Bipolar transistors

Bipolar transistor

Transistor

A transistor is a basic semiconductor element that consists of three terminals and three series-connected areas with different doping that determines the transition of the transistor (PNP or NPN). Its main task is amplification, switching and conversion of electrical signals and part of all modern electrical devices.

Bipolar transistor (PNP, NPN)

The bipolar transistor is a semiconductor crystal with two P-N junctions, which are obtained using a three-layer semiconductor structure of semiconductors with different conductivities. Depending on the alternation of the layers, two main types of bipolar transistors are distinguished: PNP and NPN. The two end layers of the bipolar transistor are called emitter and collector, and the middle layer is called base. The base has a conductivity opposite to that of the emitter and collector. As a general rule, it should be noted that the bipolar transistor is a semiconductor element that is controlled by current.

Irrespective of the connection method in the circuit, the bipolar transistor has a base-emitter transition as a control circuit, respectively, the control circuit is a collector-emitter. Depending on the mechanism of movement of current carriers, bipolar transistors can be diffuse and drift, and according to the way they are made, we distinguish alloy, mesatransistors, conversion, etc. Bipolar transistors are mainly used as amplifiers in electronic circuits. Two or more bipolar transistors can be connected to form a three-terminal amplifier. This is called a compound transistor. This scheme is applied when we want to get a larger current gain.

Transistors are classified according to the cut-off frequency into low-power, medium-power and high-power transistors, and according to the material they are made of silicon or germanium.

Types of bipolar transistor

 

• low-power transistors - up to 3 MHz
• medium power transistors - 30 to 300 MHz
• powerful transistors - over 300 MHz