I am learning to work with CMOS.

Discussion in 'General Electronics Chat' started by jaygatsby, Dec 15, 2011.

  1. jaygatsby

    Thread Starter New Member

    Nov 23, 2011
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    I've made a few circuits with 74 series TTL, counters, BCD and 7 segment drivers, things like that. They've worked out well. I've just spent a few hours making a similar circuit with CMOS chips, and things aren't going well at all.

    I found that the output of my CD4511BC BCD-to-7 Segment Latch/Decoder/Driver output Vdd to the 7 segment when it was supposed to, but during those moments when it was supposed to output 0 to an LED, the voltage dropped only about a volt.

    So I looked at the datasheet and found a typical applications page. It shows a schematic of the chip used with a common anode LED, with a transistor in between!

    TL;DR --- with CMOS I have to use transistors on the output to drive a 7 segment? In TTL I just did it directly.

    Thank you
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    You need to post your circuit. You may be using the CD4511 incorrectly. The common TTL decoder/driver is SN7447. This device sinks current and hence is used with common anode seven-segment displays. The output of the CD4511 can source 25mA and is used with common cathode seven-segment displays directly without the need for an external driver transistor.
     
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  3. jaygatsby

    Thread Starter New Member

    Nov 23, 2011
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    Ok now i understand.
     
    Last edited: Dec 16, 2011
  4. Wendy

    Moderator

    Mar 24, 2008
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    Compare the pinouts between the 7447 and the 4511. I was very surprised when I did.
     
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