Device basics

  • Adolph Blicher
Part of the Applied Physics and Engineering book series (APPLIED PHYS, volume 12)


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 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.


Current Gain Breakdown Potential Device Basic Gate Current Regenerative Feedback Mechanism 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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  1. 1.1
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Also of interest

  1. 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

Copyright information

© Springer-Verlag New York Inc. 1976

Authors and Affiliations

  • Adolph Blicher
    • 1
    • 2
  1. 1.RCA Corp.USA
  2. 2.Advanced Devices and Applications Dept.Solid State Technology CenterSomervilleUSA

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