Turn LASER on/off with microcontroller

Discussion in 'General Electronics Chat' started by CVMichael, Aug 11, 2012.

  1. CVMichael

    Thread Starter Senior Member

    Aug 3, 2007
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  2. #12

    Expert

    Nov 30, 2010
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    Don't try to modify the laser driver. It doesn't have any place to just shut it off. Use a big transistor in place of the switch.
     
  3. chrissyp

    Active Member

    Aug 25, 2008
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  4. CVMichael

    Thread Starter Senior Member

    Aug 3, 2007
    416
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    I don't have a LM2941, so I used transistors to drive the LASER from a PIC microcontroller.

    I had to put a heat sink on the LM317 because it's getting very hot. The laser is taking over 300mA

    I attached the schematic of the driver I created, and I tested it with a PIC that is powered at 3.2V, and it turns on/off the LASER just fine...

    Is there anything I can do to lower the number of parts in my schematic?
     
  5. #12

    Expert

    Nov 30, 2010
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    Take out that 22 ohm resistor so the current goes down to 250ma, as in the original design.

    There is more to discuss but the idea that you're working with what you have makes it a short list.
    A MOSFET would work for Q2 and Q3 if you had the right kind.
    Q2 could disappear if you were willing to waste 10 to 30 ma through R2.
    That drive current would be less if you had a transistor with better gain.
     
    Last edited: Aug 12, 2012
  6. chrissyp

    Active Member

    Aug 25, 2008
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    your LM317 is wired incorrectly ,the resistors should be in the output and the adjust should be connected to the load side of the resistors,BUT why so many resistors ,why not just use a 5Ω.
     
  7. #12

    Expert

    Nov 30, 2010
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    I missed that. Move the LED from pin 2 to pin 1. That will make the regulator actually regulate.
     
  8. CVMichael

    Thread Starter Senior Member

    Aug 3, 2007
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    Actually on my test PCB I have the LASER connected to ADJ, but I made a mistake when I made the schematic :D I will update the schematic when I get home.

    I put the 22 ohm resistor because the laser a was a bit brighter :) I took it off now...

    I did not put a 5 ohm resistor because I only have 5 ohm 1/4w, and it was getting hot. I used 2, 10 ohm 1/4w resistors, and now the resistors get warm, so it's better now...

    I still don't know how to use MOSFETs yet... can you please modify my schematic to work with a MOSFET?
     
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