The internal structure and operational principles of transistors lead to different types, primarily categorized into Bipolar Junction Transistors (BJTs) and Field-Effect Transistors (FETs).
Bipolar Junction Transistors (BJT):
BJTs are transistors that use both electrons and holes as charge carriers, hence the name ‘bipolar’. They come in two main types:
NPN Transistors:
NPN transistors consist of a layer of P-type semiconductor sandwiched between two N-type layers. They are commonly used because they offer better electron mobility and higher current gain compared to PNP transistors.
PNP Transistors:
PNP transistors have a layer of N-type semiconductor between two P-type layers. They operate similarly to NPN transistors but with reversed polarity.
Field-Effect Transistors (FET):
FETs control current via an electric field and are classified based on their gate structure and operation.
Junction Field-Effect Transistors (JFET):
JFETs are available in two types based on the charge carriers:
- N-channel JFET: The current flows through a channel of N-type material.
- P-channel JFET: The current flows through a channel of P-type material.
Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFET):
MOSFETs are the most widely used type of FETs due to their high input impedance and efficient switching capabilities. They come in various forms:
- N-channel MOSFET: Uses electrons as charge carriers.
- P-channel MOSFET: Uses holes as charge carriers.
- Depletion Mode MOSFET: Conducts at zero gate-to-source voltage and requires a negative gate-to-source voltage to turn off.
- Enhancement Mode MOSFET: Normally off at zero gate-to-source voltage and requires a positive gate-to-source voltage to conduct.
Insulated-Gate Bipolar Transistors (IGBT):
IGBTs combine the high input impedance of MOSFETs with the low on-state power loss of BJTs. They are used in high-power applications such as motor drives, induction heating, and power inverters.