10-09-2013, 04:56 PM
NPN TRANSISTOR:
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INTRODUCTION
Transistor is a 3 terminal device,having emitter , base and collector. These three parts are made up of extrinsic semiconductors. Now, the semiconductors can be p-type or n-type. In npn transistor, the p-type semiconductor is sandwiched between the n-type semiconductors. Therefore it is named so. The other type is pnp npn is preferred, as electrons here has higher mobility than holes, so they allow greater current and faster operation because of majority carriers as electrons.
NPN PROPERTIES:
1. Common emitter.
2. P- dopped base.
3. A small current entering the base is amplified to produce large collector and emitter current.
NPN TRANSISTOR AS AN AMPLIFIER:
The npn transistor when used as an amplifier is operating in a linear mode and when operating as a switch in saturated mode. The essential usefulness of a transistor comes from its ability to use a small signal applied between one pair of its terminals to control a much larger signal at another pair of terminals. This property is called gain. A transistor can control its output in proportion to the input signal; that is, it can act as an amplifier. Alternatively, the transistor can be used to turn current on or off in a circuit as an electrically controlled switch, where the amount of current is determined by other circuit elements.