Diode Circuits and Applications
In this chapter, we will:
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Determine the operation and characteristics of diode
rectifier circuits, which is the first stage of the process of
converting an ac signal into a dc signal in the electronic
power supply.
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Apply the characteristics of the Zener diode to a Zener
diode voltage regulator circuit.
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Apply the nonlinear characteristics of diodes to create
waveshaping circuits known as clippers and clampers.
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Examine the techniques used to analyze circuits that
contain more than one diode.
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Understand the operation and characteristics of specialized
photodiode and light-emitting diode circuits.
Block Diagram for ac to dc Converter
The diode rectifier, filter, and voltage regulator are diode circuits.
Half-Wave Rectifier
Voltage Transfer
Characteristics
Signals of Half Wave Rectifier
Input voltage
Output voltage
Diode voltage
Load Line Analysis
A load line is used in graphical analysis of nonlinear electronic circuits, representing the
constraint other parts of the circuit place on a non-linear device, like a diode or transistor. It
is usually drawn on a graph of the current vs the voltage in the nonlinear device, called the
device's characteristic curve.
Load Line Analysis
Load line when vS is
at its maximum
forward voltage.
Load line when vS is
at its most negative
value.
Load Line (con’t)
As vS varies with time, the load line also changes, which changes the
Q-point (vD and iD) of the diode.
Half-Wave Rectifier as Battery Charger
Full-Wave Rectifier
Voltage transfer characteristics
Input and output waveforms
Full-Wave Bridge Rectifier
When vS is positive, D1 and D2 are turned on (a). When vS is negative,
D3 and D4 are turned on (b).
In either case, current flows through R in the same direction, resulting in
an output voltage, vO, shown in (c).
Full-Wave Bridge Rectifier
Output Voltage of Full-Wave Rectifier
with RC Filter
The ripple on the ‘dc’ output is
VM
1
Vr =
where f =
2 fRC
2TP
Output Voltage of Full-Wave Rectifier with RC
Filter
Dt 1
=
T p
Diode conducts current for only a small portion of the period.
2Vr
VM
Equivalent Circuit During Capacitance
Charging Cycle
i C = -wCVM wt
iC , peak = +wCVM wDt
2Vr
wDt =
VM
PSpice Schematic of Diode Bridge Circuit
Steady state output voltage for a 60Hz
sine wave input with peak value of
13.4V.
Demodulation of Amplitude-Modulated Signal
Modulated input signal
Detector circuit
Demodulated output signal
Voltage Doubler Circuit
Equivalent Circuits for Input Cycles
Negative input cycle
Positive input cycle
Voltage Regulator
VZ
IL =
RL
VPS - VZ
II =
Ri
IZ = II - IL
The characteristics of the Zener diode determines VL.
Voltage Rectifier with nonzero Zener resistance
The Zener diode begins to conduct when VPS = VZ.
When VPS ≥ VZ:
VL = VZ
IL = VZ/RL,, but VZ ≠ constant
I1 = (VPS – VZ)/Ri
IZ = I1 - IL
Voltage Transfer Characteristics of
Limiter Circuit
2 Diode Circuit
Voltage transfer characteristics
Problem-Solving Technique: Multiple Diode
Circuits
1.
Assume the state of the diode.
a.
b.
If assumed on, VD = Vg
If assumed off, ID = 0.
2. Analyze the ‘linear’ circuit with assumed diode
states.
3. Evaluate the resulting state of each diode.
4. If any initial assumptions are proven incorrect,
make new assumption and return to Step 2.
Diode Logic Circuits: 2-Input OR Gate
V1 (V) V 2 (V) VO (V)
Vg = 0.7V
0
0
0
5
0
4.3
0
5
4.3
5
5
4.3
Diode Logic Circuits: 2-Input AND Gate
V
1 V
2 V
O
( V ) ( V ) ( V )
Vg = 0.7V
0
0
0
5
0
0
0
5
0
5
5
4.3
Photodiode Circuit
Optoisolator
Design DC Power Supply Circuit
Diode Clippers
A clipper (or limiter) is a circuit used to eliminate
some portion (or portions) of a waveform.
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A series clipper is in series with its load.
A shunt clipper is in parallel with its load.
Series Clippers
Negative Shunt Clipper Operation
A Positive Shunt Clipper
When the diode is conducting:
VL = VF
When the diode is not conducting:
RL
VL = Vin
RL + RS
Biased Shunt Clippers
Diode Clampers
A clamper (or
dc restorer) sets
(or restores) the
dc reference of a
waveform.
Clamper Operation
Biased clampers
Biased clampers allow a waveform to shifted above
or below a dc reference other than 0 V.
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The dc reference is determined by the biasing voltage (VB)
and the setting of the potentiometer (R1).
Zener clampers
The diodes in (a) are in a common-cathode configuration.
The diodes in (b) are in a common-anode configuration.
Voltage Doublers
n
A voltage doubler provides an output that is twice its
peak input voltage.
Half-Wave Voltage Doubler
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The term “half-wave” reflects the fact that the
output capacitor (C2) is charges during one
alternation of each input cycle and discharges
during the other.
Half-Wave Voltage Doubler Operation
Full-Wave Voltage Doublers
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The term “full-wave” reflects the fact that the
output capacitors are charged during alternate
half-cycles of the input signal.
Voltage Tripler
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A voltage tripler provides a dc output voltage that is
approximately three times the peak input voltage.
Voltage Quadrupler
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A voltage quadrupler provides a dc output voltage
that is approximately four times the peak input
voltage.
A Basic Dual-Polarity Power Supply
The output voltages are approximately equal to
the peak values of the input waveform.
LED Level Indicators
n
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The LED in circuit (a) lights when the driver
output is +5 V.
The LED in circuit (b) lights when the driver
output is 0 V.
Multisegment Display
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Multisegment display – A device used to display
alphanumeric characters (numbers, letters, symbols,
and punctuation marks).
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LED displays contain some number of diodes that are
connected in a common-cathode or a common-anode
configuration.
A liquid crystal display (LCD) consists of segments that
reflect (or do not reflect) ambient light when provided
an active input.
Seven-Segment Displays
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The display uses LEDs that are arranged in a figure 8
configuration.
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The display represented below is a common-cathode display.
Each LED lights when a positive voltage is applied to the
appropriate pin.