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Analog Electronics Lab Experiments

To Study the Characteristics of Transistor in Common Base Configuration


To Study the characteristics of transistor in Common Base configuration.

Apparatus Required:

Power supply, Transistor characteristics Kit, Connecting Leads, Voltmeter, Ammeter.

Brief Theory:

Transistor is a semiconductor device consist of two p-n junctions. It has three terminals, to handle I/P and O/P four terminals are needed. Therefore, one terminal is made common. A transistor can be connected in three Ways CB, CE, and CC.

Common base: Base is made common. I/P is connected between base & emitter and O/P is taken between base & collector.

Input charact.The curve plotted between emitter current I & the emitter-base voltage constant collector-base voltage V.

Output charact.The curve plotted between collector current I & collector-base voltage V constant emitter current I.

Circuit Diagram:



Input charact.

  1. Make the connection as per circuit diagram .
  2. Switch ‘ON’ the supply & set V = 0V
  3. Vary V in step & note down the emitter current I at each step .
  4. Set V = 1V & again repeat the same procedure .
  5. Draw the graph.

Output charact.

  1. Make the connection as per circuit diagram.
  2. Set the value of I = 1mA
  3. Vary V in step & note down the collector current I at each step.
  4. Set I = 2mA & repeat the same procedure.
  5. Draw the graph.

Observation Table:

S. No Input charact.(Vcb=Cons.)/Ie(mA)/Veb(Volts) Output charact. (Ie = Const.)/Ic(mA)/Vcb(Volts)



Result:The input and output characteristics of transformer in CB configuration has been plotted.

Discussion:With the help of output characteristics we can calculate ac & dc current gain in CB configuration.


  1. Always connect the voltmeter in parallel & ammeter in series as shown in fig.
  2. Connection should be proper & tight.
  3. Switch ‘ON’ the supply after completing the ckt.
  4. DC supply should be increased slowly in steps
  5. Reading of voltmeter & Ammeter should be accurate.


Q1:What do you mean by biasing of transistor?

A1:When dc voltages are applied across the different terminals of transistor, it is called biasing.

Q2:What is d.c. current gain in common base configuration?

A2:It is ratio of collector current(Ic) to emitter current (Ie).

Q3:What is typical value for d.c. current gain ?


Q4:What is a.c. current gain in CB confifuration?

A4:It is ratio of change in collector current to change in emitter current.

Q5:What are input characteristics?

A5:These curves relate i/p current & i/p voltage for a given value of o/p voltage.

Q6:What are output characteristics?

A6:These curves relate o/p voltage & o/p current for a given value of input current.

Q7:Which configuration has highest voltage gain?

A7:Common Emitter.

Q8:Which configuration is most widely used?

A8:Common Emitter.

Q9:What is operating point?

A9:The zero signal values of Ic & Vce.

Q10:Which reigon is heavily doped in Transistot?