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Uploaded By: Khaled Saleh
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Electronic Circuits
Dr. Farid Shawki Al-Hosarey
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Contents
Power Amplifiers
Chapter
1
Class A power Amplifies
Transformer-coupled class
A amplifier
Class B Amplifier Operation
Amplifier Distortion
Class C Power Amplifier
Troubleshooting
System Application
Thyristors
Chapter
2
The Basic 4-Layer Device
The Silicon-Controlled Rectifier
SCR Applications
The Diac and Triac
The Silicon-Controlled Switch
Optoelectronics
Chapter
3
The Phototransistor
The Light-Activated SCR
Optical Couplers
Fiber Optics
System Application
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Programmable Logic DevicesChapter
4
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Chapter 1 : Power Amplifiers
Class A power Amplifies
Amplifier operating classes
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Chapter 1 : Power Amplifiers
Class C is usually not used for delivering large amounts of power, and
thus the efficiency is not given here.
A AB B C D
Operating
Cycle
360 180 to
360
180 Less than
180
Pulse
operation
Power
Efficiency
25 % to
50%
Between
25% (50%)and 78.5%
78.5% Typically
over 90%
Comparison of Amplifier Classes
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
B
CCB
R
VI
7.0
BC II
CCCCCE RIVV
The dc bias set by VCC and RB fixes the dc base-biascurrent at:
with the collector current then being:
with the collector-emitter voltage then:
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
Transistor characteristic showing load line and Q-point13 March 2011 9
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
AC Operation13 March 2011 10
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
AC Operation13 March 2011 11
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
Power Considerations
The power into an amplifier is provided by the supply. Withno input signal, the dc current drawn is the collector biascurrent ICQ The power then drawn from the supply is:
CQCCi IVdcP )(
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
Output PowerUsing RMS signals.
The ac power delivered to the load (RC) may be expressedusing:
)()()( rmsIrmsVacP CCEo
CCo RrmsIacP )()(2
C
CE
oR
rmsVacP
)()(
2
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
Output PowerUsing Peak-to-peak signals.
The ac power delivered to the load (RC) may be expressedusing:
8
)()()(
ppIppVacP CCEo
8)()(
2
CCo RppIacP
C
CEo
R
ppVacP
8
)()(
2
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
Power Efficiency
%100)(
)(% dcP
acP
i
o
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
Maximum Power Efficiency
maximum VCE(p-p) = VCC
For the current swing it is
Using the maximum voltage swing yields:
C
CC
R
Vpp )(Imaximum C
C
CCCCCCC
R
VRVVac
88
/)(Pmaximum
2
o
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
C
CCCCCCCCCR
VRVVVdc 22
/Imaximum)(Pmaximum
2
Ci
%25%1002/
8/%100
)(Pmaximum
)(Pmaximum%maximum
2
2
i
o CCC
CCC
RV
RV
dc
ac
The maximum power input can be calculated using thedc bias current set to one-half the maximum value:
We can then calculate the maximum efficiency:
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
power loss considered here is that dissipated by the powertransistor and calculated using:
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acPdcPP oiQ
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
Example:
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Calculate the input power, output
power, and efficiency of the amplifiercircuit in Figure 1-5 for an inputvoltage that results in a base currentof 10 mA peak.
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
Example:
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
Solution:
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VRIVV
AmAII
mAR
VI
CCCCQCE
BQC
B
CC
QB
4.14)20)(48.0(20
48.05.482)3.19(25
3.19101
7.0207.03
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
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Chapter 1 : Power Amplifiers
Series-Fed Class A power Amplifies
Solution:
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acPdcPP oiQ = 8.975 W
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Chapter 1 : Power Amplifiers
Transformer-Coupled Class A Amplifier
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Chapter 1 : Power Amplifiers
Transformer-Coupled Class A Amplifier
Voltage Transformation
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Chapter 1 : Power Amplifiers
Transformer-Coupled Class A Amplifier
Current Transformation
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Chapter 1 : Power Amplifiers
Transformer-Coupled Class A Amplifier
Impedance Transformation
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Chapter 1 : Power Amplifiers
Transformer-Coupled Class A Amplifier
Operation of Amplifier Stage
DC Load lineQ-PointAC Load line
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Chapter 1 : Power Amplifiers
Transformer-Coupled Class A Amplifier
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Chapter 1 : Power Amplifiers
Transformer-Coupled Class A Amplifier
Signal Swing and Output AC Power
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Chapter 1 : Power Amplifiers
Transformer-Coupled Class A Amplifier
minmax
minmax
)(
)(
CCC
CECECE
IIppI
VVppV
The ac power developed across the transformer primarycan then be calculated using:
8)(
minmaxminmax CCCECEo
IIVV
acP
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Chapter 1 : Power Amplifiers
Transformer-Coupled Class A Amplifier
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1
1
2
2 VN
NVVL
L
L
LR
rmsVP
)(2
CL
IN
NII
2
1
2
LLLRrmsIP )(
2
The voltage delivered to the load can be calculated using
The power across the load can then be expressed as:
The the load current yields:
The output ac power then calculated using:
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Chapter 1 : Power Amplifiers
Transformer-Coupled Class A Amplifier
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Maximum Theoretical Efficiency
%50%
2
minmax
minmax
CECE
CECE
VV
VV
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Chapter 1 : Power Amplifiers
Transformer-Coupled Class A Amplifier
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EXAMPLE
Calculate the efficiency of a transformer-
coupled class A amplifier for a supply of 12 Vand outputs of:
V(p) = 12 V.V(p) = 6 V.V(p) = 2 V.
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Chapter 1 : Power Amplifiers
Transformer-Coupled Class A Amplifier
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Since VCEQ = VCC = 12 V, the maximum andminimum of the voltage swing are,respectively, resulting in
%50%024
02450%
2
VpVVV
VpVVV
CEQnCE
CEQnCE
01212)(
241212)(
min
max
resulting in
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