Lecture 15_ Feb 24 2011

# Lecture 15_ Feb 24 2011 - Review Session Bipolar Junction...

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Review Session Bipolar Junction Transistors and Circuits Lecture 15 Cover Chapters: 5, 10, 13

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npn Transistor: Complete Transport Model Equations for Any Bias i C = I S exp v BE V T - v BC V T - I S β R v V T - 1 i E = I S v V T - v V T + I S F v V T - 1 i B = I S F v V T - 1 + I S R v V T - 1 First term in both emitter and collector current expressions gives current transported completely across base region. Symmetry exists between base-emitter and base-collector voltages in establishing dominant current in bipolar transistor. Chap 5.2
Transport Model Calculations: Example Problem: Find terminal voltages and currents. Given data: V BB = 0.75 V, V CC = 5.0 V, I S = 10 -16 A, β F = 50, R = 1 Assumptions: Room temperature operation, V T = 25.0 mV. Analysis: V BE = 0.75 V, V BC = V BB - V CC = 0.75 V-5.00V = -4.25 V Evaluating the expressions for terminal currents, I C = 1.07 mA I E = 1.09 mA I B = 21.4 μ A F = I C I B = 1.07 mA 0.0214 mA = 50 α F = I C I E = mA 1.09 mA = 0.982 Chap 5.2

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pnp Transistor: Complete Transport Model Equations for Any Bias i C = I S exp v EB V T - v CB V T - I S β R v V T - 1 i E = I S v V T - v V T - I S F v V T - 1 i B = I S F v V T - 1 + I S R v V T - 1 Chap 5.3 First term in both emitter and collector current expressions gives current transported completely across base region. Symmetry exists between base-emitter and base-collector voltages in establishing dominant current in bipolar transistor.
Operation Regions of Bipolar Transistors Chap 5.6 Base-Emitter Junction Base-Collector Junction Reverse Bias Forward Bias Forward Bias Forward-Active Region Saturation Region (Closed Switch) Reverse Bias Cutoff Region (Open Switch) Reverse-Active Region (Poor Amplifier) Binary Logic States

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Simplified Cutoff Region Model In cutoff region both junctions are reverse-biased, transistor is said to be in off state v BE < 0, v BC < 0 If we assume that where -4 kT/q = -0.1 V, then the transport model terminal current equations simplify to v BE <- 4 kT q and v BC 4 q i C =+ I S β R i E =- I S F i B I S F - I S R Chap 5.7
Simplified Forward-Active Region Model

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## This note was uploaded on 03/06/2011 for the course ECE 255 taught by Professor Staff during the Spring '08 term at Purdue.

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Lecture 15_ Feb 24 2011 - Review Session Bipolar Junction...

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