1 Intro EC -Psu

8/4/2019 1 Intro EC -Psu

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Electronic Circuits 10CS32

Theory 100 + 25 = 125 Marks

Practical 50 + 25 = 75 Marks 12 Experiments

Part A Part - B6 from EC subject 6 from LD subject

a part hardware a part hardware

b part software b part software

Note: software experiment is simulation of hardwareexperiment
http://2%20ec%20syllabus.doc/


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Dos & Donts

Silence

No mobiles

No mischievousness Previous class prepared

Come prepared to laboratory


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Introduction Class

Diode


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Ohms lawCurrent = voltage / resistance

I = V / R

V = I x R

Definitions

Voltage = potential energy / unit charge, units = Volts Current = charge flow rate, units = Amps

Resistance = friction, units = Ohms

Example

Voltage drop when current flows through resistor

V1 - V2 = I RIR

V1

V2


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Schematics

+Battery

Resistor

Ground

+

VRI

Sample circuit

Ground voltage

defined = 0


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Resistors in Series


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Resistors in Parallel


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Parallel and series resistors

+

Note: these points are

connected together

I

VR1

R2

Series circuit

V = R1 I + R2 I = ReffI

Reff= R1 + R2Parallel circuit

I = V/R1 + V/R2 = V/Reff

1/Reff= 1/R1 + 1/R2

+V

R1R2I1 I2

I


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Resistive voltage divider

external connection

+

Vin

R1

R2 I

IVout

Resistive divider

I = Vin/Reff= Vout/R2

Vout = Vin (R2 / (R1 + R2) )


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Capacitors

Capacitor charging circuit

V = VR + VC = R dQ/dt + Q/C

dQ/dt + Q/RC = V/R

Q = C V (1 - exp(-t/RC))

Vout = Vin (1 - exp(-t/RC))

schematic

symbol:

capacitor

+

V R

C

IVout

Q

Vout

t

Vin

t = RC

Capacitor charging curve

time constant = RC


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AC circuits

V0 cos(2 pft)

RI =

(V0/R) cos(2 pft)

Resistive ac circuit

schematic

symbol:

AC voltage source

V0 cos(2 pft)

CI =

- 2 pf CV0 sin(2 pft)

Capacitive ac circuit

90 degree phase lag


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DC vs AC Signals


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Period, Frequency, RMS Value

T

Irms

T = 1__f

Ip

2

prms II T = period (sec)

f= frequency (Hz)

Ip = Peak Current (Amp)

Irms = rms value (Amp)


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Simplified notation: ac-circuits

V = V0 cos(2 pf t) = V0 [exp(2 pj f t) + c.c.]/2 Drop c.c. part and factor of 1/2

V = V0 exp(2 p j f t)Revisit resistive and capacitive circuits

Resistor response: I = (V0/R) exp(2 pj f t) = V / R = V/ ZR

Capacitor response: I = 2 pj f CV0 exp(2 pj f t) = (2 pj f C) V = V/ZC

Definition: Impedance, Z = effective resistance, units Ohms

Capacitor impedance ZC = 1 / (2 p jf C) Resistor impedance ZR = RImpedance makes it look like Ohms law applies to capacitive

circuits also

Capacitor response I = V / ZC


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Capacitor Circuits

Impedance ZC = 1/ (2 pjf

C) Limit of low frequency f ~ 0

ZC --> infinity

Capacitor is open circuit at low frequency

Limit of low frequency f ~ infinity

ZC --> 0 Capacitor is short circuit at low frequency

V0 cos(2 pft)

CI = V/ZC

Capacitive ac circuit


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Summary of schematicsymbols

+Battery Resistor

Ground

External

connection

Capacitor

AC voltagesource

Inductor

Non-connecting

wires -

+

Op amp

Potentiometer

Potentiometer

2-inputs pluscenter tap

Diode


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Color code

Resistor values determined by color Three main bands

1st = 1st digit

2nd = 2nd digit

3rd = # of trailing zeros

Examples red, brown, black

2 1 no zeros = 21 Ohms

yellow, brown, green

4 1 5 = 4.1 Mohm

purple, gray, orange 7 8 3 = 78 kOhms

Capacitors can have 3 numbers

use like three colors

Color

black

brown

red

orange

yellow

green

blue

violet

gray

white

Number

0

1

2

3

4

5

6

7

8

9


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Ground


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Prototyping Board - Bread Board

Example of how components are

Inserted in the protoboard


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Th PN J ti


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The PN Junction

Kristin Ackerson, Virginia Tech EESpring 2002

Steady State1

Pn

- - - - - -

- - - - - -

- - - - - -

- - - - - -

- - - - - -

+ + + + + +

+ + + + + +

+ + + + + +

+ + + + + +

+ + + + + +

Na Nd

Metallurgical

Junction

Space ChargeRegionionized

acceptorsionizeddonors

E-Field

++_ _

h+ drift h+ diffusion e- diffusion e- drift= =

Properties of Diodes


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Properties of Diodes

Kristin Ackerson, Virginia Tech EESpring 2002

Figure 1.10 The Diode Transconductance Curve2

VD = Bias Voltage

ID = Current throughDiode. ID is Negativefor Reverse Bias andPositive for ForwardBias

IS = SaturationCurrent

VBR = BreakdownVoltage

V = Barrier PotentialVoltage

VD

ID (mA)

(nA)

VBR

~V

IS


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pn junction diode


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Basic Transistor Operation

To produce a desired mode of operation, the twopn junctions must be correctly biased

NPN transistor will be used for illustration

The operation of the PNP is the same as for theNPN except that

- the roles of the electrons and holes

- the bias voltage polarities

- the current directionsare all reversed


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Modes of Operation

Forward-Active

B-E junction is forward biased

B-C junction is reverse biased

Saturation

B-E and B-C junctions are forward biased

Cut-OffB-E and B-C junctions are reverse biased


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Forward-active operating mode


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Figure 44 Illustration of BJT action.

Thomas L. Floyd

Electronic Devices, Electron Flow Version, 5e

Copyright 2005 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.

Forward biasnarrows the B-E

depletion region

Reverse bias widensthe B-C depletionregion

For the B-Cjunction to be

reverse biased, theCollector is mademore +ve than theBase


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Transistor Currents

The three currents inthe transistor are IE, IC,and I

B

IE = IC + IB

The IB is very smallcompared to the IC andIE

The IC is controlled bythe B-E voltage


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Alpha () and Beta ()

measures the portion of the emittercurrent that survives after passage

through the base to become collector

currentIC = IE

is the dc current gain of a transistor

IC = IB


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Transistor Operation
http://3%20fig316_bjt_operation.swf/

1 Intro EC -Psu

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