POTENTIAL DIVIDERS
Comparators often have potential dividers providing voltages to compare against, sometimes with sensors in.
Below are some potential dividers. Begin by following the instructions below to calculate voltages in them.
For each divider, do the following:
EXAMPLE
1 - Check voltages top and bottom (to get the
total voltages
V = 9 - 0 = 9v
9V
2 - Add up all the resistors to get the total
resistance, R.
R = 10K + 22K = 33K
R1
10K
3 - Calculate the current in the divider by using
I=V/R
Vout
4 - Now find the voltages across each resistor by
using V = I x R where I is the current from
before and R is the resistor you want to find
the voltage across.
I=V/R
= 9 / 32000
= 0.00028125
V=IxR
VR1 = 0.00028125 x 10000 = 2.81v
VR2 = 0.00028125 x 22000 = 6.19v
R2
22K
0V
Vout = ( 6.19v + 0v ) = 6.19v
Vout will be the voltage across R2 (or the resistor/s
below Vout) plus the voltage applied the other end
(usually 0v so answer is the same).
In the following potential dividers, work out the voltages across R1 (VR1) and across R2 (VR2), and Vout in
exactly the same way. They are fairly straight forward but follow the procedure above carefully.
Draw out the circuit and show ALL working
18V
10V
R1
10K
15V
R1
18K
Vout
R1
4.7K
Vout
R2
22K
R1
33K
R1
10K
Vout
R2
4.7K
0V
9V
Vout
R2
82K
0V
5V
Vout
R2
22K
0V
R2
100
0V
0V
The following have been designed to catch you out.
Just follow the steps above carefully and you should get through them ok.
Draw out the circuit and show ALL working
15V
9V
R1
11K
14V
R1
33K
10V
15V
R1
10K
R1
47K
R1
3.9K
Vout
Vout
Vout
R2
39K
-15V
Vout
R2
33K
-9V
R2
68K
R2
33K
Vout
R3
22K
6V
-10V
PotentialDividersWorksheet.lvw
R2
6.8K
R3
2.7K
-15V
P.Townshend 2010
Answers as follows.
18V
10V
R1
10K
15V
R1
18K
Vout
R1
4.7K
Vout
R2
22K
I
R1
33K
I
Vout
R2
22K
0V
= 0.0001A
= 100uA
R1
10K
Vout
R2
4.7K
0V
= 0.000563A
= 563uA
9V
Vout
R2
82K
0V
I
5V
R2
100
0V
= 0.00156A
= 1.56mA
I
0V
= 0.000091A
= 91uA
I
= 0.000891A
= 891uA
V1 = 5.625 V
V1 = 1.8 V
V1 = 7.5 V
V1 = 3 V
V1 = 8.911 V
V2 = 12.375 V
V2 = 8.2 V
V2 = 7.5 V
V2 = 2 V
V2 = 0.089 V
= 89mV
Vout= 12.375 V
Vout= 8.2 V
Vout= 7.5 V
Vout=2 V
Vout= 0.089 V
15V
9V
R1
11K
14V
R1
33K
10V
15V
R1
10K
R1
47K
R1
3.9K
Vout
Vout
Vout
R2
39K
Vout
R2
33K
-15V
R2
68K
R2
33K
-9V
R2
6.8K
Vout
R3
22K
6V
R3
2.7K
-10V
I
= 0.0006A
= 600uA
I
= 0.000273A
= 273uA
I
= 0.0001A
= 100uA
I
= 0.0002A
= 200uA
-15V
I
= 0.00224A
= 2.24mA
V1 = 6.6 V
V1 = 9 V
V1 = 4.7 V
V1 = 2 V
V1 = 8.73 V
V2 = 23.4 V
V2 = 9 V
V2 = 3.3 V
V2 = 13.6 V
V2 = 15.22 V
Vout= 8.4 V
Vout= 0 V
Vout= 9.3 V
V3 = 4.4 V
V3 = 6.05 V
Vout= -5.6 V
Vout= 6.27 V
PotentialDividersWorksheet.lvw
P.Townshend 2010