PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 43
BIPOLAR JUNCTION TRANSISTOR (BJT) CONSTRUCTION:
It is three layer semiconductor device, consisting of either two n- and one p-type layers of material or
two p- and one n-type layers.
Since three

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 44
THE CURRENTS OF A BJT:
1.
2.
3.
The collector current.
The base Current.
The Emitter Current.
Collector Current
(V /V )
It can be expressed as I =I e BE T
C S
I = saturation current or current sc

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 42
ZENER DIODE SHUNT REGULATOR:
From the circuit shown
regulation = r /(R +r )
z
z
regulation = - r | R
z
Current in the network =(V V )/R +r
s
z0
z
Voltage across r is
z
V = V
+ (Vs V )r /(R +r )
r

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 45
Emitter-Stabilized Bias Circuit:
Load Line Analysis
The collector emitter loop equation defining load line is
V =V -I (R +R )
CE CC C C E
For I =0mA
C
V =V
CE CC
And for V =0, we get
CE
I =V /(R

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 41
DIODE LOGIC GATES (OR GATE):
Y=A+B+C
EXAMPLE:
Find V and I.
SOLUTION:
D1 is ON because it is in forward biased. As 3V potential difference is applied across diode D1 and it will go in more
in con

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 38
CALCULATING CURRENTS:
Once the peak and average load voltage values are known, it is easy to determine the values of I
and I
EXAMPLE:
L(pk)
with the help of Ohms law.
ave
Determine the values I

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 39
PEAK INVERSE VOLTAGE:
Using the ideal diode model, the PIV of each diode in the bridge rectifier is equal to V2.This is the same
voltage that was applied to the diode in the full-wave center-tapp

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 35
TRANSFORMERS:
Transformers are not semiconductor devices, however, they play an integral role in the operations of
most of power supplies.
The basic schematic symbol for the transformer is as s

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 33
DC OR STATIC RESISTANCE:
When diode is subjected to a dc voltage its operating point on the characteristic curve does not change
with time. Hence the resistance of the diode can be found easily

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 40
PRALLEL CLIPPER:
The parallel configuration is defined as while the parallel variety has the diode in a branch parallel to the
load.
EXAMPLE:
Determine the output voltage for the network shown i

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 37
Negative Half Wave Rectifiers:
The analysis of negative half wave rectifier is nearly identical to that of positive half wave rectifier. The
only difference is that the voltage polarities are re

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 36
Negative Half Wave Rectifiers:
Fig. shows a half wave rectifier with diode direction is reversed. In this circuit the diode will conduct on
the negative half cycle of the input, and
V =V .
L
2
Th

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 1
International System of Units
It is built upon seven basic units.These are meter, kilogram, second, ampere, Kelvin, mole and candela.
Basic Units
The seven quantities are known to be basic in SI u

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 34
EXAMPLE:
Find the AC resistance for the curve shown at
(1) I = 2mA
D
(2) I = 25mA
D
SOLUTION:
(1) Choosing a swing of pulse minus 2mA
For
ID = 4mA, VD =.76V
And ID = 0mA , VD =0.65V
ID =4 0 = 4m

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 31
Example
Fig shows a circuit for charging a 12 volts battery. If vs is a sinusoid with 24 volts peak amplitude, find
the fraction of each cycle during which the diode conducts also find the peak v

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 29
BSIC SEMICOCONDUCTOR CONCEPTS
INTRINSIC SILICON:
A crystal of pure or intrinsic silicon has a regular lattice structure. Where the atoms are held at their
fixed positions by bonds, called Covale

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 32
Example: Consider a silicon diode with n =1.5. Find the change in voltage if the current changes from 0.1mA to
10mA.
Solution:
v/nV
i = Is e
T
v /nV
I =Is e 1
T
1
v /nV
I = Is e 2
T
2
(v v )nV
I

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 30
INTRODUCTION TO THE PN- JUNCTION DIODE.
The schematic symbol for the pn-junction diode is shown in the fig.
A diode will conduct when it meets the condition that the voltage difference between th

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 27
Example: Calculate the current I by using Thevenins theorem .
o
Solution:
We want to calculate I by using Thevenins theorem .we will follow the
0
following steps .
First step:
Removing R to calcu

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 28
Example: Find Norton equivalent circuit.
Solution:
First step:
Removing R replace open circuit with short circuit
L
by ohms Law we have
I =12/~0 A
N
Now we will insert the resistance R=~0 paralle

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 24
Source Transformation:
If we have any source embedded within a network, say this source is a current source having a value I
& there exists a resistance having a value R, in parallel to it. We ca

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 26
Example: Calculate the voltage V by using Thevenins theorem .
o
Solution:
We want to calculate V by using Thevenins theorem .we will follow the
0
following steps .
First step:
Removing R
L
Here R

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 25
THEVENINS THEOREM:
In solving any problem by Thevenins theorem. We will follow the steps as stated below
(1) First of all we will remove the load resistor( The resistor we want to calculate the u

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 23
Example:
Find current I , I and I By using Cramers rule.
1 2
3
Solution:
We will use Cramers rule to solve this example
KVL equation for loop 1
2I + 5( I I ) = -25
1
1 2
2I +5I 5I
=-25
1
1
2
7I 5

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 22
MATRICES AND DETERMINANTS
are the coefficients of the independent variables. a may be constant or functions of some parameter. A
ij
more convenient form may be obtained for the above equations by

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 21
Example:
Solution:
Calculate the voltage V
o.
we want to calculate the voltage V
V
0
0.
The circuit can be redrawn as
can be given as
V = 2k(I +I )
0
1 2
Now
I = 2V /1k
1
0
= 2(2k(I +I )/1k
1 2
=

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 18
Example:
Solution:
Calculate the voltage V
o.
We want to calculate the voltage V
o.
The circuit can be redrawn as
Now
Vx = (I - I ) 6k -(A)
2 3
I = Vx/2k -(B)
1
Put Vx from A into B we have
I = (

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 20
Example:
Solution:
Calculate the voltage V
o.
we want to calculate the voltage V
0.
The circuit can be redrawn as
Here
I = - 2mA
1
KVL equation for loop 2
2kI + 4kI + 2k(I + I ) = 12
2
2
2 1
6kI

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 19
Example:
Solution:
Calculate the current I
o.
we want to calculate the current I
0.
The circuit can be redrawn as
Here
I = 2mA
1
I = - 4mA
2
KVL for loop 3
2kI + 1k(I - I ) + 2k(I + I I ) =12
3
3

PHY301 Circuit Theory
Virtual University
PHY 301
LECTURE 16
Example:
Solution:
be redrawn as
Calculate the voltage Vac .
We want to calculate the voltage Vac. To solve this problem the circuit
can
Let the current I is flowing through the circuit. The KVL