Transfer characteristics [output voltage (V0) vs input voltage (Vi)] for a base biased transistor in CE configuration is as shown in the figure. For using transistor as a switch, it is used [figure]
- in region III
- both in region (I) and (III)
- in region II
- in region I
Answer
(2) both in region (I) and (III)
Solution
Region I: cut-off region — Vi is low, transistor is OFF, V0 is high.
Region II: active region — used for amplification.
Region III: saturation region — transistor is ON, V0 is low.
A switch must work only in the OFF and ON states,
the transistor is used in the cut-off (I) and saturation (III) regions.
Answer: (2)