n this article we will review the basic transistor types and their function. We will cover bipolar transistor, Junction FET, MOSFET and UJT transistor types. Feel free to comment with other transistor types you know.
Bipolar Transistor
Bipolar transistors are three terminal devices and act like electrically controlled switches of as current/voltage amplifiers. They come in two types either npn or pnp depending on their construction.
NPN Transistor
This type of transistor is normally off, but a small input current and a small positive voltage to its base B (relative to emitter – E) allows a large current to flow from collector to emitter, when collector is in higher voltage than emitter. Normally used in switching applications and amplifiers.
PNP Transistor
This type of transistor is normally off, but a small output current and a small negative voltage to its base B (relative to emitter – E) allows a large current to flow from emitter to collector, when emitter is in higher voltage than collector. Normally used in switching applications and amplifiers.
Junction FET
Junction field effect transistors are three terminal devices that are used as switches, amplifiers or voltage controlled resistors. Unlike bipolar transistors they don’t require a biasing current just a voltage to the gate to operate. Another difference with bipolar is that they are normally ON without any voltage to the gate.
n-channel JFET
This type of transistor in normally ON and a small negative voltage to it’s gate – G (related to source – S) stops the large current that flows from drain to source, when voltage of drain is greater than voltage on source. A unique feature is that they don’t need a current to it’s gate and are used in switching and amplifying applications.
For more detail: Basic Transistor Types
