Power Electronics

1. Power Electronics Dr. S. S. Jawale Head and Associate Professor Department of Electronics Yeshwantrao Chavan Mahavidyalaya, Tuljapur BSc-III Sem-V Paper-XV 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. • Used as a latching switch that can be turned on by the control terminal but cannot be turned off by the gate. 3

4. Symbol of Silicon Controlled Rectifier SCR 4

5. Structure 5

6. Device Operation Simplified model of a thyristor 6

7. Two Transistor Model of SCR  7

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14. V-I Characteristics 14

15. Effects of gate current 15

16. Turn-on Characteristics 16

17. Turn-off Characteristics 17

18. Methods of Thyristor Turn-on • Thermal Turn-on. • Light. • High Voltage. • Gate Current. • dv/dt. 18

19. Thyristor Ratings 19

20. Voltage Ratings 20

21. Current Ratings 21

22. Gate Specification 22

23. Phase Control Thyristors

24. 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). 24

25. Static induction Thyristors (SITHs). • Light-activated silicon-controlled rectifiers (LASCRs). • FET controlled Thyristors (FET-CTHs). • MOS controlled Thyristors (MCTs). 25

26. Bidirectional Triode Thyristors (TRIAC) 26

27. Triac Characteristics 27

28. 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. 28

29. 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. 29

30. 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. 30

31. 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. 31

32. Reverse Conducting Thyristors 32

33. 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. 33

34. 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. 34

35. Switching time in order of 1 to 6 sec. • The rating can go upto 2500V / 500A. • Process sensitive. 35

36. 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. 36

37. 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. 37

38. Example of Triac Ratings • Used in heat / light control, ac motor control circuit • V / I rating: 1200V / 300A. • Max. Frequency: 400Hz. • Switching time: 200 to 400sec. • On state resistance: 3.6m. 38

39. Example of Power Transistor Ratings • PT ratings go up to 1200V / 400A. • PT normally operated as a switch in CE config. • Max. Frequency: 400Hz. • Switching time: 200 to 400sec. • On state resistance: 3.6m. 39

40. Thank You…..