fybscit arun sir electronics
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Basics about Circuits
Basic Electric Circuit Concepts
System of Units:
We use the SI (System International) units. The system uses meters (m),
kilograms (kg), seconds (s), ampere (A), Resistance (? ) & Volts (V)
as the fundamental units.
We use the following prefixes:
pica (p): 10-12
nano (n): 10-9
micro (): 10-6
milli (m): 10-3
tera (T): 1012
giga (G) : 109
mega (M): 106
kilo (k): 103
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Basic Electric Circuit Concepts
Basic Quantities: Current
The unit of current is the ampere (A). We note that
1 ampere = 1 coulomb/second
We normally refer to current as being either direct (dc) or
alternating (ac).
i(t)i(t)
t t
dc currentac current
0 0.5 1 1 . 5 2 2 .5 3 3.5-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
ac current3
Basic Electric Circuit Concepts
Basic Quantities: Current
In solving for current in a circuit, we must assume a direction, solve
for the current, then reconcile our answer. This is illustrated below.
Circuit 1 Circuit 2
(a) (b)
I1 = 4 A I2= - 3 A
In the diagram above, current I1 is actually 4 A as assumed. The
actual positive direction of current I2 (equal to -3 A) in the opposite
direction of the arrow for I2.
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Basic Electric Circuit Concepts
Basic Quantities: Voltage
The next quantity of interest is voltage. Voltage is also called an
electromotive force (emf). It is also called potential energy.
Suppose one coulomb of charge is located at point b and one joule
of energy is required to move the charge to point a. Then we say
that Vab = 1 volt = 1 joule/coulomb = 1 newton.meter/coulomb.
Vab = 1 volt states that the potential of point a (voltage at point a)
is l volt (positive) with respect to point b.
The sign associated with a voltage is also called its polarity.
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Basic Electric Circuit Concepts
Basic Quantities: Voltage
As in the case for current, we must assume a positive direction (polarity) for
the voltage. Consider the three diagrams below.
.+
-
.
v = 4 v
a
b
vab = 4 v v = 4 v
(a) (b) (c)
Each of the above gives the same information.6
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Basic Electric Circuit Concepts
Basic Quantities:Voltage
We need to keep in mind that we assume a polarity for the
voltage. When we solve the circuit for the voltage, we may find
that the actual polarity is not the polarity we assumed.
+
-
v = -6 v
The negative sign for 6 v indicates that if
the red lead(probe) of a voltmeter is
placed on + terminal and the black
lead(probe) on the terminal the meter
will readdownscale or6v.
Adigital meter would read 6 v.7
Basic Electric Circuit Concepts
Circuit Elements:
We classify circuit elements as passive and active.
Passive elements cannot generate energy. Common examples
of passive elements are resistors, capacitors and inductors. We
will see later than capacitors and inductors can store energy
but cannot generate energy.
Active elements can generate energy. Common examples of
active elements are power supplies, batteries, operational
amplifiers.
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circuits
Fundamentals
Introduction to Electronics
(Semiconductor Devices)
Why Semiconductors?
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Ge has 32 orbiting electrons andneutrons and protons in Nucleus
Bohr Atomic Model of Ge
Nucleus
1st shell electrons
2nd shell electrons
3rd shell electrons
4th and Valence shell electrons
Bohr Atomic Model of Si
Si has 14 orbiting electrons andneutrons and protons in Nucleus
Nucleus
1st shell electrons
2nd shell electrons
3rd shell and Valence shell
electrons
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E
E
The characteristics of a semiconductor
material can be altered significantly bythe addition of certain impurity atoms
into the relatively pure semiconductor
material.
Terms: Doping, impurity, intrinsic
semiconductor
A semiconductor material that has been subjected to the
doping process is called as an Extrinsic
Materials
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Intrinsic Semiconductor Materials
Free electrons in an intrinsic semiconductorare only due to natural causes (photon lightand thermal heating). A free electron willhave its complementary hole. Electrons andholes due to only natural causes are alsocalled as intrinsic carriers.
Extrinsic Semiconductor
Base Material
(Si and Ge)
Impurity Pentavalentor Trivalent
Base Material+Pentavalent impurity n-typesemiconductor
Base Material+Trivalent impurity p-typesemiconductor
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Trivalent Impurity (p-type impurity)
Boron (B), Gallium (Ga) and Indium:
have 3 electrons in valence cellAcceptor impurity
Pentavalent Impurity(n-type impurity)
Antimony (Sb), Arsenic (As) and
Phosporous (P) : have 5 electron in valence
shell Donar Impurity
P NJunction
Doping a crystal with both types of impurities forms a
P-N junction diode.
Some electrons will cross the junction and fill holes.A pair of ions is created each time this happens.
Negativeion
Positiveion
As this ion charge builds up, it prevents furthercharge migration across the junction.
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P N
Each electron that migrates across the
junction and fills a hole effectivelyeliminates both as current carriers.
This results in a region at the junction that isdepleted of carriers and acts as an insulator.
Depletion layer
Energy
Abrupt junction
P-side
Valence band
Conduction band
N-side
In an abrupt junction, the p side bandsare at a slightly higher energy level.
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Energy
P-side
Valence band
N-side
Conduction band
Energy bands after the depletion layer has forme
To an electron trying to diffuse across the junctiothe path it must travel looks like an energy hill. It
must receive the extra energy from an outside sour
Energy hill
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Diode Types
Rectifier Diodes
Light Emitting Diodes (LED)
Photodiodes
Zener Diodes, etc
Diode Applications
Against Reverse Voltage Protection
Rectifying {AC DC }
Display (indicators, Advertise hoardings)
Light Sensing (Solar panals etc)
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Light Emitting Diode (LED) circuit How to connect LED
A
K
V s
VR
R
V
ILED
Expected ILED = 20mA,
Assuming LED has V =1.5V.
Find the value of R, if the source
voltage 5 volts.
LED
S
I
VVR
=
7 Segment Display Consist of 7+1 LEDs Available in :
Commond Anode configuration
Commond Cathode configuration
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7 Segment Display Commond anode and Commond
Cathode configuration
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7 Segment Display
Commond anode and CommondCathode configuration
7 Segment Display Application: Logic Display
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Classification of TransistorsTRANSISTORS
Bipolar Junction
Transistors
(BJT)
Field Effect
Transistors
(FET)
NPN - B JT PNP - B JTJunction
FET (JFET)
Metal Oxyde
Semiconductor FET
(MOSFET)
N-Channel
JFET
P-Channel
JFET
DepletionMode
MOSFET
EnhancedMode
MOSFET
N-Channel
D-MOSFET
P-Channel
D-MOSFET
N-Channel
E-MOSFET
P-Channel
E-MOSFET
A bipolar (junction) transistor (BJT) is athree-terminal electronic device constructed
of doped semiconductor material and may
be used in amplifying or switchingapplications. Bipolar transistors are so
named because their operation involves
both electrons and holes.
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Classification of Bipolar Junction
Transistors
Base
Collector
Emitter
IC
IB
IE
VCE
VBE
Base
Collector
Emitter
IC
IB
IE
VCE
VBE
Bipolar Junction Transistor (BJT)
NPN Transistor PNP Transistor
ass ca on o po ar unc onTransistors
Base
Collector
Emitter
IC
IB
IE
V
CE
VBE
NPN Transistor
Current Gain : or hFE
Then
And
So
B
C
I
I =
BCII =
CBE
III +=
( )II BE += 1
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NPN
NPN is one of the two types of bipolar
transistors, consisting of a layer of P-dopedsemiconductor (the "base") between two N-doped layers.
A small current entering the base is
amplified to produce a large collector andemitter current.
That is, an NPN transistor is ON" when its
base is pulled high relative to the emitter.
PNP
The other type of BJT is the PNP, consisting
of a layer of N-doped semiconductorbetween two layers of P-doped material.
A small current leaving the base is
amplified in the collector output.
That is, a PNP transistor is "on" when itsbase is pulled low relative to the emitter.
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Applications of Transistors
1. Darlington transistor (often called aDarlington pair) is a compound structureconsisting of two bipolar transistors (eitherintegrated or separated devices) connectedin such a way that the current amplified by
the first transistor is amplified further by thesecondone
2. Transistor As a Switch
An electronic amplifier, in which the input " signal" is
usually a voltage or a current. In audio applications,
amplifiers drive the loudspeakers used in PA systemsto make the human voice louder or play recorded
music.
Amplifiers may be classified according to the input
(source) they are designed to amplify (such as a guitar
amplifier, to perform with an electric guitar), the
device they are intended to drive (such as a headphone
amplifier), the frequency range of the signals (Audio,
IF, RF, and VHF amplifiers, for example), whether
they invert the signal (inverting amplifiers and non-inverting amplifiers), or the type of device used in the
amplificat ion (valve or t ube am plifier s, F ET
amplifiers, etc.).
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If for a small change in input voltage, a proportional
large change in output voltage is obtained, then we say
that, voltage amplification has taken place
Biasing in Transistor
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In order to use transistor as an amplifier, it must be operated in its
active region. The biasing of the PNP and NPN transistor for theiractive region operation and the directions of the currents are
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The field-effect transistor(FET), sometimes called aunipolar transistor, uses either electrons (in N-
channel FET) or holes (in P-channel FET) forconduction.
In FETs, the drain-to-source current flows via aconducting channel that connects the sourceregionto the drainregion.
The conductivity is varied by the electric field that is
produced when a voltage is applied between the gateand source terminals; hence the current flowingbetween the drain and source is controlled by thevoltage applied between the gate and source.
N-CHANNELP-CHANNEL
The four terminals of the FET are named source, gate,
drain, andbody(substrate).
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Operation of N-channel with VGS =0
Due to the supply voltage VDS , current starts flowingthrough the channel.
Therefore current flow through the channel get voltageacross the channel.
This voltage will Reverse BIAS the G to S p-n junction
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Thanks
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