Theory and testing methods about electronics components like- resistor , capacitor , diode , transistor , scr etc. lab testing also ...

1. BASICELECTRONICS
BYPITAMBARBEHERA

2. INTRODUCTION
Electronics is that branch of science which deals with the flow of
current or electrons through gas or vacuum.
OBJECTIVES
To introduce common electronic components used in industries
& home applications
To distinguish the characteristic differences among components

3. CONTENTS
RESISTOR
CAPACITOR
INDUCTOR
DIODE
RECTIFIERS
TRANSISTOR
INTEGRATED CIRCUIT (IC)
SILICON CONTROLLED REACTIFIER (SCR)

4. RESISTOR
Most common component in
electronic circuits.
Main function – to limit current
flow or reduce the voltage in a
circuit.
Fixed or variable.
Basic unit is ohm.
Symbol is Ω.

5. TYPESOF RESISTORS
 Wire-wound resistors
 Carbon-composition resistors
 Film-type resistors
• Carbon film
• Metal film
 Surface-mount resistors (chip resistors)
 Fusible resistors
 Thermistors
 Photoresistor/LDR

6. WIREWOUNDRESISTOR
 Special resistance wire is
wrapped around an
insulating core, typically
porcelain, cement, or
pressed paper.
 These resistors are
typically used for high-
current applications with
low resistance and
appreciable power.

7. CARBONCOMPOSITIONRESISTORS
 Made of carbon or graphite
mixed with a powdered
insulating material.
 Metal caps with tinned
copper wire (called axial
leads) are joined to the ends
of the carbon resistance
element. They are used for
soldering the connections
into a circuit.

8. FILM-TYPERESISTORS
 Film-type resistors
• Carbon film
• Metal film
 Compared to carbon
composition resistors,
carbon-film resistors have
tighter tolerances, are less
sensitive to temperature
changes and aging, and
generate less noise.

9. SURFACE-MOUNTRESISTORS/CHIPRESISTORS
 These resistors are:
• Temperature-stable and
rugged
• Their end electrodes are
soldered directly to a
circuit board.
• Much smaller than
conventional
resistors with axial
leads.

10. FUSIBLERESISTORS
Fusible resistors are wire-
wound resistors made to burn
open easily when the power
rating is exceeded.
They serve a dual function as
both a fuse and a resistor.

11. THERMISTORS
 Thermistors are
temperature- sensitive
resistors whose
resistance value changes
with changes in
operating temperature.
 Used in electronic circuits
where temperature
measurement, control,
and compensation are
desired.

12. PHOTORESISTOR/LDR
A photoresistor is a type
of resistor whose resistance decreases
when the intensity of light increases.
In other words, the flow of electric
current through the photoresistor
increases when the intensity of light
increases.
Photoresistors are also sometimes
referred as LDR (Light Dependent
Resistor), semiconductor
photoresistor, photoconductor, or
photocell. Photoresistor changes its
resistance only when it is exposed to
light.

13. RESISTORCOLORCODING
 Carbon resistors are small, so their R value in ohms is marked
using a color-coding system.
 Colors represent numerical values.
 Coding is standardized by the Electronic Industries Alliance
(EIA).

14. RESISTORCOLORCODING

15. RESISTORCOLORCODING

16. CHIPRESISTORCODINGSYSTEM
 Body color is usually white or off-white
 End terminals are C-shaped
 Three (four) digits on the body or on the film
 First 2 (3) digits indicate the first two (three) numbers
 Third (fourth) digit indicates the multiplier
 Are available in tolerances of ±1% ±5% but tolerances are not
indicated on the chip
 The letter R is used to signify a decimal point for values
between 1 to 10 ohms (1R5 means 1.5 ohms)

17. VARIABLERESISTORS
 A variable resistor is a resistor whose resistance value can be
changed.
 Rheostats and potentiometers are variable resistances used to vary the
amount of current or voltage in a circuit.
RHEOSTATS
 Three terminals.
 Connected in series with the load and the voltage source.
 Varies the current.
POTENTIOMETERS
 Three terminals.
 Ends connected across the voltage source.
 Third variable arm taps off part of the voltage.

18. VARIABLERESISTORS

19. RESISTORNOMENCLATURE
PRINTEDCODE MEANING EXAMPLE PRINTTEDVALUE
X ohm X ohm 100 ohm 100 ohm
X Ω X ohm 10 Ω 10 ohm
X R X ohm 200 R 200 ohm
X E X ohm 700 E 700 ohm
X K X kilo ohm 10 K 10 kilo ohm
XKY X.Y kilo ohm 7K3 7.3 kilo ohm
XM X mega ohm 20M 20 mega ohm
XMY X.Y mega ohm 3M5 3.5 mega ohm

20. IN SERIES

21. IN PARALLEL

22. VOLTAGEDIVIDER

23. POWERRATINGOF RESISTORS
The power rating of a resistor is a physical property
that depends on the resistor construction, especially
physical size.
• Larger physical size indicates a higher power rating.
• Higher-wattage resistors can operate at higher temperatures.
• Wire-wound resistors are physically larger with higher
wattage ratings than carbon resistors.

24. CAPACITORS
Capacitors is a component that is
able to hold or store an electric
charge.
Its physical construction consists of
two metal plates separated by an
insulator.
Capacitors are used to block direct
current (DC) but pass alternating
current (AC).
Basic unit is farad.
Symbol is F.

25. CAPACITORS
What is a capacitance?
• Properties of a capacitor that can store electric charge
What does it consist of?
• Usually consists of two conducting objects (plates or sheets)
placed near each other without touching
How is a capacitor different than a battery?
• Battery provides potential difference by storing energy
(usually chemical energy) while the capacitor stores charges
but very little energy.

26. TYPESOF CAPACITORS

27. TYPESOF CAPACITORS
 Fixed capacitors, often identified by their dielectrics:
• Ceramic, Plastic, Mica, Aluminum
• Tantalum oxide
 Electrolytic capacitors
• Large capacitance at low cost and have a shelf life
 Surface mount capacitors
• Soldered directly onto printed circuit boards
• Extremely small: High packaging density
 Variable capacitors
 Supercapacitors

28. FIXEDCAPACITORS
 Ceramic Capacitors
• Values change little with
temperature, voltage, or
aging
 Plastic Film Capacitors
 Mica Capacitors
• Low cost, low leakage, good
stability
 Electrolytic Capacitors
• Large capacitance at low
cost
• Polarized
 Surface Mount Capacitors

29. SURFACEMOUNTCAPACITORS
Surface mount capacitors are used in
high volume manufacture - quantities
used are numbered in the billions.
They are small, leadless and can be
placed onto modern printed circuit
boards using pick and place machines
used in modern manufacturing.
There are many different types of
SMD capacitor ranging from ceramic
types, through tantalum varieties to
electrolytics and more. Of these, the
ceramic SMD capacitors are the most
widely used.

30. VARIABLECAPACITORS
 Used to tune a radio
 Stationary plates and
movable plates
• Combined and mounted on
a shaft
 A trimmer capacitor is used
to make fine adjustments on
a circuit

31. SUPERCAPACITORS
 Devices with enormous
capacitance values
• Values extend into the
hundreds of farads and
beyond
• Also known as ultra
capacitors
• Used in power sources,
GPS systems, PDAs,
medical equipment, security
systems
 Voltage rating typically only a
few volts

32. IN SERIES

33. INPARALLEL

34. CAPACITORTESTINGMETHODS
Spark test method
By analog multimeter
By digital multimeter
• In resistance mode
• In capacitance mode

35. SPARKTESTMETHOD
 Disconnect the suspected capacitor
from the power supply or make sure at
least one lead of the capacitor is
disconnected.
 Make sure that the capacitor is fully
discharged.
 Now safely connect these leads to 230
V AC Supply for a very short period
(about1- 4 Sec) .
 Remove safely leads from the 230 V AC
Supply.
 Now short the capacitor terminals.
 If it makes a strong spark, then
the capacitor is good.

36. BY ANALOGMULTIMETER
 Make sure the suspected capacitor is fully
discharged.
 Select analog meter on OHM (Always, select
the higher range of Ohms).
 Connect the Meter leads to the Capacitor
terminals.
 Note The reading and Compare with the
following results.
 Short Capacitors: Shorted Capacitor will
show very low Resistance.
 Open Capacitors: An Open Capacitor will
not show any movement on OHM meter
Screen.
 Good Capacitors: It will show low

37. BY DMMIN RESISTANCEMODE
Make sure the capacitor is
discharged.
Connect the meter leads to the
capacitor terminals.
Digital meter will show some
numbers for a second. Note the
reading.
And then immediately it will
return to the OL. Every attempt
of Step 2 will show the same
result as was in step 3 and Step
4. It’s mean Capacitor is in Good
Condition.

38. BY DMMIN CAPACITANCEMODE
Make sure the capacitor is fully
discharged.
Now connect the capacitor
terminal to the multimeter
leads.
If the reading is near to the
actual value of the capacitor (i.e.
printed value on the Capacitor)
Then the capacitor is in good
condition. (Note that the reading
may be less than the actual
value of the capacitor.
If you read a significantly lower
capacitance or none at all, then

39. INDUCTOR
 A current through an inductor
creates a magnetic field
around the coil which resists
any changes in current
 This is the property of matter
which opposes the change in
current
 Measured in henrys (H)
 Algebraic Symbol is L
 Graphical Symbol

40. IN SERIES
When inductors are
connected in series, the total
inductance increases
• LT = L1 + L2 + L3 + … + Ln

41. IN PARALLEL
When inductors are
connected in parallel, the
total inductance is less than
the smallest inductance
• 1/LT = 1/L1 + 1/L2 + 1/L3 +
… + 1/Ln

42. DIODE
Diode is an electronic
component that allows current to
flow through it in one direction
but not the other.
Its main function is to change an
AC voltage into a DC voltage.
There are two leads coming out
from a diode: cathode and
anode.

43. TYPESOF DIODES
PN junction diode
Zener diode
Tunnel diode
Varactor diode
Schottky diode
Photodiode
Light emitting diode
Shockley diodes

44. DIODEBIASING

45. PN JUNCTIONDIODE
A p-n junction diode is a two
terminal device that allows electric
current in one direction and blocks
electric current in another direction
In forward bias condition, the diode
allows electric current whereas in
reverse bias condition, the diode
does not allow electric current.
The conversion of alternating
current into direct current is known
as rectification. A p-n junction diode
allows electric current when it is
forward biased and blocks electric
current when it is reverse biased.
This action of p-n junction diode
enables us to use it as a rectifier

46. ZENERDIODE
 The Zener diode operates just like the
normal diode when in the forward-bias
mode, and has a turn-on voltage of
between 0.3 and 0.7 V. However, when
connected in the reverse mode, which
is usual in most of its applications, a
small leakage current may flow. As the
reverse voltage increases to the
predetermined breakdown voltage, a
current starts flowing through the
diode. The current increases to a
maximum, which is determined by the
series resistor, after which it stabilizes
and remains constant over a wide
range of applied voltage.

47. TUNNEL DIODE
A Tunnel diode is a heavily
doped p-n junction diode in
which the electric current
decreases as
the voltage increases.
In tunnel diode, electric
current is caused by
“Tunneling”. it is used as a
very fast switching device in
computers. It is also used in
high-frequency oscillators and
amplifiers.

48. VARACTORDIODE
The diode whose
internal capacitance varies with
the variation of the reverse
voltage such type of diode is
known as the Varactor diode. It
is used for storing the charge.
The varactor diode always works
in reverse bias
The varactor diode is used in a
place where the variable
capacitance is required, and that
capacitance is controlled with
the help of the voltage.

49. SCHOTTKY DIODE
Schottky diode is a device,
which comes under the type
of a metal – semiconductor
junction diode. Barrier diode
and low voltage diodes are the
other names for Schottky
diode. When compared to a
PN junction diode, power drop
is lower in Schottky diode.

50. PHOTODIODE
A special type of PN junction
device that generates current
when exposed to light is
known as Photodiode. It is
also known as photodetector
or photosensor. It operates in
reverse biased mode
and converts light energy into
electrical energy.

51. LIGHTEMITTINGDIODE
The LED is a PN-junction diode
which emits light when an electric
current passes through it in the
forward direction. In the LED, the
recombination of charge carrier
takes place. The electron from the N-
side and the hole from the P-side are
combined and gives the energy in
the form of heat and light. The LED
is made of semiconductor material
which is colourless, and the light is
radiated through the junction of the
diode.

52. SHOCKLEYDIODES
Shockley diode is a four layer (P-N-P-
N) device. It conducts when it is
forward biased and stops conducting
when it is reverse biased. The major
difference between conventional
diode and Shockley diode is, it starts
conducting when the forward voltage
exceeds break-over voltage
Most common applications of
Shockley diode are switching circuits ,
to turn ON the SCR. In the below
circuit SCR is triggered by the shockley
diode.

53. DIODETESTINGBY DMMIN DIODEMODE

54. DIODETESTINGBY DMMIN RESISTANCEMODE

55. RECTIFIRES
A rectifier is an electrical device
that converts an Alternating
Current (AC) into a Direct Current
(DC) by using one or more P-N
junction diodes.
The rectifiers are mainly
classified into two types:
• Half wave rectifier
• Full wave rectifier
We can further classify full wave
rectifiers into
• Centre-tapped Full Wave Rectifier
• Full Wave Bridge Rectifier

56. HALF-WAVERECTIFIER
When we use a half-wave
rectifier, a significant amount
of power gets wasted as the
only one half of each cycle
passes through and the other
the cycle gets blocked.
Moreover, the half-wave
rectifier is not efficient
(40.6%) and we can not use it
for applications which need a
smooth and steady DC
output.

57. CENTRE-TAPPEDF.W.R.
A centre-tapped full wave
rectifier system consists of:
Centre-tapped Transformer
Two Diodes
Resistive Load
For centre-tapped full-wave
rectifier, ηmax = 81.2%

58. BRIDGEF.W.R
A full wave bridge rectifier is a
type of rectifier which will use
four diodes or more than that
in a bridge formation. A full
wave bridge rectifier system
consists of
Four Diodes
Resistive Load
For bridge full-wave rectifier,
ηmax = 81.2%

59. FILTERS
A Rectifier usually converts an
AC signal to a pulsating
DC signal which also has a
considerable amount of AC
component in it, known
as ripple. This is something that
is not necessary as most of the
electronic systems are driven by
pure DC. In order to remove this
ripple, filters are used.

60. CLASSIFICATIONOFFILTERS
Filter is mainly classified into two types:
• Active Filter
• Passive Filter
ActiveFilters
• Filter Circuit which consists of active components like
Transistors and Op-amps in addition to Resistors and Capacitors
is called as Active Filter.
PassiveFilters
• Filter circuit which consists of passive components such as
Resistors, Capacitors and Inductors is called as Passive Filter.

61. TYPES OFFILTERS
 Capacitor filter (C-filter)
 Inductor filter ( L-filter)
 Choke input filter (LC-filter)
 Capacitor input filter (CLC or 𝝅-filter)

62. TRANSISTOR
These devices are made up of
semiconductor material which is
commonly used for amplification
or switching purpose, it can also
be used for the controlling flow
of voltage and current. It is also
used to amplify the input signals
into the extent output signal. A
transistor is usually a solid state
electronic device which is made
up of semiconducting materials.

63. TRANSISTOR
Transistor consists of three layers of semiconductor, which have an
ability to hold current. The electricity conducting material such as
silicon and germanium has the ability to carry electricity between
conductors and insulator which was enclosed by plastic wires.
Semiconducting materials are treated by some chemical procedure
called doping of the semiconductor.
How Does Transistor Work?
• The working concept is the main part to understand how to use a
transistor or how it works?, there are three terminals in the transistor:
• Base: It gives base to the transistor electrodes.
• Emitter: Charge carriers emitted by this.
• Collector: Charge carriers collected by this.

64. CLASSIFICATIONOF TRANSISTOR

65. BIPOLARJUNCTIONTRANSISTOR(BJT)
A Bipolar junction transistor is made up of
doped semiconductor with three
terminals i.e., base, emitter & collector. In
this procedure, holes and electrons both
are involved. A large amount of current
passing into collector to emitter switches
up by modifying small current from base
to emitter terminals. These are also called
as current controlled
devices. NPN and PNP are two prime
parts of BJTs as we discussed earlier. BJT
turned on by giving input to base because
it has lowest impedance for all transistors.
Amplification is also highest for all
transistors.

66. TRANSISTORCONFIGURATIONS
Generally, there are three types of configurations and their
descriptions with respect to gain is as follows:
Common Base (CB) Configuration: It has no current gain but has
voltage gain.
Common Collector (CC) Configuration: It has current gain but no
voltage gain.
Common Emitter (CE) Configuration: It has current gain and voltage
gain both.

67. JFET
JFET is the simplest type of field-effect transistor in which the current
can either pass from source to drain or drain to source. Unlike bipolar
junction transistors (BJTs), JFET uses the voltage applied to the gate
terminal to control the current flowing through the channel between
the drain and source terminals which results in output current being
proportional to the input voltage. The gate terminal is reverse-biased.
It’s a three-terminal unipolar semiconductor device used in electronic
switches, resistors, and amplifiers. It anticipates a high degree of
isolation between input and output which makes it more stable than a
bipolar junction transistor. Unlike BJTs, the amount of current allowed
is determined by a voltage signal in a JFET.

68. MOSFET
MOSFET is a four-terminal semiconductor field effect transistor
fabricated by the controlled oxidation of silicon and where the
applied voltage determines the electrical conductivity of a
device. MOSFET stands for Metal Oxide Semiconductor Field
Effect Transistor. The gate which is located between the source
and drain channels is electrically insulated from the channel by a
thin layer of metal oxide. The idea is to control the voltage and
current flow between the source and drain channels. MOSFETs
play a vital role in integrated circuits because of their high input
impedance. They are mostly used in power amplifiers and
switches, plus they play a critical role in embedded system
design as functional elements.

69. JFET& MOSFET

70. TRANSISTORASA SWITCH
A Transistor switch, which is used for opening or closing of a circuit, that
means the transistor is commonly used as a switch in the electronic
devices only for the low voltage applications because of its
low power consumption. Transistor work as a switch when it is in cutoff
and saturation regions.

71. TRANSISTORBIASING
The supply of suitable external dc voltage is called as biasing.
Either forward or reverse biasing is done to the emitter and
collector junctions of the transistor. These biasing methods
make the transistor circuit to work in four kinds of regions such
as Active region, Saturation region, Cutoff region and Inverse
active region

72. TRANSISTORBIASING
EMITTER JUNCTION COLLECTOR JUNCTION REGION OF OPERATION
Forward biased Forward biased Saturation region
Forward biased Reverse biased Active region
Reverse biased Forward biased Inverse active region
Reverse biased Reverse biased Cutoff region

73. NPN TRANSISTORSWITCHINGCIRCUIT

74. PNP TRANSISTORSWITCHINGCIRCUIT

75. POWERRATING
According to power capacity transistor are 3 types
• Low power transistor (<2W)
• Medium power transistor (2 to 10W)
• High power transistor (>10W)

76. TRANSISTORNOMENCLATURE
B C 556
Semiconducting material Main function Type code

77. SEMICONDUCTINGMATERIAL
A = Germanium
B = Silicon
C = Gallium Arsenide
R = Compound materials

78. MAINFUNCTION
A = Diode - low power or signal
B = Diode - variable capacitance
C = Transistor - audio frequency, low
power
D = Transistor - audio frequency, power
E = Tunnel diode
F = Transistor - high frequency, low power
G = Miscellaneous devices
H = Diode - sensitive to magnetism
L = Transistor - high frequency, power
N = Photocoupler
P = Light detector
Q = Light emitter
R = Switching device, low power, e.g.
thyristor, diac, unijunction
S = Transistor - switching low power
T = Switching device, low power, e.g.
thyristor, triac
U = Transistor - switching, power
W = Surface acoustic wave device
X = Diode multiplier
Y = Diode rectifying
Z = Diode - voltage reference

79. TYPE CODE
• NPN – BC546,BC547,BC548,BC549,BC550
• PNP – BC556,BC557,BC558,BC559,BC560
Suffix
On some occasions there may be a suffix letter that is added:
• A = low gain
• B = medium gain
• C = high gain
• No suffix = gain unclassified

80. TRANSISTORTESTINGMETHODS
RESISTANCE MODE
DIODE MODE
hFE (Hybrid parameter forward current gain, common emitter)

81. BYDMM
RESISTANCEMODE
Low Resistance – Collector
High Resistance – Emitter
Diode mode
Low voltage – emitter
High voltage - collector

82. HFE

83. INTEGRATEDCIRCUITS
• An integrated circuit (IC) is a miniature, low cost electronic circuit
consisting of active and passive components fabricated together on a
single crystal of silicon. The active components are transistors and diodes
and passive components are resistors and capacitors.

84. DEPENDINGUPONTHENUMBEROF ACTIVEDEVICESPERCHIP,THERE
AREDIFFERENTLEVELSOFINTEGRATION

85. REGULATORIC
IC (integrated circuit)
It stands for integrated circuit.
It is commonly used in electronic circuit.
When more no. of electronics components fabricated in single chip is known as IC.
REGULATING IC
There are the regulator which provide fixed or variable output voltage to the load.
Regulating IC are of two types:-
• Fixed regulating IC
• Variables regulating IC

86. FIXEDREGULATINGIC
In a fixed voltage regulator IC the output voltage is maintained at a fixed
voltage for the load.
It is divided into two types-
• POSITIVE FIXED VOLTAGE REGULATING IC
• NEGATIVE FIXED VOLTAGE REGULATING IC

87. FIXEDREGULATINGIC
These regulators provide a constant output voltage. A popular example is the
7805 IC which provides a constant 5 volts output.
A fixed voltage regulator can be a positive voltage regulator or a negative voltage
regulator. A positive voltage regulator provides with constant positive output
voltage.
 All those IC’s in the 78XX series are fixed positive voltage regulators. In the IC
nomenclature – 78XX; the part XX denotes the regulated output voltage the IC is
designed for. Examples: - 7805, 7806, 7809 etc.
A negative fixed voltage regulator is same as the positive fixed voltage regulator
in design, construction & operation. The only difference is in the polarity of
output voltages. These IC’s are designed to provide a negative output voltage.
Example: - 7905, 7906 and all those IC’s in the 79XX series.

88. POSITIVEFIXEDVOLTAGEREGULATINGIC
The voltage regulating IC which
gives only positive fixed voltage at
the output terminal when input is
given more than its output voltage.
There are 3 terminals from left
hand side 1stpin is input, 2nd pin is
ground and 3rd pin is output.
Ex. 7805, 7809, 7812, 7824 etc.

89. NEGATIVEFIXEDVOLTAGEREGULATING IC
The voltage regulating IC which
gives only negative fixed voltage at
the output side or terminal when
the input is given more than its
output voltage.
There are 3 terminals from left
hand side 1st pin is ground, 2nd pin
is input and 3rd pin is output.
Ex. 7905, 7912, 7909, 7924 etc.

90. VARIABLES VOLTAGE REGULATOR
An adjustable voltage regulator is a kind of regulator whose regulated output
voltage can be varied over a range. There are two variations of the same; known
as positive adjustable voltage regulator and negative adjustable regulator.
LM317 is a classic example of positive adjustable voltage regulator, whose output
voltage can be varied over a range of 1.2 volts to 57 volts. LM337 is an example of
negative adjustable voltage regulator.
LM337 is actually a complement of LM317 which are similar in operation &
design; with the only difference being polarity of regulated output voltage.
There may be certain conditions where a variable voltage may be required. Right
now we shall discuss how an LM317 adjustable positive voltage regulator IC is
connected.

91. SILICONCONTROLLEDRECTIFIER
The Silicon Controlled Rectifier (SCR) is
the most important and mostly used
member of the thyristor family. SCR can
be used for different applications like
rectification, regulation of power and
inversion, etc. Like a diode, SCR is a
unidirectional device that allows the
current in one direction and opposes in
another direction.
SCR is a three terminal device; anode,
cathode and gate as shown in figure. SCR
has built in feature to turn ON or OFF and
its switching is controlled by biasing
conditions and gate input terminal.

92. WORKINGORMODESOF OPERATIONOF SCR
Depending on the biasing given to the SCR, the operation of SCR is divided
into three modes. They are
• Forward blocking Mode
• Forward Conduction Mode and
• Reverse Blocking Mode

93. FORWARDBLOCKINGMODE
In this mode of operation, the Silicon Controlled Rectifier is connected such that
the anode terminal is made positive with respect to cathode while the gate
terminal kept open. In this state junctions J1 and J3 are forward biased and the
junction J2 reverse biased.
Due to this, a small leakage current flows through the SCR. Until the voltage
applied across the SCR is more than the break over voltage of it, SCR offers a very
high resistance to the current flow. Therefore, the SCR acts as a open switch in
this mode by blocking forward current flowing through the SCR

94. FORWARDCONDUCTIONMODE
In this mode, SCR or thyristor comes into the conduction mode from
blocking mode. It can be done in two ways as either by applying positive
pulse to gate terminal or by increasing the forward voltage (or voltage
across the anode and cathode) beyond the break over voltage of the SCR.
Once any one of these methods is applied, the avalanche breakdown
occurs at junction J2. Therefore the SCR turns into conduction mode and
acts as a closed switch thereby current starts flowing through it.

95. REVERSEBLOCKING MODE
In this mode of operation, cathode is made positive with respect to anode.
Then the junctions J1 and J3 are reverse biased and J2 is forward biased.
This reverse voltage drives the SCR into reverse blocking region results to
flow a small leakage current through it and acts as an open switch

96. SCRTURNON METHODS(SCRTRIGGERING)
With a voltage applied to the SCR, if the anode is made positive with respect to
the cathode, the SCR becomes forward biased. Thus, the SCR comes into the
forward blocking state. The SCR can be made to conduct or switching into
conduction mode is performed by any one of the following methods.
• Forward voltage triggering
• Temperature triggering
• dv/dt triggering
• Light triggering
• Gate triggering

97. SCRFIRINGCIRCUITS
As we have seen in above that out of various triggering methods to turn
the SCR, gate triggering is the most efficient and reliable method. Most of
the control applications use this type of triggering because the desired
instant of SCR turning is possible with gate triggering method. Let us look
on various firing circuits of SCR.
• Resistance (R) Firing Circuit
• Resistance – Capacitance (RC) Firing Circuit

98. RESISTANCE(R) FIRINGCIRCUITOF SCR

99. RESISTANCE – CAPACITANCE(RC) FIRINGCIRCUITOF
SCR

100. TESTINGOF SCR