Transfer characteristics [output voltage ($V_o$) vs input voltage ($V_i$)] for a base biased transistor in CE

Question

Transfer characteristics [output voltage ($V_o$) vs input voltage ($V_i$)] for a base biased transistor in CE configurations are as shown in the figure. For using the transistor as a switch, it is used:

Accepted Answer

In the transfer characteristics of a Common Emitter (CE) transistor, the graph is divided into three distinct regions: 
1. Region I (Cut-off region): The input voltage is very low, and the output voltage is high. The transistor does not conduct and acts as an open switch (OFF state).
2. Region II (Active region): The output voltage decreases linearly with an increase in input voltage. The transistor is used as an amplifier in this region.
3. Region III (Saturation region): The input voltage is high, and the output voltage drops to a very low, near-zero value. The transistor conducts fully and acts as a closed switch (ON state).
Therefore, for a transistor to function as a switch, it must operate between the cut-off region (I) and the saturation region (III).

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