LM339

Discussion in 'General Electronics Chat' started by mbohuntr, Apr 7, 2009.

  1. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Another foolish question... I picked up a LM338 comparator to use in a recent expieriment, then realized the output was really a ground that could only sink 50mA. The light just came on, is this used to bias pnp transistors? What else can the 338 be used for? thanks, Mike
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Are you sure about the part number? A quick check of the datasheet indicates that the LM338 is a 3-terminal adjustable voltage regulator.

    hgmjr
     
  3. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    My bad, I meant LM339.:rolleyes:
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Comparators are very useful for "squaring up" signals that have slow transition times, particularly for inputs to logic devices.

    Use a 1k to 1.2k pull-up resistor on the output, and supply a small amount of feedback via a large resistor to the non-inverting input to provide hysteresis. That won't give you much source/sink capability, but it's fine for logic levels.

    If you needed more current sourced/sunk at the output, you could always add transistors or MOSFETs.
     
  5. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    Read the LM339 datasheet carefully. It only show typical 16mA output current.

    50mA shown in the datasheet is the input current.
     
  6. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Thanks, looks like it will stay on the shelf till I find a good use for it... I'll have to see what transistors can be biased w/ <16mA.
     
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