7447 vs. 7448

Discussion in 'General Electronics Chat' started by hondabones, Mar 26, 2010.

  1. hondabones

    Thread Starter Active Member

    Sep 29, 2009
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    I have studied the data sheets on both of these chips and cannot figure out which one is best for driving common cathode displays. If some of you have read my other posts you will understand that I don't want to make the same mistakes. Like I did when I bought common anode displays and I had a common cathode driver. lol. Any suggestions?
     
  2. k7elp60

    Senior Member

    Nov 4, 2008
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    The 7448 is designed to drive common cathode circuits, while the 7447 is designed to drive common anode circuits. You can use a 4511 and it will drive either depending upon its set up.
     
  3. hondabones

    Thread Starter Active Member

    Sep 29, 2009
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    How do you set the 4511 to drive anode?

    Thanks for the info on the other chips. Very useful.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Take a look at the 4543, also. See your other thread; I added a schematic and some notes.
     
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  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    You need inverting transistors to handle a common anode display - the 4511 is designed for common cathode.

    You should be aware that a 4000 series CMOS IC and old TTL (74XX) do not play well together. Specifically, the TTL HIGH level is not enough to switch the input of a CMOS gate. Life is easier if you use the same logic family throughout a project.
     
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  6. hondabones

    Thread Starter Active Member

    Sep 29, 2009
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    For learning purposes I ended up using the two together. See my learning adventure here: http://forum.allaboutcircuits.com/showthread.php?t=35657

    My actual project will be all TTL. I am using common cathode displays. k7elp60 posted that the 7448 is the one designed to drive them.

    I was curious of the 4511 because that is what I have now for my experiments. I can't, however, drive the dual anode displays because of their circuitry. I want to convert the 4511 so they could, and then hopefully learn to drive the anode displays. Thread here: http://forum.allaboutcircuits.com/showthread.php?t=36149
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    My impression about CMOS (something I was rather sure of actually) is anything over ½Vcc is a high, and anything under ½Vcc is a low. I've successfully mixed them, but it has been measured in decades. TTL high is around 3.4V last I checked.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    It does look almost a sloppy as TTL in the manual - 1.5 volts low and 3.5 volts high. My experience is that it's not that forgiving, and really likes highs closer to the Vcc level.
     
  9. k7elp60

    Senior Member

    Nov 4, 2008
    478
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    I was wrong, the 4511 is for common cathode displays. I was thinking 4543. The 4543 is good as it will also drive LCD displays. The Ph pin(6) is at ground or Vss for common cathode or Vdd for common anode, the for LCD pin 6 is connected to a oscillator.
     
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