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Power rail names

Discussion in 'General Electronics Discussion' started by Tha fios agaibh, Sep 8, 2016.

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  1. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    It seems odd to me some of the identifying terms used for power rails; like Vcc or Vdd.

    Yes, It makes sense when more than one collector or drain are similarly connected to the positive rail, but what about when you have a circuit with both mixed bjt and fets, or mixed N type and P type transistors on the same rail? (For instance both a drain and a source connection to the same rail) What's the criteria for properly identifying them?

    John
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    hey John ... Mainly because it isn't really used as a device specific thing as you are assuming
    that is ... Vcc is very commonly used to denote the positive rail regardless of the circuit type or components within

    have a read through .....
    https://en.wikipedia.org/wiki/IC_power-supply_pin

    here's an interesting response on another forum .....


    am sure there's more comments out there
     
    Tha fios agaibh likes this.
  3. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Thanks Dave, makes sense.
     
  4. OBW0549

    OBW0549

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    Jul 5, 2016
    No criteria, really, nor any "proper" usage; they are just a commonly-used naming convention that helps us quickly and intuitively determine what kind of voltage, positive or negative, they represent. When I see "Vdd" or "Vcc" I expect a positive supply voltage; and when I see "Vss" or "Vee" I expect a negative voltage.

    There's really little more to it than that.
     
  5. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Thanks. I was wondering because It's possible to have the opposite polarity depending on transistor type.

    Another thing that seemed odd to me, is how a N type mosfet has its "source" connected to Negative and its drain hooked to a positive source.

    I will try not to overthink this stuff.
    Lol.
     
    OBW0549 likes this.
  6. OBW0549

    OBW0549

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    Jul 5, 2016
    Yup. Just accept the conventions for what they are: conventions. (It's probably a good idea to follow them, too; if someone sees a negative supply voltage labeled "Vdd" their head will probably explode.)
     
    Tha fios agaibh likes this.
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