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SESK: Stuff Everyone Should Know · sesk.info/hamg-g6a07

What two operating points does a bipolar transistor use when it works as a switch?

Saturation and cutoff.

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  1. Saturation and cutoff ✔
  2. The active region (between cutoff and saturation)
  3. Peak and valley current points

Why: A switch is either fully on or fully off. For a bipolar transistor, fully on is saturation and fully off is cutoff. The active region in between is not used for switching.

Huh, didn't know that: A MOSFET's gate is separated from its channel by a thin insulating layer.

The dad joke
A transistor switch has two moods, saturated and cut off, just like me before coffee.
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References

Answer: Saturation and cutoff. A switch is either fully on or fully off. For a bipolar transistor, fully on is saturation and fully off is cutoff. The active region in between is not used for switching.

  1. NCVEC 2023-2027 General Class Pool and Syllabus (6th Errata, Feb 4 2026) ncvec.org/downloads/General%20Class%20Pool%20and%20Syllabus%202023-2027%20Public%20Release%20with%206th%20Errata%20Feb%204%202026.pdf
    Saturation and cutoff
    Checked 2026-10-11.

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