Electronics/Transistors
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[edit] Transistor
Transistor is a Solid State Device made by joining three positive-typed and negative-typed Semi Conductors together . In general, all transistor has three pins namely Base , Collector and Emitter . Transistor is a bi polar Device that is transistor has two junctions namely BE and CE
[edit] Construction
A lightly doped region called base is sandwiched between two regions called the emitter and collector respectively. The collector handles large quantities of current, hence its dopant concentration is the highest. The emitter's dopant concentration is slightly lesser, but its area is larger to provide for more current than the collector. The collector region should be heavily doped because electron-hole pair recombine in that region, while the emitter is not such a region. We can have two varieties in this kind of transistor.
[edit] NPN Transistor
NPN made from joining one Positive-Typed Semi Conductor in between two Negative-Typed Semi Conductors . Here a lightly doped p-type semiconductor (semiconductor with more holes than electrons) is sandwiched between two well-doped n-type regions. It is like two pn-junctions facing away. An IEEE symbol for the npn transistor is shown here. The arrow between the base and emitter is in the same direction as current flowing between the base-emitter junction. Power dissipated in the transistor is
- P = VCEIC, where VCE is the voltage between the collector and the emitter and IC is the collector current.
[edit] PNP Transistor
PNP Transistor made from joining one Nagative-Typed Semi Conductor in between two Positive-Typed Semi Conductors
[edit] Transistor Operation
[edit] Amplifier
Transistor conducts current when Base Voltage is greater than BE junction's voltage . Current is non zero .
- IB ≠ 0
- IE = α IB
- IC = β IB
[edit] Switch
The characteristic that Transistor conduct or non conduct current make transistor suitable for Electronic Switching . Transistor conducts current when Base Voltage is greater than BE junction's voltage . Current is non zero . This correspond to a Closed Switch . Transistor does not conduct current when Base Voltage is less than BE junction's voltage . Current is zero . This correspond to a Opened Switch
