Driver/Buffer datasheet voltages

Discussion in 'General Electronics Chat' started by SPQR, Feb 17, 2013.

  1. SPQR

    Thread Starter Member

    Nov 4, 2011
    379
    48
    Hello again,

    I'm going through a "driver/buffer" stage, and have purchased some representative samples of about 20 different types.

    Before I start building circuits, I'd like to learn a bit more about each one.
    I'm building a spreadsheet with a series of variables regarding each buffer, and I'm stumped on some voltages:

    SN74HC125 -
    Introduction - "Wide operating voltage range of 2-6V"
    Page 2 - "supply voltage range - -0.5-7V"
    Page 3- "VCC supply voltage - 2-6V"
    Why the difference?

    SN7417 -
    "open collector" - I understand the implications of this
    "sinking 40mA" - this I understand
    Page 2&3 - "supply voltage Vcc = 7V"
    __________"output voltage = 15V"
    Don't think that this is a voltage amplifier, so does the output voltage mean that you can attach up to 15V to the open collector? Like a 15V motor?

    Thanks again.
     
    Last edited: Feb 17, 2013
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    On the sn74hc125: the -0.5 v to 7 v number is the absolute maximum supply range that would probably not damage the chip. The 2 v to 6 v range is the recommended operation range over which many of the other parameters are measured. So, although you could put 1 v on the supply, since it will not damage the part, you are not supplied with any guaranteed characteristics for the chip outputs...
     
  3. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    On the sn7417: the open collector output means there is a BJT transistor with no connection to its collector inside the chip. The output load can be connected between the collector and a voltage as high as 15 v, so a 15 v motor would be one option. When there is no current flowing through the load, the voltage at the collector would be 15 v, the maximum allowed by this part before the transistor collector can be damaged.
     
  4. SPQR

    Thread Starter Member

    Nov 4, 2011
    379
    48
    Very, very nice - Thank you!

    I've read many datasheets over the last few months and I marvel at such a fantastic, organized, engineering profession,
    that can have such variation in nomenclature.

    So for the 125
    Introduction - "Wide operating voltage range of 2-6V"
    Page 2 - "supply voltage range - -0.5-7V"
    Page 3- "VCC supply voltage - 2-6V"

    Two different concepts with three different names.
    So I'm going to label the columns with MY names::)

    Supply Voltage = Sup V
    Tolerable Supply Voltage Range = Tol Vcc

    In terms of the 7417, it's what I figured - that would make sense.
    So my new name:
    Maximum Applied Voltage to Collector Output - Max Coll Volt

    Thanks again! Very helpful!
     
  5. w2aew

    Member

    Jan 3, 2012
    219
    64
    The key is to look at the headings above each of the tables. On page 2, it says "absolute maximum ratings". This are the ratings, which if exceeded, will damage the part. On page 3, these are the "recommended operating conditions". Self explanatory.
     
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  6. SPQR

    Thread Starter Member

    Nov 4, 2011
    379
    48
    Yep, just noted those!
    I'll have to be REALLY carefull in future.
    Thanks!
     
  7. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    How is the current of 15V motor?
     
  8. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    I think the motor example was just to try to understand the concept of a 15 volt output on the part. The OP stated he knew the part on could sink 40 mA. So, motor specifications were not questioned.
     
  9. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    The motor specifications maybe not the question, but when a load needed 40mA connecting to the 40mA sink could be caused a problem.
     
  10. SPQR

    Thread Starter Member

    Nov 4, 2011
    379
    48
    Exactly!

    In terms of the open collector output, I usually think of motors/LEDs/solenoids being connected and "doing something".
    It was a random example that I understand, at my level.
     
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