ABSTRACT
A junction field-effect transistor or junction field-effect transistor (JFET) is a type of transistor in which the current flow through the device between the drain and source electrodes is controlled by the voltage applied to the gate electrode. An important application of a JFET is as a constant current source or as a current regulator diode. Any JFET can be used as a current regulating diode. There are, however, JFETs that are especially made for this application. Bipolar junction transistors (BJT) are often used for the amplification of electrical signals. The BJT is often used as a switching device, especially in digital circuits, and in high-power applications. Thus field effect transistor do have the disadvantage of a much lower transfer conductance and, therefore, lower voltage gain than BJTs operating under similar quiescent current levels; but they do have the major advantage of a much higher input impedance and a much lower input current.
