What is a transistor? What's the role?

1. What is a transistor? What's the role?
Transistors are also called semiconductor diodes, which can be said to be the most important devices in electronic circuits. Its main function is the current amplification and switching, oscillation. The transistor is made of two PN junctions made of semiconductor material. Its three electrodes are connected to the three zones inside the tube ( emission region, base area and collector area ). The transistor has two types of NPN and PNP type, and the transistor structure and circuit symbol are shown in Figure 61. Figure 6-1a is shown as the internal structure and graphical symbols of the PNP type transistors. It is shown in the figure that it consists of three semiconductors and consists of two PN junctions, namely, a collector junction and a emitter junction, and a total of three electrodes, the collector, the base and the emitter. The working current in the transistor has the collector current Ic, the base current IB, the emitter current Ie; Ic and IB from the emitter stream. The direction of the emitter arrow in the circuit symbol indicates the flow direction of the current. Ie=IB+Ic, because IB is small (negligible), then Ic IE.
Figure 6-1b shows the internal structure and graphic symbols of NPN type transistors, which are different from those of PNP transistors.
The location of P type.N semiconductor is different, and the other is basically the same. The direction of the current is out of the emitter, the base current and the collector current are all inflow from the transistor, which can be seen from the direction of the emitter arrow in the symbol of the NPN type transistor circuit.

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