The document describes the mathematical modeling of electrical components like resistors, inductors and capacitors using Laplace transforms. It provides an example of modeling an RC circuit. The RC circuit is represented by two equations in the time domain, which are then transformed to the s-domain using Laplace transforms. This yields the transfer function of the circuit, relating the output voltage to the input current. The circuit and transfer function are then represented as a block diagram.
18. Model of Capacitance
C
i(t)
v(t)
0
0
1
( ) ( )
1
( ) ( )
1 1
( ) ( )
v t i t dt
C
v t i t dt
C
V s I s
C s
=
=
=
L L
Take Laplace :
22. Example : Electrical Circuit
RC Circuit :
1( )
v t 2 ( )
v t
1
R
2
R
C
( )
i t
1 2 1
0
1
( ) ( ) ( ) ( )
R i t R i t i d v t
C
+ + =
Mathematical Model time-domain
23. Example : Electrical Circuit
RC Circuit :
1( )
v t 2 ( )
v t
1
R
2
R
C
( )
i t
1 2 1
0
2 2
0
1
( ) ( ) ( ) ( )
1
( ) ( ) ( )
R i t R i t i d v t
C
R i t i d v t
C
+ + =
+ =
Mathematical Model time-domain
24. Example : Electrical Circuit
RC Circuit :
1( )
v t 2 ( )
v t
1
R
2
R
C
( )
i t
1 2 1
0
2 2
0
1
( ) ( ) ( ) ( )
1
( ) ( ) ( )
R i t R i t i d v t
C
R i t i d v t
C
+ + =
+ =
Mathematical Model time-domain
Two equations form the mathematical model of the circuit
25. Example : Electrical Circuit
RC Circuit :
1 2 1
0
2 2
0
1
( ) ( ) ( ) ( )
1
( ) ( ) ( )
R i t R i t i d v t
C
R i t i d v t
C
+ + =
+ =
L L
L L
Taking the Laplace Transform
1( )
v t 2 ( )
v t
1
R
2
R
C
( )
i t
26. Example : Electrical Circuit
RC Circuit :
1 2 1
0
2 2
0
1
( ) ( ) ( ) ( )
1
( ) ( ) ( )
R i t R i t i d v t
C
R i t i d v t
C
=
+ =
L + L + L L
L L L
Taking the Laplace Transform
1( )
v t 2 ( )
v t
1
R
2
R
C
( )
i t
27. Example : Electrical Circuit
RC Circuit :
1 2 1
0
2 2
0
1
( ) ( ) ( ) ( )
1
( ) ( ) ( )
R i t R i t i d v t
C
R i t i d v t
C
=
+ =
L + L + L L
L L L
Taking the Laplace Transform
1( )
v t 2 ( )
v t
1
R
2
R
C
( )
i t
28. Example : Electrical Circuit
RC Circuit :
1 2 1
2 2
1 1
( ) ( ) ( ) ( )
1 1
( ) ( ) ( )
R I s R I s I s V s
C s
R I s I s V s
C s
=
+ =
+ +
Taking the Laplace Transform
1( )
v t 2 ( )
v t
1
R
2
R
C
( )
i t
29. Example : Electrical Circuit
RC Circuit :
1 2 1
2 2
( )
( ) ( ) ( )
( )
( ) ( )
I s
R I s R I s V s
Cs
I s
R I s V s
Cs
=
+ =
+ +
Taking the Laplace Transform
1( )
v t 2 ( )
v t
1
R
2
R
C
( )
i t
30. Example : Electrical Circuit
RC Circuit :
1 2 1
2 2
( )
( ) ( ) ( )
( )
( ) ( )
I s
R I s R I s V s
Cs
I s
R I s V s
Cs
=
+ =
+ +
Circuit Transform
Time-domain to s-domain
1( )
v t 2 ( )
v t
1
R
2
R
C
( )
i t
1( )
V s 2 ( )
V s
1
R
2
R
1
Cs
( )
I s
31. Example : Electrical Circuit
RC Circuit :
1 2 1
2 2
( )
( ) ( ) ( )
( )
( ) ( )
I s
R I s R I s V s
Cs
I s
R I s V s
Cs
=
+ =
+ +
s-domain
1( )
V s 2 ( )
V s
1
R
2
R
1
Cs
( )
I s
Next step : Transfer Function
32. Example : Electrical Circuit
RC Circuit :
1 2 1
2 2
( )
( ) ( ) ( )
( )
( ) ( )
I s
R I s R I s V s
Cs
I s
R I s V s
Cs
+ + =
+ =
s-domain
1( )
V s 2 ( )
V s
1
R
2
R
1
Cs
( )
I s
Input Output
Transfer Function = Output
Input
33. Example : Electrical Circuit
RC Circuit :
1 2 1
2 2
( )
( ) ( ) ( )
( )
( ) ( )
I s
R I s R I s V s
Cs
I s
R I s V s
Cs
+ + =
+ =
s-domain
1( )
V s 2 ( )
V s
1
R
2
R
1
Cs
( )
I s
Input Output
Transfer Function = Output
Input
2
1
( )
( )
V s
V s
=
34. Example : Electrical Circuit
RC Circuit :
s-domain
1( )
V s 2 ( )
V s
1
R
2
R
1
Cs
( )
I s
Input Output
Transfer Function = Output
Input
2
1
( ) ( )
( ) ( )
V s C s
V s E s
= =
Output = C(s)
Input = E(s)
E(s) C(s)
35. Example : Electrical Circuit
RC Circuit :
Block Diagram
E(s) C(s)
Systems
Transfer Function = Output
Input
( )
( )
C s
E s
=
Input Output
37. Example : Electrical Circuit
RC Circuit :
Block Diagram
E(s) C(s)
RC Circuit
1 2 1
1 2 1
1
1 2
( )
( ) ( ) ( )
1
( ) ( )
( )
( )
1
I s
R I s R I s V s
Cs
I s R R V s
Cs
V s
I s
R R
Cs
+ + =
+ + =
=
+ +
2 2
2 2
2
2
( )
( ) ( )
1
( ) ( )
( )
( )
1
I s
R I s V s
Cs
I s R V s
Cs
V s
I s
R
Cs
+ =
+ =
=
+
38. Example : Electrical Circuit
RC Circuit :
Block Diagram
E(s) C(s)
RC Circuit
1
1 2
( )
( )
1
V s
I s
R R
Cs
=
+ +
2
2
( )
( )
1
V s
I s
R
Cs
=
+
39. Example : Electrical Circuit
RC Circuit :
Block Diagram
E(s) C(s)
RC Circuit
1 2
1 2 2
( ) ( )
1 1
V s V s
R R R
Cs Cs
=
+ + +
40. Example : Electrical Circuit
RC Circuit :
Block Diagram
E(s) C(s)
RC Circuit
2
2
1
1 2
1
( )
1
( )
R
V s Cs
V s R R
Cs
+
=
+ +
41. Example : Electrical Circuit
RC Circuit :
Block Diagram
E(s) C(s)
RC Circuit
2
2
1 2
1
1
( )
1
( )
R Cs
V s Cs
R Cs R Cs
V s
Cs
+
=
+ +
42. Example : Electrical Circuit
RC Circuit :
Block Diagram
E(s) C(s)
RC Circuit
2 2
1 1 2
( ) 1
( ) 1
V s R Cs
V s R Cs R Cs
+
=
+ +
43. Example : Electrical Circuit
RC Circuit :
Block Diagram
E(s) C(s)
RC Circuit
( )
2 2
1 1 2
( ) 1
( ) 1
V s R Cs
V s R R Cs
+
=
+ +
44. Example : Electrical Circuit
RC Circuit :
Block Diagram
E(s) C(s)
RC Circuit
( )
2 2
1 1 2
( ) 1
( )
( ) ( ) 1
V s R Cs
C s
E s V s R R Cs
+
= =
+ +
45. Example : Electrical Circuit
RC Circuit :
Block Diagram
E(s) C(s)
RC Circuit
( )
2
1 2
1
( )
( ) 1
R Cs
C s
E s R R Cs
+
=
+ +