1. Electronics The Eleventh and Twelfth Lectures
Seventh week
30/ 1/ 1438 هـ / 2/ 1438 هـ
أ / سمر السلمي

2. Outline for today Solving the Second homework
Chapter 3: Bipolar junction transistor
Calculation gain coefficient β and α
Calculation Emitter Efficiency coefficient γ
The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits
I – V Characteristic of BJT in emitter common configuration and load line
I – V Characteristic of BJT and his job as Switch

3. Time of Periodic Exams The third homework
The first periodic exam in / 2 / 1438 هـ , Please everyone attend In her group
The third homework
I put the third homework in my website in the university homework Due Tuesday 22 / 2/ 1438 H in my mailbox in Faculty of Physics Department , I will not accept any homework after that , but if you could not come to university you should sent it to me by in the same day

4. Solving the Second homework

5. How amplification occurs in the transistor
Here also, we deal with npn type and active mode but we now use emitter common configuration . When hole current enters from base, potential reduce between emitter and base (forward bias). If WB the thickness of base is small, we will assume that % 1 of electronic current recombine with hole current in base and 99% of electronic current go toward collector
Therefore, output current from collector IC
almost 99% higher from base current IB
Thus, we can say when a small amount of
current enters of IB , it will create high
current of IE also of IC because most
electronic current go from emitter to
collector. We can say IE ≈ IC =

6. Calculation gain coefficient β and α
Gain coefficient α when base common configuration & gain coefficient β when common emitter configuration .
We start with gain coefficient β when common emitter configuration , so when we discussed about amplification in this configuration, we mentioned how base current effect on emitter current. thus, gain coefficient β is ratio between collector current &base current
When we assume that few recombination in base duo to its small thickness so IE ≈ IC
Here emitter current proportional with emitter doping and base current proportional with base doping. therefore, gain coefficient β equal to is ratio between collector doping & base doping
Here also efficiency transistor depend on gain coefficient , so when gain coefficient is big , the efficiency transistor is increases

7. Calculation gain coefficient β and α
Gain coefficient α when base common configuration & gain coefficient β when common emitter configuration.
However, the Gain coefficient α when base common configuration equal to is ratio between collector current & emitter current
We can find relation between gain coefficient β & gain coefficient α Or

8. Calculation gain coefficient β
In the diode, we derive diffusion current density for excess of minority - carriers of electrons and holes
Since transistor is as two diodes, diode’s calculation will be the same for transistor’s calculation . current density equal to current per area (the area is the same for 3 part) therefore, for npn
And when assume base thickness is small (WB ≈ Ln ) also from previously relation
By substitute in gain coefficient
this relation is approximately =

9. Calculation gain coefficient β
Final approximately relation for gain coefficient β in npn is
Where is time of minority – carriers life in base
And is time of transit electrons to base =

10. Calculation Emitter Efficiency coefficient γ
It know as ratio between electronic current (npn) which injection from emitter and total current
Since total current is , therefore:
In transistor of n+p n type , so IEp < IEn . therefore =

11. The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits
Previously, we discussed about gain coefficient α and β to two of common base configuration & common emitter configuration , respectively. In two cases the equation was
Here, we will calculate voltage, current and power gains Av , Ai & Ap respectively for the three common configurations in addition to the characteristics of their circuits.
In the three circuits, we will focus at active mode . Aslo, we must remember the equation
IE = IB + IC =

12. emitter common configuration
The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits
emitter common configuration
This circuit is the most important and used in
amplifiers for transistor
input current is base current & output
current is collector current
input voltage is Vin & output voltage is Vout .
the output signal opposite to input signal ,mean Out of phase with 180o , so it is Inverting Amplifier circuit
input resistance Rin is lower duo to forward bias & output resistance RL is higher duo to reverse bias
Current gain is
Voltage gain is
The gain in this circuit less than base common configuration
power gain is

13. base common configuration
The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits
base common configuration
input current is emitter current & output
current is collector current
input voltage is Vin & output voltage is Vout .
the output signal the same to input signal ,mean In of phase , so it is non inverting Amplifier circuit
the ratio between output resistance RL &input resistance Rin is higher
Current gain is
In most case approximate value is one and IB is small, thus IE ≈ IC
Voltage gain is
power gain is

14. collector common configuration
The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits
collector common configuration
input current is base current & output
current is emitter current
input voltage is Vin & output voltage is Vout .
the output signal the same to input signal ,mean In of phase , so it is non inverting Amplifier circuit
input resistance Rin is higher & output resistance RL is lower
in the circuit input voltage contact direct to base while output voltage is taken from load resistance
Current gain is
Voltage gain is
Always is less than one duo to
power gain is

15. The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits
Characteristic
Common
Base
Emitter
Collector
Input Impedance
Low
Medium
High
Output Impedance
Very High
Phase Angle 0o
180o
Voltage Gain
Current Gain
Power Gain

16. I – V Characteristic of BJT
In chapter two, we study I – V Characteristic of diode in lecture and Lab, so we know about proportional relation in addition to load line. Also, in this chapter we will study I – V Characteristic of BJT and its calculation and duo to different contact methods, there will be different curves , however, the relation always proportional
I – V Characteristic emitter common I – V Characteristic base common

17. I – V Characteristic of BJT in emitter common configuration and load line
we will deal with emitter common configuration to see
relation between IC & VCE
1- we notice that IC increases rapidly by change VCE
at beginning in region called Saturation Region. Than,
The increase becomes very slow unnoticed which
consider as constant in region called
Amplification Region or Active Region.
2- when we change IB , IC will also change
duo to input voltage (means that IC
control by IB)
3- the third region called Cut Off Region
which is region under current value IB =0

18. I – V Characteristic of BJT in emitter common configuration and load line
4 - load line will cut y- axis Saturation point (S –point) and x- axis cut off point (C –point)
5- at operation point (Q- point) cut of load line with I – V Characteristic
load line equation
6- from equation and figure, we notice
cut off point when IB =0 & IC =0 thus
VCE = VCC
Saturation point when VCE =0 thus
The mean operation point is )

19. I – V Characteristic of BJT and his job as Switch
we can describe job’s BJT as switch
1- Saturation Region:
which represent an close switch (Fully-ON)
input voltage and base contact with VCC
VBE > 0.7V
the maxim value of collector current
The two junction at forward bias
ideal Saturation at VCE =0

20. I – V Characteristic of BJT and his job as Switch
we can describe job’s BJT as switch
2- Cut Off Region :
which represent an close switch (Fully-OFF)
input voltage and base contact with
grounded 0V
VBE < 0.7V
The two junction at reverse bias
There no current flow to collector
IC = 0