![]() ![]() We saw previously that a bipolar junction transistor is constructed using two PN-junctions in the main current carrying path between the Emitter and the Collector terminals. There are two main types of field effect transistor, the Junction Field Effect Transistoror JFET and the Insulated-gate Field Effect Transistoror IGFET), which is more commonly known as the standard MetalOxide Semiconductor Field Effect Transistor or MOSFETfor short. This very high input impedance makes them very sensitive to input voltage signals, but the price of this high sensitivity also means that they can be easily damaged by static electricity. The Field Effect Transistor has one major advantage over its standard bipolar transistor cousins, in that their input impedance, ( Rin ) is very high, (thousands of Ohms), while the BJT is comparatively low. The Field Effect Transistor on the other hand is a "Unipolar" device that depends only on the conduction of electrons ( N-channel) or holes ( P-channel). As their name implies, Bipolar Transistors are "Bipolar" devices because they operate with both types of charge carriers, Holes and Electrons. ![]() The control of current flowing in this channel is achieved by varying the voltage applied to the Gate. The current path between these two terminals is called the "channel" which may be made of either a P-type or an N-type semiconductor material. The field effect transistor is a three terminal device that is constructed with no PN-junctions within the main current carrying path between the Drain and the Source terminals, which correspond in function to the Collector and the Emitter respectively of the bipolar transistor. This is also true of FET's as there are also two basic classifications of Field Effect Transistor, called the N-channel FET and the P-channel FET. We remember from the previous tutorials that there are two basic types of Bipolar Transistor construction, NPN and PNP, which basically describes the physical arrangement of the P-type and N-type semiconductor materials from which they are made. The Field Effect Transistor is a three terminal unipolar semiconductor device that has very similar characteristics to those of their Bipolar Transistor counterparts ie, high efficiency, instant operation, robust and cheap and can be used in most electronic circuit applications to replace their equivalent bipolar junction transistors (BJT) cousins.įield effect transistors can be made much smaller than an equivalent BJT transistor and along with their low power consumption and power dissipation makes them ideal for use in integrated circuits such as the CMOS range of digital logic chips. As their operation relies on an electric field (hence the name field effect) generated by the input Gate voltage, this then makes the Field Effect Transistor a "VOLTAGE" operated device. The Field Effect Transistor, or simply FEThowever, uses the voltage that is applied to their input terminal, called the Gate to control the current flowing through them resulting in the output current being proportional to the input voltage. ![]() In the Bipolar Junction Transistor tutorials, we saw that the output Collector current of the transistor is proportional to input current flowing into the Base terminal of the device, thereby making the bipolar transistor a "CURRENT" operated device (Beta model). Round Shell Connector/Aviation Connector. ![]()
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