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Thyristor A four layer semiconductor device, consisting of alternating P-type and N-type materials (i.e., PNPN), with three P-N junctions. Thryristors usually have three electrodes: anode, cathode, and gate (control electrode). As a result, a thyristor can be turned on (the meaning of "on" being dependent on the type of thyristor you're dealing with) via a current at the gate. A thyristor then doesn't require any control (gate) current once it is turned on; the thyristor will continue to conduct until a minimum holding current is no longer maintained between the anode and cathode. Thyristors, then, act like a semiconductor analog of a mechanical switch -- the two stable states are "on" and "off," with nothing in between. Thus the name given these devices comes from the Greek thyra ("door," implying something that is either open or closed). The most common type of thyristor is the
silicon-controlled rectifier (SCR);
you will also run across triacs,
and programmable unijunction
transistors (PUTs). |
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