When both the junctions of bipolar junction transistor (BJT) are in forward biased, then in which region BJT will operate?
Right Answer is:
Saturation region
SOLUTION
The output characteristics can be divided into three distinct regions. namely, the active region, the saturation region, and the cut-off region.
Saturation Region
The region of the output characteristics where both junctions (emitter and collector) are forward biased, is known as the saturation region of the transistor.
The saturation region is located to the left of the ordinate. VCB is slightly positive for a p–n-p transistor in this region. This forward biasing of the collector-base junction causes the collector current to change exponentially with the collector-base forward voltage, as in p-n diode. The large change in the collector current for a small change in VCB in the saturation region is thus accounted for. A forward bias implies that the collector p material is at a positive potential relative to the base n material. A hole current thus flows from the collector to the base, i.e., in a direction opposite to the original hole current due to the transistor action. When the forward-bias is sufficiently large, the hole flow from the collector to the base predominates, forcing Ic to be positive, as shown in Fig.
Note:-
Cutoff region: in this region transistor acts as off switch.
Saturation region: transistor acts as on switch.
Active region: transistor acts as an amplifier