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ENAD Formula Sheet

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The key takeaways are about second order circuit analysis including characteristic equations, solutions to natural and step responses, and damping factors. It also discusses useful Laplace transform pairs and frequency selective circuits.

The different types of transient responses for second order circuits are overdamped response, underdamped response, and critically damped response. The document provides the general solutions for the natural response and step response of each case.

Some common frequency selective circuit transfer functions discussed are the general form for low-pass filters, high-pass filters, band-pass filters, and band-reject filters. Each is expressed as a function of s in the Laplace domain.

Formula

Sheet for ELEN30009 Electrical Network Analysis and Design




Second Order Transient Analysis of RLC Circuits




Characteristic Equation
Neper frequency or damping factor

(rad/s)
2
2
s + 2 s + 0 = 0

1

Parallel RLC, =
2RC



R

Series RLC, =
2L



Resonant radiant frequency (rad/s)
Damped radiant frequency (rad/s)

1
0 =
d = 0 2 2

LC


General solutions to natural response of
second-order circuits

2
2
Overdamped response, 0 <

x t = A1e s1t + A2e s2t

s1 , s2 = 2 02


02 > 2
Underdamped response,

x ( t ) = B1e t cos d t + B2e t sin d t
s1 , s2 = jd




02 = 2
Critically damped response,

t
+ D2e t
x t = D1te

s1 = s2 =

()

()


General solutions to step response of
second-order circuits

2
2
Overdamped response, 0 <
x t = X f + A '1 e s1t + A '2 e s2t

s1 , s2 = 2 02



2
2
Underdamped response, 0 >
x t = X f + B '1 e t cos d t
+ B '2 e t sin d t
s , s = j
1 2
d


02 = 2
Critically damped response,
t
t

()

()

x ( t ) = X f + D '1 te

s1 = s2 =

22

+ D '2 e







Distinct Real Roots


Repeated Real Roots


Distinct Complex Roots


Repeated Complex Roots


Useful Transform Pairs



F(s)

K
s+a

Ke at u ( t )

(s + a)
K
s + j
K

( s + j )

f(t)

Kte at u ( t )

2 K e t cos ( t + ) u ( t )

s + + j
K

( s + + j )

2t K e t cos ( t + ) u ( t )



Convolution Integral

y ( t ) = h ( t ) x ( t ) = x ( t ) h (t )


y ( t ) = h ( t ) x ( t ) = h ( ) x ( t ) d

y (t ) = x (t ) h (t ) =

x ( ) h (t ) d


Frequency selective circuits


General form of transfer function for
low-pass filters
K

H (s) =


General form of transfer function for
high-pass filter
Ks

H (s) =

s + C


General form of transfer function for
band-pass filter
s
H ( s ) = 2
2


General form of transfer function for
band-reject filter

s 2 + 02

H (s) = K

s + s + 0

s + C

23

s 2 + s + 02


Magnitude of transfer function, defined at
at cutoff frequency, C

H ( jC ) =

1
H max
2


Cutoff frequencies of bandpass and
bandreject filters

2

C1 ,C1 = + 2 + o


Two Port Terminal Equations

V1 = z11 I1 + z12 I 2
V2 = b11V1 b12 I1


V2 = z21 I1 + z22 I 2
I 2 = b21V1 b22 I1



I1 = y11V1 + y12V2
V1 = h11 I1 + h12V2


I 2 = y21V1 + y22V2
I 2 = h21 I1 + h22V2



V1 = a11V2 a12 I 2
I1 = g11V1 + g12 I 2

I1 = a21V2 a22 I 2

V2 = g 21V1 + g 22 I 2

24

25

26

27




Transformers (positive dot convention)

M = k L1L2
di
di
v1 = L1 1 + M 2
dt
dt

N2
v1
N1
N
i2 = 1 i1
N2
v2 =

v2 = M

di1
di
+ L2 2
dt
dt

N2
v1
N1
N
i2 = ! 1 i1
N2
v2 = !

28

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