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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/