A bipolar transistor is a type of transistor that uses both electrons and holes as charge carriers. It has three terminals: emitter, base, and collector. A unipolar transistor, also known as a field-effect transistor, uses only one type of charge carrier (either electrons or holes) and has three terminals: source, gate, and drain.
In a bipolar transistor, the base-emitter junction is forward biased, which allows the flow of majority carriers (electrons or holes) from the emitter to the base. This creates a larger current flow from the collector to the emitter. In a unipolar transistor, the gate voltage controls the conductivity of the channel between the source and drain, allowing for the flow of majority carriers.
Bipolar transistors are commonly used in amplifiers, switches, and digital circuits. Unipolar transistors are often used in switching circuits, voltage regulators, and power supplies. Both types of transistors are essential components in electronic devices such as computers, smartphones, and televisions.
Bipolar transistors have a higher gain (amplification) compared to unipolar transistors. However, unipolar transistors have a lower saturation voltage and can handle higher currents. Additionally, the switching speed of unipolar transistors is faster than that of bipolar transistors.
Some common types of bipolar transistors include NPN and PNP transistors, which are both made of silicon and have different biasing directions. Common unipolar transistors include JFETs (junction field-effect transistors) and MOSFETs (metal-oxide-semiconductor field-effect transistors), which are made of different materials and have different structures and characteristics.