1. Power Electronics Lecture(8)
Prof. Mohammed Zeki Khedher
Department of Electrical Engineering
University of Jordan 1

2. Thyristors Most important type of power semiconductor device.
Have the highest power handling capability.they have a rating of 5000V / 6000A with switching frequencies ranging from 1KHz to 20KHz. 2

3. Is inherently a slow switching device compared to BJT or MOSFET.
Used as a latching switch that can be turned on by the control terminal but cannot be turned off by the gate. 3

4. Silicon Controlled Rectifier
SCR
Symbol of
Silicon Controlled Rectifier 4

5. Structure 5

6. Simplified model of a thyristor
Device Operation
Simplified model of a thyristor 6

7. Two Transistor Model of SCR 7

8. 8

9. 9

10. 10

11. 11

12. 12

13. 13

14. V-I Characteristics 14

15. Effects of gate current15

16. Turn-on Characteristics16

17. Turn-off Characteristics17

18. dv/dt Triggering 18

19. 19

20. Switching Characteristics (linearized)
Switching Power Loss is proportional to:
switching frequency
turn-on and turn-off times

21. Methods of Thyristor Turn-on
Thermal Turn-on.
Light.
High Voltage.
Gate Current.
dv/dt. 21

22. Thyristor Ratings First Subscript Second Subscript Third Subscript
D  off state
W  working
M  Peak Value
T  ON state
R  Repetitive
F  Forward
S Surge or non-repetitive
R  Reverse 22

23. Voltage Ratings 23

24. Current Ratings 24

25. Gate Specification 25

26. Diodes
Diode Product Range

27. Phase Control Thyristors

28. Fast switching Thyristors

29. Thyristor Types Phase-control Thyristors (SCR’s).
Fast-switching Thyristors (SCR’s).
Gate-turn-off Thyristors (GTOs).
Bidirectional triode Thyristors (TRIACs).
Reverse-conducting Thyristors (RCTs). 29

30. Static induction Thyristors (SITHs).
Light-activated silicon-controlled rectifiers (LASCRs).
FET controlled Thyristors (FET-CTHs).
MOS controlled Thyristors (MCTs). 30

31. PHASE-CONTROL THYRISTORS : primarily for rectifying line frequency voltage and currents (phase controlled AC and DC motor drivers and high voltage power transmission). Average current 4000A, blocking voltage 5-7kV and on-state voltage 1.5-3V
INVERTER-GRADE THYRISTORS: small turn-off times (from a few µs to100µs depends on their blocking voltage and on-state voltage drops), and small on-state voltage,
2500V-1500A.
LIGHT-ACTIVATED THYRISTORS: triggered by a pulse of light guided by optical fibers to a sensitive region, used primarily in high voltage application such as high voltage power transmission 4kV-3kA

32. Devices SITH = Static Induction Thyristor
GTO = Gate Turn Off Thyristor
MOS = Metal Oxide Semiconductor
MCT = MOS Controlled Thyristor
MTO = MOS Turn Off Thyristor
ETO = Emitter Turn Off Thyristor
IGCT = Insulated Gate Controlled Thyristor
TRIAC = Triode Thyristor
LASCR = Light Activated SCR

33. Devices.. NPN BJT = NPN Bipolar Junction Transistor
IGBT = Insulated Gate Bipolar Junction Transistor
N-Channel MOSFET = N-Channel Metal Oxide Silicon Field Effect Transistor
SIT = Static Induction Transistor
RCT = Reverse Conducting Thyristor
GATT = Gate Assisted Turn Off Thyristor

34. Power Semiconductor Devices, their Symbols & Characteristics34

35. DEVICE SYMBOLS & CHARACTERISTICS35
Prof. M. Madhusudhan Rao, E&C Dept., MSRIT

36. 36

37. 37

38. Phase Control Thyristor
These are converter thyristors.
The turn-off time tq is in the order of 50 to 100sec.
Used for low switching frequency.
Commutation is natural commutation
On state voltage drop is 1.15V for a 600V device. 38

39. They use amplifying gate thyristor.39

40. Fast Switching Thyristors
Also called inverter thyristors.
Used for high speed switching applications.
Turn-off time tq in the range of 5 to 50sec.
On-state voltage drop of typically 1.7V for 2200A, 1800V thyristor.
High dv/dt and high di/dt rating. 40

41. Bidirectional Triode Thyristors (TRIAC)41

42. Triac Characteristics42

43. Gate Turn-off Thyristors
Turned on by applying positive gate signal.
Turned off by applying negative gate signal.
On state voltage is 3.4V for 550A, 1200V GTO.
Controllable peak on-state current ITGQ is the peak value of on-state current which can be turned-off by gate control. 43

44. Gate-Turn-Off Thyristors (GTO)
Slow switching speeds
Used at very high power levels
Require elaborate gate control circuitry

45. GTO Turn-Off
Need a turn-off snubber

46. Advantages over SCRs Elimination of commutating components.
Reduction in acoustic & electromagnetic noise due to elimination of chokes.
Faster turn-off, therefore can be used for higher switching frequencies.
Improved efficiency of converters. 46

47. Advantages over BJTs Higher voltage blocking capabilities.
High on-state gain.
High ratio of peak surge current to average current.
A pulsed gate signal of short duration only is required. 47

48. Disadvantages of GTOs On-state voltage drop is more.
Due to multi cathode structure higher gate current is required.
Gate drive circuit losses are more.
Reverse blocking capability is less than its forward blocking capability. 48

49. Reverse Conducting Thyristors49

50. Anti-parallel diode connected across SCR on the same silicon chip.
This diode clamps the reverse blocking voltage to 1 or 2V.
RCT also called Asymmetrical Thyristor (ASCR).
Limited applications. 50

51. Static Induction Thyristors
Turned-on by applying positive gate voltage.
Turned-off by applying negative gate voltage.
Minority carrier device.
Low on-state resistance & low voltage drop.
Fast switching speeds & high dv/dt & high di/dt capabilities. 51

52. Switching time in order of 1 to 6 sec.
The rating can go upto 2500V / 500A.
Process sensitive. 52

53. Light-Activated Silicon Controlled Rectifiers
Turned-on by direct light radiation on silicon wafer.
Gate structure is sensitive for triggering from practical light sources.
Used in high voltage and high current applications. Example: HVDC transmission, Static reactive power compensation. 53

54. Rating could be has high as 4KV / 1500A. di/dt rating is 250A / sec.
Offers complete electrical isolation between light triggering source & power circuit.
Rating could be has high as 4KV / 1500A.
di/dt rating is 250A / sec.
dv/dt rating is 2000V / sec. 54

55. Photo-SCR coupled isolator

56. Bipolar Junction Transistors (BJT)
Used commonly in the past
Now used in specific applications
Replaced by MOSFETs and IGBTs

58. FET Controlled Thyristors
Combines a MOSFET & a thyristor in parallel as shown.
High switching speeds & high di/dt & dv/dt. 58

59. Turned on like conventional thyristors.
Cannot be turned off by gate control.
Application of these are where optical firing is to be used. 59

60. MOS-Controlled Thyristor
New device that has become commercially available.
Basically a thyristor with two MOSFETs built in the gate structure.
One MOSFET for turning ON the MCT and the other to turn OFF the MCT. 60

61. MCT

64. Features Low on-state losses & large current capabilities.
Low switching losses.
High switching speeds achieved due to fast turn-on & turn-off.
Low reverse blocking capability. 64

65. Gate pulse width not critical for smaller device currents.
Gate controlled possible if current is less than peak controllable current.
Gate pulse width not critical for smaller device currents.
Gate pulse width critical for turn-off for larger currents. 65

66. MOSFET 66
Prof. M. Madhusudhan Rao, E&C Dept., MSRIT

67. MOSFETs Easy to control by the gate
Optimal for low-voltage operation at high switching frequencies
On-state resistance a concern at higher voltage ratings

73. IGBT

77. IGBT 77
Prof. M. Madhusudhan Rao, E&C Dept., MSRIT

78. Advantages of IGBT Combines the advantages of BJT & MOSFET
High input impedance like MOSFET
Voltage controlled device like MOSFET
Simple gate drive, Lower switching loss
Low on state conduction power loss like BJT
Higher current capability & higher switching speed than a BJT. ( Switching speed lower than MOSFET) 78
Prof. M. Madhusudhan Rao, E&C Dept., MSRIT

79. Applications of IGBT ac and dc motor controls.
General purpose inverters.
Uninterrupted Power Supply (UPS).
Welding Equipments.
Numerical control, Cutting tools.
Robotics & Induction heating. 79
Prof. M. Madhusudhan Rao, E&C Dept., MSRIT

81. MCT

85. Comparison of Controllable Switches

87. Summary of Device Capabilities