Question
What are the operating points for a bipolar transistor used as a switch?
Answer Options
- A) Saturation and cutoff
- B) The active region (between cutoff and saturation)
- C) Peak and valley current points
- D) Enhancement and depletion modes
Correct Answer: A
Explanation
A bipolar junction transistor (BJT) can be used either as a linear amplifier or as a digital switch. When used as a switch, the transistor is toggled between two extreme operating regions to represent the ‘ON’ and ‘OFF’ states.
The ‘OFF’ state is cutoff, where the base-emitter junction is zero- or reverse-biased, stopping all current flow through the collector-emitter path. The ‘ON’ state is saturation, where maximum base current is applied, forcing the collector-emitter path to conduct maximum current, effectively shorting the path. Switching between saturation and cutoff is the basis of its function as a digital switch.
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