1. ECE 442 Power Electronics1 SCR/Thyrisitor pnpn structure with 3 pn junctions

2. ECE 442 Power Electronics2 Cross-section of the pnpn structure Apply a forward bias voltage to the Anode-Cathode Junctions J1 and J3 are forward biased Junction J2 is reverse biased Only a small amount of current flows from A to K The device is in it’s OFF or “Forward Blocking” State J1 J2 J3 + V AK - I A = 0

3. ECE 442 Power Electronics3 SCR/Thyristor (continued) + AK V AK- Increase the Anode-Cathode voltage until “breakdown” occurs. Anode current increases. “Conducting state” IAIA

4. ECE 442 Power Electronics4 Thyristor Volt-Ampere Characteristic

5. ECE 442 Power Electronics5 Two-Transistor Model

6. ECE 442 Power Electronics6 Effects of Increasing Gate Current

7. ECE 442 Power Electronics7 Line-Commutated Thyristor Circuit

8. ECE 442 Power Electronics8 Forced-Commutated Thyristor Circuit

9. ECE 442 Power Electronics9 Triac – Bi-directional Thyristor

10. ECE 442 Power Electronics10 Triac Volt-Ampere Characteristic