TRANSISTOR IN COMMON EMITTER CONFIGURATION AIM To study the characteristics and to determine the current gain of a NPN junction transistor in common emitter configuration. APPARATUS REQUIRED Transistor - BC /BC107, bread board, micro ammeter, milli ammeter, voltmeters, variable DC power supply and connecting wires. FORMULA BE V CE ∆ ∆ ( Ω ), r o CE I B = ∆ ∆ ( Ω ), β = ∆ ∆ V CE (No unit) Where, r i → Input impedance (Ω) ∆ V BE → The change in base-emitter voltage (volt) ∆ I B → The change in base current (µA) r o → Output impedance (Ω) ∆ V CE → The change in collector-emitter voltage (volt) ∆ I C → The change in collector current (mA) β → Current gain of the transistor (No unit) CIRCUIT DIAGRAM Collector Base Emitter BC Transistor Figure (a) NPN - Junction transistor and its symbol (Transistor is held with the flat surface facing us) I E I B I C V BE V BB V CE V CC µA mA Ω Figure (b) NPN junction transistor in CE configuration Note A resistor is connected in series with the base to prevent excess current flowing into the base. XII- - ) XII- - ) - - - - PRACTICAL Precautions • Care should be taken to connect the terminals of ammeters, voltmeters, and dc power supplies with right polarity.
• The collector and emitter terminals of the transistor must not be interchanged. PROCEDURE ¾ The connections are given as shown in the diagram. ¾ The current and voltage at the input and output regions can be varied by adjusting the DC power supply. (i) Input characteristic curve: V BE vs I B ( V CE constant) • The collector-emitter voltage V CE is kept constant.
• The base-emitter voltage V BE is varied in steps of .1V and the corresponding base current ( I B