Electrical circuit ii lecture 1 with source file.

1. Electrical Circuit II
EEE-121
Md. Mokarram Hossain Chowdhury
Lecturer
Department of Electrical & Electronic Engineering
Stamford University Bangladesh

2. Resonance In Electric Circuits
 Any passive electric circuit will resonate if it
has an inductor and capacitor.
 Resonance is characterized by the input
voltage and currentbeing in phase. The driving
point impedance (or admittance) is completely
real when this condition exists.
 In this presentation we will consider (a) series
resonance, and (b) parallel resonance.

3. Series Resonance
Consider the series RLC circuit shown below
V = VM 0
V
The input impedance is given by:
The magnitude of the circuit current is;
1
( )Z R j wL
wC
  
2 2
| |
1
( )
mV
I I
R wL
wC
 
 

4. Series Resonance
Resonance occurs when
2πfrL =
1
2π𝑓𝑟𝐶
At resonance we designate w as wo and write
This is an important equation to remember. It
applies to both series And parallel resonant
circuits.
1
wL
wC

1
ow
LC


5. Series Resonance

6. Series Resonance

7. Series Resonance

8. Series Resonance
 The magnitude of the current response for the
series resonance circuit is as shown below.
Half power point
Bandwidth:
BW = wBW = w2 – w1
mV
R
2
mV
R

9. Series Resonance
The peak power delivered to the circuit is;
The so-called half-power is given when
We find the frequencies, w1 and w2, at which this
half-power occurs by using;
2
mV
P
R

2
mV
I
R

2 21
2 ( )R R wL
wC
  

10. Series Resonance
After some insightful algebra one will find two
frequencies at which the previous equation is
satisfied, they are:
And
The two half-power frequencies are related to the
resonant frequency by
2
1
1
2 2
R R
w
L L LC
 
    
 
2
2
1
2 2
R R
w
L L LC
 
   
 
1 2ow w w

11. Series Resonance
The bandwidth of the series resonant circuit is given
by;
We define the Q (quality factor) of the circuit as;
Using Q, we can write the bandwidth as;
These are all important relationships
2 1b
R
BW w w w
L
   
1 1o
o
w L L
Q
R w RC R C
 
    
 
ow
BW
Q


12. Series Resonance

13. Series Resonance
Q-factor: The quality factor of RLC circuit is the
voltage magnification in the circuit at resonance.
Voltage Magnification =
𝑉𝐿
𝑉
or
𝑉𝑐
𝑉

14. Parallel Resonance
 Circuit Current is in phase with the voltage applied
 Phase angle Zero
 Power factor cosØ = 1







jwL
jwC
R
VI
11

15. Parallel Resonance
 Zrl=R1+jXL
 Y= 1/Zrl
 Y= 1/R1+jXL
 Y= 1/R1+jXL * R1-jXL/R1-jXL
 Y=R1-jXL/R12+XL2
 *****

16. Parallel Resonance
Determine the resonant frequency for the circuit
below
jwRCLCw
jwLLRCw
jwC
jwLR
jwC
RjwL
Z NI






)1(
)(
1
)
1
(
2
2
At resonance, the phase angle of Z
must be equal to zero.

17. Resonance
jwRCLCw
jwLLRCw


)1(
)(
2
2
LCw
wRC
LCRw
wL
22
1()( 


12222
 CRwLCw
)(
1
22
CRLC
wo


Analysis
For zero phase;
This gives;
or

18. Parallel Resonance
A series RLC resonant circuit has a resonant
frequency admittance of 2x10-2 S(mohs). The Q
of the circuit is 50, and the resonant frequency
is10,000 rad/sec. Calculate the values of R, L,
and C. Find the half-power frequencies and the
bandwidth.

19. Thank you
for your kind attention
Question ?