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24 Volt AND gates?

Discussion in 'Electronic Basics' started by [email protected], Apr 23, 2007.

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  1. Guest

    In college, I was used to using 5 volt signals for logic, but does
    anyone know if they make IC's that support 24 volt (DC) signals as an
    AND gate, or even a family of 24 volt logic gates?

    Thanks in advance.
    Jeff
     
  2. 18 volts (4000 series CMOS) is the highest voltage logic I
    am aware of. You may have to make your gates with diodes
    and comparators.
     
  3. Guest

  4. Doug Miller

    Doug Miller Guest

    Or relays, if easy availability is more important than size or power
    consumption ...
     
  5. Guest

    Becareful with that first example. If you applt +24 to the bottom
    transistor and ground to the upper one, you reverse bias the base
    emitter junction of the top one beyond it zener voltage, which will
    not only make the gate malfunction (the output high will be weak) the
    reverse base current will slowly reduce the gain of the upper
    transistor.
     
  6. Guest

  7. Guest

    Does that circuit require that the inputs be allowed to source
    current? I would be driving it with "high side" drivers that can't
    source current.
     
  8. Guest

    Looking at the datasheet:
    http://w3.id.tue.nl/fileadmin/id/objects/E-Atelier/doc/Datasheets/Transistoren/PN2222A.pdf
    which value would I be concerned about to find out what the limit is
    on the zener voltage? Would it be the Base-Collector breakdown
    voltage?

    Thanks.
    Jeff
     
  9. Guest

  10. Guest

    The diode transistor logicshown sources current out through the inputs
    that must be sunk to ground to pull the input low. And the schematic
    shown is a NAND, not an AND.

    But the circuit can be rearranged for pull up inputs and converted to
    and. What must the output drive?
     
  11. feebo

    feebo Guest

    not just trannies... use a sprinkling of diodes too and it all becomes
    very easy and a very real proposition... if you start looking at
    circuits in this light, you'll be surprised how many include the logic
    primitives in this form. Sometimes I will use a DTL configuration
    rather than chuck a chip in and leave 3/4 of it unused (although I do
    weigh the costs in such a decision)
     
  12. Guest

    A motor controller that is expecting 24 volts signal to activate the
    drive. There's no serious current draw.
     
  13. What does the input voltage go to when nothing is connected?
    In other words, must the gate output pull positive or
    negative?
     
  14. Martin

    Martin Guest

    While doing it in discretes is certainly possible, unless your logic
    is very minimal
    (less than 4 or 5 gates worth) it may be worth just throwing a
    regulator into the circuit and using standard gates.

    I think that for anyone here to give an answer that really is the best
    solution (however you may chose to define best: (least cost, smallest,
    simplest etc...)) you need to give MUCH more detail about what you are
    trying to do.

    Tell us the end result you are looking for, what you have already
    aquired hardware wise
    or are committed to not changing, where your inputs come from, etc.

    I strongly suspect you should not be doing your logic at 24 volts, but
    should be changing another part of your circuit to take logic level (5
    or 12 volt) inputs.

    Martin
     
  15. kell

    kell Guest

  16. kell

    kell Guest

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