Transistor Configuration

CE, CB, CC Configurations:
        Transistor Configuration:

• We know that transistor has three terminals namely emitter(E), base(B), collector(C).
• However, when a transistor is connected in a circuit, we require four terminals (ie) two terminals for input and two terminals for output.
• This difficulty is overcome by using one of the terminals as common terminal.
• Depending upon the terminals which are used as a common terminal to the input and output terminals, the transistors can be connected in the following three different configuration.
• Common base configuration                            
• Common emitter configuration
• Common collector configuration

• Common base configuration:

• In this configuration base terminal is conncted as a common terminal.
•  The input is applied between the emitter and base terminals.The output is taken between the collector and base terminals.

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• Common emitter configuration:

•  In this configuration emitter terminal is conncted as a common terminal.
• The input is applied between the base and emitter terminals.The output is taken between the collector and base terminals.

                     3. Common collector configuration:

• In this configuration collector  terminal is conncted as a common terminal.
• The input is applied between the base and collector terminals.The output is taken between the emitter and collector terminals

CB, CE,CC Characteristics :

• Common base  Characteristics :

                       
   Input characteristics:

                  Diagram

• The output(CB) voltage is maintained constant and the input voltage (EB) is set at several convenient levels.For each level of input voltage, the input current IE is recorded.
• IE is then plotted versus VEB to give the common-base input characteristics.

  
          
Output characteristics:

                    Diagram

• The emitter current IE  is held constant at each of several fixed levels. For each fixed value of IE ,  the output voltage VCB is adjusted in convenient steps and the corresponding levels of collector current IC are recorded

• .For each fixed value of IE,  IC is almost equal to IE  and appears to remain constant when VCB is increased.     

• Common-Emitter Characteristics :

                       
   Input characteristics:

                  Diagram

• The output voltage VCE is maintained constant and the input voltage VBE is set at several convenient levels.For each level of input voltage, the input current IB is recorded.
• IB is then plotted versus VBE to give the common-base input characteristics.

  
          
Output characteristics:

                    Diagram

• The Base current IB  is held constant at each of several fixed levels. For each fixed value of IB ,  the output voltage VCE is adjusted in convenient steps and the corresponding levels of collector current IC are recorded

• .For each fixed value of IB,  IC level is Recorded at each VCE  step.For each IB  level, IC is plotted versus VCE  to give a family of characteristics.

• Common-Collector Characteristics :

                       
   Input characteristics:

                  Diagram

• The common-collector input characteristics are quite different from either common base or common-emitter input characteristics.
• The difference is due to the fact that the input voltage (VBC) is largely determined by (VEC)   level .

                              
                                VEC = VEB + VBC
                                VEB =  VEC - VBC
         
Output characteristics:

                    Diagram

• The operation is much similar to that of C-E configuration.When the base current is ICO,  the emitter current will be zero and consequently no current will flow in the load.
• When the base current is increased, the transistor passes through active region and eventually reaches saturation. Under the saturation conditions all the supply voltage, except for a very small drop across the transistor will appear across the load resistor.