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Difficulty: MediumTransistors

An electronics technician is testing a bipolar junction transistor (BJT) configured as an electronic switch. When the base receives sufficient input voltage and current to drive the transistor into full conduction with minimum resistance between the collector and emitter, in which operating region is the transistor functioning?

  1. A
    Cutoff region
  2. Saturation regionAnswer
  3. C
    Active region
  4. D
    Breakdown region

Answer

Saturation region
When a bipolar junction transistor is driven with sufficient base current to achieve maximum conduction, it operates in the saturation region. In saturation, both internal PN junctions are forward-biased, reducing the collector-to-emitter voltage (VCEV_{CE}) to a fraction of a volt (typically around 0.2 V0.2\text{ V}), effectively behaving like a closed mechanical switch.

Step-by-Step Solution

1
Identify the circuit role and desired state of the transistor
The transistor operates as an electronic switch driven into full conduction (fully ON).
Transistors in switching circuits toggle between two primary binary states: fully OFF and fully ON.
2
Relate the fully ON switching condition to the characteristic BJT operating regions
Full conduction with minimal collector-to-emitter voltage drop occurs in the saturation region.
When both the base-emitter and base-collector junctions become forward-biased due to sufficient base drive, the transistor enters saturation, maximizing current flow through the load.

Key Concept

BJT Operating Regions and Switching States
Estimated Time:1m 0s
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Topics

Transistors

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