cd4046 wave form problem

Discussion in 'Analog & Mixed-Signal Design' started by Amir Sarikhan, Jun 30, 2016.

  1. Amir Sarikhan

    Thread Starter Member

    May 29, 2015
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    Hi all
    I used a cd4046 to to produce a square and triangle wave
    It has a constant current on the capacitor pin so producing also a triangular wave form on that pin . The circuit works well at pspice
    but in my board I get different results as pictures below
    please help me
     
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  2. crutschow

    Expert

    Mar 14, 2008
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    You don't show a schematic of the constant-current source and my crystal ball is out-of-order, so how can we tell what's wrong?
     
  3. Amir Sarikhan

    Thread Starter Member

    May 29, 2015
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    Hi thanks for your response . I read on a web site that it has some kind of constant current on capacitor pins and it is shown on spice simulation but the problem is that on board I did not get same result .what is the reason ?
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    We can't see your board from here!
     
  5. Amir Sarikhan

    Thread Starter Member

    May 29, 2015
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    my board:
     
  6. Ramussons

    Active Member

    May 3, 2013
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    How does the modern generation do "electronics" without a schematic ? :confused::eek:
     
  7. Amir Sarikhan

    Thread Starter Member

    May 29, 2015
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    I sent pspice schematic .
     
  8. Amir Sarikhan

    Thread Starter Member

    May 29, 2015
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    Friends please reply me if you do not receive my pictures .
     
  9. Kjeldgaard

    Member

    Apr 7, 2016
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    16
    Now I have to refresh how the VCO in the 4046 is constructed. A example of the data sheet can be Texas Instruments: CD4046

    On page 11, there is an expanded block diagram of the VCO. It can be seen that the timing capacitors one end is connected to ground when charging with the constant current of opposite end of the capacitor, and after a half cycle time is changed to the opposite terminals of the capacitor.

    So that will measure a sawtooth curve when measured at one end of the time capacitor.
     
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  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Try connecting the resistor that presently goes to pin 12 to pin 11 instead.
     
  11. crutschow

    Expert

    Mar 14, 2008
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    Why do you have pin 15 connected to V+?
    It should be left open or connected to ground.
     
  12. Amir Sarikhan

    Thread Starter Member

    May 29, 2015
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    it is connected to ground not v+
    thanks
    I read that page
    you say right
    but why pspice draws a triangular wave ?
     
  13. crutschow

    Expert

    Mar 14, 2008
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    Yes, I mis-traced the connection.

    Kjeldgaard is correct. You will measure a sawtooth voltage from one end of the capacitor to common as the circuit shows.
    What, exactly is the Pspice plot measuring?
     
  14. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Do you now have a resistor between pin 11 and ground?
     
  15. ramancini8

    Member

    Jul 18, 2012
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    This is a good example of why you should not DESIGN with a program, any program.
     
  16. Amir Sarikhan

    Thread Starter Member

    May 29, 2015
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    [​IMG]
    Yes , of course
    I think so
     
  17. crutschow

    Expert

    Mar 14, 2008
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    I meant at what point in the circuit is the Pspice voltage being measured?
     
  18. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Can you post a link to the Pspice model of the 4046? The spice model I downloaded doesn't work properly.
     
  19. Amir Sarikhan

    Thread Starter Member

    May 29, 2015
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    Hi sorry for late response
    I did not download it , it was in my library list
     
  20. schmitt trigger

    Active Member

    Jul 12, 2010
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    If you require to generate a triangular wave from a square wave, use an integrator.
     
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