Lm339

Discussion in 'General Electronics Chat' started by Lanz, Nov 10, 2009.

  1. Lanz

    Thread Starter Active Member

    Oct 30, 2008
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    I want to do a comparator circuit with LEDs as output to show the voltage difference.Im using LM339 for now.Is there any other comparator which can drive more than 4 LEDs.

    [​IMG]
     
    Last edited: Nov 10, 2009
  2. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    You can use a NPN or a PNP transistor driven by the LM339, and it will drive more than four LEDs. I suggest the use of a 2N3904 if you wish to use a NPN, or a 2N3906 if you wish to use a PNP. If you use a NPN, the LEDs will light when its input is driven high. If you opt for a PNP, the LEDs will light when its input is driven low.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Lanz,
    Would you please attach a schematic of the circuit you're considering as it is now? Having a schematic available is worth thousands of words.

    .png format is preferred; they are not "lossy" like .jpg images, and .pdf files take too long to load.

    Use the "Go Advanced" button, and then "Manage Attachments" to navigate to where the image is stored on your computer.
     
  4. Lanz

    Thread Starter Active Member

    Oct 30, 2008
    153
    0

    The circuit almost like above.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Last edited: Nov 10, 2009
  6. Lanz

    Thread Starter Active Member

    Oct 30, 2008
    153
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    I dont know how the circuit i attach work?
    But as far as i can see,the LED will be ON when the desired voltage (High and Low) reached at the input pin.
    What i need is when its
    3V=LED 1 will be ON and other LED OFF
    6V=LED 2 will be ON and other LED OFF
    9V=LED 3 will be ON and other LED OFF
    12V=LED 4 will be ON and other LED OFF

    But for VU based IC,when its
    3V=LED 1 will be ON and other LED OFF
    6V=LED 1&2 will be ON and other LED OFF
    9V=LED 1,2&3 will be ON and other LED OFF
    12V=All LED ON

    Am i correct?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Actually, it won't work properly.
    There is no fixed voltage reference. So, the voltages across the resistor divider for the noninverting (+) comparator inputs will change along with the inverting (-) inputs. So, the only way you'll see a change in the outputs is by changing the setting of Rv.

    Then you need a window comparator for each LED.

    The LM3914, LM3915, LM3916 IC's have a variety of options. They can work in "dot" or "bar" modes, and there is also an "exclamation" mode; a combination of dot and bar.
     
  8. Lanz

    Thread Starter Active Member

    Oct 30, 2008
    153
    0
    Only now i know its called window comparator for this kind of situation(circuit).



    Im impressed.Interesting IC.Really need to be experimented.

    Thanks for the info Sgtwookie.Really appreciated.Do u have any related circuits?
     
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