what is Vcc, Vss, Vdd & Vee?

Discussion in 'Homework Help' started by onlyvinod56, Oct 14, 2009.

  1. onlyvinod56

    onlyvinod56 Thread Starter Active Member

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    hello...everyone

    what is the meaning of Vcc....
    i know that Vcc is the supply voltage for the electronic circuit.....
    then what about the other things.....

    can anybody contrast the "ground" from the Vss...
     
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  2. t06afre

    t06afre AAC Fanatic!

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    In older days Vcc was often used for the 5 volt rail in TTL systems, Vdd for other positive supply rail, and Vee for negative supply rail. All measured in respect to ground. Then I make designs I prefer to labels like V+5, V+12, and V-12 etc
     
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  3. onlyvinod56

    onlyvinod56 Thread Starter Active Member

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    ok...thats good...but....
    why they are named as CC.......DD..........SS............EE

    is there anything linked about collector...drain.....source.....emitter?
     
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  4. blueroomelectronics

    blueroomelectronics Senior Member

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    Cathode, Drain, Source, Emitter.
     
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  5. onlyvinod56

    onlyvinod56 Thread Starter Active Member

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    cathode means something related to negative.........right
    but Vcc will be considered as +ve...........

    waht about this?
     
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  6. bertus

    bertus Administrator

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  7. AlexR

    AlexR Well-Known Member

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    They are all supply voltages. Vcc = Collector supply voltage, Vee = Emitter supply, Vdd = Drain supply, Vss = source supply.

    The voltages can be negative or positive depending on the the device and the circuit configuration. In circuits using NPN transistors Vcc is generally positive but if you were using PNP transistors then Vcc would be negative. In a circuit with a mixture of PNP and NPN devices Vcc take the polarity of the predominant technology used (generally it would be positive).
     
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  8. newtonn

    newtonn New Member

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    this thread is great bcos have learn from it.
    thks to the creator and the contributor.
     
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  9. WBahn

    WBahn Moderator

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    They are derived from a more general naming convention.

    If you have Va, Vb, or other voltages with a single subscript, then what is meant is the voltage of that node with respect to some reference node. That reference node is "ground" or "common" and is usually just indicated as "GND" or something similar. You are free to pick any node you want as your reference node, but usually one or two nodes are the most reasonable candidates.

    If you have Vab or other voltages with two subscripts, then what is meant is the voltage of the first node with respect to the second node or

    Vab = Va - Vb

    This notation is actually quite useful because it allows you to figure out an unknown voltage step by step.

    For instance, let's say that I want to know Vac but I only know Vab and Vbc. Well, I can use the subscipts to tell me that

    Vac = Vab + Vbc

    This is true because

    Vac = Vab + Vbc

    Vac = (Va - Vb) + (Vb - Vc) = Va + (-Vb + Vb) - Vc = Va - Vc

    So in an expression, I can combine to voltages provided the first subscript on one of them is the same as the second subscript on the other by dropping the common subscript and keeping the other two in their same position.

    So Vaf = Vab + Vbc + Vcd + Vdf

    So, at this point, what would Vcc or Vee (or any other voltage with a repeated double subscript) be?

    Vxx = Vx - Vx = 0V

    Since any voltage with a repeated subscript will be 0V, the convention was adopted that a repeated subscript would indicate that the voltage was referring to a supply voltage, usually a DC supply. The letter would generally have some relevance to what the purpose of the supply was.

    For BJT circuits, the three common supplies are Vcc, Vee, and Vbb for the collector, emitter, and base voltage supplies. The Vbb is sometimes an actual supply, but more often it is the thevenin equivalent voltage associated with the base bias network. One fine point is that, by general convention, Vcc and Vee are associated with the collector and emitter sides of an NPN transistor. This is commonly, but not universally, the case even if the only transistors in the circuit are PNP transistors. A quick glance at the schematic will tell you if this is the case or not.

    For MOSFET circuits, the three common suppies are Vdd, Vss, and Vgg for the drain, sourse and gate supply voltages. The same remarks regarding polarity apply here.

    The strict meaning of these has been lost among a growing number of people, and hence you will often see Vcc used as the positive supply in CMOS circuits and see Vdd in BJT circuits.

    In many circuits, Vss/Vee is the same as the ground node, in which case it may or may not ever be noted as being Vss or Vee. In other circuits, there may be a more reasonable choice for the ground reference that is, generally, somewhere between the two values making Vss/Vee negative.
     
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  10. plant

    plant New Member

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    Thanks to WBahn for this detailed reply.
    btw, I'm replying because I don't see the "Thanks" button on any posts.
    heh, but I have the "Thanks" button now that I've made a post.
     
    Last edited: Jun 14, 2013
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  11. vk6zgo

    vk6zgo Active Member

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    Of course,all bets are off when you run into vacuum tube circuits,where Vbb,or in earlier versions, Ebb means the tube's Anode supply rail or B+.

    In this context,it dates from the days when radios had "A" & "B" batteries--
    "A" for filaments,& "B" for HT.

    When mains supplies were developed,the old names were continued.
     
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  12. KL7AJ

    KL7AJ Senior Member

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    The original designation for VCC was: VOLTAGE, common collector....meaning the rail that all the collectors were attached two. Now that we have FET's there can be Vss, Vdd, and Vee: the latter being the common EMITTER source....especially in positive ground systems.

    I sill like the term B+ for any positive supply! :)

    Eric the Old
     
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  13. vk6zgo

    vk6zgo Active Member

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    Oh yes! I forgot about grid bias batteries,which were "C" batteries!:D
    I don't know if they used Vc for them or not>
     
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  14. WBahn

    WBahn Moderator

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    But if VCC meant "Voltage, common collector", then shouldn't the "Voltage, common emitter" source be VCE? And shouldn't the others be Vcs and Vcd?

    The explanation centering on repeated subscripts seems much more consistent, to me.

    As with many historical origins of terms used in the common parlance, or jargon, of a particular field, it is probably impossible to say anything truly definitive either way.

    Interestingly, for a long time the defacto convention has been that repeated UPPER CASE subscripts meant DC supplies. This, primarily, because upper case subscripts generally denote DC (or perhaps total) quantities while lower case subscripts denote AC (or small signal) quantities. This was pretty closely adhered to when diagrams and equations where largely hand drawn or professionally lettered when done for publication. But now with so much documentation being done in code (schematics, programs, simulation scripts, and so on), it is often seen as less confusing to use Vcc instead of VCC. Like many other people, I don't really know which side of the fence I come down on this and I know I am guilty of being inconsistent in how I do it.
     
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