Introduction:Some parameters can be defined for bipolar junction transistors that act as figures of merit in quantifying its performance. Most of such, however not all, are measured and specified for forward active mode of operation. A few parameters differentiate among electron and hole currents however such are not of particular interest and attention is confined to such that are based on the terminal currents of device. These can be assumed from the physical model shown in figure below that formed the basis of Ebers-Moll model.Ebers-Moll Equations are as shown below:IE = IES (eVBE/VT -1) – αR ICS (eVBC/VT -1)IC = αF IES (eVBE/VT -1) – ICS (eVBC/VT -1)IB = (1 - αF) IES (eVBE/VT -1) + (1 - αR) ICS (eVBC/VT -1)Forward Transfer Ratio:It is defined for the forward active mode of operation as the ratio of collector and emitter terminal currents. In forward active mode, the base-collector junction is reverse biased and hence eVBC/VT << 0 and therefore the currents approximate to:IE ≈ IES eVBE/VTIC ≈ αF IES eVBE/VT = αF IEIB ≈ (1 - αF) IES eVBE/VT = (1 - αF) IEThen,Forward transfer ratio = IC/IE = (αF IES eVBE/VT)/(IES eVBE/VT) = αF
Figure: Model Showing Forward and Reverse Current Components
Figure: Minority Carrier Concentration in the Base Region
Forward Current Gain, βF:Beneath steady-state conditions in forward active mode, the volume of minority charge stored in the base region is constant. The greater portion of this is charge in transit to the collector that forms the electronic component of collector current. A small percentage of minority charge continually rejoins with majority carriers that are replaced with holes supplied by an external base current. As the base region is very thin and is sandwiched among the two junctions, it is not surprising that the volume of minority charge exist in the base exercises a profound influence on the behavior of transistor. However, the excess minority charge in the base region can be forced to modify by modulating the base current with an external signal. Atomic forces operating cause both the recombining charge and the charge in transit to collector to differ in sympathy. The junction voltages will adjust, in response to currents flowing, to conform to exponential laws governing them. Though, as the charge in transit to the collector is much bigger than the recombination charge, a big change in absolute charge terms is induced in the collector current than is present in the base current due to the signal. Therefore, the transistor is observed to amplify the input signal to the base as shown in figure below.
Figure: The Current Amplifying the Property of Bipolar Transistor
This current amplifying the property is explained by the current gain of the transistor in forward active mode that is taken simply as the ratio of the collector and base currents. Thus:Forward current gain, βF = IC/IB = (αF IES eVBE/VT)/(1 - αF) IES eVBE/VT = αF/(1 - αF)Alternatively,βF = IC/IB = IC/(IE – IC) = (IC/IE)/[1 – (IC/IE)] = αF/(1 - αF)Typical values of βF range from 40 to 100 for integrated transistors however can be as high as 300 to 500 for discrete devices.Reverse Transfer Ratio and Current Gain, αR, βRThe parameters above can as well be defined for the reverse active mode if the B-E junction is reverse biased and the B-C junction is forward biased. Though such parameters are not of great interest as the transistor is much inefficient from an amplifying view point in this mode. Usually αR = 0.1 - 0.5 and βR = 0.1 – 1.0.Minority Carrier Lifetime, τBIt is the average amount of time; a minority carrier can survive after being injected to the base region before rejoining with a majority carrier. It mainly depends on the physical properties of device, like the doping concentration and dimensions. Usually τB = 50 - 100ns.Forward Transit Time, τFIt is the average time it takes a minority carrier injected to the base region to make the transition to the collector region whenever the transistor is operating in forward active mode. This can be shown as:τF = (Wb2)/2Db = (1/2) (Wb/Lb)2 τbIn general τF = 0.1 – 0.5nsThe above parameters will be employed in the analysis of static and dynamic performance of transistor as a circuit switching element.
Latest technology based Electrical Engineering Online Tutoring Assistance
Tutors, at the www.tutorsglobe.com, take pledge to provide full satisfaction and assurance in Electrical Engineering help via online tutoring. Students are getting 100% satisfaction by online tutors across the globe. Here you can get homework help for Electrical Engineering, project ideas and tutorials. We provide email based Electrical Engineering help. You can join us to ask queries 24x7 with live, experienced and qualified online tutors specialized in Electrical Engineering. Through Online Tutoring, you would be able to complete your homework or assignments at your home. Tutors at the TutorsGlobe are committed to provide the best quality online tutoring assistance for Electrical Engineering Homework help and assignment help services. They use their experience, as they have solved thousands of the Electrical Engineering assignments, which may help you to solve your complex issues of Electrical Engineering. TutorsGlobe assure for the best quality compliance to your homework. Compromise with quality is not in our dictionary. If we feel that we are not able to provide the homework help as per the deadline or given instruction by the student, we refund the money of the student without any delay.
Theory and lecture notes of Firms Investment Decision all along with the key concepts of Net present Value Criterion, Firm’s Discount Rate, Nominal Discount Rates and Cash Flows. Tutorsglobe offers homework help, assignment help and tutor’s assistance on Firms Investment Decision.
Pharmaceuticals tutorial all along with the key concepts of Antibiotics, Production of Penicillin, Production of Acetylsalicylic acid or aspirin and Production of Tetracycline
tutorsglobe.com economic importance assignment help-homework help by online biology in human welfare tutors
Ratios can be collected into categories, with each category relating to a specific aspect of financial performance or position.
Avail top-rated Budget and Budgetary Controls Assignment Help and get assured top-notch grades by submitting a masterpiece.
Vibrational Spectroscopy tutorial all along with the key concepts of Vibrational coordinates, Newtonian mechanics, Quantum mechanics, Intensities
tutorsglobe.com factoring versus short term loan assignment help-homework help by online factoring tutors
www.tutorsglobe.com offers software engineering approaches homework help, assignment help, case study, writing homework help, online tutoring assistance by computer science tutors.
To disclose information about their several operating segments an IASB standard (IFRS 8 Operating Segments) needs listed companies.
TutorsGlobe.com Nucleus and Radioactivity Assignment Help-Homework Help by Online Access Chemistry Tutors
Online ACT exam preparation and online act tutoring package offered by TutorsGlobe are the most comprehensive and customized collection of study resources on web, offering best collection of act practice papers, quizzes, act test papers, and guidance.
tutorsglobe.com seed assignment help-homework help by online flowers fruits and seeds tutors
The different roles that non-executives are expected to play provide potential for conflict. In developing strategy, co-operation between the executive and non-executive directors is essential.
Alkene Synthesis from Alcohol tutorial all along with the key concepts of Preparation of Cyclohexene from Cyclohexanol, Dehydration, Laboratory display of Distillation
www.tutorsglobe.com offers chemical analysis homework help, chemical analysis assignment help, online tutoring assistance, inorganic chemistry solutions by online qualified tutor's help.
1941086
Questions Asked
3689
Tutors
1465025
Questions Answered
Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!