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

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

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

BJT configurations GAIN CONFIG

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

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

BJT Fabrication

PNP Physical Currents

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

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

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

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

PNP BJT Common Emitter Characteristic

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