lm317

Discussion in 'The Projects Forum' started by Gadersd, Jul 11, 2013.

  1. Gadersd

    Thread Starter Member

    Dec 8, 2012
    98
    1
    How do I use the lm317? I saw this circuit and I am curious on how the lm317 controls the voltage and current. Does current flow from the adj pin to the vout pins or the other way around?
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
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    The scehmatic is too small to see properly, but I think it is a just a "LM317 used as a constant current source".

    You could google that phrase for more info, all it normally needs is a LM317 and a resistor, and the resistor value sets the constant current.
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,227
    The LM317 regulates by adjusting the VOUT current to maintain a constant 1.2V between the ADJ pin and the VOUT pin. So the output voltage/current depends upon how external resistors are connected to the circuit.

    The LM317 data sheet shows how to use it.

    Only a small bias current flows out of the ADJ pin.
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,716
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    You really need to provide a better image. Get in the habit of viewing the image after you make your post to ensure that it is readable and editing as needed.
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    Its a Constant Current source from the battery driving your Laser Diode.


    Like this circuit
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,093
    3,031
    Gadersd, I told you in your duplicate thread on this topic that your image was too small and that the circuit was a constant current arrangement. It's not cool to start multiple threads and waste people's time with the same thing over and over.

    This thread of your's is barely different as well. Why not start a single thread on "Laser diode driver" and keep the discussion in one place?
     
  7. Gadersd

    Thread Starter Member

    Dec 8, 2012
    98
    1
    Now I understand how to output a constant current with it. What voltage will it output in Dodgydave's example?
     
  8. wayneh

    Expert

    Sep 9, 2010
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    Voltage will vary with the load, to maintain the current. You cannot control both at the same time unless you have a constant power controller.
     
  9. Gadersd

    Thread Starter Member

    Dec 8, 2012
    98
    1
    Will it try to output as much voltage that is required for the current?
     
  10. wayneh

    Expert

    Sep 9, 2010
    12,093
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    Yes exactly. That voltage will be limited to the supply minus the dropout.
     
  11. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,004
    1,523
    I'm totally surprised that all of the OPs threads on this topic haven't been shut down. From the electronics knowledge he's showing, doesn't any one see the folly of helping to build a "burning laser"? Almost every one of the posts, he asks about overdriving the module, I only see this with a bad out come.:(

    Or are you guys figuring he'll never get it to work and let the smoke out of his laser module?

    @Gadersd, a burning laser is not the ideal first project!! A working one can be very dangerous. To yourself or others. May be you should build a few smaller projects first and work your way up to this?
     
  12. wayneh

    Expert

    Sep 9, 2010
    12,093
    3,031
    I've never been able to figure out when threads get closed and when they do not. No automotive, no rail guns or perpetual motion, that's all simple enough. But general safety seems to be case by case. That's probably fine, but I waffle between "free exchange on any topic without judgement" and "this mope needs to be protected from himself".
     
    shortbus likes this.
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