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Solutions To BJT Questions

1) The document provides information on biasing BJTs and sample exam questions related to analyzing BJT circuits using the IB-VBE characteristic. 2) One question asks to determine the collector current and voltage of a BJT circuit using the given IB-VBE curve, and plot the IC-VCE characteristic. 3) Another question involves using the Ebers-Moll model to analyze a BJT circuit and determine currents, operation region, and electron/hole flow directions.

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585 views9 pages

Solutions To BJT Questions

1) The document provides information on biasing BJTs and sample exam questions related to analyzing BJT circuits using the IB-VBE characteristic. 2) One question asks to determine the collector current and voltage of a BJT circuit using the given IB-VBE curve, and plot the IC-VCE characteristic. 3) Another question involves using the Ebers-Moll model to analyze a BJT circuit and determine currents, operation region, and electron/hole flow directions.

Uploaded by

solanteg
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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BJTs-Biasing

CHECK YOURSELF-POINT

Q: How do you perform a more accurate analysis if the IB-VBE characteristic of the BJT is provided.

Middle East Technical University, EE 212-Semiconductor Devices and Modeling, Lecture Notes

BJTs-Biasing

12.4 A 9.5 A

VBB =RBB x IB + VBE + IE x RE

0.65 V

3.33 = 33.3 x 103 x IB + VBE + 101 x IB x 2.33 x 103 VBE = 3.33 268.63 x 103 x IB VCE = VCC ICRC IERE = 10 100 x IB x 3x103 101 x IB x 2.33 x 103 = 4.91 V
Middle East Technical University, EE 212-Semiconductor Devices and Modeling, Lecture Notes

BJTs-EXERCISE QUESTIONS Q.1: (to be solved on white board) IB-VBE characteristic of the npn BJT used in the following
circuit is given below. Emitter injection efficiency and base transport factor of the BJT are both equal to 0.995. Contribution of the thermally generated minority carriers around the B-C depletion region to base current is negligible. a) Find the collector current and collector-emitter voltage of the BJT in the following circuit, and plot the IC-VCE characteristic of the BJT on the provided graph.

Base Current ( A)

100 75 50 25 0 0.00 0.25 0.50 0.75

Base Emitter Voltage (V)

BJTs-EXERCISE QUESTIONS

Middle East Technical University, EE 212-Semiconductor Devices and Modeling, Lecture Notes

BJTs-EXERCISE QUESTIONS Q.3 (to be solved on white board) The following circuits are constructed by using the
same Si BJT with F=R=0.9.
0.7 V

0.8 V + V BE -

Circuit 1

+ V BE -

10 mA

Circuit 2

a) Use the Ebers Moll Model to determine IE, IB and IC in Circuit 2. b) What is the operation region of the BJT in Circuit 2. c) Show and label the electron and hole flow directions due to minority carrier injection for the BJT of Circuit 2. Is the collector current in Circuit 2 controllable by VBE? Explain your reasoning.

+ 0.8 V Middle East Technical University, EE 212-Semiconductor Devices and Modeling, Lecture Notes

BJTs-EXERCISE QUESTIONS

F = R = 0.9 , F x IES = R x ICS => IES = ICS IF = 10 mA = IES (e0.7/0.025-1) => IES =ICS = 6.9 x 10-15 A

Middle East Technical University, EE 212-Semiconductor Devices and Modeling, Lecture Notes

BJTs-EXERCISE QUESTIONS

VBE = VBC => IF = IR = IES (e0.8/0.025 1) = 545 mA IE = IF 0.9 x IR = 0.1 x IF = 54.5 mA IC = 0.9 x IF IR = -0.1 x IF = - 54.5 mA , IB = IE IC = 109 mA

Middle East Technical University, EE 212-Semiconductor Devices and Modeling, Lecture Notes

BJTs-EXERCISE QUESTIONS Q.5 (to be solved on white board) Find the emitter current and VCE in the following circuit
constructed with a BJT having a very large . Comment on the value of VCE (note that a small current is flowing through RB) .
5V

RC RB 10 K

14 K

RE

4.6 K

-5 V

Middle East Technical University, EE 212-Semiconductor Devices and Modeling, Lecture Notes

BJTs-EXERCISE QUESTIONS

-5+ 4.6k x IE+0.7+ IBx10k + IE x 14 k = 5 V


Negligible => IE = 0.5 mA VCE=(5-14 x 0.5) (-5 + 4.6 x 0.5) = 0.7V

Middle East Technical University, EE 212-Semiconductor Devices and Modeling, Lecture Notes

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