Question

Plot the input characteristics of BJT mentioning different regions.

Answer 1

BJT: BJT stands for Bipolar Junction Transistor. A BJT is a three-terminal semiconductor that can amplify a signal and has 2 p-n junctions. The three terminals are

1. Emitter E
2. Base B
3. Collector C

Different configurations of a BJT:

BJT is available in 3 configurations:

a) CB Common Base configuration-For a fixed emitter current$I_E$, emitter-base voltage$V_{EB}$ increases with an increase in common base voltage $V_{CB}$.

b) CC Common collector configuration -It is obtained from input base current $I_B$and input common base voltage$V_{CB}$ at constant output emitter-collector voltage.$V_{EC}$

c) CE Common emitter configuration -For increased input base current$I_B$,base-emitter voltage$V_{BE}$ increases with an increase in collector-emitter voltage.$V_{CE}$

Regions of operation in the characteristic curve:

1. Cut-off region- When the base power supply is set to zero, and the current $I_B$becomes zero. Current $I_C$does not flow and the transistor acts as an open circuit in this region.
2. Saturation region - When the collector supply voltage is set to zero and the base produces a current $I_B$. No current flows through the collector In this region, the collector current reaches a certain largest current
3. Active/Linear region -In this region, Common collector voltage$V_{CC}$ is increased and collector-emitter voltage$V_{CE}$ may increase.
4. Breakdown region- In this region common collector voltage is increased due to which collector-emitter voltage can be increased which may increase the reverse bias of BC junction. The high reverse bias makes the junction break down.

The above mentioned are the input characteristics graphs of the BJT transistor and the regions that are part of the graphs.