The document provides an overview of a class on fundamentals of power electronics. It covers topics like power electronics, power control using devices like thyristors, characteristics of SCR including V-I characteristics and different turn on/off methods. Diagrams are included to explain concepts like two transistor analogy of SCR, different commutation techniques etc. The document acts as notes for a class on basic concepts of power electronics.

1. Fundamental of Power Electronics
(FPE)
Class:- EE3I
Date:-
07/09/2020
BY
Y.R.Kute

2. Power Electronics:- Power Electronics
is the branch of electrical
Engineering that deals with control
and conversion of Electric Power
Class:- EE3I
Date:-
07/09/2020
• Electrical Engineering deals with
very large power (Voltage and
Current)
• Electronics Engineering deals with
very low voltage (Say 5Volt or 12
Volt)
Power Electronic makes use of Solid state
devices (Semiconductor Devices) for control
and conversion)

3. Power Electronics Basically deals with
Control and Conversion of Electric
Power
Class:- EE3I
Date:-
07/09/2020
Control:- Power Electronic Devices are
used for Controlling Electric Power from
Source to load
Eg:- Fan Speed Regulator
Conversion:- This deals with conversion of
Electric Power from One form to other
Eg:- Rectifier, Inverter, Chopper,
Cycloconverter

4. Class:- EE3I
Date:-
07/09/2020
Control Application
Electric Fan
Regulator
Conversion
Application
Rectifier

5. Applications of Power
Electronics
Class:- EE3I
Date:-
07/09/2020
1. Power supply for Battery operated
vehicles
2. In induction Heating applications
3. In Railway Locomotives
4. Washing machine, Dryers, Air
conditioning
5. In fan Regulator , Light dimmer
application
6. In motor control application for
controlling AC and DC motors.

6. Class:- EE3I
Date:-
07/09/2020
Thyristor
Power control
Thyristor
Triggering
Devices
Unidirectional Bidirectional
SCR LASCR
SUS
SCS LASCS
TRIAC
UjT SBS
DIA
C
SUS

7. Silicon Controlled
Rectifier(SCR)
Class:- EE3I
Date:-
07/09/2020
SCR is Silicon Controlled Rectifier,
it is Four layer , three terminal, three
junction Semiconductor Device.
Structure of
SCR
Symbol of
SCR
Package of
SCR

8. P and N Type
o f
Semiconductors
Class:- EE3I
Date:-
07/09/2020
P type of Semiconductor is formed by adding
/Doppping trivalent impurity to Semiconductor
(Si or Ge)
P type of impurities are.. Boron, Gallium, Aluminum,
Indium
N type of Semiconductor is formed by
adding/Dopping Penta valent impurity to
Semiconductor (Si or Ge)
N type of impurities are…Phosphorus, Antimony,
Arsenic, Bismuth
N-Type has
Electrons
P - Type has
Holes
1
1

9. Forward and Reverse
Bias
Class:- EE3I
Date:-
07/09/2020
Forward Bias –
On state
P terminal
+Ve
N terminal -
Ve
Reverse Bias –
On
state
P terminal -
Ve
N terminal
+Ve
+
+
-
-
Note:- Current Flows through Device in
Forward Bias
Note:- No Current Flows through Device in
Reverse Bias

10. SCR Special
Features
Class:- EE3I
Date:-
07/09/2020
1. It is four layer Three terminal device
2. Gate Terminal is used to turn on the
3. It can handle very large amount of
voltage, current and power.
4. It can be easily turned on with Gate
Terminal.
5. Power Delivered to load can be easily
controlled with SCR

11. V-I characteristics of
SCR
Class:- EE3I
Date:-
07/09/2020

12. V-I characteristics of
SCR
Class:- EE3I
Date:-
07/09/2020
V-I characteristics
of SCR is divided
into three states
1. Forward Blocking
State
2. Forward
Conduction State
3. Reverse Blocking
State
•

13. V-I characteristics of
SCR
Class:- EE3I
Date:-
07/09/2020
Forward Blocking
State:-
+
-
+ -
(I)
(V)
Vbo
Forward
Blocking
State
0
Junction J1:- Forward
Bias
J2:-
Reverse Bias
J3:-
Forward Bias
Small
Leakage
Current

14. V-I characteristics of
SCR
Class:- EE3I
Date:-
07/09/2020
Forward Conduction
State:-
+
+ -
(I)
(V)
Vbo
Forward
Blocking
State
-
Forward
Conduction
State
0
Junction J1:- Forward
Bias
J2:-
Reverse Bias
J3:-
Forward Bias

15. V-I characteristics of
SCR
Class:- EE3I
Date:-
07/09/2020
Reverse Blocking
State:-
+
+
-
(I)
(V) Vbr
-
Reverse
Blocking
State
0
Reverse
Leakage
Current
-
+
Junction J1:- Reverse
Bias
J2:-
Forward Bias
J3:-
Reverse Bias

16. V-I characteristics of
SCR
Class:- EE3I
Date:-
07/09/2020
Forward Conduction
State:-
+
+ -
(I)
(V)
Vbo
-
Forward
Conduction
State
+
+ + + +
Ig0
Ig1
Ig2
Ig3
Ig3 > Ig2 > Ig1 > Ig0
0
Junction J1:- Forward
Bias
J2:-
Reverse Bias
J3:-
Forward Bias

17. V-I characteristics of
SCR
Class:- EE3I
Date:-
14/09/2020
Forward Conduction
State:-
+
+ -
(I)
(V)
Vbo
-
Holding
Current
+
+ + + +
Ig0
Ig1
Ig2
Ig3
Ig3 > Ig2 > Ig1 > Ig0
0
Junction J1:- Forward
Bias
J2:-
Reverse Bias
J3:-
Forward Bias
Latching
Current
IL
IH

18. Important
Definition
Class:- EE3I
Date:-
14/09/2020
1. Forward Break over voltage (Vbo):-
Maximum voltage applied across SCR in forward blocking state
without initiating forward condition is called as Forward Break
over voltage(Vbo)
2. Reverse Break over voltage (Vbr):-
Voltage across SCR in Reverse Blocking state at which device
enters into Breakdown.
3. Forward Leakage Current
Small current flowing through SCR in forward Blocking
state due to minority carrier is called as Forward Leakage
Current . It is very small of the order of nano amp or micro
amp

19. Important
Definition
Class:- EE3I
Date:-
14/09/2020
4. Holding Current (IH) :-
It represent minimum current that can flow through SCR and
can hold it in On state. When current becomes less than Holding
current SCR turns into OFF state.
5. Latching Current (IL)
It represents Minimum current that must flow through
SCR to latch into On state. It is always greater than Holding
Current.
6. On State Voltage :-
Voltage across SCR when it enters into forward conduction
state. It is very low of the order of 1Volt or 1.5 volt

20. Class:- EE3I
Date:-
16/09/2020
Two Transistor Analogy of
SCR
Equivalent to
Equivalent
to

21. Class:- EE3I
Date:-
16/09/2020
Two Transistor Analogy of
SCR
Ia- Anode Current
Ig- Gate Current
Ik- Cathode Current
Ia=Emitter current of PNP transistor
Ig=Base current of NPN transistor
Ik=Emitter current of NPN transistor

22. Class:- EE3I
Date:-
16/09/2020
Two Transistor Analogy of
SCR
IA- Anode Current
ICO1- Leakage current of PNP
transistor
ICO2- Leakage current of NPN
transistor
α1 - Common base current gain of
PNP transistor
α2 - Common base current gain of
NPN transistor

23. Symbol and
Characteristics of Power
Semiconductor Devices
Class:- EE3I
Date:-
16/09/2020
1. SCR (Silicon Controlled Rectifier)
2. LASCR (Light Activated Silicon Controlled Rectifier)

24. Class:- EE3I
Date:-
16/09/2020
3. TRIAC (Triode AC)
4. DIAC (Diode AC)
5. UJT (Uni Junction
Transistor)
6. SBS (Silicon Bilateral
Switch)
7. SCS (Silicon Controlled
Switch)

25. Turn on Methods
of SCR
Class:- EE3I
Date:-
28/09/2020
Process of turning on SCR is also called as
Triggering of SCR or Firing of SCR
• Forward Voltage Triggering
• Gate Triggering
• dv/dt Triggering
• Temperature Triggering
• Light Triggering
Turn on Methods of SCR are as follows

26. Turn on Methods
of SCR
Class:- EE3I
Date:-
28/09/2020
1. Forward Voltage Triggering
In this method Gate current IG=0 , Anode is
at positive potential w.r.t. cathode , If anode
voltage is increased to break over voltage VBO
,
 SCR turns into On condition. This method is
called as Forward Voltage Triggering. In actual
practice this method is not used as it requires
large anode to cathode voltage and also large
current Generation occurs.
 It may cause damage to the thyristor. In
this method avalanche breakdown occurs
+
-

27. Turn on Methods
of SCR
Class:- EE3I
Date:-
28/09/2020
2. Gate Triggering
Gate Triggering is a simple reliable and
efficient method. At a desired moment of
turn- On suitable positive voltage is applied to
Gate terminal. This result in gate current. As
the value of Gate Current (IG ) increases
required anode to cathode Voltage decreases.
 Gate current of magnitude 20mA to 200mA
is applied.

28. Class:- EE3I
Date:-
28/09/2020
3. dv/dt Triggering
When anode to cathode voltage is positive
outer junction J1 and J3 get forward biased
and inner junction J2 reverse biased Junction
behaves as a Capacitor
Charging Current of Capacitor depends upon rate
of rise of forward Voltage
 If forward Voltage is suddenly applied then
Charging current would be large. Due to this
phenomenon SCR enters into Turn On state.
However this dv/dt turn On has to be avoided
Rate of change of applied voltage is kept below the
specified rate.
J1
J2
J3

29. Class:- EE3I
Date:-
28/09/2020
4. Light Triggering
 Light can be used to turn On SCR
by causing Breakdown of the junction
J2 with junction J1 and J3 forward
Biased
 In Light triggered SCR gate
region is made up of Light sensitive
material, When a ray of light of
suitable intensity and wavelength is
incident on the Gate junction of SCR
Gate current increases it makes
forward bias SCR to enter into On state
Light Radiation

30. Turn on Methods
of SCR
Class:- EE3I
Date:-
28/09/2020
4. Thermal Triggering
 Width of depletion layer of SCR
decreases with increase in junction
temperature
 Therefore in SCR when anode
voltage is nearer to breakdown voltage
device is triggered by increasing
junction temperature
 By increasing junction temperature
reverse bias junction collapses thus
device starts to conduct.
Temp.

31. Turn OFF Methods
of SCR
Class:- EE3I
Date:-
28/09/2020
 Transition of SCR from On state to Off state is called as
Turn off method of SCR
 Process of turning off SCR is also called as Commutation
of SCR
 Time required to turn SCR Off from On state is Called
as Turn off Time of SCR
SCR can be turned off / Commutation can be achieved by
1. Reducing current flowing through SCR below Holding current by
decreasing Forward Voltage
2. Reducing current flowing through SCR below Holding current by
increasing load impedance
3. By reverse voltage across SCR forcing zero current to flow
through SCR

32. Types of
Commutation
Class:- EE3I
Date:-
28/09/2020
Commutation is basically classified into two types
 Natural commutation
-> In this process of commutation No external circuit is applied, to
turn off SCR, SCR turns off at its own.
Eg. Class F commutation
 Forced commutation
-> In this process of commutation external circuit is applied, to turn it
off. SCR doesn’t turns off at its own.
Eg. Class A, Class B, Class C, Class D, Class E commutation

33. Class:- EE3I
Date:-
28/09/2020
Classification of Commutation
Techniques
Natural commutation
1. Class F commutation (AC Line Commutation)
Forced commutation
1. Class A Commutation (Resonant Commutation)
2. Class B Commutation (Self Commutation)
3. Class C Commutation (Complimentary Commutation)
4. Class D Commutation (Auxiliary Commutation)
5. Class E Commutation (External Pulse Commutation)

34. Class:- EE3I
Date:-
28/09/2020
 This method of Commutation is also called as Resonant Commutation
 Commutation component L and C are connected in series or parallel
with the load
 In this technique Current through L and C components is reduced to
natural zero due to L and C component
1. Class A Commutation ( Resonant Commutation)

35. Class:- EE3I
Date:-
28/09/2020
This method of Commutation is also called as Self Commutation
 Here, SCR is turned off by Resonating L and C component, but they do not carry
load current.
 Here, initially capacitor C charges with upper plate positive, As soon as SCR is
turned on capacitor discharges through SCR and starts charging in opposite
direction
 Making upper plate of capacitor negative and lower plate positive, thus negative
voltage is applied across SCR which in turns turns it off
2. Class B Commutation ( Self Commutation )

36. Class:- EE3I
Date:-
28/09/2020
2. Class B Commutation ( Self Commutation )
+
-

37. Class:- EE3I
Date:-
28/09/2020
 This method of Commutation is also called as Complimentary Commutation
 This method consist of main thyristor T1 and complimentary Thyristor T2 in
parallel with T1
 Triggering of One SCR turns off other SCR and vice versa
 When SCR T1 is turned on current flows through Load 1 and T1 also current flows
through Load2- Capacitor C- T1

 When T2 is turned on Voltage across capacitor appears across SCR which is
negative voltage turns it into off State
3. Class C Commutation (Complimentary Commutation )

38. Class:- EE3I
Date:-
28/09/2020
3. Class C Commutation (Complimentary Commutation )
OFF

39. Class:- EE3I
Date:-
28/09/2020
3. Class C Commutation (Complimentary Commutation )
ON
+ -
OFF

40. Class:- EE3I
Date:-
28/09/2020
 This method of Commutation is also called as Auxiliary Commutation.
 Here, commutation elements are Capacitor, Inductor and Auxiliary Thyristor.
 As shown in circuit T1 is main SCR and T2 is auxiliary SCR.
 Here initially T1 is turned on thus capacitor C charges with polarity as upper
plate negative and lower plate positive.
 In order to turn off SCR T1, SCR T2 is turned ON thus voltage of Capacitor.
appears across SCR T1 turning it off, as capacitor voltage of reveres polarity is
applied.
4. Class D Commutation (Auxiliary Commutation )
-
+

41. Class:- EE3I
Date:-
28/09/2020
 This method of Commutation is also called as External Pulse Commutation.
 Here reverse voltage is applied to the current carrying SCR from external pulse
source.
 Pulse transformer is used to apply commutating pulse.
 Voltage at secondary of pulse transformer appears across SCR T1 as reverse
voltage and turns it OFF.
5. Class E Commutation
(External Pulse Commutation)

42. Class:- EE3I
Date:-
28/09/2020
 It is AC line Commutation method.
 If supply is Alternating voltage, load current flows during the positive half cycle.
 During negative half cycle the SCR will turn OFF.
 Duration of negative half cycle must be greater than turn off time of SCR.
 It is natural commutation, It doesn’t requires any additional Commutation circuit.
 This method is used in controlled Rectifiers.
Class F Commutation
(AC Line Commutation)

43. Class:- EE3I
Date:-
12/10/2020
SCR Protection Circuits
1. Over voltage protection.
2. Over current protection.
3. High dv/dt protection.
4. High di/dt protection.
5. Thermal protection.

44. Class:- EE3I
Date:-
12/10/2020
1. Over voltage protection
Over voltage across SCR is one of the cause
of failure of SCR
This can be avoided by using
1. Snubber circuit
2. Non-Linear Device

45. Class:- EE3I
Date:-
12/10/2020
a. Snubber circuit
Over voltage across SCR is one of the cause
of failure of SCR
This can be avoided by using

46. Class:- EE3I
Date:-
12/10/2020
b. Non Linear Device
Over voltage across SCR is one of the cause
of failure of SCR
This can be avoided by using

47. Class:- EE3I
Date:-
12/10/2020
2. Over Current protection
Over Current through SCR is one of the cause
of failure of SCR
This can be avoided by using Circuit Breakers,
Fast Responding Fuse

48. Class:- EE3I
Date:-
12/10/2020
3. High dv/dt protection
High dv/dt through SCR is one of the cause of
failure of SCR
This can be avoided by using Snubber Circuit

49. Class:- EE3I
Date:-
12/10/2020
4. High di/dt protection
High di/dt through SCR is one of the cause of
failure of SCR
This can be avoided by using inductor Circuit

50. Class:- EE3I
Date:-
12/10/2020
5. Thermal Protection of SCR
High Temperature of SCR is one of the cause
of failure of SCR
This can be avoided by using Heat sink Circuit

51. Class:- EE3I
Date:-
12/10/2020
Overall Protection of SCR

52. Class:- EE3I
Date:-
14/10/2020
Different Gate Trigger Circuits
1. UJT Triggering (UJT Relaxation Oscillator)
2. PUT Triggering (PUT Relaxation Oscillator)

53. Class:- EE3I
Date:-
14/10/2020
UJT Triggering
(UJT Relaxation Oscillator)

54. Class:- EE3I
Date:-
14/10/2020
UJT Triggering
(UJT Relaxation Oscillator)

55. Class:- EE3I
Date:-
14/10/2020
PUT Triggering
(PUT Relaxation Oscillator)

56. Class:- EE3I
Date:-
14/10/2020
PUT Triggering
(PUT Relaxation Oscillator)

57. Class:- EE3I
Date:-
14/10/2020
Opto-coupler based
triggering

58. Class:- EE3I
Date:-
23/12/2020
Phase Controlled Rectifiers:-
Uncontrolled Rectifiers:- The rectifiers using
diodes operates on AC supply voltage ,
Which converts A.C. Voltage into fixed dc
voltage
Controlled Rectifiers:- The rectifiers
using SCR’s operates on AC supply
voltage , Which converts A.C. Voltage
into variable dc voltage by varying firing
angle (α)

59. Class:- EE3I
Date:-
13/01/2021
Phase Controlled Rectifiers:-
Phase Control:- Controlled Rectifiers converts
A.C. Voltage into Variable DC voltage. They
makes use of Technique called as phase angle
control to change firing angle or delay angle or
Phase angle.
Firing Angle (α) :- In AC circuits we can turn on
the SCR with the help of gate triggering circuits
at any angle with respect to applied voltage.
• Angle with respect applied input voltage at
which SCR is turned on is called as Firing Angle
(α)
• Firing angle can have any value between 0 to 180
degree
Conduction Angle:- Angle for which SCR is in
conduction state is called as conduction angle
Conduction angle=(180- α)

60. Class:- EE3I
Date:-
13/01/2021
Classification of Phase
Controlled Rectifiers:-
1Φ Controlled
Rectifier
Half wave Controlled
Rectifier
Full wave Controlled
Rectifier
Mid Point Converter
Bridge Converter
Full Converter
(4 SCR’s)
Semi Converter
(2 Diode & 2SCR’s)

61. Class:- EE3I
Date:-
13/01/2021
Types of Load in Phase
Controlled Rectifiers:-
Resistive Load (R) Inductive Load (RL)

62. Class:- EE3I
Date:-
13/01/2021
Single Phase half Wave Controlled
Rectifier with Resistive load:-

63. Class:- EE3I
Date:-
13/01/2021
Inductive load
 Inductor doesn’t like change, in voltage (It opposes
Change).
 It tries to maintain same circuit condition.
 In case of controlled rectifier, Inductor reverses polarity
of voltage across it in order to maintain same circuit
conditions.
 When it reverses its polarity, It discharge the energy
stored in magnetic field. Because of that SCR remains in On state even
in negative half cycle.

64. Class:- EE3I
Date:-
13/01/2021
Single Phase half Wave Controlled
Rectifier with Inductive load:-

65. Class:- EE3I
Date:-
13/01/2021
Single Phase half Wave Controlled
Rectifier with Inductive load and
Free wheeling diode:-

66. Class:- EE3I
Date:-
13/01/2021
Free wheeling diode
 Free wheeling diode is connected in parallel with Inductive load
 It doesn’t allows inductor to reverse its polarity
 Energy stored in inductor is dissipated through Free wheeling
diode and resistor R.
 It improves power factor
 Load voltage doesn’t goes negative due to presence of free
wheeling diode

67. Class:- EE3I
Date:-
13/01/2021
Single Phase half Wave Controlled
Rectifier with Resistive load:-

68. Class:- EE3I
Date:-
13/01/2021
Single Phase Full Wave Controlled
Rectifier with Inductive load:-
Center tap Rectifier

69. Class:- EE3I
Date:-
13/01/2021
Single Phase Full Wave Controlled
Rectifier with Inductive load &
Free Wheeling diode:-
Center tap Rectifier
Center tap
Rectifier

70. Class:- EE3I
Date:-
13/01/2021
Single Phase Full Wave Controlled
Rectifier with Inductive load:-

71. Class:- EE3I
Date:-
13/01/2021
Single Phase Full Wave Controlled
Rectifier with Inductive Load:-

72. Class:- EE3I
Date:-
13/01/2021
Single Phase Full Wave Controlled
Rectifier with Inductive Load &
Free wheeling Diode:-

73. Class:- EE3I
Date:-
13/01/2021
Semi converter
( 2-SCR & 2 PN junction diode)

74. Class:- EE3I
Date:-
13/01/2021
Power Electronic
Circuits….

75. Class:- EE3I
Date:-
13/01/2021
Burglar Alarm

76. Class:- EE3I
Date:-
13/01/2021
Battery Charger using SCR

77. Class:- EE3I
Date:-
13/01/2021
Emergency Lighting system

78. Class:- EE3I
Date:-
13/01/2021
Emergency Lighting system

79. Class:- EE3I
Date:-
13/01/2021
Fan Speed Regulator

80. Class:- EE3I
Date:-
13/01/2021
Switch Mode Power Supply

81. Class:- EE3I
Date:-
13/01/2021
Switch Mode Power Supply

82. Class:- EE3I
Date:-
13/01/2021
UPS

83. Class:- EE3I
Date:-
13/01/2021
UPS