Transistor functions as a switch. Explain.

Explanation

The transistor in saturation and cut-off regions functions like an electronic switch that helps to turn ON or OFF a given circuit by a small control signal.

• Presence of de source at the input (saturation region):
When a high input voltage `(V_(m)=+5V)` is applied, the base current `(I_(B))` increases and in turn increases the collector current. The transistor will move into the saturation region (turned ON). The increase in collector current `(I_(C))` increases the voltage drop across `R_(C)` thereby lowering the output voltage, close to zero. The transistor acts like a closed switch and is equivalent to ON condition.
• Absence of de source at the input (cut-off region):
A low input voltage `(V_(in)=0V)`, decreases the base current `(I_(B))` and in turn decreases the collector current `(I_(C))`. The transistor will move into the cut-off region (turned OFF). The decrease in collector current `(I_(C))` decreases the drop across `R_(C)`, thereby increasing the output voltage, close to +5 V. The transistor acts as an open switch which is considered as the OFF condition.
It is manifested that, a high input gives a low output and a low input gives a high output. In addition, we can say that the output voltage is opposite to the applied input voltage. Therefore, a transistor can be used as an inverter in computer logic circuitry.