Learn about bipolar transistors

Learn about bipolar transistors

 "Bipolar" means that both carriers of electrons and holes are involved in motion at the same time when they operate. Bipolar junction transistors (Bipolar Junction transistors—BJT), also known as semiconductor transistors, is a device that combines two PN junctions through a certain process, with PNP and NPN two combination structures; Three poles are led out externally: collector, emitter and base, the collector leads from the collector region, the emitter leads out of the emitting region, and the base leads out from the base region (the base region is in the middle); BJT has amplification effect, important relying on its emitter current can be transmitted through the base area to reach the collector area and realized, in order to ensure this transmission process, on the one hand, to meet the internal conditions, that is, the concentration of impurities in the emission area is required to be much greater than the concentration of impurities in the base area, and the thickness of the base area is very small, on the other hand, to meet the external conditions, that is, the emitting junction should be forward biased (plus forward voltage), the collector junction should be reverse biased; There are many types of BJT, according to the frequency, there are high-frequency diodes, low-frequency diodes, according to the power, there are small, medium and large power diodes, according to semiconductor materials, there are silicon transistors and germanium transistors; The forms of amplification circuits are: common emitter, common base and common collector amplification circuit.