Figure: Bipolar Transistor Shown as Two Back-to-Back p-n Junctions. Chapter 2: Bipolar Junction Transistor (BJT) There are two p-n junctions: emitter-base (EB) junction and collector-base (CB) junction. three terminal device forming the basis of a Bipolar Transistor, or BJT for short. Transistors are three terminal active devices made from different semiconductor. Electronics Tutorial about the Bipolar Transistor also called the Bipolar Junction Transistor or BJT including the Transistor Types and Construction.
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There are four regions of operation of a BJT transistor. (example for a pnp BJT). • Since it has three leads, there are three possible amplifier types: VEB. VCB. 5. Transistor Structure. With diodes there is one p-n junction. With bipolar junction transistors (BJT), there are three layers and two p-n junctions. Lec Bipolar Junction Transistor (BJT). Course Instructors: ❖ Dr. A. P. VAJPEYI. Department of Physics,. Indian Institute of Technology Guwahati, India. 1.
Thus for saturation both junctions are forward biased.
Option d 3. Ebers Moll model is one of classical models of BJT for small signals. This model is based on interacting diode junctions and is applicable to any transistor operating modes Option a 4. When the effective base width of the transistor is changed by varying the collector junction voltage is called base width modulation or Early effect.
Option d 6. B and output junction R.
B Option a 7. Which one of the following is correct? This is true when base width is constant, but when the base collector voltage reverse bias is increased the base width will be reduced. This reduced base width causes the minority carries to increase, which causes increase in diffusion current.
IC increases with VCE. This deviation is known as Early effect or base width modulation. If the base width in a bipolar junction transistor is doubled, which one of the following statements will be TRUE?
As the base width is increased, the base current will increase thus reducing the collector current. Early voltage will increase.
NPN bipolar transistor symbol and the construction of its junctions Fig. Distribution of currents in NPN transistor Bipolar Transistor — Principle of operation Main feature of bipolar transistors is the possibility to control a high current with usage of small one. Here, it is worth noting to not exceed the voltage of the junction silicon or germanium diodes , which could result in the flow of large base current and possible damage to the transistor.
Base-Emitter voltage inject majority carriers from the emitter through the junction to the base — in N-P-N electrons and in P-N-P holes. Carriers injected from the emitter into the base region float the phenomenon of diffusion into the region of Base-Collector junction region where their concentration is lower.
Here, under the impact of the electric field in the depletion region they are attracted to the collector.
Reverse-active mode inverted mode — Base-Emitter junction is reverse biased and Base-Collector is forward biased. Bipolar Transistor — Current-voltage characteristics Fig.
Family of current-voltage characteristics of the bipolar transistor OE Fig. The electrons in the base are called minority carriers because the base is doped p-type, which makes holes the majority carrier in the base. To minimize the fraction of carriers that recombine before reaching the collector—base junction, the transistor's base region must be thin enough that carriers can diffuse across it in much less time than the semiconductor's minority-carrier lifetime.
Having a lightly doped base ensures recombination rates are low. In particular, the thickness of the base must be much less than the diffusion length of the electrons.
The collector—base junction is reverse-biased, and so negligible electron injection occurs from the collector to the base, but carriers that are injected into the base and diffuse to reach the collector-base depletion region are swept into the collector by the electric field in the depletion region. The thin shared base and asymmetric collector—emitter doping are what differentiates a bipolar transistor from two separate and oppositely biased diodes connected in series.
Voltage, current, and charge control[ edit ] The collector—emitter current can be viewed as being controlled by the base—emitter current current control , or by the base—emitter voltage voltage control.
These views are related by the current—voltage relation of the base—emitter junction, which is the usual exponential current—voltage curve of a p—n junction diode. Detailed transistor models of transistor action, such as the Gummel—Poon model , account for the distribution of this charge explicitly to explain transistor behaviour more exactly.
However, because base charge is not a signal that is visible at the terminals, the current- and voltage-control views are generally used in circuit design and analysis. In analog circuit design, the current-control view is sometimes used because it is approximately linear.
However, to accurately and reliably design production BJT circuits, the voltage-control for example, Ebers—Moll model is required . The voltage-control model requires an exponential function to be taken into account, but when it is linearized such that the transistor can be modeled as a transconductance, as in the Ebers—Moll model , design for circuits such as differential amplifiers again becomes a mostly linear problem, so the voltage-control view is often preferred. For translinear circuits , in which the exponential I—V curve is key to the operation, the transistors are usually modeled as voltage-controlled current sources whose transconductance is proportional to their collector current.