1. SCR/Thyrisitor pnpn structure with 3 pn junctions

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

4. Thyristor Volt-Ampere Characteristic

5. Two-Transistor Model

6. Effects of Increasing Gate Current

7. Line-Commutated Thyristor Circuit

8. Forced-Commutated Thyristor Circuit

9. Triac – Bi-directional Thyristor

10. Triac Volt-Ampere Characteristic