how far can LM317t run before it hits led?

Discussion in 'The Projects Forum' started by StormFish, Feb 3, 2009.

  1. StormFish

    Thread Starter New Member

    Jan 30, 2009
    7
    0
    i was wondering how car can the wire be from the lm317t to the LEDs ... i remember reading somewhere it said it can't go too far from the regulator to the LED's itself

    if you guys can give me examples of what you've done before like 3ft, 5ft or 10ft ... thanks
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    That depends on the current you supply to the LEDs and the gauge of the wire. Generally you want to minimize R.I^2 losses.
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    If you are using long wires remember to the 330nF and 100nF on the input and output of the regulator respectively to avoid any oscillations.
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    As MIK3 said, it is the oscillations that are the reason. The caps should address that nicely, so I wouldn't worry about it.
     
  5. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Ya its there in the data sheet itself... adding caps for longer lengths of wire from filter..
     
  6. StormFish

    Thread Starter New Member

    Jan 30, 2009
    7
    0
    sorry about not leaving the 411 ...

    its going to be on my car .. so about 12v .... with a 22gauge wire ... 3v, 100ma to the leds
     
  7. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    22gage wire will offer .016 Ohms per foot. That's per lead, of course. So a hundred feet with two conductors will total 3 Ohms or so.
     
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