AC Thyristor Operation

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Select from an SCR (Silicon Controlled Rectifier) or a TRIAC (TRIode for Alternating Current) to observe the output voltage characteristics. Load current is optionally shown for a resistive as well as for a resistive-inductive load.

Contributed by: Harley H. Hartman (March 2011)
Open content licensed under CC BY-NC-SA



This Demonstration provides a graphical representation as well as calculated values for the output voltage of both a simple SCR and simple TRIAC circuit. You can select from an SCR, an SCR with current shown, or a TRIAC. You can then change the triggering angle of the device. If the SCR with load is selected, you can adjust the resistance as well as the inductance of the load. Triggering angle and conduction angles are also displayed. The average DC output voltage is given by , where is the trigger angle and is the cut-off angle. The RMS value of the output voltage is given by , where is the conduction angle.

Formulas and principles referenced from: D. Hart, Introduction To Power Electronics, Upper Saddle River, NJ: Prentice Hall, 1996.

Equations referenced from: SCR Manual, 5th ed., (D. R. Grafham and J. C. Hey, eds.), New York: General Electric Company, 1972.

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