Teach Yourself Electricity and Electronics, Sixth Edition, 6th Edition

22

CHAPTER

Field-Effect Transistors

THE BIPOLAR DEVICE ISN’T THE ONLY FORM OF TRANSISTOR THAT CAN SWITCH, AMPLIFY, OR OSCILLATE. A field-effect transistor (FET) can also do these things. Two main types of FET exist: the junction FET (JFET) and the metal-oxide-semiconductor FET (MOSFET).

Principle of the JFET

In a JFET, an electric field within the device affects the amount of current that can flow through it. Charge carriers (electrons or holes) move from the source (S) electrode to the drain (D) electrode to produce a drain current I_D that normally equals the source current, I_S. The rate of flow of charge carriers—that is, the current—depends on the voltage at a control electrode called the gate (G). Fluctuations in gate voltage E_G cause changes ...