Summary
Thyristors are three-terminal solid-state switches whose bistable state depends on a regenerative feedback mechanism occuring in a p-n-p-n structure.
The silicon-controlled rectifier (SCR) is a device belonging to the class of thyristors with the ability of unidirectional conduction. After defining the switching and holding points of an SCR, the gate turn-on conditions are examined, and it is shown that the V–I coordinates of the switching point are dependent on small-signal current gains of the p-n-p and n-p-n SCR sections. The turn-on occurs when the sum of small-signal alphas is equal to unity.
In the case of a shorted emitter, the turn-on condition is simplified to a product of small-signal current gain and avalanche multiplication factor Mα 1= 1.
At zero potential applied to the center junction the current flowing through the device is I v and at this current level the sum of DC alphas αN and αP is equal to unity.
The holding current I h is greater than I 1 and, therefore, the V–I coordinates of the holding point are dependent on the sum of DC alphas.
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References
W. Fulop. Three terminal measurements of current amplification factors of controlled rectifiers. IEEE Trans. Electron Devices, 10: 120–135, 1963.
F. E. Gentry. Turn on criteria for pnpn devices. IEEE Trans. Electron Devices, ED-11: 74, 1964.
J. F. Gibbons. A critique of the theory of pnpn devices. IEEE Trans. Electron Devices, ED-11: 406–413, 1969
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F. E. Gentry, F. W. Gutzwiller, N. Holonyak, Jr., and E. E. Von Zastrow. Semiconductor Controlled Rectifiers. Englewood Cliffs, N.J.: Prentice-Hall, 1964.
Also of interest
W. Fulop, W. Fong Yan, M. R. Joadat-Ghasabi, and C. A. Hogarth. Three-terminal current gain measurements of high-power thyristors. Int. J. Electron., 33 (6): 601–609, 1972.
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© 1976 Springer-Verlag New York Inc.
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Blicher, A. (1976). Device basics. In: Thyristor Physics. Applied Physics and Engineering, vol 12. Springer, New York, NY. https://doi.org/10.1007/978-1-4612-9877-9_1
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