Lecture 3-2
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Transcript of Lecture 3-2
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5/21/2018 Lecture 3-2
1/10
1Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
Voltage and Current
Division Rules
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5/21/2018 Lecture 3-2
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2Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
To apply the voltage and current
division rules.
Objectives
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5/21/2018 Lecture 3-2
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3
Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
Voltage Division
For example, we know
i = VTOTAL/ (R1 + R2 + R3)
so the voltage over the first resistoris
V1=i R1 = R1 VTOTAL/ (R1 + R2 + R3)
To find the voltage over an individual resistance in series, take the total series
voltage and multiply by the individual resistance over the total resistance.
321
1
1
RRR
RVv++
=
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4
Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
Example
determine the voltage across each resistor
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5
Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
Example
determine the voltage acrosseach resistor
21 RRvi s
s
+
=
s
s
vRR
Rv
vRR
Rv
21
2
2
21
1
1
+
=
+
=
iS
iS
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Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
SummaryThe source voltage v is divided among the resistors in direct proportionto their resistancesthe larger the resistance, the larger the voltage drop.
This is called the principle of voltage division,
In generalIf a voltage divider has N resistors (R1,R2, . . . , RN) in series with the
source voltage v, the nth
resistor (Rn) will have a voltage drop of
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5/21/2018 Lecture 3-2
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7
Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
Current Division
If we know the current flowing into two parallel resistors, we can find out how
the current will divide up in one step.
1
1
R
vi =
+
=
21
21
1
1
1
RR
RRi
Ri
21
2
1
RR
Rii
+
=
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Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
R2 = 0 implies that i1 = 0, i2 = i.R2 = , that is, R2 is an open
R2, then
Req = R1
Note that this differs slightly from the voltage division formula for series resistors
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9
Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
+
=
+
=
+=+==
21
1
2
21
2
1
2
12
1
2
1
11
2
1
12
RR
Rii
RR
Rii
R
RRi
R
Riii
R
Rii
s
s
s
Example
Find i1 and i2 in terms of is
21 iii
s +=
2211 RiRi =
R1
is i
1 R
2 i2
v1 = v2
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5/21/2018 Lecture 3-2
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10
Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
Example
Use Voltage and current division rules to find Vo and io2
36
36=
+
Step 1
Step 2
Step 1