2008-09-09

Understanding Transistors

Understanding Transistors

1. Transistor are solid state semiconductor devices that are used to amplify current.
2. These semiconductors are mostly made of silicon and germanium.
3. It has THREE terminals emitter (E), base (B), and collector (C). The emitter emits or sends charge carriers through the thin base layer to be collected by the collector.
4. Transistors can also form parts of the integrated circuits in the microchips. There are 2 types of transistor:
a. n-p-n transistor has thin layer of p-type silicon sandwiched between two layers of n-type silicon.
b. p-n-p transistor has thin layer of n-type silicon sandwiched between two layers of p-type silicon.
5. In a n-p-n transistor the emitter sends negative electrons to the collector.



6. In a p-n-p transistor, the p-type emitter sends positive holes to the collector.


7. In both cases, the arrow on the emitter shows the direction of conventional (i.e.positive charge) current flow.


Functions of terminal in a transistor

Terminal : Function
Emitter (E): Supplies Charge carriers to C.
Collector(C) : Receives charge carriers from E.
Base (B):  Controls the flow of charge carriers from E to C or C to E.

Flow of current in a transistor

1. There are two parts to a transistor circuit: Base circuit and Collector circuit.
2. The current which flows in the base circuit is called the base current, IB while the current which flows in the collector’s circuit is called the collector current, IC.
3. Transistors are composed of three parts – a base, a collector, and an emitter.
4. The base is the gate controller device for the larger electrical supply. The collector is the larger electrical supply, and the emitter is the outlet for that supply. By sending varying levels of current from the base, the amount of current flowing through the gate from the collector may be regulated. In this way, a very small amount of current may be used to control a large amount of current, as in an amplifier.
5. IE = IB + IC

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