LM317, 555 and other chips

Discussion in 'General Electronics Chat' started by PackratKing, Oct 15, 2011.

  1. PackratKing

    Thread Starter Well-Known Member

    Jul 13, 2008
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    Included in the poop sheets for these few chips just for example, is a scematic picturing what appears to be a representation of the circuit components inside the chip..............No indication of other component values, tho' the transistors in it are identified PNP or NPN ..................so here is the question.........:rolleyes:

    Is it possible to start with an appropriate voltage / current design, and use this unspecified schematic to build an L.S.I. version of the chip in question ?

    I hear some saying " why would you even want to " and I completely agree........though what an education in circuit design it would be !!
     
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
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    It may or may not be possible to base a workable circuit on a such a schematic, depending amongst other things on whether a complete detailed circuit or a simplified version is shown. The circuits will of course generally be tailored around integrated components, taking advantage of things like close Vbe matching that do not apply with discrete components.

    Wouldn't these circuits represent intellectual property of the IC manufacturer though, even if shown in publicly available datasheets?

    I'm puzzled by your reference to LSI though: Large Scale Integration, as in complex logic - what's that got to do with these relatively small circuits?
     
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  3. SgtWookie

    Expert

    Jul 17, 2007
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    How do you think their competitors do it? ;)

    Actually, you meant build one from discrete components, not make a LSI (large scale integration) version. These IC's are SSI (small scale) anyway; as they have few components.
     
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  4. PackratKing

    Thread Starter Well-Known Member

    Jul 13, 2008
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    Good point..........I wonder about the validity of intellectual property, since it shows point-to-point connections, without much component identification......that is the short half of reverse-engineering.....It would take some kind of effort to skull out the necessary values.

    Pardon my nomenclature.........I may have LSI confused with building it all with discrete components.
     
  5. #12

    Expert

    Nov 30, 2010
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    As Adjuster said, the representations omit a lot of details, but they are good enough to give me a block diagram so I can tell how the chip functions, whether to expect electrons to be going in or coming out of a pin, which way the offset will go when I put a resistance in series with the pin, and such as that.

    A good example of why it can't be done the same way with discrete components is about the on-chip matching of parts. 4 Instance, a current mirror as symbolized in an IC gives miserable results in discrete components because of temperature and gain differences in discrete components. Even if you glue two transistors together for temperature tracking, the gain differences will cause really bad errors unless you add resistance in the emitter circuits.

    Then there are transistors with 4 collectors and 2 emitters. I never saw one of those at Radio Shack!
     
    Last edited: Oct 15, 2011
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  6. KJ6EAD

    Senior Member

    Apr 30, 2011
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    I tried to build a 741 op amp on a breadboard using discrete components. There were more than 20 transistors in less than 4 inches of board length. It was a work of art but it never worked. The data sheet diagram was simplified enough to make the missing components critical. Had I known more about op amp theory at the time, I might have been able to make it work. :rolleyes:
     
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  7. PackratKing

    Thread Starter Well-Known Member

    Jul 13, 2008
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    Thanks again to one an all.

    This was more an exercise in sheer curiosity than any real plans to build, since the cost in components, unless one could rely on salvage, ho ho :p would be something else again.................:rolleyes:
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Why not try creating a component model of a 555 timer using LTSpice or another simulator, and see how it works? National Semiconductors' datasheet has a complete schematic with the part values.

    You might start with sections of the schematic, like building the trigger comparator (Q7-Q13), experimenting with it, and then the threshold comparator (Q1-Q6) or vice-versa.
     
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  9. PackratKing

    Thread Starter Well-Known Member

    Jul 13, 2008
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    I shall certainly look into that.
    I like NatSemi materials anyway, and have some war-torn volumes of their books, i.e. one on voltage regulation.
     
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