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Chapter 2
Diode application
1
Objectives
● Explain and analyze the operation of both half and full wave
rectifiers
● Explain and analyze filters and regulators and their
characteristics
● Explain and analyze the operation of diode limiting and ● Explain and analyze the operation of diode limiting and
clamping circuits
● Explain and analyze the operation of diode voltage multipliers
● Interpret and use a diode data sheet
● Troubleshoot simple diode circuits
2
Load-Line Analysis
The load line plots all possible
combinations of diode current (ID)
and voltage (VD) for a given circuit.
The maximum ID 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 identifies ID and
VD for a particular diode in a given
circuit.
3
Load-Line AnalysisExample
• For the series diode configuration of Fig. 2.3a , employing the diode characteristics of Fig. 2.3b , determine:
• a. VDQ and IDQ.
• b. VR
4
Series Diode Configurations
Forward BiasConstants
• Silicon Diode: VD = 0.7 V
• Germanium Diode: VD = 0.3 V
Analysis (for silicon)
• V = 0.7 V (or V = E if E < 0.7V)• VD = 0.7 V (or VD = E if E < 0.7V)
• VR = E – VD
• ID = IR = IT = VR / R
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Series Diode Configurations
Reverse BiasDiodes ideally behave as open circuits
Analysis
• VD = E
• V = 0 V• VR = 0 V
• ID = 0 A
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Series Diode ConfigurationsExample
For the series diode configuration of Figure below, determine VD, VR, and ID .
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Series Diode ConfigurationsExample
For the series diode configuration of Figure below, determine VD, VR, and ID .
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Series Diode ConfigurationsExample
For the series diode configuration of Figure below, determine I, V1, V2 and V0 .
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Series Diode ConfigurationsExample
For the series diode configuration of Figure below, determine I, V1, V2 and V0 .
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Parallel ConfigurationsExample
Determine Vo , I1 , ID1, and ID2 for
the parallel diode configuration of
Figure below
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Parallel ConfigurationsExample
Determine I1 , I2, and ID2 for the parallel diode configuration of Figure below
12
Parallel ConfigurationsExample
Determine I1 , I2, and ID2 for the parallel diode configuration of Figure below
13
Half-Wave Rectification
The diode only
conducts when it is
forward biased,
therefore only half
of the AC cycle
passes through thepasses through the
diode to the
output.
The DC output voltage (VDC) is 0.318Vm, where Vm = the peak AC voltage.
14
Half-Wave Rectification
VK =0.7 V and vo = vi – VK
When Vm » VK
15
Half-Wave RectificationExample
a. determine the dc level of the output for the network of Figure belowSketch
the output vo and
b. Repeat part (a) if the ideal diode is replaced by a silicon diode.
16
Half-Wave RectificationExample
a. determine the dc level of the output for the network of Figure belowSketch
the output vo and
b. Repeat part (a) if the ideal diode is replaced by a silicon diode.
17
PIV (PRV)
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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Full-Wave Rectification
The rectification process can be improved by using a
full-wave rectifier circuit.
Full-wave rectification produces a greater DCFull-wave rectification produces a greater DC
output:
• Half-wave: Vdc = 0.318Vm
• Full-wave: Vdc = 0.636Vm
19
Full-Wave Rectification
Bridge Rectifier
• Four diodes are connected in a bridge configuration
• VDC = 0.636Vm
20
Full-Wave Rectification
Center-Tapped Transformer
Rectifier
Requires
• Two diodes
• Center-tapped transformer
VDC = 0.636Vm
21
Summary of Rectifier Circuits
Rectifier Ideal VDC Realistic VDC
Half Wave RectifierVDC = 0.318Vm VDC = 0.318Vm – 0.7
Bridge Rectifier VDC = 0.636Vm VDC = 0.636Vm – 2(0.7 V)
Vm = peak of the AC voltage.
In the center tapped transformer rectifier circuit, the peak AC voltage is the
transformer secondary voltage to the tap.
Center-Tapped Transformer
Rectifier VDC = 0.636Vm VDC = 0.636Vm – 0.7 V
22
Diode Clippers
The diode in a series clipper “clips” any voltage that
does not forward bias it:• A reverse-biasing polarity• A forward-biasing polarity less than 0.7 V (for a silicon
diode)
23
Diode Clippers
Series clipper with dc supply
24
Diode Clippers
Adding a DC source in series with the clipping
diode changes the effective forward bias of the
diode.
25
Biased ClippersExample
Determine the output waveform for the sinusoidal input of Figure below.
26
Parallel Clippers
The diode in a parallel clipper
circuit “clips” any voltage that
forward bias it.
DC biasing can be added in DC biasing can be added in
series with the diode to change
the clipping level.
27
Parallel ClippersExample
Determine vo for the network of Figure below.
28
Parallel ClippersExample
Determine vo for the network of Figure below.
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Summary of Clipper CircuitsSeries
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Summary of Clipper CircuitsParallel
31
Clampers
A diode and capacitor can be combined
to “clamp” an AC signal to a specific DC
level.
32
Biased Clamper CircuitsExample 1
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.camping level.
33
Summary of Clamper Circuits
34
Voltage-Multiplier Circuits
Voltage multiplier circuits use a combination of diodes and capacitors to step
up the output voltage of rectifiercircuits.
• Voltage Doubler
• Voltage Tripler
• Voltage Quadrupler
35
Voltage Doubler
This half-wave voltage doubler’s output can be calculated by:
Vout = VC2 = 2Vm
where Vm = peak secondary voltage of the transformer
36
Voltage Doubler
• Positive Half-Cycle
o D1 conducts
o D2 is switched off
o Capacitor C1 charges toVm
• Negative Half-Cycle
o D1 is switched offo D1 is switched off
o D2 conducts
o Capacitor C2 charges toVm
Vout = VC2 = 2Vm
37
Voltage Tripler and Quadrupler
38
Practical Applications
• Rectifier Circuits
– Conversions of AC to DC for DC operated circuits
– Battery Charging Circuits
• Simple Diode Circuits
– Protective Circuits against– Protective Circuits against
– Overcurrent
– Polarity Reversal
– Currents caused by an inductive kick in a relay circuit
• Zener Circuits
– Overvoltage Protection
– Setting Reference Voltages
39