electronic circuits for mechatronics elct 609 (spring 2019...
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Electronic Circuits for
Mechatronics ELCT 609
(Spring 2019)
Lecture 4: Bi-polar Junction
Transistor Physical StructureDr. Eman Azab
Assistant Professor
Office: C3.315
E-mail: eman.azab@guc.edu.eg
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
1
Introduction Why we call it Transistor?
The name came as an abbreviation of the device job!
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
2
Input Voltage
Scaled with a predefined Trans-conductance gain
Output Current
Transistor Function
Bipolar Junction
Transistor (BJT)Physical Structure and I-V Characteristics
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
3
BJT Physical Structure Two back to back PN Junctions
NPN or PNP Transistor
Three terminal device, for NPN: Base (P-Type), Emitter and
Collector (N-Type)
Emitter-Base Junction (EBJ)
Collector-Base Junction (CBJ)
Emitter doping is higher than Collector doping
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
4
NPN BJT Transistor PNP BJT Transistor
BJT I-V characteristics1. BJT NPN Transistor in Cutoff Mode
Emitter-Base is Reverse biased
Collector-Base Junction is Reverse biased
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
5
EBJ Reverse
CBJ Reverse
Cutoff Mode C B EI I I 0
Q
BJT I-V characteristics2. BJT NPN Transistor in Active Mode
EBJ is Forward biased and electrons pass through the Base
to the collector due to the Base small area
Electrons from the Emitter are collected at the Collector
side
The transistorβs Collector current can be modeled by a
current dependent current source
Is depends on doping and width of the Base
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
6
C F BI I
BEC s
T
VI I exp
V
Q
BJT I-V characteristics3. NPN Transistor in Reverse Active mode
Collector-Base Junction is Forward biased
Emitter-Base Junction is reverse biased
Emitter and collector reverse their roles
However, BJT has an asymmetrical physical structure
The current gain from Base to Emitter is very small
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
7
E R BI I R F
EBJ Reverse
CBJ Forward
Reverse Active Mode
Q
ππ΅πΆ β 0.5π
BJT I-V characteristics4. NPN Transistor in Saturation Mode
Both junctions are Forward biased
The total current is the EBJ diffusion current subtracted from
CBJ diffusion current
BJT could be used as a closed switch in Saturation mode
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
8
BEJ Forward
BCJ Forward
Saturation Mode
ππ΅πΈ β 0.7π
ππ΅πΆ β 0.5πC F BI I
Q
ππΆπΈ β 0.2π
BJT NPN I-V Characteristics IC versus VBE and VCE
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
9
IC = Is expVBEVT
For Active
ONLY
Q
BJT NPN I-V Characteristics IC versus VCE
The Early effect
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
10
CEBEC S
T A
vVi I exp( ) 1
V V
C Ao
CE C
i Vr
v I
Q
BJT Large Signal Model in
Active Mode
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
11
Q
BJT PNP Physical Structure BJT PNP Transistor
PNP is the NPN Complementary
structure
Two back to back PN Junctions
Three terminal device: Base (N-
type), Emitter and Collector (P-type)
Emitter-Base Junction
Collector-Base Junction
Emitter doping is higher than
Collector doping
Same I-V Characteristics as NPN
Transistor
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
12
Q
PNP BJT Transistor
BJT PNP Physical Structure BJT PNP Transistor in Active Mode
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
13
EBJ Forward
CBJ Reverse
Active Mode
Q
BJT Modes of OperationElectrical Equations of BJT
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
14
BJT NPN Modes of Operation
Mode BEJ BCJ Equations Condition
Cutoff Reverse Reverse πΌπΆ = πΌπΈ = πΌπ΅=0ππ΅πΈ < 0.7ππ΅πΆ < 0.5
Active
(Forward)
Forward
Reverse
ππ΅πΈ = 0.7πΌπΈ = πΌπΆ + πΌπ΅
πΌπΆ = π½πΉπΌπ΅ = πΌπΉπΌπΈ
πΌπΉ =π½πΉ
1 + π½πΉ
ππ΅πΆ < 0.5Or
ππΆπΈ > 0.2
Saturation
Forward
Forward
ππ΅πΈ = 0.7ππ΅πΆ = 0.5ππΆπΈ = 0.2πΌπΈ = πΌπΆ + πΌπ΅
πΌπΆ < π½πΉπΌπ΅
Reverse Active
Reverse
Forward
ππ΅πΆ = 0.5πΌπΆ = πΌπΈ + πΌπ΅
πΌπΈ = π½π πΌπ΅ = πΌπ πΌπΆ
πΌπ =π½π
1 + π½π
ππ΅πΈ < 0.7
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
15
Q
Q
BJT PNP Modes of Operation
Mode EBJ CBJ Equations Condition
Cutoff Reverse Reverse πΌπΆ = πΌπΈ = πΌπ΅=0ππΈπ΅ < 0.7ππΆπ΅ < 0.5
Active
(Forward)
Forward
Reverse
ππΈπ΅ = 0.7πΌπΈ = πΌπΆ + πΌπ΅
πΌπΆ = π½πΉπΌπ΅ = πΌπΉπΌπΈ
πΌπΉ =π½πΉ
1 + π½πΉ
ππΆπ΅ < 0.5Or
ππΈπΆ > 0.2
Saturation
Forward
Forward
ππΈπ΅ = 0.7ππΆπ΅ = 0.5ππΈπΆ = 0.2πΌπΈ = πΌπΆ + πΌπ΅
πΌπΆ < π½πΉπΌπ΅
Reverse Active
Reverse
Forward
ππΆπ΅ = 0.5πΌπΆ = πΌπΈ + πΌπ΅
πΌπΈ = π½π πΌπ΅ = πΌπ πΌπΆ
πΌπ =π½π
1 + π½π
ππΈπ΅ < 0.7
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
16
Q
Q
Calculating DC operating
pointSolved Exercise
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
17
Solved Example Find the DC Operating point of the Transistors?
Given: VBE=0.7V ,Ξ²=10
(Ans.: IB=0.023mA, IC=0.23mA, IE=0.253mA, VCE=9.54V, Active )
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
18
Solution Steps:1. Identify the BJT Type
2. Place the terminals name on the circuit
3. Write a KVL in the INPUT Loop
Input loop for BJT is any loop containing VBE
4. Assume the BJT mode (most of the time active)
5. Calculate the currents and voltages
6. Write KVL in the OUTPUT loop
Output loop for BJT is any loop containing VCE
7. Verify your assumption!
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
19
Example Find the DC Operating point of the Transistors?
Given: VEB=0.7V ,Ξ²=10
(Ans.: IB=93Β΅A, IC=0.93mA, IE=1.023mA, VEC=8.14V, Active )
Dr. Eman Azab
Electronics Dept., Faculty of IET
The German University in Cairo
20
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