Q. What the major advantages FET transistors over BJT transistors?
a. BJT transistor (bipolar junction transistor) is a bipolar device - the prefix bi-revealing that the conduction level is a function of two charge carriers, electrons and holes where as the FET is a unipolar device depending solely on electron or hole conduction.
b. For the FET an electric field is established by the charges present that will control the conduction path of the output circuit without the need for direct contact between the controlling and controlled quantities.
c. FET has high input impedance. This permits high degree of isolation between input and output circuits.
d. FETs are more temperature stable than BJTs.
e. FETs are usually smaller in construction than BJTs, making them particularly useful in integrated-circuit (IC) chips.
f. A FET has a negative temperature coefficient of resistance. This avoids the risk of thermal runaway.
g. Compared to BJT a FET has a longer life period and high efficiency
h. In FET, there are no junctions as in an ordinary transistor. The conduction is through an n-type or p-type semiconductor material. For this reason, noise level in FET is small.