![]() Diffused transistors, along with other components, are elements of integrated circuits for analog and digital functions. The superior predictability and performance of junction transistors quickly displaced the original point-contact transistor. The junctions can be made in several different ways, such as changing the doping of the semiconductor material as it is grown, by depositing metal pellets to form alloy junctions, or by such methods as diffusion of n-type and p-type doping substances into the crystal. A bipolar transistor allows a small current injected at one of its terminals to control a much larger current flowing between the terminals, making the device capable of amplification or switching.īJTs use two p–n junctions between two semiconductor types, n-type and p-type, which are regions in a single crystal of material. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. From top to bottom: TO-3, TO-126, TO-92, SOT-23Ī bipolar junction transistor ( BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. The Collector current (IC) also flows due to the presence of holes.Typical individual BJT packages. The remaining holes that do not recombine with electrons in the Base travel to the Collector. This is the Emitter current (IE) and holes are the majority of charge carriers in the Emitter current. Due to this movement of electrons current is generated. Thus nearly all the holes cross the depletion region and enter the Base region. ![]() The loss of holes in the emitter should be equal to the number of electrons present in the Base layer, but the number of electrons in the Base is very small because it is a very lightly doped and thin region. The Emitter-base junction is in the forward bias, thus a very large number of holes from the emitter cross the depletion region and enter the Base but very few electrons enter in Emitter from the base and recombine with the holes. Thus, the Collector-Base junction is connected in reverse bias.ĭue to the type of bias the Emitter-Base depletion region is narrow and the collector-base depletion region is wide. Similarly, the positive terminal of the second source is connected with the Base terminal and the negative terminal is connected with the Collector terminal. ![]() Thus, the Emitter-Base junction is connected in forward bias. The positive terminal of the source is connected with the Emitter terminal and the negative terminal is connected with the Base terminal. However, as the width of the middle layer is very small and lightly doped, significantly fewer free electrons are present in the Base region.Īlso, read about Electrical Power here Working Principle of PNP Transistor In the N-type semiconductor region of the base, a large number of free electrons are available. The area of the Emitter and Collector layer is more compared to the base layer. Therefore, the depletion region at both junctions penetrates towards the base region. The Emitter and Collector regions are heavily doped compared to the Base regions. The construction of a PNP transistor includes sandwiching a layer of N-type semiconductors between two layers of P-type semiconductors. Learn more about Electrical Resistance here Construction of PNP Transistor The base forms two circuits, the input circuit with the emitter and the output circuit with the collector. The collector-base junction is always reverse biased and lightly doped.īase – The central section of the transistor is known as the base. Thus, conventional current flows toward the base from the emitter.Ĭollector – Collector region as the name suggests collects the major portion of the charge. The emitter pushes the holes towards the base. The emitter is always forward biased with respect to the base. PNP TransistorĪs the name suggests, a PNP transistor has a layer of N-type semiconductor sandwiched between two P-type semiconductors.Ī PNP transistor as seen in the picture above includes three terminals:Įmitter – Emitter is the section that supplies the majority of charge carriers. Read on, to learn more about PNP transistors, their construction, working principle, uses and how it differs from an NPN transistor with FAQs. ![]()
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