Controllable Power Semiconductors

Part of the Macmillan Engineering Series book series (MECS)


A semiconductor diode cannot be controlled. With a positive anode voltage it will conduct at the commencement of this voltage and will cease conduction when the anode is driven to a potential negative with respect to the cathode. When operating from an a.c. supply line it will therefore conduct for one half cycle and block the other half cycle. In contrast to this there are several semiconductor devices which have the ability to conduct in one or both directions and whose conduction can be initiated or terminated, irrespective of the polarity of the supply voltage. In this chapter four such controllable semiconductors are discussed. Principal amongst these is the thyristor, which can act only as a rectifying element, and is capable of controlling several megawatts of power. This is followed closely in popularity by the triac, which is bidirectional in operation, and its unidirectional counterpart the logic triac. The power transistor is capable of rectification only and can operate in the linear mode if required. Due to the large dissipation this would involve it is rarely run as anything but a switch. Finally, a modification of the thyristor, the gate turn-off switch, is currently available for relatively low power levels only.


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Copyright information

© Macmillan Publishers Limited 1972

Authors and Affiliations

  • F Mazda
    • 1
  1. 1.ITT Components Group EuropeUK

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