1. SCRs -1 Copyright © by John Wiley & Sons 2002 Thyristors (SCRs) Lecture Notes OUTLINE SCR construction and I-V characteristics. Physical operation of SCRs. Switching behavior of SCRs dv/dt and di/dt limitations and methods of improving them. SCR drive circuit considerations.

2. SCRs -2 Copyright © by John Wiley & Sons 2002 Gate and cathode metallization for slow (phase control) thyristor. Gate and cathode metallization for fast (inverter grade) SCR Thyristor (SCR) Geometry Cross-sectional view showing vertical orientation of SCR. SCRs with kiloamp ratings have diameters of 10 cm or greater.

3. SCRs -3 Copyright © by John Wiley & Sons 2002 Thyristor circuit symbol. Thyristor I-V Characteristics

4. SCRs -4 Copyright © by John Wiley & Sons 2002 Two transistor equivalent circuit One dimensional SCR model. SCR Model and Equivalent Circuit

5. SCRs -5 Copyright © by John Wiley & Sons 2002 Thyristor Turn-on Process

6. SCRs -6 Copyright © by John Wiley & Sons 2002 Thyristor On-state Latchup SCR with negative gate current

7. SCRs -7 Copyright © by John Wiley & Sons 2002 Thyristor On-state Operation

8. SCRs -8 Copyright © by John Wiley & Sons 2002 Thyristor Turn-on Behavior

9. SCRs -9 Copyright © by John Wiley & Sons 2002 Thyristor Turn-off Behavior Turn-off waveforms

10. SCRs -10 Copyright © by John Wiley & Sons 2002 Use shaped gate current pulse for rapid turn-on. Thyristor di/dt Limit at Turn-on

11. SCRs -11 Copyright © by John Wiley & Sons 2002 Thyristor Re-applied dv/dt Limits Rate effect

12. SCRs -12 Copyright © by John Wiley & Sons 2002 Use of pilot thyristor to increase turn-on gate current to main thyristor. Larger gate current increases amount of initial conducting area of cathode and thus improves di F /dt capabiities. Diode allowes negative gate current to flow from main SCR. Interdigitated gate-cathode structure used to greatly increase gate-cathode periphery. Distance from periphery to center of any cathode region significantly shortened. Ability of negative gate current to break latching condition in on-state increased. Combination of pilot thyristor, diode, and iterdigitated gate-cathode geometry tgermed a gate-assisted turn-off thyristor or GATT Methods of Improving Thyristor di/dt Rating

13. SCRs -13 Copyright © by John Wiley & Sons 2002 Improvement in dv/dt Rating Via Cathode Shorts

14. SCRs -14 Copyright © by John Wiley & Sons 2002 Thyristor Gate Trigger Requirements Equivalent circuit of SCR drive circuit