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Dumb Question

Discussion in 'Electronic Design' started by litw, Apr 21, 2004.

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  1. litw

    litw Guest

    What do Vdd, Vss, Vcc etc. stand for? I know they are basically power
    supplies but what's the exact meaning? Thanks!
  2. Tim Wescott

    Tim Wescott Guest

    The "dd" means "drain", "ss" means "source", "cc" means "collector",
    etc. The doubled subscript means "the supply that goes to..." rather
    than "the voltage at", which would be "Vc", "Vd", etc.
  3. Guest

    A first attempt, I am sure someone will correct me if I'm wrong

    Vcc - positive power, "c" comes from collector in bipolar technology.
    Vee - negative power (think of ground in conjunction with Vcc), "e" comes from emitter in bipolar technology.
    Vdd - positive power,"d" comes from Drain in FET technology
    Vss - negative power, "s" comes from Source in FET technology.

  4. Some other good answers, but here is some history:

    In the old days of valve ( tube ) electronics, there were two main supplies.
    The heater supply for the cathodes of the tubes came from the first
    battery - the A battery. So it got called Va.

    And the plate supply - the accelerating voltage - was supplied by the second
    battery, naturally the B battery, so Vb.

    Sometimes to generate other low voltages in the circuit, eg for grid bias
    supplies, there were other batteries, so C, D, E batteries. ( this was way
    before the days of self-bias circuits, and it was just as easy to stick in
    another battery than add expensive complicated things like resistors )

    Then transistors came along, and because the voltages were all low, but not
    heater supplies, Vc came to be used for the supply voltage. Of course the c
    came to be understood to be the Collector as well, which was easy.

    Then they realised it was necessary to differentiate between the supply and
    the voltage actually at the node, so the doubled nomenclature was invented,
    so Vcc for the supply, Vc at the terminal.

    The extension to FETS with their drain and source is obvious.


    Adrian Jansen
    J & K MicroSystems
    Microcomputer solutions for industrial control
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