Temperature controller

Discussion in 'General Electronics Chat' started by manuel09, May 2, 2010.

  1. manuel09

    Thread Starter Member

    Aug 29, 2009
    15
    0
    I just tried to use LM317 input 24vdc output 21.5~22V and have a good result , Thank you for all advises.
    (240R+trimmer 5K) direct to 6leds, at this time just try without additional resistor stable at 490mA. I would like to drive at maximum 750mA by change the resistor value.
    Prevent overheat, I need to add temperature controller please advise for simple scheme precision.
    Assumed critical temperature 50deg C and ideal 35-38C max.
     
    Last edited: May 2, 2010
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The original thread got a bit tangled -http://forum.allaboutcircuits.com/showthread.php?t=31738 , so I have placed the new question in a new thread.

    We need more input from you - what are some parameters? How much power has to be controlled? How precisely must the temperature be maintained? What factors might cause problems?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The LM317 really needs about 3v "headroom" when used as a current regulator.

    This is based on the typical dropout of 1.7v, plus the nominal Vref (measured from the OUT terminal in respect to the ADJ terminal) of 1.25v; 1.7v+1.25v = 2.95v. However, the dropout varies as a function of current through the regulator and the temperature of the regulator.

    See the "dropout voltage" plot in National Semiconductor's datasheet for the LM117/LM317, page 6, 2nd down on the right.
     
  4. manuel09

    Thread Starter Member

    Aug 29, 2009
    15
    0
    In regards driving 6leds @3W in a string, what do you think to LM317
    is this good choice or any other convenience ICs?
    I choose this thought easy and very simple, but not sure is this common or not pls advise because I have a plan to make 6 parallel in a board.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    In this case, "3W LEDs" is rather ambigous.

    We also need their Vf @ current rating.

    However, I suspect that you're going to need something like a BuckPuck to drive them.
     
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