Bipolar Junction Transistor
Types of Transistor Configuration
Transistor is an electronic device which is primarily used to amplify the electric current.
We know that transistor has three terminals namely emitter (E), base (B), and collector (C). But to connect a transistor in the circuit, we need four terminals: two terminals for input and other two terminals for output.
But the transistor does not have four terminals, then how do we connect transistor in a circuit. It is not as difficult as you think. One of the three terminals is used as common to both input and output.
When a transistor is to be connected in a circuit, one terminal is used as the input terminal, the other terminal is used as the output terminal and the third terminal is common to the input and output.
That means here input is applied between the input terminal and common terminal, and the corresponding output is taken between the output terminal and common terminal.
Depending upon the terminal which is used as a common terminal to the input and output terminals, the transistor can be connected in the following three configurations. They are:
- Common base (CB) configuration
- Common emitter (CE) configuration
- Common collector (CC) configuration
In every configuration, the base-emitter junction JE is always forward biased and the collector-base junction JC is always reverse biased to operate the transistor as a current amplifier.
Common base (CB) configuration
In common base configuration, emitter is the input terminal, collector is the output terminal, and base is the common terminal. The base terminal is grounded in the common base configuration. So the common base configuration is also known as grounded base configuration.
Common emitter (CE) configuration
In common emitter configuration, base is the input terminal, collector is the output terminal, and emitter is the common terminal. The emitter terminal is grounded in the common emitter configuration. So the common emitter configuration is also known as grounded emitter configuration.
Common collector (CC) configuration
In common collector configuration, base is the input terminal, emitter is the output terminal, and collector is the common terminal. The collector terminal is grounded in the common collector configuration. So the common collector configuration is also known as grounded collector configuration.
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