Transistor has many functions and types. This article will review one transistor's type. That is Bipolar Junction Transistor. Hopefully, this article will provide you good information.
Bipolar Junction Transistor's basic construction, similar to diode, is built of N- and P- semiconductor material. But, transistor hires three semiconductor's material. Its consequence is in 2 PN Junctions. The Collector, Base and Emitter refer to the connections to the semiconductor area. The PN junction between the collector and the base area is called as the Collector Junction. Current cannot flow in through the collector and emitter unless voltage bias is applied to the base.
The thinness of the base region is the key of the transistor's operation. The holes of the emitter area will not be able to pass through the base region to the collector region if the base region was too thick. They will re-alter with the electrons before reaching collector's area. The hole which is injected into the N- base region is minority carriers. Therefore, minority Carrier Injection is the basic of bipolar transistor operation.
Either PNP or NPN sandwich of semiconductor material is a place where bipolar junction transistor may construct. The major difference between both arrangements is the voltage's polarity. You must remember that emitter junction must be forwarded biased. P- must be positive with respect to the emitter (NPN arrangement). This makes the electron is injected into the P- base region. The injected electrons pass through the base region into collector region by making the collector region positive.
To gain proper transistor operation, the emitter collector junction must be reversed biased and the emitter junction must be forwarded bias.
In short, it can be said that the basic control device is transistor. The value of the base current controls the collector current. That is an Electronically Controlled Variable Resistor (transistor).