Figure below shows both n-p-n and p-n-p transistors biased in the active mode of operation.īiasing Circuits of BJTTo make the Q point stable different biasing circuits are tried. The BE junction is forward biased whereas the CB junction is reverse biased. Active Mode of BJTIn order to use the transistor as an amplifier, it must be operated in the active mode.
The BJT operates like a closed switch in the saturation mode.If a BJT is in saturation mode than it should satisfy the following condition,Where β DC is common emitter amplification factor or gain. The CB as well as BE junctions are forward biased. Saturation Mode of BJTThe transistor is fully on in this state. The BJT is equivalent to an open switch in this mode. In the cutoff mode both the base emitter as well as collector base junction is reverse biased. Cutoff Mode of BJTThe is fully off in this state. Depending on whether the two junctions of the transistor are forward or reverse biased, a transistor is capable of operating in three different modes. In order to use the BJT for any application like amplification, the two junctions of the transistor CB and BE should be properly biased according to the required application.
