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Potential Divider
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A potential (or voltage) divider is made up of two resistors. The
output voltage from a potential divider will be a proportion of the
input voltage and is determined by the resistor values.
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Operation
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Consider a standard resistor connected across a voltage supply. If
you were able to open it up and measure the voltage at any point along
it you would find the voltage varied linearly along it (assuming the
resistance was constant along it's length). For example if the resistor
was connected between 10V and 0V the voltage half-way along it would
be 5V. Similarly the voltage 10% from the 0V end would be 1V. The diagram
below illustrates this:
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A potential divider works in the same way. Obviously a resistor is
normally enclosed so you can't tap the voltage off at any point along
it, so two resistors are used; the tap point being between these resistors.
The diagram below shows a potential divider circuit with the standard
component notation used:
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Potential Divider
Circuit |
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V1 is the voltage in and V2 is the voltage out.
Equation
The voltage out of the divider is determined by the resistor values
using the equation:
V = supply voltage x R2/R1+R2
Example:
V= 9v x 2000
1000+2000
v = 9v x (2000/3000 ohms)
V = 9v x 0.6666666 ohms
V = 6v |
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An alternative way to work out the answer is to:
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1. Add both resistors together.
2. Divide the voltage by the sum of both resistors.
3. Take the largest resistor and multiply it by the answer
found in stage two.
1K + 2K = 3K
9v/3k (is the same as 9/3) = 3
2k x 3 = 6v |
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