circuit divider

Discussion in 'Homework Help' started by learjet, Jan 27, 2008.

  1. learjet

    Thread Starter New Member

    Jan 27, 2008
    1
    0
    I jest started on circuit dividers and id there a best way or forumla that calculates circuit dividers my professor does not do it easy....if you can help that would be great.


    Thanks all
    Mike
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Do you mean voltage dividers? If so the sum of the resistances gives you Rt. Current is given by Ohm's law, I = E/R. That current is common to all the resistors, so the drop across any of them also follows from Ohm's law, E = IR.
     
  3. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Voltage will be proportional to resistance. For a two resistor divider, Er1/(Er1+Er2) = R1/(R1+R2).

    Here's an example: If we have a 90Vrms(max) sine wave we need to sample, and our circuit can safely accept 6Vrms(max), we know 6/90 = 6/(6+84). This tells us the ratio between the two resistors will be 6:84 = 1:14. We can then pick through standard resistor values and choose two with roughly a 1:14 ratio. 1.4M and 10K both at 1% would do nicely for this example.

    Another example: We find a divider with a 137K R1 in series with a 221K R2. Applied voltage across the divider is 12Vdc. Since, Er1=(Er1+Er2)*R1/(R1+R2), divider output = 12*137/(137+221) = 4.59Vdc
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    For more information, take a look at the material in the AAC ebook on the topic of Voltage dividers.

    hgmjr
     
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