1. Electronic Principles 7th Edition Albert Malvino & David J Bates
Ref. Books
Electronic devices and circuit theory – Robert Boylestad
Basic Electronics – A. P. Godse & U. A. Bakshi
Rizwan H. Alad & Vasim A. Vohra

2. Part 1 Syllabus Chap. 6 Bipolar Junction Transistors
Chap. 7 Transistor Fundamentals
Chap. 8 Transistor Biasing
Chap. 9 Transistor AC Models
Chap. 10 Voltage Amplifiers
Chap. 11 CC and CB Amplifiers
Chap. 12 Power Amplifiers
Chap. 23 Oscillators

3. Transistor Three doped regions Emitter, Base and Collector
Base region is much thinner as compared to the collector and emitter
npn and pnp
Emitter is heavily doped, Base is lightly and collector is intermediate
Collector regions is physically largest

5. After Diffusion
Before Diffusion
Each of Dep. Layer barrier potential app. 0.7 V at 25o C
Unbiased transistor is like two back-to-back diodes

6. Bipolar Junction Transistors
A bipolar transistor essentially consists of a pair of PN Junction diodes that are joined back-to-back.
There are therefore two kinds of BJT, the NPN and PNP varieties.
The three layers of the sandwich are conventionally called the Collector, Base, and Emitter.

7. Modern Transistors

8. NPN Bipolar Junction Transistor
One N-P (Base Collector) diode one P-N (Base Emitter) diode

9. PNP Bipolar Junction Transistor
One P-N (Base Collector) diode one N-P (Base Emitter) diode

10. Analogy with Transistor :Fluid-jet operated Valve

11. *The Biased Transistor
Heavily doped emitter inject
free electrons into the base
Lightly doped base pass
electrons on to the collector
Collector collects or gathers
electrons from the base
Biasing method – Emitter junction FB
Collector junction RB

12. Summary
Forward biased emitter diode, forcing the free electrons in the emitter to enter the base
Thin and lightly doped base diffuse electrons into collector
Collector, through RC and into the positive terminal of VCC

13. sedr42021_0503.jpg
Figure 5.3 Current flow in an npn transistor biased to operate in the active mode. (Reverse current components due to drift of thermally generated minority carriers are not shown.)

14. Transistor Currents IE – Largest emitter current
Emitter electrons flow to the collector, IC ≈ IE
IB ≤ 0.01 IC
KCL, IE = IC + IB

15. BJT  and  From the previous figure IE = IB + IC Define dc = IC / IE
DC alpha is slightly less than 1
Low power transistor αdc > 0.99 and High power transistor αdc > 0.95
Define dc = IC / IB - known as a current gain

16. BJT  and  Then dc = IC / (IE –IC) = dc /(1- dc)
Assignment – Derive dc = dc /(1+ dc)
Then IC = dc IE & IB = (1-dc) IE
Solved Example 6.1, 6.2, 6.3

17. NPN BJT Current flow

18. The CE connection CE, CC and CB
CE because emitter is common to both VBB and VCC
Left loop – Base loop
Right loop – collector loop

19. The CE connection
Base Loop, VBB source and RB – current limiting resistor
Changing VBB or RB, change base current and IB Change than IC change
IB controls IC

20. Notation Single Subscripts Double Subscripts Used for Node voltages
VB – voltage between base and ground
VC and VE
VCE = VC – VE
VCB and VBE
Voltage source – VBB and VCC
VBE – voltage between points B and E
VCE – voltage between points C and E

21. The Base Curve / Input Characteristics
Graph IB versus VBE
Like ordinary diode
Ohm’s low to Base loop
Ideal diode VBE = 0 and second app. VBE = 0.7 V

22. Collector Curve / output Characteristics
Graph IC versus VCE
Ohm’s low to Collector loop
Fixed value of based current, vary VCC and measure IC and VCE

23. Transistor Characteristics
Input Characteristics
Output Characteristics

24. Active Region, Constant collector current
After collector diode reverse biased, it collect all the electrons that reach its deplation layer
Further increased VCE cannot increased IC
Collector can collect only those free electrons that emitter injects
VCE > VCE(max), collector diode break down
Power Dissipation PD = VCEIC
PD < PD(max)

25. Operating Region of Transistor
Active region, middle region – normal operation of transistor
Emitter diode – FB and Collector diode – RB
Breakdown region – transistor will be destroyed
Saturation region – rising part of curve, VCE between zero and few tenth of volt
Collector diode has insufficient positive voltage to collect all the free electrons injected into the base

26. Operating Region of Transistor
Cut off region – IB = 0 but still small collector current
Because collector diode RB – Reverse minority carrier + Surface leakage current

27. BJT Operating Regions

29. Analogy with Transistor in Active Region: Fluid-jet operated Valve
In active region this stopper does not really have
noticeable effect on the flow rate
Emitter Base Junction – FB
Collector Base Junction – RB

30. Analogy with Transistor Cutoff Fluid-jet operated Valve
Emitter Base Junction – RB
Collector Base Junction – RB

31. Analogy with Transistor Saturation Fluid-jet operated Valve
The valve is wide open; changing valve position a little bit
does not have much influence on the flow rate.
E-B Junction – FB
C-B Junction – FB