1. Power Electronics Lecture(9) Prof. Mohammed Zeki Khedher Department of Electrical Engineering University of Jordan 1

2. Short pulse

3. Long pulse

4. Pulse train generator

5. Pulse train with timer and AND gate

6. 6 Gate Triggering Methods - Efficient & reliable method for turning on SCR. Types  R - Triggering.  RC - Triggering.  UJT - Triggering.

7. 7 R-Triggering Resistance firing circuit

8. 8 RC Triggering RC half-wave trigger circuit

13. Gate triggering characteristics

14. Gate input characteristics

15. IGM w IG r p o n s x q y z 1 3 4Load line m VG VGD FIGURE 18.2 Typical gate characteristics of an SCR.

16. Gate protection circuit

17. High temperature due to:

18. Copyright © by John Wiley & Sons 2003 Snubbers - 18 Snubber Circuits Lecture Notes Outline A.Overview of Snubber Circuits B.Diode Snubbers C.Turn-off Snubbers D.Overvoltage Snubbers E.Turn-on Snubbers F.Thyristor Snubbers

19. Copyright © by John Wiley & Sons 2003 Snubbers - 19 Overview of Snubber Circuits for Hard-Switched Converters Function: Protect semiconductor devices by: Limiting device voltages during turn-off transients Limiting device currents during turn-on transients Limiting the rate-of-rise (di/dt) of currents through the semiconductor device at device turn-on Limiting the rate-of-rise (dv/dt) of voltages across the semiconductor device at device turn-off Shaping the switching trajectory of the device as it turns on/off Types of Snubber Circuits 1.Unpolarized series R-C snubbers Used to protect diodes and thyristors 2.Polarized R-C snubbers Used as turn-off snubbers to shape the turn-on switching trajectory of controlled switches. Used as overvoltage snubbers to clamp voltages applied to controlled switches to safe values. Limit dv/dt during device turn-off 3.Polarized L-R snubbers Used as turn-on snubbers to shape the turn-off switching trajectory of controlled switches. Limit di/dt during device turn-on

20. Copyright © by John Wiley & Sons 2003 Snubbers - 20 Need for Diode Snubber Circuit

21. Copyright © by John Wiley & Sons 2003 Snubbers - 21 Effect of Adding Snubber Resistance Snubber Equivalent Circuit Diode voltage as a function of time

22. Copyright © by John Wiley & Sons 2003 Snubbers - 22 Need for Snubbers with Controlled Switches Step-down converter Switching trajectory of switch

23. Copyright © by John Wiley & Sons 2003 Snubbers - 23 Turn-off Snubber for Controlled Switches Step-down converter with turn-off snubber Equivalent circuit during switch turn-off.

24. Copyright © by John Wiley & Sons 2003 Snubbers - 24 Turn-off Snubber Operation

25. Copyright © by John Wiley & Sons 2003 Snubbers - 25 Turn-on Snubber Step-down converter with turn-on snubber Snubber reduces V sw at switch turn-on due drop across inductor L s. Will limit rate-of-rise of switch current if L s is sufficiently large. Switching trajectory with and without turn-on snubber.

26. Copyright © by John Wiley & Sons 2003 Snubbers - 26 Thyristor Snubber Circuit Phase-to-neutral waveforms 3-phase thyristor circuit with snubbers

27. Trajectory comparision with and without capacitor

28. Turn off snubber circuit