current voltage dividers2
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Voltage dividersVariable resistors
ElectronicsSimple voltage dividers
Terry Sturtevant
Wilfrid Laurier University
October 1, 2012
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Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
Applications of Kirchhoff’s Voltage Law
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Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
V s R 1
R 2
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V l di id V l di id ( l d)
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Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
V s R 1
R 2
V s = V R 1 + V R 2
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Voltage dividers Voltage divider (no load)
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Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
V s R 1
R 2
A voltage divider “divides” the supply voltage
It’s useful when you need a different voltage than the supply
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividers Voltage divider (no load)
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Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
V s R 1
R 2
Part of V s across R 1
A voltage divider “divides” the supply voltage
It’s useful when you need a different voltage than the supply
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividers Voltage divider (no load)
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Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
V s R 1
R 2
Part of V s across R 1
V R 2 = V s − V R 1
A voltage divider “divides” the supply voltage
It’s useful when you need a different voltage than the supply
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividers Voltage divider (no load)
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Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
Since the current is the same in both resistors, the voltage isdivided between the two; thus it is a voltage divider.
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Voltage dividers Voltage divider (no load)
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gVariable resistors
g ( )Voltage divider (with load RL )
Since the current is the same in both resistors, the voltage isdivided between the two; thus it is a voltage divider.
Voltage divider circuits are very common, even when one or both circuit elements aren’t resistors.
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Voltage dividers Voltage divider (no load)
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gVariable resistors
g ( )Voltage divider (with load RL )
Since the current is the same in both resistors, the voltage isdivided between the two; thus it is a voltage divider.
Voltage divider circuits are very common, even when one or both circuit elements aren’t resistors.
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividers Voltage divider (no load)
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gVariable resistors
g ( )Voltage divider (with load RL )
V s
R 1
R 2
V out
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividers Voltage divider (no load)( )
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Variable resistors Voltage divider (with load RL )
V s
R 1
R 2
V out
Usually a voltage divider is drawn like this so it looks like a
ladder.
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividersV i bl i
Voltage divider (no load)V l di id ( i h l d RL )
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Variable resistors Voltage divider (with load RL )
V s
R 1
R 2
V out
Usually a voltage divider is drawn like this so it looks like a
ladder.As you climb the ladder, the voltage increases.
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividersV i bl sist s
Voltage divider (no load)V lt di id ( ith l d RL )
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Variable resistors Voltage divider (with load RL )
V s
R 1
R 2
V out
Since I 1 = I 2,
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
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Variable resistors Voltage divider (with load RL )
V s
R 1
R 2
V out
Since I 1 = I 2, (by Kirchhoff’s current law,)
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
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Variable resistors Voltage divider (with load RL )
V s
R 1
R 2
V out
Since I 1 = I 2, (by Kirchhoff’s current law),
and V s = V R 1 + V R 2 ,
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
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Variable resistors Voltage divider (with load RL )
V s
R 1
R 2
V out
Since I 1 = I 2, (by Kirchhoff’s current law),
and V s = V R 1 + V R 2 ,(by Kirchhoff’s voltage law),
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
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Variable resistors Voltage divider (with load RL )
V s
R 1
R 2
V out
Since I 1 = I 2, (by Kirchhoff’s current law),
and V s = V R 1 + V R 2 ,(by Kirchhoff’s voltage law),so V s = I 1R 1 + I 1R 2
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
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g ( )
V s
R 1
R 2
V out
Since I 1 = I 2, (by Kirchhoff’s current law),
and V s = V R 1 + V R 2 ,(by Kirchhoff’s voltage law),so V s = I 1R 1 + I 1R 2 = I (R 1 + R 2)
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
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( )
V s
R 1
R 2
V out
Since I 1 = I 2, (by Kirchhoff’s current law),
and V s = V R 1 + V R 2 ,(by Kirchhoff’s voltage law),so V s = I 1R 1 + I 1R 2 = I (R 1 + R 2)
I = V s R 1+R 2
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Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
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V s
R 1
R 2
V out
So V out = V 2 = IR 2
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Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
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V s
R 1
R 2
V out
So V out = V 2 = IR 2 = V s R 1+R 2
R 2
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Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
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V s
R 1
R 2
V out
So V out = V 2 = IR 2 = V s R 1+R 2
R 2
= V s
R 2R 1+R 2
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Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
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V s
R 1
R 2
V out
If R 1 gets smaller , then
V out = V s R 2R 1+R 2
gets bigger .
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Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
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V s
R 1
R 2
V out
V out = V s
R 2R 1+R 2
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V s
R 1
R 2
V out
If R 1 gets bigger , then
V out = V s R 2R 1+R 2
gets smaller .
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Voltage dividersVariable resistors
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Voltage divider (no load)
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Voltage dividersVariable resistors
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Voltage divider (no load)
If R 1 = 5Ω , R 2 = 10Ω, V s = 5V
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Voltage dividersVariable resistors
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Voltage divider (no load)
If R 1 = 5Ω , R 2 = 10Ω, V s = 5V
V out
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividersVariable resistors
Voltage divider (no load)Voltage divider (with load RL )
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Voltage divider (no load)
If R 1 = 5Ω , R 2 = 10Ω, V s = 5V
V out
= V s
R 2R 1+R 2
= 5
105+10
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Voltage dividersVariable resistors Voltage divider (no load)Voltage divider (with load RL )
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Voltage divider (no load)
If R 1 = 5Ω , R 2 = 10Ω, V s = 5V
V out
= V s
R 2R 1+R 2
= 5
105+10
= 3.3V
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividersVariable resistors Voltage divider (no load)Voltage divider (with load RL )
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Voltage divider (with load RL )
V s R 1
R 2 R L
Load will reduce the output voltage
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Voltage divider (with load RL )
V s R 1
R 2 R L
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Voltage dividersVariable resistors Voltage divider (no load)Voltage divider (with load RL )
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Voltage divider (with load RL )
V s R 1
R 2 R L
,
Some current goes through R 2, but some goes through R L so theeffective value of R 2 is reduced.
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Voltage dividersVariable resistors Voltage divider (no load)Voltage divider (with load RL )
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If R 1 = 5Ω , R 2 = 10Ω, V s = 5V and R L = 10Ω
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If R 1 = 5Ω , R 2 = 10Ω, V s = 5V and R L = 10Ω
Parallel resistance of R 2 and R L = R 2R LR 2+R L
= 10×1010+10 = 5Ω
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If R 1 = 5Ω , R 2 = 10Ω, V s = 5V and R L = 10Ω
Parallel resistance of R 2 and R L = R 2R LR 2+R L
= 10×1010+10 = 5Ω
Thus V out
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If R 1 = 5Ω , R 2 = 10Ω, V s = 5V and R L = 10Ω
Parallel resistance of R 2 and R L = R 2R LR 2+R L
= 10×1010+10 = 5Ω
Thus V out
= V s R p
R 1+R p = 5
55+5
Terry Sturtevant Electronics Simple voltage dividers
Voltage dividersVariable resistors Voltage divider (no load)Voltage divider (with load RL )
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If R 1 = 5Ω , R 2 = 10Ω, V s = 5V and R L = 10Ω
Parallel resistance of R 2 and R L = R 2R LR 2+R L
= 10×1010+10 = 5Ω
Thus V out
= V s R p
R 1+R p = 5
55+5
= 2.5V
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Voltage dividersVariable resistors
V i bl i t
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Variable resistors
Often it is useful to have variable resistors in a circuit.
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Variable resistors
Often it is useful to have variable resistors in a circuit.These are sometimes called potentiometers or trimmers.
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Here is a trimmer.
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Here is a trimmer. The top line should look familiar.
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The potentiometer has three pins.
The resistance given is between the two end pins.
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The potentiometer has three pins.
The resistance given is between the two end pins.
The third pin is called the wiper.
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The potentiometer has three pins.
The resistance given is between the two end pins.
The third pin is called the wiper.
A small screwdriver can be used to move the wiper from one
end to the other, or anywhere in between.
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The potentiometer has three pins.
The resistance given is between the two end pins.
The third pin is called the wiper.
A small screwdriver can be used to move the wiper from one
end to the other, or anywhere in between.The resistance between the two end pins will be constant.
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The potentiometer has three pins.
The resistance given is between the two end pins.
The third pin is called the wiper.
A small screwdriver can be used to move the wiper from one
end to the other, or anywhere in between.The resistance between the two end pins will be constant.
If you want a resistance which varies, just use the wiper andone end pin.
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Here’s a different view. The wiper is in the middle.
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From the top, this one has 10 dashes to represent intervals of roughlyR /10.
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This is a slightly different style.
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Variable resistors
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The potentiometer can be used for a variable voltage divider.
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The potentiometer can be used for a variable voltage divider.
Connect the two ends of your supply to the two end pins.
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Voltage dividers
Variable resistors
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The potentiometer can be used for a variable voltage divider.
Connect the two ends of your supply to the two end pins.
Measure the output voltage on the wiper.
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Voltage dividers
Variable resistors
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The potentiometer can be used for a variable voltage divider.
Connect the two ends of your supply to the two end pins.
Measure the output voltage on the wiper.
Adjusting the wiper will change the output voltage from oneend of the supply to the other, or to anywhere in between.
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