A transistor when connected in CE mode has:-
Right Answer is:
A low input resistance and high output resistance
Out of the three transistor connections, the common-emitter circuit is the most efficient. It is used in about 90 to 95 percent of all-transistor applications. The main reasons for this are :
- The transistor circuit will have a moderately high input impedance
- Low output impedance
- The moderately high current gain
- Moderately high voltage gain and the very good and wide range of frequency response and hence find dominant applications in voltage, current and power amplifiers.
High current gain
In common emitter connection, Ic is the output current and IB is the input current. The collector current here is expressed as:
Ic = βIB + ICEO
Where β = Current Gain
ICEO = Collector-Emitter current
As the value of β is very large, therefore, the output current IC is much more than the input current IB. This increases the current gain effectively. The current gain of CE arrangement ranges from 20 to
High Voltage and Power Gain
As we have seen above, CE arrangement has a high current gain. This in turn, increases the voltage and power gain of the CE circuit. In comparison to CB and CC circuits, the common emitter connection has the highest voltage and power gain. For this reason, the CE transistor connection is often used for amplifying purposes.