Transistor

Modern transistors are divided into two main categories: bipolar junction transistors (BJTs) and field effect transistors (FETs). Application of current in BJTs and voltage in FETs between the input and common terminals increases the conductivity between the common and output terminals, thereby controlling current flow between them. The transistor characteristics depend on their type. See Transistor models.

The term "transistor" originally referred to the point contact type, but these only saw very limited commercial application, being replaced by the much more practical bipolar junction types in the early 1950s. Ironically both the term "transistor" itself and the schematic symbol most widely used for it today are the ones that specifically referred to these long-obsolete devices.[1] For a short time in the early 1960s, some manufacturers and publishers of electronics magazines started to replace these with symbols that more accurately depicted the different construction of the bipolar transistor, but this idea was soon abandoned.

In analog circuits, transistors are used in amplifiers, (direct current amplifiers, audio amplifiers, radio frequency amplifiers), and linear regulated power supplies. Transistors are also used in digital circuits where they function as electronic switches, but rarely as discrete devices, almost always being incorporated in monolithic Integrated Circuits. Digital circuits include logic gates, random access memory (RAM), microprocessors, and digital signal processors (DSPs).