For the purposes of the bipolar transistors are three layers of semiconductor combined. The consequence of npn areas can be equivalent pnp combination to be realized. The contacts in the various layers designated with emitter (E), base (B) and collector (C). The specificity of a transistor is that a current between the emitter and collector by a small stream between the base and emitter can be controlled.



Figure 13: bipolar with Symbol

This behavior can be summarized as follows for a npn transistor explain:
The contacts base and emitter operate a pn transition in the direction of passage, as he discussed above. It therefore takes electrons from the n-conductive emitter in the p-conductive base. Since this layer is very weak and is endowed also very thin, is not a complete recombination of the injected charge carriers. A large number of electrons can therefore be up to the border area to turn n-conductive layer penetrate collector. Through the transition in this area predominant field distribution, however, these electrons in the collector weitergesaugt. At the same time be injected into the base holes (from the + pole of the tension between the base and emitter) held back.
Ultimately, therefore a high current flow from emitter to the collector generates, while the electricity between the base and emitter is very weak.



14: bipolar with wiring for the senior state