8/3/2019 Diode Applications 3
1/31
Diode Applications
8/3/2019 Diode Applications 3
2/31
LoadLoad--Line AnalysisLine Analysis
22
The load line plots all possible
combinations of diode current (ID)
and voltage (VD) for a given circuit.
The maximumID equalsE/R, and
the maximumV
D equalsE
.
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.
8/3/2019 Diode Applications 3
3/31
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
8/3/2019 Diode Applications 3
4/31
Series Diode ConfigurationsSeries Diode Configurations
Diodes ideally behave as open circuits
Analysis
VD = E
VR = 0 V
ID = 0 A
44
Reverse BiasReverse Bias
8/3/2019 Diode Applications 3
5/31
Parallel ConfigurationsParallel Configurations
55
mA142
mA28
D2I
D1I
mA28.33k
V.7V10
R
DVE
RI
V9.3
R
V
V0.7O
VD2
VD1
V
V0.7D
V
!!!
!
!
!
!
!!!
!
8/3/2019 Diode Applications 3
6/31
A. Rectifiers
8/3/2019 Diode Applications 3
7/31
- converts the alternating current input signalto a pulsating direct current
8/3/2019 Diode Applications 3
8/31
ACSignal
+Vp
-Vp
Vp-p
1 cycle
Frequency the no.of cycles in a second;
Hz
Period the time it
would take to
complete one cycle; s Wavelength
distance covered by
one cycle; m
NOTE:
2 P rmsV V! 2 P rmsV V!
8/3/2019 Diode Applications 3
9/31
HalfHalf--Wave RectificationWave Rectification
99
The diode only
conducts when it is
forward biased,
therefore only halfof the AC cycle
passes through the
diode to the
output.
8/3/2019 Diode Applications 3
10/31
Derivation (half-wave rectifier)
The DC output voltage is 0.318Vm, where Vm = the peak AC voltage.
8/3/2019 Diode Applications 3
11/31
PIV (PRV)PIV (PRV)
1111
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
8/3/2019 Diode Applications 3
12/31
FullFull--Wave RectificationWave Rectification
1212
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:
8/3/2019 Diode Applications 3
13/31
FullFull--Wave RectificationWave Rectification
1313
Bridge RectifierBridge Rectifier
Four diodes are connected ina bridge configuration
VDC = 0.636Vm
8/3/2019 Diode Applications 3
14/31
FullFull--Wave RectificationWave Rectification
1414
CenterCenter--Tapped TransformerTapped Transformer
RectifierRectifier
Requires
Two diodes
Center-tapped transformer
VDC = 0.636Vm
8/3/2019 Diode Applications 3
15/31
Derivation (full-wave rectifier)
The DC output voltage is 0.636Vm, where Vm = the peak AC voltage.
8/3/2019 Diode Applications 3
16/31
Summary ofRectifier CircuitsSummary ofRectifier Circuits
1616
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
8/3/2019 Diode Applications 3
17/31
B. WaveshapingCircuits
8/3/2019 Diode Applications 3
18/31
Diode Clippers / LimitersDiode Clippers / Limiters
used to clip-off portions of an ACsignal voltages above or below acertain kind.
1818
The diode in a series clipperseries clipper clipsany voltage that does not forward
bias it:
A reverse-biasing polarity
A forward-biasing polarity less than0.7 V (for a silicon diode)
8/3/2019 Diode Applications 3
19/31
Biased ClippersBiased Clippers
1919
Adding a DC source in
series with the clipping
diode changes the
effective forward bias of
the diode.
8/3/2019 Diode Applications 3
20/31
Parallel ClippersParallel Clippers
2020
The diode in a parallel clipperparallel clipper
circuit clips any voltage that
forward bias it.
DC biasing can be added in
series with the diode to change
the clipping level.
8/3/2019 Diode Applications 3
21/31
Summary of Clipper CircuitsSummary of Clipper Circuits
2121
moremore
8/3/2019 Diode Applications 3
22/31
Clampers / DC restorersClampers / DC restorers
2222
A diode and capacitor can be
combined to clamp an AC
signal to a specific DC level.
8/3/2019 Diode Applications 3
23/31
8/3/2019 Diode Applications 3
24/31
Summary of Clamper CircuitsSummary of Clamper Circuits
2424
8/3/2019 Diode Applications 3
25/31
Zener DiodesZener Diodes
2525
The Zener is a diode operated
in reverse bias at the Zener
Voltage (Vz).
When Viu VZ The Zener is on
Voltage across the Zener is VZ Zener current:IZ=IRIRL The Zener Power: P
Z
=VZ
IZ
When Vi< VZ The Zener is off
The Zener acts as an open circuit
8/3/2019 Diode Applications 3
26/31
Zener Resistor ValuesZener Resistor Values
2626
ZKRLIII !
min
min
max
L
Z
LI
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 isgiven 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:
8/3/2019 Diode Applications 3
27/31
VoltageVoltage--Multiplier CircuitsMultiplier Circuits
Voltage Doubler
Voltage Tripler Voltage Quadrupler
2727
Voltage multiplier circuits use a combination of diodes andcapacitors to step up the output voltage of rectifier circuits.
8/3/2019 Diode Applications 3
28/31
Voltage DoublerVoltage Doubler
2828
This half-wave voltage doublers output can be calculated by:
Vout = VC2 = 2Vm
where Vm = peak secondary voltage of the transformer
8/3/2019 Diode Applications 3
29/31
Voltage DoublerVoltage Doubler
2929
Positive Half-Cycle
o D1 conducts
o D2 is switched off
o Capacitor C1 charges to Vm
Negative Half-Cycle
o D1 is switched off
o D2 conducts
o Capacitor C2 charges to Vm
Vout= VC2 = 2Vm
8/3/2019 Diode Applications 3
30/31
Voltage Tripler and QuadruplerVoltage Tripler and Quadrupler
3030
8/3/2019 Diode Applications 3
31/31
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
3131
Top Related