2. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    Can't be sure but I think these are basically a glorified LED. It is better to operate them with a constant current.

    A simple way to get started is to put a resistor in series with each one. This forces current sharing.

    It says it takes 300mA at 3V. So if you put a 3.3 ohm in series with each one and used a slightly higher supply voltage of 4V, this should work. For testing I would use a variable power supply and raise the voltage slowly.

    It might be possible to connect them in series and use a 6V supply but you would have to be careful. Once again, test with a variable power supply.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Depends, they likely have built in drive circutry, in which case you don't want to screw it up guessing. Green lasers are anything but LEDs, though they do have some generalities in common. They usually start off as IR lasers, and feed through a specialized crystal that upconverts most of the IR laser to green (which is X2 the frequency of the IR). The high quality ones then filter out the IR laser, the low quality ones don't. This can be bad, since IR doesn't trigger the avoidance response which makes your eye avert if it is exposed, and with some mirrors (and prisms) the IR laser goes one way while the green laser goes another.

    If you look at the OP link it shows the circuitry I was talking about.

    I would give each laser it's own regulator chip from the common power supply, making sure it was well filtered. It is possible that there is a digital power supply regulator (similar to a buck boost power supply) built into the laser power supply, and the signals are interfering with each other.

    The other approach is something like a Pi filter for each laser to isolate them from each other.
     
  4. jdub765

    Thread Starter Member

    Mar 5, 2009
    15
    0
    Thanks for all the info!

    Hmm... I guess any circuit to isolate the two lasers would cause a voltage drop, and I already ordered one 12v to 3v adaptor when I ordered the lasers... Maybe I ought to just buy another adaptor...
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    The Pi filter might work, and should be a bit cheaper. Build one for each laser, you can wind your own coils.
     
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