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Lecture 10 Bipolar Junction Transistor (BJT) BJT 1-1

Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

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Page 1: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

Lecture 10

Bipolar Junction Transistor (BJT)

BJT 1-1

Page 2: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

Outline Bipolar Junction Transistor (BJT) – Cont’d

BJT configurations DC biasing circuits and analysis

BJT 1-2

Page 3: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

Test Yourself

Choose the more appropriate answer

1) The β of a transistor is its (a) current gain (b) voltage gain (c) power gain (d) internal resistance

BJT 1-3

Page 4: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

BJT Configurations

BJT 1-4

The base is common to both input (emitter–base) and output (collector–base) of the transistor

Common-Base configuration

Page 5: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

BJT Configurations

BJT 1-5

This curve shows the relationship between of input current (IE) to input voltage (VBE) for three output voltage (VCB) levels

Common-Base configuration

Emitter (or input)

Characteristics

Page 6: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

BJT Configurations

BJT 1-6

This graph demonstrates the output current (IC) to an output voltage (VCB) for various levels of input current (IE)

Common-Base configuration Collector (or output)

Characteristics

Page 7: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

BJT Configurations

BJT 1-7

• The emitter is common to both input (base-emitter) and output (collector-emitter)

• The input is on the base and the output is on the collector

Common-Emitter configuration

Page 8: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

BJT Configurations

BJT 1-8

Common-Emitter configuration

Collector (or output) Characteristics Base (or input) Characteristics

Page 9: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

BJT Configurations

BJT 1-9

• The input is on the base and the output is on the emitter • The characteristics are similar to those of the common-

emitter configuration, except the vertical axis is IE

Common-Collector configuration

Page 10: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

I-V characteristics of BJT

BJT 1-10

Load line

Page 11: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

I-V characteristics of BJT (cont’d)

BJT 1-11

Page 12: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

Operating Limits for Each BJT Configuration

BJT 1-12

• VCE is at maximum and IC is at minimum (IC_min= ICEO) in the cutoff region • IC is at maximum and VCE is at minimum (VCE_min = VCEsat = VCEO) in the

saturation region • The transistor operates in the active region between saturation and

cutoff

Page 13: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

Power Dissipation in BJT

Common-base

Common-emitter

Common-collector

BJT 1-13

CCBCmax IVP

CCECmax IVP

ECECmax IVP

Page 14: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

Example (1)

BJT 1-14

Analyze the BJT circuit, shown in the figure, to get the values of: IB, IC, IE,α,VCE, VCB, VBE and max. power dissipated in the BJT

Page 15: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

BJT Biasing

Definition: The DC voltages applied to a transistor in

order to turn it on so that it can amplify the AC signal

BJT 1-17 No Bias

Good Bias

Page 16: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

BJT Circuits at DC

The BJT operation mode depends on the voltages at EBJ and BCJ

The I-V characteristics are strongly nonlinear

Simplified models and classifications are needed to speed up the hand-calculation analysis

BJT 1-18

Page 17: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

DC analysis of BJT circuits

Step 1: assume the operation mode

Step 2: use the conditions or model for circuit analysis

Step 3: verify the solution

Step 4: repeat the above steps with another assumption if necessary

BJT 1-19

Page 18: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

DC Biasing Circuits

Fixed-bias circuit

Emitter-stabilized bias circuit

Voltage divider bias circuit

DC bias with voltage feedback circuit

BJT 1-20

Page 19: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

Fixed-bias circuit

BJT 1-21

Base-Emitter Loop

From Kirchhoff’s voltage law:

+VCC – IBRB – VBE = 0

Solving for base current:

B

BECCB

R

VVI

Collector-Emitter Loop

/R

VVII

B

BECCBC

Collector current:

From Kirchhoff’s voltage law: CCCCCE RIVV

Page 20: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

Example (2)

BJT 1-22

Design the following circuit so that Ic = 2 mA and Vc= 5 V. For this particular transistor, β =100 and VBE=0.7 V

Page 21: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

Solution To design the circuit, we need to determine

values of RC and RE

We assume BJT works in active mode

Ic = 2 mA = (15- Vc)/ RC then RC = 5 kΩ

VB = 0 V, VBE = 0.7 V

VE = VB – VBE = 0 – 0.7 = - 0.7 V

RE = (VE -(-15))/ IE

IE = (β +1)/ β Ic = 2.02 mA

RE = 14.3/2.02 = 7.07 kΩ

BJT 1-23

Page 22: Lecture 10 Bipolar Junction Transistor (BJT)eng.staff.alexu.edu.eg/.../Lecture_10_BJT.pdf · Bipolar Junction Transistor (BJT) – Cont’d ... I-V characteristics of BJT (cont’d)

BJT 1-24

Lecture Summary

Covered material Bipolar Junction Transistor (BJT) – Cont’d

BJT configurations DC biasing and analysis

Material to be covered next lecture

Continue BJT DC biasing and analysis

• Examples

BJT switching time