revision
TRANSCRIPT
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Half-wave Rectifier
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Bi-phase Rectifiers
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Bridge Rectifiers
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Operation of Bridge Rectifiers
(cont.)
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Operation of Bridge Rectifiers
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Summary of Types Of Rectifiers using non-Ideal Diode(Silicon)
Type of rectifier Half-wave Bi-phase (Centretap)
Bridge Rectifier
1 Output Peak (Vp (out))
2 Output Average(VAVG)
3 Peak Inverse Voltage (PIV)
4 Output Frequency(f) Equal Input Frequency
Double Input Frequency
Double Input Frequency
)out(pV
)out(pV2
)out(pV2
7.0V )s(p 7.02
V )s(p 4.1V )s(p
)s(pV 7.0V )s(p 7.0V )s(p
7.0V )out(p 7.0V2 )out(p 7.0V )out(p
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Summary of Types Of Rectifiers using Ideal Diode
Type of rectifier Half-wave Bi-phase (Centretap)
Bridge Rectifier
1 Output Peak (Vp (out))
2 Output Average(VAVG)
3 Peak Inverse Voltage (PIV)
4 Output Frequency(f) Equal Input Frequency
Double Input Frequency
Double Input Frequency
)out(pV
)out(pV2
)out(pV2
)s(pV2
V )s(p)s(pV
)s(pV )s(pV )s(pV
)out(pV )out(pV2)out(pV
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For Full Wave Rectifier With Capacitance Input Filter
)rect(VCfR
1V p
L)pp(r
)rect(VCfR2
11V p
L)DC
Note: f is the output frequency
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Series Diode Clippers
Series Negative Clipper
Series Positive Clipper
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Parallel Diode Clippers
Parallel Negative Clipper
Parallel Positive Clipper
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Biased Diode ClippersBiased Negative Clipper
Biased Positive Clipper
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Biased Double-Diode Clippers
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Positive Clamper
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Negative Clamper
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Biased Clamper
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Zener Diode08. How does the zener impedance affect the voltage across the terminals of the device?
9. (a) shows the original circuit. (b) Zener diode represented using the second approximation. What is the max and min IZ and VZ?
10. This is a typical loaded voltage regulator. Do you know the value of IZ?
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BJT Schematic Symbols
NPN PNP
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BJT Biasing
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BJT Biasing
NPN Biasing PNP Biasing
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Common Emitter
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Common Emitter
• It is called the common-emitter configuration because the emitter is common or reference to both the input and output terminals (in this case common to both the base and collector terminals).
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Common Collector
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Common Base
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Configuration Characteristics
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Current Gain• The dc current gain produced by an amplifier is the ratio
of output current to input current, i.e.,
• In the case of a transistor operating in common emitter mode, the input current is the base current, IB, whilst the output current is the collector current, IC.
(Cont.)
in
outDC I
I
B
CDC I
I
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DC usually designated as hFE on transistor data sheets.
• h is derived from an ac hybrid equivalent circuit.• The subscript FE is derived from forward-current
amplification and common-emitter configuration.
• Typical values of DC range from less than 20 to 200 or higher.
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Current Gain
DC is a very important BJT parameter.
DC is not truly constant but varies with both collector current and with temperature.
• A transistor data sheet usually specifies DC at specific IC values.
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Current Gain
• If a steady bias current is superimposed with an a.c. current, this will produce a collector current which varies above and below its d.c. current value respectively.
• The small signal ac current gain is then given by,
B
Cac I
I
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Ratio of dc collector current to dc emitter current, DC (Common Base
Mode)DC = IC/IE
• Typically, values of DC range from 0.95 to 0.99 or greater but it is always less than 1.
• The small signal ac ratio is then given by,
E
Cac I
I
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• The relationship of DC and DC is given as,
DCDC
DC
1
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DC Equivalent of a BJT
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Output Characteristics
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Cutoff
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Midpoint Bias
• Without an ac signal applied to a transistor, specific values of IC and VCE exist.
• The IC and VCE values exist at a specific point on the dc load line.
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Base Bias
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Base Bias
RB
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Base Bias
• For silicon transistors, VBE equals 0.7V.
• The collector circuit is represented as a current source whose value is dependent only on the values of DC and IB.
• Collector supply voltage variations will have little or no effect on the collector current, IC.
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Current and Voltage Analysis
B
BEBBB
BEBBBB
R
VVI
VRIV
0
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CCCCCE
CECCCC
RIVV
VRIV
0
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BECECB
BECECB
VVV
VVV
0
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In the active region (not operating in saturation or cutoff)
VV
II
BE
BDCC
7.0
The collector circuit acts as a current source with a high internal impedance.
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Base Bias
• More practical to use VCC as a single bias source.
• The base supply voltage, VBB has been omitted and RB is connected to the positive (+) terminal of VCC.
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B
BECCDCC
CCCCCE
B
BECCB
R
VVI
RIVV
R
VVI
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Eg :
(Cont.)
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CBE
BDCC
III
II
B
BEBBB R
VVI
CCCCCE RIVV
BECECB VVV
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Base Bias
• For base bias, IC is dependant on DC.• But DC varies with temperature and also
varies from one transistor to another.• Variations in DC causes IC and VCE to change
thus changing the Q point of the transistor (near or at cutoff or saturation).
• This might cause distortion in the output signal.
• Base bias provides a very unstable Q point.
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DC Load Line• The DC load line is a graph that allows us
to determine all the possible combination of IC and VCE for a given amplifier.
• A specific point on the DC load line gives a fixed value of IC and VCE is called the Q point.
• Q stands for quiescent currents and voltages with no ac input signal.
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Base Bias
• For silicon transistors, VBE equals 0.7V.
• The collector circuit is represented as a current source whose value is dependent only on the values of DC and IB.
• Collector supply voltage variations will have little or no effect on the collector current, IC.
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Current and Voltage Analysis
B
BEBBB
BEBBBB
R
VVI
VRIV
0
![Page 52: Revision](https://reader031.vdocument.in/reader031/viewer/2022020115/55524a5db4c905954f8b4c24/html5/thumbnails/52.jpg)
CCCCCE
CECCCC
RIVV
VRIV
0
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BECECB
BECECB
VVV
VVV
0
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In the active region (not operating in saturation or cutoff)
VV
II
BE
BDCC
7.0
The collector circuit acts as a current source with a high internal impedance.
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Base Bias
• More practical to use VCC as a single bias source.
• The base supply voltage, VBB has been omitted and RB is connected to the positive (+) terminal of VCC.
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B
BECCDCC
CCCCCE
B
BECCB
R
VVI
RIVV
R
VVI
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Eg :
(Cont.)
![Page 59: Revision](https://reader031.vdocument.in/reader031/viewer/2022020115/55524a5db4c905954f8b4c24/html5/thumbnails/59.jpg)
CBE
BDCC
III
II
B
BEBBB R
VVI
CCCCCE RIVV
BECECB VVV
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Voltage Divider Bias
• This is the most popular way to bias a transistor.
• Transistors biased in this manner are stable.
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Current and Voltage Analysis
ECCCCCE
CE
E
EE
BEBE
CCB
RRIVV
II
R
VI
VVV
VRR
RV
21
2
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The dc load line
• The dc load line intersects the IC axis at a the saturation point where IC is maximum and VCE is almost 0.
EC
CEsatC
CCoffCE
ECCCCCE
RR
VI
VV
RRIVV
![Page 63: Revision](https://reader031.vdocument.in/reader031/viewer/2022020115/55524a5db4c905954f8b4c24/html5/thumbnails/63.jpg)
DC Load Line
![Page 64: Revision](https://reader031.vdocument.in/reader031/viewer/2022020115/55524a5db4c905954f8b4c24/html5/thumbnails/64.jpg)
Eg
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DC Load Line for Voltage Divider Bias
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Emitter Bias
• If both positive and negative power supplies are available, emitter bias gives a solid Q-point that is fixed (fluctuates very little with temperature variation and transistor replacement).
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Emitter Bias
• The emitter supply voltage, VEE, forward-biases the emitter-base junction through the emitter resistor, RE.
• The base voltage, VB=0V, because the IBRB voltage drop is very small due to the small value of base current, IB, which is typically only a few microamperes.
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EC
EECCsatC
EECCoffCE
ECCEECCCE
EC
DC
BE
BEEEE
RR
VVI
VVV
RRIVVV
II
RR
VVI
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Emitter Bias
• If both positive and negative power supplies are available, emitter bias gives a solid Q-point that is fixed (fluctuates very little with temperature variation and transistor replacement).
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Emitter Bias
• The emitter supply voltage, VEE, forward-biases the emitter-base junction through the emitter resistor, RE.
• The base voltage, VB=0V, because the IBRB voltage drop is very small due to the small value of base current, IB, which is typically only a few microamperes.
![Page 71: Revision](https://reader031.vdocument.in/reader031/viewer/2022020115/55524a5db4c905954f8b4c24/html5/thumbnails/71.jpg)
EC
EECCsatC
EECCoffCE
ECCEECCCE
EC
DC
BE
BEEEE
RR
VVI
VVV
RRIVVV
II
RR
VVI
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Collector Feedback Bias• This type of
biasing is more stable than the base bias.
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Collector Feedback Bias
• The base resistor, RB, is connected to the collector, rather than to the supply voltage, VCC, as in the case with base bias.
• Collector-feedback bias is much more stable than the bias bias.
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Collector Feedback Bias
• Assume DC increases due to temperature.
• This produces an increase in the collector current, IC, which, in turn, increases the voltage dropped across Rc.
• This causes the VCE to decrease, thus decreasing the voltage drop across the base resistor, RB.
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Collector Feedback Bias
• Then, this reduces the base current, IB, which causes IC to decrease by an amount that almost completely offsets the original increase in the current, IC.
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Collector Feedback Bias
• Assume DC decreases.
• This causes the IC to decrease. This, in turn, causes VCE to increase, which then cause IB to increase due to the increased voltage drop across the base resistor, RB.
• The increase in IB causes IC to increase.
• This almost completely offsets the original change in IC caused by the reduction in DC.
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Collector Feedback Bias
• RB is usually chosen such that the Q point is placed in the middle of the dc load line.
• To satisfy this condition, choose RB to equal DC Rc . CCCCCE
DC
B
BECC
C
RIVV
RRC
VVI
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04/12/23 6-78
SummaryBasic AC h-parameters
hi - input impedance (resistance) with output short circuited.
hr - reverse voltage transfer function with input open circuited.
hf - forward current transfer function with output short circuited.
ho - Output admittance (conductance) with input open circuited.
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04/12/23 6-79
Complete h-parameter equivalent circuit
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04/12/23 6-80
Common emitter h-parameter equivalent circuit
~
hie
hreVouthfe Ib hoe
Vout
Ib
E
CB
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04/12/23 6-81
Approximate hybrid equivalent circuit
hie hfe Ib Vout
Ib
E
CB
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04/12/23 6-82
Approximate hybrid equivalent circuit
• Since hr is normally a relatively small quantity, its removal is approximated by and , resulting in a short-circuit equivalent for the feedback element as shown.
• The resistance determined by 1/ho is often large enough to be ignored in comparison to a parallel load, permitting its replacement by an open circuit equivalent for the CE and CB models.
0rh0orVh
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04/12/23 6-83
Common-Emitter Fixed Bias Configuration
VI
V0
__
Zin
Z0
II
Io
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04/12/23 6-84
SummaryBasic AC h-parameters
hi - input impedance (resistance) with output short circuited.
hr - reverse voltage transfer function with input open circuited.
hf - forward current transfer function with output short circuited.
ho - Output admittance (conductance) with input open circuited.
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Complete h-parameter equivalent circuit
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Common emitter h-parameter equivalent circuit
~
hie
hreVouthfe Ib hoe
Vout
Ib
E
CB
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Approximate hybrid equivalent circuit
hie hfe Ib Vout
Ib
E
CB
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Approximate hybrid equivalent circuit
• Since hr is normally a relatively small quantity, its removal is approximated by and , resulting in a short-circuit equivalent for the feedback element as shown.
• The resistance determined by 1/ho is often large enough to be ignored in comparison to a parallel load, permitting its replacement by an open circuit equivalent for the CE and CB models.
0rh0orVh
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Common-Emitter Fixed Bias Configuration
VI
V0
__
Zin
Z0
II
Io
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Equivalent Circuit
RB
RC
Input
OutputB
E
C
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AC equivalent circuit
voutvin
iin
iout
RB hie hfeib 1/hoeRC
Zi
Z0
IbIC
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Zi and Z0 (Input Impedance and Output Impedance)
oeCC
ieBi
hRRZ
hRZ
10
iin
iout
RB hie hfeib 1/hoe RC
Zi
Z0
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Voltage Gain AV
Cbfe
CCC
RIh
RIRIV 00
V0
iout
RB hie hfeib 1/hoe RC
IC
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Cie
ife
ie
ib
Rh
VhV
h
VI
0
Vi
iout
RB hie hfeib 1/hoe RC
Ib
V0
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ie
Cfe
iV
Cie
ife
h
Rh
V
VA
Rh
VhV
0
0
The negative sign in the resulting equation for AV reveals that a 180o phase shift occurs between the input and output signals.
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Current Gain Ai
fei
oi
ifebfeC
ib
ieB
hI
IA
IhIhII
and
II
thenhR
0
,
Assuming
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Eg: Find Zin, Z0, Ai and Av
RB = 330kRC = 2.7k hfe=120hie=1.175khoe=20A/V
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Voltage Divider Bias
• Note that R1 and R2 remain part of the input circuit while R3 is part of the output circuit.
• The parallel combination of R1 and R2 is defined by RP
21
2121 //
RR
RRRRRP
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R1R2
R3
Input
OutputB
E
C
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Rp
R3
Input
OutputB
E
Cibiin
iout*RP = R1 // R2
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AC equivalent circuit
vin voutRp hiehfeib 1/hoe R3
iin ioutib
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Zi and Z0
oeCC
iepi
hRRZ
hRZ
10
iin
iout
Rp hie hfeib 1/hoe RC
Zi
Z0
RP = R1 // R2
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AV
Cbfe
CCC
RIh
RIRIV 00
V0
iout
Rp hie hfeib 1/hoe RC
IC
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Cie
ife
ie
ib
Rh
VhV
h
VI
0
Vi
iout
Rp hie hfeib 1/hoeRC
Ib
V0
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ie
Cfe
iV
Cie
ife
h
Rh
V
VA
Rh
VhV
0
0
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Ai
ieP
Pfei hR
RhA