Transistor Characteristics

In physics, the graph representing the relationships between the current and the voltage of any transistor of any configuration is called Transistor Characteristics. Any two-port network which is analogous to transistor configuration circuits can be analysed using three types of characteristic curves. They are

  • Input Characteristics: The curve describes the changes in the values of input current with the variation in the values of input voltage keeping the output voltage constant.
  • Output Characteristics: The curve is got by plotting the output current against output voltage keeping the input current constant.
  • Current Transfer Characteristics: This characteristic curve describes the variation of output current in accordance with the input current, keeping the output voltage constant.

Configuration Of Transistor

Any transistor circuit can be designed using three types of configuration. Three configurations of the transistor are based on the connection of the transistor terminal. The three types of transistor circuit configurations are:

  • Common Emitter Transistor
  • Common Base Transistor
  • Common Collector Transistor(emitter follower).

Each of these three circuit configurations has its own characteristics curve. Based on the requirement the type will be chosen for the circuit.

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Common Emitter (CE) Configuration of Transistor

In CE Configuration, the Emitter terminal of the transistor will be connected common between the output and the input terminals.

Common Emitter

Common Emitter (CE) Configuration of Transistor

The transistor characteristic under Common Emitter configuration is as follows:

Transistor Characteristics Definition Formula/Expression Characteristic Curve
Input Characteristics The variation of emitter current(IB) with Base-Emitter voltage(VBE), keeping Collector Emitter voltage(VCE) constant. \(R_{in}=\frac{\Delta V_{BE}}{\Delta I_{B}}|V_{CE}=Constant\) Common Emitter-1
Output Characteristics The variation of collector current(IC) with Collector-Emitter voltage(VCE), keeping the base current(IB) constant. \(R_{out}=\frac{\Delta V_{CE}}{\Delta I_{C}}|I_{B}=Constant\) Common Emitter-2
Current Transfer Characteristics The variation of collector current(IC) with the base current(IB), keeping Collector-Emitter voltage(VCE) constant.

The resulting current gain has a value greater than 1.

\(\alpha =\frac{\Delta I_{C}}{\Delta I_{B}}|V_{CB}=Constant\) Common Emitter-3

Common Base (CB) Configuration of Transistor

In CB Configuration, the base terminal of the transistor will be connected common between the output and the input terminals.

Common Base

Common Base (CB) Configuration of Transistor

The transistor characteristic under Common Base configuration is as follows:

Transistor Characteristics Definition Formula/Expression Characteristic Curve
Input Characteristics The variation of emitter current(IE) with Base-Emitter voltage(VBE), keeping Collector Base voltage(VCB) constant. \(R_{IN}=\frac{\Delta V_{BE}}{\Delta I_{E}}|V_{CB}=Constant\) Common Base-1
Output Characteristics The variation of collector current(IC) with Collector-Base voltage(VCB), keeping the emitter current(IE) constant. \(R_{OUT}=\frac{\Delta V_{CB}}{\Delta I_{B}}|I_{E}=Constant\) Common Base-2
Current Transfer Characteristics The variation of collector current(IC) with the emitter current(IE), keeping Collector Base voltage(VCB) constant.

The resulting current gain has a value less than 1.

\(\alpha =\frac{\Delta I_{C}}{\Delta I_{B}}|V_{CB}=Constant\) Common Base-3

Common Collector (CC) Configuration of Transistor

In CE Configuration, the Collector terminal of the transistor will be connected common between the output and the input terminals.

Common Collector

Common Collector (CC) Configuration of Transistor

The transistor characteristic under Common Collector configuration is as follows:

Transistor Characteristics Definition Characteristic Curve
Input Characteristics The variation of emitter current(IB) with Collector-Base voltage(VCB), keeping Collector Base voltage(VCB) constant. Common Collector-1
Output Characteristics The variation of emitter current(IE) with Collector-Emitter voltage(VCE), keeping the base current(IB) constant. Common Collector-2
Current Transfer Characteristics The variation of Emitter current(IE) with the base current(IB), keeping Collector-Emitter voltage(VCE) constant. Common Collector-3

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