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Intro EE - Voltage Divider Design circuit

  • Engineering
  • Thread starter krtica
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  • #1
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The link is an image with the question and circuit representation:
http://i49.tinypic.com/2mmwg8l.png


Here are the equations I used:

V_out/V_in = R_2/(R_1 + R_2) {using the node method}

R_thevenin (R_th) = R_2*R_1/(R_1+R_2)

And given the conditions =>

10 < R_th < 30

Manipulating this inequality I found that 50 < R_1 < 150, which left me with three possible values for R_1 (56, 68, 82).

Using the first equation, I put in the numbers, which gave me 0.2=R_2/(R_2+56) and solved for R_2 with every value I put in for R_1 (56, 68, 82).

R_2 values were 14, 17, and 20, respectively, which came to equate to 15, 18, and 22 when compared to the original set of resistors and the 10% condition.

I tried putting in the values of these resistors I used, because all gave me the right ratio of voltages, but they're incorrect.


Pardon how nuanced I may seem, it's been too long since I've done any physics..
 

Answers and Replies

  • #2
NascentOxygen
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Here are the equations I used:

V_out/V_in = R_2/(R_1 + R_2) {using the node method}

R_thevenin (R_th) = R_2*R_1/(R_1+R_2)
I think you are on the right track.
And given the conditions =>

10 < R_th < 30
This should be, 10,000 ≤ R_th ≤ 30,000
Manipulating this inequality I found that 50 < R_1 < 150, which left me with three possible values for R_1 (56, 68, 82).
Aren't you missing some candidates here?
R₁ ∈ {56k,68k,82k,100k,120k,150k}
 
  • #3
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Wouldn't it just be the three since your given all the resistances available in the set E12?
 
  • #4
NascentOxygen
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120kΩ = 12 x 104
 
  • #5
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Right! Thanks.
 

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