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Bipolar Transistors
One of the two types of transistor are bipolar transistors. From diode we learnt about PN junctions. Now with bipolar transistor we add another layer to make it PNP or NPN depending on what type we add. Either type has the same function, the middle layer acts like a gate that controls the current flowing through all three layers.
The three layers, or contact are normally called the Emitter, base and collect. The middle layer, the base, is very thin and has only a small amount of doping elements compared to the other two so a small current going from the emitter to the base will allow a much larger current to flow from the emitter to the collector.
And as with diodes, the require a small amount of voltage to work, for silicon this is 0.6 volt and current or voltage that exceeds what the transistor is designed for may damage it and the circuit it is in.
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