A BJT operates as a switch

The applications of BJT and the biasing conditions are shown below:

• BJT is never operated in the reverse active region
• The main application of the BJT is as an amplifier, and this is possible under small-signal conditions.
• The characteristics of I_C – V_be is as shown below:

• Current variations are linear in this region.
• Non-linear behavior becomes linear in that small region.
• DC operating point is needed so that we can apply the signal at that point to get the amplified signal.
• The remaining applications of transistor i.e. ON & OFF switch are possible under the large-signal conditions.