35
What are the advantages of Network Theorems ? What is the main difference between Thevenin’s Theorem and Norton’s Theorem ?
What are the advantages of Network Theorems ?
What is the main difference between Thevenin’sTheorem and Norton’s Theorem ?
Why the load current is reduced in practical current source.
We increase the shunt resistance in practical current source
DC Voltage
SourceDC current
source
Ideal Sources
Ideal Current Source
+
-
VIs
Is
V
Ideal Current Source
+
-
VIs RL
V = Is RL
As RL V
Practical Current Source
+
-
VIs
Is
V
RSh
Rsh
VIsI −=
I = Load currentIs = Supply Current from SourceV = Load VoltageRsh = Shunt Resistance
IIR
IIIs R +=
Practical Current Source
Using Current Divider Rule
mAI
KM
MmAI
L
L
990.9
)11(
110
=
+
=
10 mA1MΩ 1KΩ
10 mA10 MΩ 1KΩ
mAI
KM
MmAI
L
L
999.9
)11(
110
=
+
=
Using Current Divider Rule
ideal current source Vs Practical Current Source
Rs is infinite Have some Rs
ideal current source Vs Practical Current Source
Rs is infinite
Supplies constant current to the load Whatever voltage is across load
Have some Rs
Is changes with the voltagei.e. V increases Is Decreases
ideal current source Vs Practical Current Source
Rs is infinite
Supplies constant current to the load Whatever voltage is across load
Can supply any amount of Voltage across load, Voltage depends only on RL
Have some Rs
Is changes with the voltagei.e. V increases Is Decreases
Supply limited voltage across load
Ideal Voltage Source
VVs
V
I
+- RL
Ideal Voltage Source
VVs
V
I
+- RL
Apply KVL-Vs + V = 0
V = VsLoad voltage V independent of load Current
Practical Voltage Source
V
I
Practical Voltage Source
V
IApply KVL-Vs + I Rs + V = 0
V = Vs – I RsLoad voltage V is depending on load Current
Ideal
Practical
Ideal Voltage Source Vs Practical Voltage Source
Internal Resistance Rs should be zero Internal Resistance Rs should be minimum
Ideal Voltage Source Vs Practical Voltage Source
Internal Resistance Rs should be zero
Supplies constant voltage to the load Whatever current is across load
Internal Resistance Rs should be minimum
Vs changes with the currenti.e. As I increases Vs Decreases
Ideal Voltage Source Vs Practical Voltage Source
Internal Resistance Rs should be zero
Supplies constant voltage to the load Whatever current is across load
Can supply any amount of Voltage across load,
Voltage depends only on RL
Internal Resistance Rs should be minimum
Vs changes with the currenti.e. As I increases Vs Decreases
Supply limited voltage across load
KVL
•The sum of voltage drops around a closed path must equal zero.
KCL
•The sum of currents leaving a closed surface or point must equal zero.
Review of Kirchhoff’s Current Law& Kirchhoff’s Voltage Law
KVL Tricks
+
-V2
Path
+
-V1
Path
+-V3
Path
+ V1
- V2
+ V3
Path 1: 0vvv b2a =++−
vcva
+
−
+
−
3
21
+ −
vb
v3v2
+ −
+
-
ab c
Writing KVL Equations
Path 1: 0vvv b2a =++−
Path 2: 0vvv c3b =+−−
vcva
+
−
+
−
3
21
+ −
vb
v3v2
+ −
+
-
ab c
Writing KVL Equations
Path 1: 0vvv b2a =++−
Path 2: 0vvv c3b =+−−
Path 3: 0vvvv c32a =+−+−
vcva
+
−
+
−
3
21
+ −
vb
v3v2
+ −
+
-
ab c
Writing KVL Equations
Elements in Parallel
KVL clockwise, start at top:
Vb – Va = 0
Va = Vb
In order to satisfy KCL, what is the value of i?
KCL says:
24 μA + -10 μA + (-)-4 μA + -i =0
18 μA – i = 0
i = 18 μA
i10 mA
24 mA -4 mA
Kirchhoff’s Current Law (KCL)
Elements in Series
i1 = i2
i1 – i2 = 0
Mesh Current Analysis Nodal Voltage Analysis
Using KCL
Using Kirchhoff's Current Law
Equation No
1 : 10 = 50I1 + 40I2
Using Kirchhoff's Current Law
Equation No
1 : 10 = 50I1 + 40I2Equation No
2 : 20 = 40I1 + 60I2
Using Kirchhoff's Current Law
I3 = I1 + I2
I1 = -0.142 AmpsI2 = 0.428 AmpsI3 = 0.286 Amps
Equation No
1 : 10 = 50I1 + 40I2Equation No
2 : 20 = 40I1 + 60I2
Mesh Current Analysis
Only label inside loops in a clockwise direction with circulating currents
i1 = I1 , i2 = -I2 and I3 = I1 – I2
10 = 10 I1 + 40 I1 – 40 I2
-20 = 20 I2 + 40 I2 – 40 I1
1
2
Mesh Current Analysis
[ V ] gives the total battery voltage for loop 1 and then loop 2
[ I ] loop currents which we are trying to find
[ R ] resistance matrix
[ R-1 ] inverse of the [ R ] matrix
Mesh Current Analysis
I3 = I1 – I2 -0.143 – (-0.429) = 0.286 Amps
Same as found by Kirchhoff’s circuit law
Nodal Voltage Analysis
Reference node = D
Nodal Voltage Analysis
Reference node = D
Va = 10v
Vc = 20v
Vb = ?
Nodal Voltage Analysis
Reference node = D
