SCR/Thyrisitor pnpn structure with 3 pn junctions
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
SCR/Thyristor (continued) + AK V AK- Increase the Anode-Cathode voltage until “breakdown” occurs. Anode current increases. “Conducting state” IAIA
Thyristor Volt-Ampere Characteristic
Two-Transistor Model
Effects of Increasing Gate Current
Line-Commutated Thyristor Circuit
Forced-Commutated Thyristor Circuit
Triac – Bi-directional Thyristor
Triac Volt-Ampere Characteristic