1. Basics of Bipolar Junction Transistor
By Dr. Vaibhav Jain Associate Professor, Dept. of Physics, D.A.V (PG) College, Bulandshahr, U.P., India.
ECE 663

2. The Bipolar Junction Transistor
The transistor is a versatile device usually configured to perform as a switch or as an amplifier. The bipolar junction transistor (BJT) is the most common type and has three leads: 3 3
Collector
Collector 2 2
Base
Base 1
Emitter 1
Emitter
PNP Transistor
NPN Transistor
In a transistor, the flow of current from the collector to the emitter is controlled
by the amount of current flowing into the base of the transistor. If no current
flows into the base, no current will flow from the collector to the emitter (it acts
like an open switch). If current flows into the base, then a proportional amount
of current flows from the collector to the emitter (somewhat like a closed switch).
Kit Building Class Lesson 3

3. Bipolar Junction Transistors: Basics+ - IE IB IC
IE = IB + IC ………(KCL)
VEC = VEB + VBC ……… (KVL)

4. BJT configurations
GAIN
CONFIG

5. Bipolar Junction Transistors: Basics+ - IE IB IC
VEB >-VBC > 0  VEC > 0 but small
IE > -IC > 0  IB > 0
VEB, VBC > 0  VEC >> 0
IE, IC > 0  IB > 0
VEB < 0, VBC > 0  VEC > 0
IE < 0, IC > 0  IB > 0 but small

6. Bipolar Junction Transistors: Basics
Bias Mode
E-B Junction
C-B Junction
Saturation
Forward
Active
Reverse
Inverted
Cutoff

7. BJT Fabrication

8. PNP Physical Currents

9. PNP transistor amplifier action
IN (small)
OUT (large)
Clearly this works in common emitter
configuration

10. Common Base DC current gain - PNP
Common Base – Active Bias mode:
IC = aDCIE + ICB0
ICp = aTIEp
= aTgIE
aDC = aTg
IC = aTgIE + ICn

11. Common Emitter DC current gain - PNP
Common Emitter – Active Bias mode:
IE = bDCIB + ICE0
bDC =
aDC /(1-aDC)
IC = aDCIE + ICB0
= aDC(IC + IB) + ICB0
GAIN !! IE IB IC
IC = aDCIB + ICB0
1-aDC

12. Common Emitter DC current gain - PNP
Thin base will make aT  1
Highly doped P region will make g  1

13. PNP BJT Common Emitter Characteristic

14. Thank You