![]() ![]() The three circuits or biasing arrangements which are practically used are explained below.įixed Bias or Base BiasIn this condition a single power source is applied to the collector and base of the transistor using only two s. When the BJT is biased such that the Q point is halfway between cutoff and saturation than the operates as a CLASS-A amplifier. The Q point represents the DC biasing condition. ![]() Output in any of the transistor configurations) which represents the DC through the transistor and across it when no ac signal is applied. The Q point is also called as operating bias point, is the point on the DC load line (a load line is the graph of output vs. 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.
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