Question

A bipolar junction transistor is said to be in active mode if:

• A. Base-emitter junction is forward biased and collector-emitter junction is reverse biased
• B. Base-emitter junction is reverse-biased and collector-emitter junction is forward biased
• C. Both the junctions are forward biased
• D. Both the junctions are reverse biased

Hint:

Remember the difference between the three regions of operation of BJT which are the cut off region (both junctions reversed biased), the active region (EB junction forward biased and CB junction reversed biased) and the saturation region (both junctions forward biased). The base current acts as the control signal, allowing you to increase the current flow between the collector and emitter.

Answer 1

The Correct Option is A

A bipolar junction transistor (BJT) has three regions: the emitter, the base, and the collector. It also features two junctions: the base-emitter junction and the collector-base junction. A BJT operates in active mode when its base-emitter junction is forward biased and its collector-base junction is reverse biased. For an NPN transistor, this means the base voltage (Vb) is higher than the emitter voltage (Ve), and the collector voltage (Vc) is higher than the base voltage (Vb); for a PNP transistor, these polarities are reversed. In active mode, the BJT functions as an amplifier, enabling a small change in base current to produce a significant change in collector current. This mode is optimal for amplification in BJT circuits.