bipolar junction transistor

in a bipolar junction transistor (used as an amplifier) the collector current is alpha times the emitter current and alpha is always less than one ,but amplification means the input signal should be multiplied a factor so that we get a magnified output,but here the output (collector current) is almost equal (slightly less than the emitter current) that is current at the output is not magnified than the input emitter current,but why is it called an current amplifier ,please let me know about it
and also i am not able to understand similarly about an bipolar junction transistor as a voltage amplifier


  • lal
    Alpha is the amplification in common base configuration. Here the input is given between emitter-base and output is taken across collector-base. In this case amplification is less than one.
    But in common emitter configuration beta is the gain which is very high, usually in the range of 200. Here the input is given accross base-emitter jnction and output is taken accross collector-emitter. It is this common emitter configuration that is used for amplification.
  • pradeep madhav
    pradeep madhav
    ok then it means for a current amplifier input current is the base current and output current is the collector current.
    but base currents in a transistor is of the order of microamperes ,but suppose if i want to amplify a current of magnitude 1ampere ,then it would destroy the transistor (to avoid the damage of transistor we might place a resistor across the base terminal ) but then the base current (input current) value will be reduced ,so what would happen then .

    (2)and also let me know what exactly happens inside the transistor operated in a common emitter mode(as an amplifier)
  • roxy_1001
    Dude there are different transistors in market with different current voltage * power ratings...
    If your input voltage exceeds the maximum rated voltage then it will distroy your transistor..

    There are two types of components Small signal & Large signal ...
    Small signal transistors are used upto several mA or upto 1Amp... but If you want to amplify current 1 Amp or more than that you will have to use Large signal transistors called as Power transistors ... they are bulky one and usually comes in Metal can pack they require heat sinks for temperature compensation ...

    Hope this will help you..😁 If you have more doubts ask..
  • pradeep madhav
    pradeep madhav
    we know that in a common collector configuration of a bipolar junction transistor the collector terminal should appear in common between the input and output terminals but look at the link given below Common Collector
    (in the above link the top right diagram figure 1 (basic npn common collector circuit ) the emitter appear in common between the input pair of terminals (emitter base terminals ) and output pair of terminals (collector emitter terminals) ,but it is the case of a common emitter configuration ,but still why do we call it as a common collector configuration .and also check this link here also emitter appears in common between the common collector configuration
  • lal
    In the Wiki article of common colletor configuration, its clearly explained. In the first paragraph itself it is clearly said, collector may be connected to ground reference or a power supply rail. It doesn't mean that emitter is common, if in the diagram emitter is shown in bottom. You may please refer to the article once again and make it clear to yourself.
    You know, self study is the best!😉
  • pradeep madhav
    pradeep madhav
    we know that a zener diode operated in a reverse biased condition , eventhough when the reverse voltage applied across the zener diode increases more than its breakdown voltage the voltage drop across the zener diode remains constant ,why does this happen ? what actually happens inside the zener diode during that situation

You are reading an archived discussion.

Related Posts

How close to an edge of unreinforced concrete trench fill foundation is it possible to erect a brickwork wall, say 140mm wide? If the applied bearing pressure below foundation is...
If you have any queries regarding your summer training 2010, please post it here. This will help, have you seen 3 idiots (recent India BOX office super hit), you will...
Microsoft Small Basic 0.8 Size :- 4.67 MB Microsoft Small Basic is a project that is aimed at making computer programming accessible to beginners. The project comprises a simple programming...
without fully startup or (from the startup) our os able to read external dirve like pen drive what is the reason behind it (i think plug play in the bios...
what is the function of memory in bios setup. 😁