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What is the function of a BJT transistor?
A bipolar junction transistor (bipolar transistor or BJT) is a type of transistor that uses both electrons and holes as charge carriers. A bipolar junction transistor, also called bipolar transistors, is a three-terminal device that can function as electronic switches or signal amplifiers.
What is BJT and diode?
The diode is a semiconductor device which allows the current to flow only in one direction, whereas the transistor transfers the resistance from the low resistance region to high resistance region. The BJT uses both the electrons and hole as a charge carrier, and the FET is a unipolar transistor.
How does a BJT work in a bipolar junction transistor?
A BJT uses a small current at its base to control a much larger collector current. Before we go any further, it may be useful to define some important terms concerning the operation of a bipolar junction transistor.
Why is a BJT off when the base voltage is low?
Remember that a typical silicon diode needs about 0.7 V to turn on and conduct. So, with less than 0.7 V on the base the transistor is off because the low voltage does not forward bias the BE diode. If we were to apply a negative voltage to the NPN BJT in figure 4 the situation worsens; the p-n junction between the base and emitter widens.
How does the BJT work in saturation mode?
Saturation refers to a region of operation where maximum collector current flows and the BJT acts like a closed switch from collector to emitter. In this mode the BC junction forward biases and maximum current flows. The collector current cannot increase any more, even with an increase in base current.
What are the three terminals of a BJT?
Recall that there are two main types of BJTs and that the BJT is a three terminal device, as we can see in figure 1. The three terminals are the base, collector, and emitter. Figure 1: the two main types of bipolar junction transistors are NPN and PNP.