Thyristor Physics pp 1-14 | Cite as

# Device basics

## 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 α_{N} and α_{P} 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

- 1.1W. Fulop. Three terminal measurements of current amplification factors of controlled rectifiers.
*IEEE Trans. Electron Devices, 10*: 120–135, 1963.CrossRefGoogle Scholar - 1.2F. E. Gentry. Turn on criteria for pnpn devices.
*IEEE Trans. Electron Devices*,*ED-11*: 74, 1964.CrossRefGoogle Scholar - 1.3J. F. Gibbons. A critique of the theory of pnpn devices.
*IEEE Trans. Electron Devices, ED-11*: 406–413, 1969Google Scholar - 1.3aJ. F. Gibbons. and Graphical analysis of the
*I-V*characteristics of generalized pnpn devices.*Proc. IEEE, 55*(8): 1366–1374, 1967.CrossRefGoogle Scholar - 1.4R. W. Aldrich and N. Holonyak, Jr. Two-terminal asymmetrical and symmetrical silicon negative resistance switches.
*J. Appl. Phys., 30*: 1819–1824, 1959.ADSCrossRefGoogle Scholar - 1.5F. E. Gentry, F. W. Gutzwiller, N. Holonyak, Jr., and E. E. Von Zastrow.
*Semiconductor Controlled Rectifiers*. Englewood Cliffs, N.J.: Prentice-Hall, 1964.Google Scholar

### 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.CrossRefGoogle Scholar