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 has two junctions: the base-emitter junction and the collector-base junction. The active mode of a BJT is when the base-emitter junction is forward biased (meaning that the voltage at the base is higher than the emitter for an NPN transistor, and the opposite for a PNP transistor)and the collector-base junction is reverse biased (the voltage at the collector is higher than the base for an NPN transistor, and vice-versa for a PNP). In an NPN transistor, for example, theactive mode is achieved when:
• The base-emitter junction is forward biased meaning that the base voltage (Vb) emitter voltage (Ve), and the
• The collector-base junction is reverse biased meaning the collector voltage (Vc) base voltage (Vb).
In active mode, the BJT acts as an amplifier, where a small change in the base current can cause a large change in the collector current. This region is most useful for amplification in BJT circuits.