The emitter junction is much higher doped than the collector junction. The internal structure of a transistor and the amount of doping in each P and N material (which determine the thickness of the depletion region in a PN junction) determine which side is the emitter and which is the collector. The other two terminals are called the emitter and the collector. In a transistor, irrespective of the type (PNP or NPN), the middle terminal is called the base. There are other types of classification, based on transistor functioning and performance in a circuit.Īs can be easily understood from Figure 1, a transistor has three terminals. This classification is based on the polarity in the structure. It is easy to understand that depending on how they are put together, two basic types of transistors can result, as shown in Figure 1.įigure 1 Two basic types of transistors: (a) PNP and (b) NPN.Īccordingly, the two types of a junction transistor are PNP and NPN. Recalling that a PN junction has a P side and an N side, imagine you want to put two of them together. Junction transistor: Same as bipolar junction transistor, which includes an ordinary transistor.īipolar junction transistor: Another name for junction transistor. Nonetheless, note that a transistor is a completely different device than a diode, meaning that one cannot put two diodes together and expect to have a transistor. In other words, from the structure viewpoint, it is similar to two diodes put together during the manufacturing process. The reason for calling it junction transistor is because it contains two PN junctions. There are various types of transistors and the simplest form of the transistor is a junction transistor, also called bipolar junction transistor. Still one can find devices such as stereo amplifiers and radio receivers that use vacuum tubes, but they are rare and expensive, in addition to being bulky and heavy in comparison to solid-state electronics that use transistors and semiconductor technology. Before transistors were invented, all electronic devices were made with vacuum tubes.
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