TTL

Discussion in 'Homework Help' started by md yasir, Dec 16, 2015.

  1. md yasir

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    Sep 14, 2015
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    what are the advantages of open collector TTL
     
  2. WBahn

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    Since this is YOUR homework, how about offering up YOUR suggestions and we can provide feedback and comments about them.
     
  3. JoeJester

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  4. Papabravo

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    Could it be TTL with open collectors?
     
  5. crutschow

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    To add to PB's facetious remark, there are a few TTL circuits that have open collector outputs rather than the standard totem-pole.
     
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  6. Papabravo

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    In 1970 they may have had advantages over the competitive products which were RTL and DTL, but now maybe not so much.
     
  7. JoeJester

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    I knew PapaBravo and crutschow knew the answer ... I'm sure the TS didn't. We shall see if they return.
     
  8. WBahn

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    The main uses today are for doing wired-OR and wired-AND logic (you see this a LOT in IC circuits, less so in discrete designs) and the ability to do some degree of level shifting by acting as a low-side switch.
     
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  9. crutschow

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    So once again if the op waits long enough, we answer his homework question. :rolleyes:
     
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  10. dtekumse

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    Dec 15, 2015
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    Well, since you guys already did all the work, as crutschow noticed, maybe I can (mis)use this thread for a bit of off-topic (if off-topic is possible to a thread titled "TTL").

    Where did you study these circuits, I mean at what level of education? If University, which one and when? And, in general, what is your experience, to what extent this logic family is studied these days?

    I just started as a teaching assistant at a Faculty and I am interested to see what others do. Maybe this will not be completely off-topic if I ask our student here, md yasir, where did he get the assignment from?
     
  11. md yasir

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    Sep 14, 2015
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    in digital electronics subject bachelor of technology @dtekumse
     
  12. Papabravo

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    That's not really much of an answer.

    @dtekumse
    I received a Master's degree in Electrical Engineering from the University of Michigan in 1970. I first encountered TTL chips on the job after graduation. DEC computers of that era were still built with discrete DTL and I was familiar them from my part time summer work. Three years later RCA and National introduced CMOS, which although kinda slow at the time had great promise for low power circuits. Going forward I don't see much utility in SSI and MSI logic other than the education market.
     
  13. WBahn

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    Yep, I got tricked on this one. Lost sight of the original question.
     
  14. Papabravo

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    I still don't think it was much of an answer, unless "there aren't any anymore" was the answer the professor was looking for.
     
  15. WBahn

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    I don't think yours went too far, but mine (which was in response to yours) really did. Oops.
     
  16. crutschow

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    I believe you can still buy specific TTL circuits with an open collector output as shown in this listing here.
     
  17. KL7AJ

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    Open collector TTL allows you to drive a physical device that uses some current, such as a relay or lamp. The external device acts as the "pull up" for the output stage.
    So-called "lamp driver" TTL chips are VERY expensive for some reason (I know...we just had to replace a bunch of them where I work), so I usually use an external open collector transistor.
    Hope this helps,
    Eric
     
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  18. KL7AJ

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  19. Papabravo

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    The original question was about advantages. My response was about the lack of advantages not the lack of available parts. They'll be on the grey market for at least another decade by which time their lifetime will have exceeded half a century.
     
  20. crutschow

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    Apparently I misunderstood. :oops:
    When you stated "there aren't any anymore" was the answer the professor was looking for, I thought you meant that TTL devices with an open collector output were no longer available.
     
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