lecture 3-2.pdf
TRANSCRIPT
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1Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
Voltage and Current
Division Rules
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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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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
R R R
RV v++
=
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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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Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
Example
determine the voltage acrosseach resistor
21 R Rvi s
s
+
=
s
s
v R R
Rv
v R R
Rv
21
2
2
21
1
1
+
=
+
=
i S
i S
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Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
Summary•The source voltage v is divided among the resistors in direct proportionto their resistances•the larger the resistance, the larger the voltage drop.
•This is called the principle of voltage division ,
•In generalIf a voltage divider has N resistors (R 1,R 2, . . . , R N ) in series with the
source voltage v , the n th
resistor (R n ) will have a voltage drop of
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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
R R
R Ri
Ri
21
2
1
R R
Rii
+
=
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Dr.-Eng. Hisham El-Sherif
Electronics and Electrical Engineering Department
ELCT708: Electronics for Biotechnology
R 2 = 0 implies that i 1 = 0, i 2 = i .R 2 = , that is, R 2 is an open
R 2, then
R eq = R 1
Note that this differs slightly from the voltage division formula for series resistors
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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
R R
Rii
R R
Rii
R
R Ri
R
Riii
R
Rii
s
s
s
Example
Find i1 and i2 in terms of is
21 iii
s +=
2211 Ri Ri =
R1
is i
1 R
2 i2
v1 = v2
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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