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Newb question about voltage dividers

Discussion in 'General Electronics Discussion' started by jke, Oct 12, 2010.

  1. jke

    jke

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    Oct 12, 2010
    I have a very simple question about voltage dividers.

    Why bother with the 2nd resistor? Aren't you reducing the signal to the desired level with the first one? What's the point of creating the parallel circuit after the first resistor?

    Thanks.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    A voltage divider with one resistor is like a seesaw with the pivot at one end rather than the middle.

    assuming a load impedance far greater than the resistor value, the resistor does not reduce the level at all.

    A voltage divider is designed to give a relatively constant portion of its input signal to a high, possibly unknown, and possibly variable load impedance. For that you require two resistors with values chosen to provide the division ratio desired and to drive the required load while keeping the ratio within tolerance.

    Yrs the load is in parallel with one leg of the divider. In some cases, if this is a constant or near constant value it can form a voltage divider with the addition of a single series resistor. You cant do this if the resistance is highly variable or unknown.

    if the resistance of the load varies very widely you may use an amplifier with feedback to maintain a constant output in the face of changing (or even low impedance) loads. A voltage regulator is a special case of amplifier.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Hey, it's only a 6 year old question!
     
    KJ6EAD likes this.
  4. BobK

    BobK

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    Jan 5, 2010
    And nobody answered until now. LOL.

    Bob
     
  5. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    I was just rereading the internet myself and correcting what omissions and errors I find. It seems there have been a few changes since I first read it. ;)
     
    (*steve*) likes this.
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