# Voltage Divider

Discussion in 'Homework Help' started by Steve1992, May 7, 2006.

1. ### Steve1992 Thread Starter Senior Member

Apr 7, 2006
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0
Vout = Vin x R2 / (R1 + R2)

If Vin is 12V and I want Vout to be 4.5V

What would the equation/math be to find the values for R2 and/or R1 if given.
If R1 is given R2 would be a common factor?

2. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
There is no unique solution. There must be some other condition. For example R1 + R2 must be 20K Ohms. Now there is a unique solution because you have two equations and two unknowns.

3. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Duplicate -- Delete

4. ### Papabravo Expert

Feb 24, 2006
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5. ### Papabravo Expert

Feb 24, 2006
10,340
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Duplicate -- Delete

6. ### Papabravo Expert

Feb 24, 2006
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7. ### Papabravo Expert

Feb 24, 2006
10,340
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8. ### Papabravo Expert

Feb 24, 2006
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Duplicate - Delete

May 30, 2006
17
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Et = 12v

you need to know the current. so use .1 amp arbitrarily.

It = .1amp

find R1 and R2

by using Rt = Et/It or 12v/.1amps
= 120ohms total resistance

if you want 4.5 volts then R1 = 4.5v-12v = 7.5v drop
7.5v / .1amps = 75 ohms = R1
4.5v / .1amps = 45ohms = R2

the same curent flows through both resistors. so that is used to find the total resistance

and ratio is used to find voltage drops

and resistances are in proportion to current.