current limiter

Discussion in 'The Projects Forum' started by xmen33, Feb 9, 2012.

  1. xmen33

    Thread Starter New Member

    Aug 27, 2011
    20
    0
    Hi,
    I went to make a simple current limiter 3A and can deal with 12V.
    What about using 2 parallel LM317T or is there are any better way to do this ?
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    How accurate does it have to be? Do you want a source or a sink?

    If you don't need extreme accuracy BJT transistors are natural born current limiters. The parts count can be pretty low using them, even at high currents.
     
  3. xmen33

    Thread Starter New Member

    Aug 27, 2011
    20
    0
    I will use it to supply a Unipolar stepper motor drive .
    I will use 3 driver and each drive will put limiter to it.
    I using tip122 to drive the motor and here the circuit
    [​IMG]
     
  4. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,227
    This may do what you need. Q2 in the circuit is your tip122 transistors. For a 3A limit, R2 should be ≈ 0.22Ω. R1 should be selected to give about 12mA base current into Q2.
     
  5. russpatterson

    Member

    Feb 1, 2010
    351
    16
    I ran into problems trying to gang LM317's as current limiters (running them in parallel). It didn't work and seem to fry some of the LM317's.
     
  6. xmen33

    Thread Starter New Member

    Aug 27, 2011
    20
    0
    So what the value of R1, and which transistor Q1 that i should use ?
    #Note that i will put the current limiter at the supply point
     
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    What action should the limiter do?

    Go into constant current mode and force the current to not exceed 3A?

    If you are working from the high side, you could used an unbalanced current mirror so that it ratios something like 100:1 and use the smaller current side to flag the current limit action.
     
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