In a common emitter NPN transistor the relation between collector current and emitter current is given as The equation for collector supply voltage is given asįrom the above equation the collector current for common emitter NPN transistor is given as The output collector current in common emitter NPN transistor can be calculated by applying Kirchhoff’s Voltage Law (KVL). The equation for base current of a bipolar NPN transistor is given by, So the base voltage must be greater than the voltage drop 0.7V otherwise the transistor will not operate. Some amount of voltage drop presented between base and emitter, such as 0.7V. To allow current flow between emitter and collector properly, it is necessary that the collector voltage must be positive and also greater than the emitter voltage of transistor. Here the base terminal acts as input and the collector-emitter region acts as output. fully-ON state, then electrons flow generated and the current (IC) flows from emitter to the collector. If the sufficient positive voltage is applied to the base terminal i.e. If the base voltage increases over emitter voltage then the transistor becomes more switched until it is in fully ON state. If the base voltage is equal to the emitter voltage then the transistor is in OFF state. Here the base terminal and collector terminals always contain positive voltages with respect to emitter terminal. Here both the loads RB and RL can limit the current flow through the corresponding terminals. The collector terminal connected to the voltage VCC through the load RL. In the above circuit connections we observed that the supply voltage VB is applied to the base terminal through the load RB. The working of NPN transistor is quite complex. Here the collector terminal always connected to the positive voltage, the emitter terminal connected to the negative supply and the base terminal controls the ON/OFF states of transistor depending on the voltage applied to it. The above figure shows the NPN transistor circuit with supply voltages and resistive loads. Now let us see the operation of the NPN transistor with explanation. In this structure we can observe the three terminals of transistor, circuit currents and voltage value representations. The above figure shows the symbol and structure of NPN transistor. The NPN transistor is mostly used for amplifying and switching the signals. The NPN transistor has three terminals – emitter, base and collector. Generally the NPN transistor is the most used type of bipolar transistors because the mobility of electrons is higher than the mobility of holes. The flowing of these electrons from emitter to collector forms the current flow in the transistor. Here the majority charge carriers are the electrons. The NPN transistor consists of two n-type semiconductor materials and they are separated by a thin layer of p-type semiconductor. NPN transistor is one of the Bipolar Junction Transistor (BJT) types. Output Characteristics of NPN Transistor.α, β and γ Relationship in NPN Transistor.
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