Ham Radio General Class Practice Test

What are the stable operating points for a bipolar transistor used as a switch in a logic circuit?

1. Its saturation and cut-off regions

2. Its active region (between the cut-off and saturation regions)

3. Its peak and valley current points

4. Its enhancement and deletion modes

The correct answer is: Its saturation and cut-off regions

In a bipolar transistor used as a switch in logic circuits, the stable operating points are indeed found in the saturation and cut-off regions. When a transistor is in the saturation region, it is fully "on," allowing maximum current to flow through it, which is ideal for a logic circuit in a high state. Conversely, when the transistor is in the cut-off region, it is fully "off," allowing no current to flow, representing a low state in the circuit. These two states (saturation and cut-off) provide the binary logic function (1 and 0) that is essential for digital circuits. The active region, while important for amplification purposes, does not provide the binary states required for switching operations effectively. In the active region, the transistor can operate partially on, which is not suitable for a logic circuit where a clear distinction between on and off states is necessary. The peak and valley current points refer to maximum and minimum current conditions, which may be significant in certain contexts but are not the defining stable operating points for switching in logic circuits. Lastly, the enhancement and depletion modes pertain specifically to field-effect transistors (FETs) rather than bipolar transistors, further establishing that the discussion of operating points must focus on saturation and