Bipolar transistors - definition
Bipolar transistors - definition
Bipolar transistors (Bipolar Junction Transistor, BJT) are three-terminal semiconductor active elements used to amplify electrical signals and switch currents in analogue and digital circuits. It is made up of three semiconductor layers with alternating conductivity types: n-type and p-type, which creates two junctional potential barriers - emitter-base and base-collector. Two types of Bipolar transistors are distinguished depending on the arrangement of the layers: NPN and PNP, differing in the direction of current flow and the polarity of the supply voltages.
Bipolar transistors operate by controlling the flow of majority charge from the emitter to the collector via a thin base layer. The base current, although small, allows a much larger collector current to be controlled, allowing current and voltage gain. In the active mode, the emitter-base junction is polarised in the conduction direction and the base-collector junction is polarised in the inward direction. A characteristic feature of a Bipolar transistor is its dependence on control current, unlike Unipolar transistors (e.g. MOSFETs), which respond to voltage.
Bipolar transistors exhibit high linearity and wide bandwidth, making them useful in amplifier, generator, mixer and signal buffer circuits. They are used both in simple discrete circuits and in complex integrated circuits. Their technical parameters, such as current gain, limiting frequency or loss power, are selected according to the application, signal level and required dynamic characteristics. Special versions with increased connector surface area, thermal resistance and ability to conduct high currents are used in power circuits.
Transfer Multisort Elektronik (TME) is one of the world’s largest global distributors of electronic components, electrotechnical parts, workshop equipment, and industrial automation. The catalog includes over 1,500,000 products from 1,300 leading manufacturers. TME’s modern logistics centers in Łódź and Rzgów (Poland), with a combined area of over 40,000 m², ship nearly 6,000 packages daily to customers in more than 150 countries.
TME also invests in the development of knowledge and skills of young engineers and electronics enthusiasts through the TME Education project, and supports the tech community by organizing the TechMasterEvent series, promoting innovation and experience exchange.
