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ECE 442 Power Electronics1 SCR/Thyrisitor pnpn structure with 3 pn junctions
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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
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ECE 442 Power Electronics3 SCR/Thyristor (continued) + AK V AK- Increase the Anode-Cathode voltage until “breakdown” occurs. Anode current increases. “Conducting state” IAIA
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ECE 442 Power Electronics4 Thyristor Volt-Ampere Characteristic
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ECE 442 Power Electronics5 Two-Transistor Model
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ECE 442 Power Electronics6 Effects of Increasing Gate Current
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ECE 442 Power Electronics7 Line-Commutated Thyristor Circuit
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ECE 442 Power Electronics8 Forced-Commutated Thyristor Circuit
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ECE 442 Power Electronics9 Triac – Bi-directional Thyristor
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ECE 442 Power Electronics10 Triac Volt-Ampere Characteristic
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