Besides, the doping intensity of base is lowest. The base region is very small as compared to emitter and collector region. When forward biased is applied to the emitter-base junction, the electrons in N-region will repel from the negative terminal of the battery and will move towards the base region. This will make the wide depletion layer at the collector-base junction and narrow depletion layer at emitter-base junction. To reverse bias the collector-base junction, the N-terminal is connected to the positive terminal of the V CB and the P-terminal is connected to the negative terminal of the battery V CE. Therefore, the N-terminal of emitter-base junction is connected to the negative terminal of V BE, and the P-terminal of the battery is connected to the positive terminal of the V BE. The base-emitter junction should be forward biased, and the collector-base junction should be reversed biased. The collector is made of larger size as compared to emitter because if the size of the collector is large it will collect more and more charge carriers and the heat can also dissipate through the junction of the larger area easily. The emitter and collector region are not interchangeable because the size of the emitter is less as compared to the size of the collector. This results in the formation of an N-type semiconductor.Īre emitter and collector interchangeable? The base of P-type is sandwiched between the emitter and collector of N-type. emitter and the last one is collector which is moderately doped.

Thus, it is always formed by three layers, in which one is lightly doped, i.e. In this condition, the base formed by connecting it back to back will not have uniform doping which is the pre-requisite condition for the transistor. If it is formed by connecting two diodes back to back, then the resulting structure will have four doped regions because each of the diodes has 2 doped region. But it is not like that, it is just for imagining the construction. It is often said that transistor is formed by connecting two diodes back to back. The NPN transistor is formed with the help of three layers of which two are of the N-type semiconductor, and the other one is P-type semiconductor. The symbol which is used to denote NPN transistor in electronic circuits is given in the diagram below. Thus, the mobility of charge carriers in NPN will be more than that of PNP. In NPN transistors the majority carriers are electrons, and in PNP the majority carriers are holes. The NPN transistor is preferred over PNP transistor because the mobility of electrons is more than the mobility of holes. collector-base junction, it generates current. emitter-base junction to the junction which consists of high resistance region, i.e. These electrons when move from low resistance junction, i.e.

Npn transistor