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Chapter 2:
Diode Applications
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Load-Line AnalysisLoad-Line Analysis
22
The load line plots all possible
combinations of diode current (ID)
and voltage (VD) for a given
circuit. The maximumID equals
E/R, and the maximum VD equals
E.
The point where the load line and
the characteristic curve intersect is
the Q-point, which identifiesID
and VD for a particular diode in a
given circuit.
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Series Diode ConfigurationsSeries Diode Configurations
Constants
Silicon Diode: VD = 0.7 V
Germanium Diode: VD = 0.3 V
Analysis (for silicon)
VD = 0.7 V (or VD =EifE< 0.7 V)
VR = E VD
ID = IR = IT= VR / R
33
Forward BiasForward Bias
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Series Diode ConfigurationsSeries Diode Configurations
Diodes ideally behave as open circuits
Analysis
VD = E
VR = 0 V
ID= 0 A
44
Reverse BiasReverse Bias
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Parallel ConfigurationsParallel Configurations
55
mA14
2
mA28
D2I
D1I
mA28
.33k
V.7V10
R
DVE
RI
V9.3R
V
V0.7O
VD2
VD1
V
V0.7D
V
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Half-Wave RectificationHalf-Wave Rectification
66
The diode only
conducts when it is
forward biased,
therefore only half
of the AC cycle
passes through the
diode to the
output.
The DC output voltage is 0.318Vm, where Vm = the peak AC voltage.
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
PIV (PRV)PIV (PRV)
77
Because the diode is only forward biased for one-half of the AC cycle, it is
also reverse biased for one-half cycle.
It is important that the reverse breakdown voltage rating of the diode be
high enough to withstand the peak, reverse-biasing AC voltage.
PIV (or PRV) > Vm
PIV = Peak inverse voltage
PRV = Peak reverse voltage
Vm
= Peak AC voltage
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Full-Wave RectificationFull-Wave Rectification
88
Half-wave: VVdcdc = 0.318= 0.318VVmm
Full-wave: VVdcdc = 0.636= 0.636VVmm
The rectification process can be improved by
using a full-wave rectifier circuit.
Full-wave rectification produces a greaterDC output:
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Full-Wave RectificationFull-Wave Rectification
99
Bridge RectifierBridge Rectifier
Four diodes are connected in a
bridge configuration VDC = 0.636Vm
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Full-Wave RectificationFull-Wave Rectification
1010
Center-Tapped TransformerCenter-Tapped Transformer
RectifierRectifier
Requires
Two diodes
Center-tapped transformer
VDC = 0.636Vm
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Summary of Rectifier CircuitsSummary of Rectifier Circuits
1111
Vm= peak of the AC voltage.
IIn the center tapped transformer rectifier circuit, the peak AC voltageis the transformer secondary voltage to the tap.
RectifierRectifier IdealIdeal VVDCDC RealisticRealistic VVDCDC
Half Wave Rectifier VDCDC = 0.318Vm VDCDC = 0.318Vmm 0.7
Bridge Rectifier VDCDC = 0.636Vm VDCDC = 0.636Vm 2(0.7 V)
Center-Tapped Transformer
RectifierVDCDC = 0.636Vm VDCDC = 0.636Vm 0.7 V
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Important Equations
TRANSFORMER EQUATIONS
=
=
= 0.707
HALF-WAVE RECTIFIER EQUATIONS (TRANSFORMER COUPLED)
= 0.7 = /
= = / = = /
= = /2 = = /2
PIV=V2 fout= fin
Efficiency of Rectification = n = (/)100%CENTER-TAPPED FULL-WAVE RECTIFIER EQUATIONS (TRANSFORMER COUPLED)
= /20.7 = /
= = 2/ = = 2/
=
=
/2
=
=
/2
PIV=V2 0.7 fout= 2fin
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Diode ClippersDiode Clippers
1212
The diode in a series clipperseries clipperclipsany voltage that does not forward
bias it:
A reverse-biasing polarity
A forward-biasing polarity less than0.7 V (for a silicon diode)
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Biased ClippersBiased Clippers
1313
Adding a DC source in
series with the clipping
diode changes the
effective forward bias of
the diode.
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Parallel ClippersParallel Clippers
1414
The diode in a parallel clipperparallel clipper
circuit clips any voltage that
forward bias it.
DC biasing can be added inseries with the diode to change
the clipping level.
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Summary of Clipper CircuitsSummary of Clipper Circuits
1515
moremore
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Summary of Clipper CircuitsSummary of Clipper Circuits
1616
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
ClampersClampers
1717
A diode and capacitor can be
combined to clamp an AC
signal to a specific DC level.
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Biased Clamper CircuitsBiased Clamper Circuits
1818
The input signal can be any type
of waveform such as sine, square,
and triangle waves.
The DC source lets you adjust
the DC camping level.
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Summary of Clamper CircuitsSummary of Clamper Circuits
1919
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Zener DiodesZener Diodes
2020
The Zener is a diode operatedin reverse bias at the Zener
Voltage (Vz).
When Vi VZ The Zener is on Voltage across the Zener is VZ Zener current:IZ=IRIRL The Zener Power:PZ= VZIZ
When Vi< VZ The Zener is off
The Zener acts as an open circuit
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Zener Resistor ValuesZener Resistor Values
2121
ZKRLIII
min
min
max
L
Z
L
I
VR
min
max
L
Z
L
L
L
R
V
R
VI
Zi
Z
L
VV
RVR
min
IfR is too large, the Zener diode cannot conduct because the available amount of
current is less than the minimum current rating,IZK. The minimum current is
given by:
The maximum value of resistance is:
IfR is too small, the Zener current exceeds the maximum current
rating,IZM. The maximum current for the circuit is given by:
The minimum value of resistance is:
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Voltage-Multiplier CircuitsVoltage-Multiplier Circuits
Voltage Doubler
Voltage Tripler
Voltage Quadrupler
2222
Voltage multiplier circuits use a combination of diodes and
capacitors to step up the output voltage of rectifier circuits.
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Voltage DoublerVoltage Doubler
2323
This half-wave voltage doublers output can be calculated by:
Vout = VC2 = 2Vm
where Vm = peak secondary voltage of the transformer
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Voltage DoublerVoltage Doubler
2424
Positive Half-Cycle
o D1 conductso D2 is switched off
o Capacitor C1 charges to Vm
Negative Half-Cycle
o D1 is switched off
o D2 conductso Capacitor C2 charges to Vm
Vout = VC2 = 2Vm
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Copyright 2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Voltage Tripler and QuadruplerVoltage Tripler and Quadrupler
2525
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Copyright 2009 by Pearson Education, Inc.
S R 0 4 8 A
Electronic Devices and Circuit Theory, 10/e
R b t L B l t d d L i N h l k
Practical ApplicationsPractical Applications
Rectifier Circuits Conversions of AC to DC for DC operated circuits
Battery Charging Circuits
Simple Diode Circuits
Protective Circuits against
Overcurrent Polarity Reversal
Currents caused by an inductive kick in a relay circuit
Zener Circuits
Overvoltage Protection
Setting Reference Voltages
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