Problems with LM319

Discussion in 'General Electronics Chat' started by letomas, Nov 9, 2012.

  1. letomas

    Thread Starter New Member

    Nov 9, 2012
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    Hello everybody !

    Im trying to make a comparator with a LM319, and it doesn´t work .

    Does anybody know what the problem is ?

    [​IMG]
     
  2. Ron H

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    Apr 14, 2005
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    Your schematic looks OK. Do you have DC blocking caps between your signal sources and the inputs? If so, you need a resistor from each input to ground.
     
  3. letomas

    Thread Starter New Member

    Nov 9, 2012
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    Thanks Mr. Ron ! I made the circuit in real life but it didn´t work , any solution ?
     
  4. Ron H

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    What do you get on the output?
     
  5. crutschow

    Expert

    Mar 14, 2008
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    Define "doesn't work".
     
  6. letomas

    Thread Starter New Member

    Nov 9, 2012
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    [​IMG]

    I have to do this kind of pulse, i can make it with a PIC but i need a pulse with +9V , so i need a high speed amplifier or comparator,That´s why i used a LM319.

    The circuit in real life is the following:

    [​IMG]
     
  7. letomas

    Thread Starter New Member

    Nov 9, 2012
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    the output voltage is 0V , the LM319 doesn´t wanna work :(
     
  8. letomas

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    Nov 9, 2012
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    by " doesn´t work" i mean that the configuration for a comparator do nothing :eek: , i don´t if i am clear, sorry for my english :)
     
  9. Ron H

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    The internal bias network is common to both comparators. Floating inputs on the unused comparator will upset the bias on the one you are using. If you tie both unused inputs to ground, the unused comparator may oscillate. Try connecting one of the unused inputs to ground, and the other one to your 3.5V divider.
     
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  10. SgtWookie

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    Jul 17, 2007
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    A 1uS pulse is going to take around 10MHz bandwidth or better to pass. How did you lay out your circuit? If it's on a breadboard with long, loopy interconnecting wires and long leads to your caps, that's where your problem lies.
     
  11. letomas

    Thread Starter New Member

    Nov 9, 2012
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    I know that working with a pulse width of 1useg is not a good idea working in a breadboard, thats why i used a sinusoidal wave , a triangular wave and a square wave of many frequencies, those signel were compared with a constant voltage value (3.5V) . But i couldn´t get something at the output of the LM319 , just 0V .
     
  12. Ron H

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    Did you try what I suggested in post #9?
    Also, post a picture of your breadboard.
     
  13. letomas

    Thread Starter New Member

    Nov 9, 2012
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    I dont have it right now, and i´m working in other project, on friday i am going to do that and i´ll post a picture of my breadboard. sorry for the delay

    Thank you all for your help

    :)
     
  14. Ron H

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    I'll ask for the third time: Did you try what I suggested in post #9?
     
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  15. letomas

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    Nov 9, 2012
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    i did what you suggest and.... IT FINALLY WORKS.

    Thank you so much Mr Ron :)
     
  16. JoeJester

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    Apr 26, 2005
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    If the OP wants a zero to 9 volt peak signal, why is he using a +/- 12V supplies? That would give +/- output.

    The OPs hand drawing indicates the input and output signals.
     
  17. Ron H

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    According to the datasheet, he needs the negative supply if his input swings to ground (see input voltage range spec in datasheet), although, if the other input pin never goes below 3V, it should work OK without the negative supply.
    LM319 has separate negative rail connections (pins 3 and 8) for the output. In his schematic, they are connected to ground, so the output will not go lower than that.
    Perhaps you were thinking of LM393?
     
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