I often come across circuits saying that the transistors therein are in common collector (or common emitter or common base) configuration. What is all these configurations about and what is their significance?

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    \$\begingroup\$ Again too broad. -1 for not having bothered to read the rules, or ignoring them if you did. Try asking separate questions about each type of transistor configuration. \$\endgroup\$ Commented Jul 28, 2013 at 15:46
  • \$\begingroup\$ If it is too broad, I don't ask you to write down everything. People could rather suggest some websites or books which have good information about this \$\endgroup\$ Commented Jul 28, 2013 at 16:15
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    \$\begingroup\$ insufficient preliminary research \$\endgroup\$ Commented Jul 28, 2013 at 17:18
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    \$\begingroup\$ Just supplying links isn't how we do things here. Again, ask separate questions. \$\endgroup\$ Commented Jul 28, 2013 at 22:12

2 Answers 2


The input (current) is applied to two legs, the output (current) is applied to two legs. But a transistor has only three legs, so one legs must be common to both the input and the output. That is the 'common' the configuration refers to.

The three choices have very different characteristics. From http://www.tpub.com/neets/book7/25f.htm:

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  • \$\begingroup\$ Or in a slightly simpler manner: to which pin the input is connected? To which pin the output is connected? The third one is common. I like this rule of thumb! \$\endgroup\$
    – Vasiliy
    Commented Jul 28, 2013 at 16:48

A transistor can be used for various applications. These applications require the transistor to be connected in one of the given configurations : 1) common emitter(most widely used configuration ) 2) common base and 3) common collector. In common emitter the emitter terminal is connected to both ,the collector and base. In common base, the base is connected to both ,the collector and emitter. In common collector the emitter terminal is connected to both ,the emitter and base.

This is a basic description of what those configurations imply. I suggest you read up on wikipedia as the specific functions and characteristics can make for an entire chapter.


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