Correct symbol for Logical NOR; need help with substitution

Discussion in 'The Projects Forum' started by ICR, Apr 20, 2009.

  1. ICR

    Thread Starter Member

    Apr 20, 2009
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    Hi, I'm new to this forum, but I have thousands of posts on many other forums. (user ic-racer on APUG, AudioKarma, TheAmpGarage and some others)

    I am working on restoring closed loop photography enlarger designed in the 80s.

    I have one main problem to which I can't seem to get a good answer on the other forums.

    I need to know the correct symbol for logical NOR.

    I'm looking for a udn5714m chip and the replacement I was directed to looks like a logical OR (TD62479P) and it does not work.

    So, I have a datasheet that says udn5714m is logical NOR, but the datasheet shows a picture of logical OR.

    I have a cross reference sheet that links udn5714m to TD62479P, but I also have the datasheet on TD562479p that shows it to be logical OR.

    I have a datasheet to udn5713m that shows it to be Logical NOR!

    My original schematic has logial NOR symbols for the udn5714m.
     
    Last edited: Apr 20, 2009
  2. ICR

    Thread Starter Member

    Apr 20, 2009
    15
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    Datasheet for my original component SAYS logical NOR but shows a picture of logical OR!
    [​IMG]
     
  3. bertus

    Administrator

    Apr 5, 2008
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  4. ICR

    Thread Starter Member

    Apr 20, 2009
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    This sheet from Allegro links the UDS5714 to TD562479p:
    [​IMG]
     
  5. ICR

    Thread Starter Member

    Apr 20, 2009
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    OK, good I have been going on the assumption that NOR has the little circle, so if that is the case, some of these datasheets don't seem to make sense. If I'm going to call the datasheets wrong, I'd like a second opinion.
     
  6. ICR

    Thread Starter Member

    Apr 20, 2009
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    So, here is a comparison of the two datasheets:
    [​IMG]
     
  7. ICR

    Thread Starter Member

    Apr 20, 2009
    15
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    Here is my schematic. It shows the UDS5714 as a NOR symbol (its colored blue).
    [​IMG]
     
  8. ICR

    Thread Starter Member

    Apr 20, 2009
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    To make things more confusing, this datasheet of the sister component of the UDS5714 shows the UDS5713 to be a logical NOR!

    But there is no question that the component I removed from the board is UDS5714, not 13! (I have 3 other identical working power boards that all have the UDS5714 in them.
    [​IMG]
     
  9. ICR

    Thread Starter Member

    Apr 20, 2009
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    So, the questions are:
    1) Is the UDS5714 a logical NOR or logical OR?
    2) If the UDS5714 is logical NOR then would the correct substitution be TD62478P?
    3) Or does anyone know where the original component (UDS5714) could be purchased (making this whole thread moot).
     
  10. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    I'm going to speculate that the transistor is considered an inverter, but there is no way to tell for sure. I would match the internal drawing as best I could. Frankly, I've never seen a device quite like it, but then nothing unusual about that. There's ton's I don't know. ;)
     
  11. ICR

    Thread Starter Member

    Apr 20, 2009
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    So, if my UDS5714 is a NOR then
    a) The Sprauge datasheet is wrong AND
    b) the Allegero datasheet on UDS5713 is wrong

    If my UDS5714 is OR then my schematic is wrong (sorry my schematic did not come out well, but it shows the symbol with the little circle, therefore, NOR).
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    The output NPN transistor is indeed a logic inverter. That effectively changes the OR gate to a NOR gate.

    In the 5713, there is a logical NOR gate driving an NPN transistor; when you invert the output of an OR gate twice, you wind up with a NOTted NOR gate, which is an OR gate (with a good bit more propagation delay though).

    The TD62479P does indeed look like a drop-in replacement for your original that's dead. Check for other problems.
     
  13. Papabravo

    Expert

    Feb 24, 2006
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    Ding..Ding..Ding! Give that man a kewpie doll those trnasistor stages are indeed inverters and must be taken into account if they are wired in the common emitter configuration. Careful about using those Sprague parts for a new design; they were obsoleted in the late 1980's
     
  14. ICR

    Thread Starter Member

    Apr 20, 2009
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    I'm going to have to read this a couple times, but this probably answers the question.

    Good news for the project, after 3 months of searching I found a source for the original 5714, this should solve the problems.
     
  15. ICR

    Thread Starter Member

    Apr 20, 2009
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    Ok, I am seeing that the little symbols inside the component diagrams on the datasheets DON'T correspond to the OVERALL function of the chip (because of the inverting transistors in the chip).

    BUT...what about that output matrix listed for the TD62479P? (Post #6) I would interpret that as an OR matrix. But the original part is the 5714 (not the 5713). So the correct replacement should be the TD62478P right?
     
  16. ICR

    Thread Starter Member

    Apr 20, 2009
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    Ok, I really appreciate the answers so far. That clears up the UDS7514M datasheet nomenclature and diagram. It also is consistent with my schematic (which shows a NOR symbol for the entire component).

    Now, how would I go about interpreting these truth tables to find a suitable substitute that has an overall NOR function??
    It looks like the truth tables are not taking into account the inverting transistors. Also, that first one probably has an error, it should probably be AND or NAND.

    [​IMG]
     
  17. SgtWookie

    Expert

    Jul 17, 2007
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    The TD62476P has two NAND gates with NPN driver transistors (that act logically as inverters) on the outputs.
    Cin is the common input to the two NAND gates. Unless Cin is a logic low, the outputs can never turn on.

    If Cin is low, then if I1 is a logic low, then Q1 will conduct (ON). Same story for I2, Q2.

    Its' truth table is opposite that of the TD62477P, which is two AND gates with NPN driver transistors (that act logically as inverters) on the output.

    Remember though, that in the truth table that you posted, an ON output is a logic low (0), and an OFF output is a logic high (1).

    TD62479P has an "overall NOR" function, because the gate is an OR gate with (logically inverting) NPN driver transistors on the outputs.
     
  18. ICR

    Thread Starter Member

    Apr 20, 2009
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    I really appreciate you help in this matter. I think I understand it now.
     
  19. ICR

    Thread Starter Member

    Apr 20, 2009
    15
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    Ok, just to sum it up:

    1) I mistook the little diagrams in the datasheet to represent the whole component; I did not figure in the inverting last transistor stage.

    2) I did not realize the truth table I posted used ON to mean 0.

    3) So, the TD62479P DOES have the same logic as the origial 5714m, BUT, it does not work as a substitution for some reason that I will never find out, because...

    4) I was able to locate original 5714m components and ordered them today. BTW I got them from Omega/Satter.

    Again, thanks everyone for helping me figure this out.
     
  20. SgtWookie

    Expert

    Jul 17, 2007
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    OK, as I said before... if the TD62479P did not work in your circuit, neither will the original 5714M, because you either installed the TD62479P incorrectly, or there is another problem that you have not yet discovered.
     
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