This mode is achieved by reducing base voltage less than both emitter and collector voltage. In this mode, transistor acts as an off-state of the switch.
There’s no collector current and hence no emitter current. There are no external supplies connected. The operation in this region is completely opposite to the saturation region. In case of NPN collector, the arrow mark is outward, which shows the flow of current from collector to emitter. The arrow mark in PNP transistor is inward, which shows the flow of current from emitter to collector. The current will either flow from emitter to collector or from collector to emitter. The difference between PNP and NPN symbol is the arrow mark at the emitter which shows the direction of flow of current. The current will flow from the collector to emitter because the collector terminal is more positive than emitter in NPN connection. When the anodes of two diodes are connected together it forms an NPN transistor. In NPN bipolar transistor, the P-type semiconductor is sandwiched between two N-type semiconductors. NPN type is exactly opposite to PNP type. Related Post: What is PNP Transistor? Construction, Working & Applications.The emitter, in this case, is at high potential to both collector and base. So, in PNP type current flows from emitter to collector. The emitter-base junction is forward bias while collector-base junction is reverse bias.
While the anodes of the diodes that are on the opposite sides are known as the collector and the emitter. The cathodes of the diodes are connected together at a common point known as base. PNP transistors can be formed by connecting cathodes of two diodes. In PNP bipolar transistor, the N-type semiconductor is sandwiched between two P-type semiconductors. Both connections are disused here briefly. This three-layer device formed by back to back connection has specific names. The base-collector junction shows high resistance because this junction is reversed bias. Being the middle portion of the BJT allows it to control the flow of charge carriers between emitter and collector. The base is the most lightly doped portion of the BJT. The base is the middle portion between collector and emitter & it forms two PN junctions between them. While in PNP transistor, it collects holes emitted by emitter. The collector of NPN transistor collects electrons emitted by emitter.
The reason for reverse biasing is to remove charge carriers (electrons or holes) from the collector-base junction. Collector-base junction should be always reversed biased in both PNP and NPN transistors. The collector is heavily doped but the doping level of the collector is in between the lightly doping level of base and heavily doped level of emitter. electrons or holes) is known as collector. The portion on the opposite side of the Emitter that collects the emitted charge carriers (i.e. These terminals are briefly discussed here. These terminals are knowns as collector, emitter and base.
The junction of the base with emitter is known as the Emitter-Base junction while the junction of the base with the collector is known as the Collector-Base junction. The middle portion (base) forms two junctions with the emitter & collector. The emitter and collector sandwich the base in between them. These three portions are called Emitter, Collector, and Base. These transistors are known as PNP or NPN bipolar junction transistors depending on whether P or N-type is sandwiched.īasically, transistors have three portions and two junctions. BJT transistors are formed after connecting two PN junctions back to back. When P-type and N-type material are connected together then it becomes a PN-junction diode. While in P-type semiconductor, the number of holes is greater than the number of electrons. If the number of electrons are greater than the number of holes (positive carriers) then that is known as N-type semiconductor material. Nowadays, the use of BJT is decreasing because CMOS technology took place in the design of digital ICs.Īfter doping an intrinsic semiconductor with Trivalent or Pentavalent impurities a P-type semiconductor or N-type semiconductor respectively is made. The invention of transistor changed the concept of electrical circuits to integrated circuits (IC). While the first transistor was invented 70 years ago but till now it changed the world from mysterious big computers to small smartphones.
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