Thyristor circuits basics

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


Phase control and zero-voltage switching are the basic power control methods used in the SCR and triac circuits. Phase control is achieved by resistive or resistive—capacitive networks or by triggering pulses derived from such devices as diacs, unijunction transistors, two-transistor trigger circuits, and neon bulbs.

In order to turn off the thyristor, it is necessary to reduce the main current below the holding-current level. In an ac circuit, the current passes through zero every half cycle so the turn off of the thyristor also is assured every half cycle. The commutation of a thyristor in a DC circuit requires, however, the use of additional circuitry.

To avoid either false triggering or damage to a thyristor due to transients, some simple protective networks are usually recommended.

Practical applications of SCRs and/or triacs are shown in the circuits of light dimmers, universal motor controllers, heat controllers, and DC-to-AC inverters.


Half Cycle Gate Current Firing Angle Inverter Circuit Silicon Control Rectifier 
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. 17.1
    RCA. Solid state power circuits. Technical Series SP-52, RCA Solid State Division, 1971.Google Scholar
  2. 17.2
    GE SCR Manual, 5th ed., Syracuse, N.Y.: General Electric, 1972.Google Scholar
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    J. M. Neilson. Light dimmers using Triacs. RCA Application Note AN-3778.Google Scholar
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    B.D. Bedford and G. R. Hoft. Principles of Inverter Circuits. New York: John Wiley, 1964.Google Scholar
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Also of interest

  1. G. J. Deboo and C. Burrows. Integrated Circuits and Semiconductor Devices. New York: McGraw-Hill, 1971.Google Scholar
  2. P. Atkinson. Thyristors and Their Applications. London: Mills & Boon,1972.Google Scholar
  3. F. F. Mazda. Thyristor Control. New York: John Wiley, 1973.Google 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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