Bipolar Junction TransistorRonel G. JandiInstructor

TRANSISTOR

A semiconductive device used for amplification and switching applications.William Shockley, John Bardeen and Walter Brattain were the co-inventors of transistor at Bell Laboratories in 1947.

BIPOLAR JUNCTION TRANSISTOR (BJT) The term Bipolar is because two type of charges (electrons and holes) are involved in the flow of electricityThe term Junction is because there are two pn junctionsThere are two configurations for this device

NPN and PNP Transistors

NPN TransistorTransistor CurrentsIE = IB + IC

PNP Transistor

Parts and Proper BiasParts :1) Collector- moderately doped (collector carrier) -the doping is between that of the emitter and the base - largest of the three regions2) Base - Lightly doped (control) - controls the flow of carriers from emitter and collector -smallest3) Emitter - Heavily doped- 2nd largest - emits carrierPROPER BIAS OF TRANSISTOR For proper operation of the circuit1) Emitter base junction should be forward bias2) Collector-base junction should be reversed bias

Transistor Operation

BJT CONFIGURATIONSCommon BaseCommon CollectorTypical values: 0.001 to 0.9999InputInputForward Current Gain

Relationship of and IE = IB + ICMultiply with 1/ Ic[IE = IB + IC] 1/ IcIE IB ICIC IC IC1 / = 1 + 1/

Example No 1. Determine DC, IE, and DC for a transistor where IB = 50A and IC = 3.65mA.

= / ( + 1 )

Current and Voltage AnalysisVCE = Voltage drop from collector to emitterVCB = Voltage drop from collector to baseVBE = Voltage drop from base to emitter IC = Current into the collectorIB = Current into the base IE = Current out of the emitter.

. Example 2) Determine IB, IC, IE, VBE, VCE, and VCB in the circuit. The transistor has a DC = 150

Example 3) Sketch an ideal family of collector curves for the circuit for IB = 10A to 50A in 10A increments. DC = 100 and that VCE does not exceed breakdown. VCC. DC = 100

Collector Characteristic Curves

Cutoff, Saturation, and The DC load line

Maximum Transistor RatingsIc = PD(max)/VCEVCE = PD(max)/IC

Example 5) The transistor has the following maximum ratings: PD(max) =800mW, VCE(max) = 15V, and IC(max) = 100mA. Determine the maximum value to whichh VCC can be adjusted without exceeding a rating.. DC = 100VBBVCC

Derating PDmax)Example 6) A certain transistor has PD(max) of 1W at 25C. The derating factor is 5mw/C . What is the PD(max) at a temperature of 70C ?

The Transistor as a switcha) CutoffB) Saturation

Example 7)a) For the transistor, what is VCE when VIN = 0V?b) What minimum value of IB is required to saturate this transistor if DC is 200? Neglect VCE(sat).c) Calculate the maximum value of RB when VIN = 5V.RBVCCVINRC+ 10V

DC Operating point

DC Load Line

Linear Operation

Waveform Distortion

Example 1) Determine the Q-point, and find the maximum peak value of base current for linear operation. Assume DC = 200.VBBVCC10V20VRBRC33047k

BASE BIASVCCRBRC+VCCRBRC

+VCC IBRB - VBE = 0

Example 2) The Base bias circuit is subjected to increase in temperature from 25C to 75C. If DC = 100 at 25C and 150 at 75C, determine the percent in Q-point values (IC and VCE) over the temperature range. Neglect any change in VBE and the effects of leakage current.+VCCRBRC12V560100k

VOLTAGE DIVIDER BIAS+VCCRERCR1R2I2 + IBI2IBICIE

+VCCR1R2A+VCCRCREVIN+-IIN+-VBEIESimplified Voltage-Dividera)Unloadedb) LoadedInput Resistance at the BaseRIN(base) = DCRE

+VCCAR1R2RIN(base)Analysis of Voltage-Divider Circuit

Example 3) Determine VCEand IC. Assume DC = 100 +VCCRERCR1R210k5.6k1k560

The EndThose who are enamored of practice without science are like a pilot who goes into a ship without rudder or compass and never has any certainty where he is going. Practice should always be based upon a sound knowledge of theory.

Leonardo da Vinci(1452-1519)Italianartist, engineer, and inventor. Notebooks

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