Operating Regions of a BJT

A Bipolar Junction Transistor (BJT) is a three-layer semiconductor device that consists of two pn junctions. These junctions are the collector-base (CB) junction and the base-emitter (BE) junction. Depending on the biasing conditions of these junctions, the BJT can operate in different regions. The operating regions of a BJT are as follows:

1. Cutoff Region:
When both the collector-base junction and the base-emitter junction are reverse-biased, the BJT is said to be in the cutoff region. In this region, the BJT is in an off state, and no current flows through it.

2. Active Region:
In the active region, the collector-base junction is reverse-biased, while the base-emitter junction is forward-biased. This is the region where the BJT operates as an amplifier. The current flowing through the BJT is controlled by the base current, and the collector current is proportional to the base current. The BJT operates in an active mode where it can amplify signals.

3. Saturation Region:
When both the collector-base junction and the base-emitter junction are forward-biased, the BJT is said to be in the saturation region. In this region, the BJT is fully turned on, and the collector current is at its maximum value. The BJT operates as a closed switch, allowing a large current to flow from the collector to the emitter.

4. Reverse Active Region:
In the reverse active region, the collector-base junction is forward-biased, while the base-emitter junction is reverse-biased. This region is rarely used in practical applications and is mainly used for testing purposes. In this region, the BJT operates with reversed current flow, and the collector current is controlled by the base current.

Answer:
Based on the given biasing conditions (collector-base junction forward-biased and base-emitter junction forward-biased), the BJT is operating in the saturation region. In this region, the BJT acts as a closed switch, allowing a large current to flow from the collector to the emitter. This biasing configuration is commonly used in digital applications and for switching purposes.