When a BJT is used as switch, its mode of operation switches between:a...
Different modes of BJT operations
For switching Application BJT is operated in cut off (off switch) and saturation (on switch)
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When a BJT is used as switch, its mode of operation switches between:a...
Explanation:
Operating Modes of a BJT:
- A Bipolar Junction Transistor (BJT) can be operated in three different modes - cut-off, active, and saturation.
Switching Between Cut-off and Saturation Regions:
- When a BJT is used as a switch, it operates between the cut-off and saturation regions.
- In the cut-off region, the BJT is in an off state, with both the base-emitter and base-collector junctions being reverse-biased.
- In the saturation region, the BJT is in an on state, with both junctions being forward-biased.
Switching Operation:
- When the BJT is turned on, it transitions from the cut-off region to the active region.
- As the base-emitter junction becomes forward-biased, the BJT enters the active region and starts conducting current.
- Further increasing the base current drives the BJT into saturation, where it operates as a closed switch with minimal voltage drop across it.
- When the BJT is turned off, it transitions from the saturation region back to the cut-off region.
- By controlling the base current, the BJT can be effectively used as a switch to toggle between the cut-off and saturation regions.
Conclusion:
- Therefore, when a BJT is used as a switch, its mode of operation switches between the cut-off region (off state) and the saturation region (on state), allowing for efficient control of current flow.