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CHAPTER 17
DIODES AND APPLICATIONS
HALF-WAVE RECTIFIERS
• The basic DC power supply
– The dc power supply converts the standard
220 V,50 Hz into a constant dc voltage
– They consist of three parts : Rectifier, Filter,
and Regulator
– The dc voltage produced by a power supply is
used to power all types of electronic circuits,
such as television receivers, stereo systems,
VCRs, CD player
Power supply
Figure 17-1
The Half-Wave Rectifier
Figure 17-2
Average Value of
the Half-wave
output voltage
VAVG=Vp (out) / 
Effect of Diode Barrier Potential on
Half-Wave Rectifier Output Voltage
• During the positive half-cycle, the input
voltage must overcome the barrier potential
before the diode becomes forward-biased
Vp (out) =Vp (in) - 0.7 V
Figure 17-5
Peak Inverse Voltage (PIV)
• The maximum value of reverse voltage,
sometimes designated as PIV, occurs at
the peak of each negative alternation of
the input cycle when the diode is reversebiased
Figure 17-7
FULL-WAVE RECTIFIERS
• The full-wave rectifier is the most commonly
used type in dc power supplies
• allowing unidirectional current to the load during
the entire input cycle differ from the half-wave
rectifier that allows only during one-half of the
cycle
Figure 17-9
Average Value of the Full-wave rectified output voltage
VAVG= 2Vp (out) / 
Center-Tapped Full-Wave Rectifier
• Using two diode connected to the secondary of a centertapped transformer
– At the positive half-cycle
• Forward-biases the upper diode D1
• Reverse-biases the upper diode D2
– At the negative half-cycle
• Reverse-biases the upper diode D1
• Forward-biases the upper diode D2
Center-Tapped Full-Wave Rectifier
Effect of the Turn Ratio on FullWave Output Rectifier
• If the turn ratio of the transformer is 1:1,
the output of the rectifier is equal to ½ of
the input voltage Vp
• Owing to the voltage input is
approximately equal to the output voltage,
we must use the step-up transformer
Peak Inverse Voltage (full-wave
rectifier)
VD 2 
Vp (sec)
2
Vp ( out) 
Vp (sec)
2
 Vp (sec) 
  Vp (sec)
  
2 

Vp (sec)
2
 2Vp (sec)
PIV  Vp (sec)  2Vp ( out)
Full-Wave Bridge Rectifier
Bridge Output Voltage
PIV  Vp (sec)  Vp ( out)
POWER SUPPLY FILTER AND
REGULATORS
• After passed the rectifier, the output of the
power supply is filtered for reduce the
ripple, on the other hand, for make an
output smoothly
– Capacitor-Input filter
– Ripple Voltage
• The voltage which change due to charging and
discharge of the capacitor is called “ripple voltage”
Ripple Factor (r)
• Ripple factor is the
ratio of the Vr to VDC,
expressed as :
Vr
r
 100%
VDC
NOTE: the frequency in the full-wave rectifier is
twice of the half-wave rectifier
Ripple Voltages for half-wave and
full-wave
Surge Current in the CapacitorInput Filter
IC Regulators
• An integrated circuit regulator is a device that is
connected to the output of a filtered rectifier and
maintains a constant output voltage
• The capacitor-input filter reduces the input ripple
to the regulator to an acceptable level and it is
combined in IC regulator.
• The most IC regulators have three terminal
– Input terminal
– Output terminal
– Reference terminal
IC Regulators
Basic regulated power supply
Percent Regulation
• Line regulation
– Specifies how much change occurs in the
output voltage for a given change in the input
voltage
Line regulation =
• Load regulation
∆VOUT
∆VIN
100%
– Specifies how much change occurs in the
output voltage over a certain range of load
current value
VNL- VFL
Load regulation =
VFL 100%
Diode Limiting and Clamping
Circuits
• Diode Limiters
– Diode limiters (clipper) cut off above or below
specified levels
Vout
 RL 
Vin
 
 RS  RL 
Diode Limiting and Clamping
Circuits
• Diode Limiters
– Adjustment of the limiting level
Diode Clampers
• Diode clamper known as a dc restorer
– Add a dc level to an ac signal
Diode Clampers
ZENER DIODES
• The zener diode is a
silicon pn junction device
and operate in the
reverse breakdown
region
symbol
Zener Breakdown (Vz)
• Two types of reverse breakdown in a
zener diode
– Avalanche
• also occures in the rectifier diode
– Zener
• Occurs in a zener diode at low reverse voltages
NOTE : Zeners with breakdown voltage of 1.8 to
200 V are commercially available
Breakdown Characteristic
Zener Equivalent Circuit
Zener diode impedance
• The ration of ∆Vz to ∆Iz is the zener diode
impedance
Zz =
∆VOUT
∆VIN
• Normally, ZZ is specified at IZT
• ZZ is approximately constant over the full
range of reverse-current values
Zener Voltage Regulation
• Zener diodes can be used for voltage
regulation in noncritical low-current
applications
Zener Voltage Regulation
• As the input voltage varies, the zener
diode hole the constant voltage across the
output terminals
Zener Regulation with a Varying
Load
• The zener diode maintains a constant
voltage across RL as long as the zener
current is greater than IZK and less than
IZM, this process is called load regulation
Percent Regulation
• Line regulation
– Specifies how much change occurs in the
output voltage for a given change in the input
voltage
• Load regulation
– Specifies how much change occurs in the
output voltage over a certain range of load
current value
VARACTOR DIODES
• A varactor is basically a reverse-biased pn
junction that utilizes the inherent
capacitance of the depletion region
• The depletion region acts as a capacitor
dielectric
A
C
d
  dielectric constant
VARACTOR DIODES
VARACTOR DIODES
VARACTOR DIODE APPLICATIONS
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1
2 LC
LEDs and PHOTODIODES
• There are two types of optoelectronic
devices
– The Light Emitting Diode (LED)
– The photodiode (light detector)
The Light Emitting Diode (LED)
• When the device is forward-biased,
electrons across the pn junction from the
n-type material and recombine with the
holes in the p-type material
• When recombination takes place, the
recombining electrons release energy in
the form of heat and light
The Light Emitting Diode (LED)
• The semiconductive materials used in LEDs are
gallium arsenide(GaAs), galium arsenide
phosphide (GaAsP), and Gallium phosphide
(GaP)
• Silicon and Germanium are not used because
they are very poor at producing light
• GaAs LEDs emit infrared (IR) radiation
• GaAsP produces either red or yellow visible light
• GaP emits red or green visible light
The Light Emitting Diode (LED)
electroluminescence
symbol
The Light Emitting Diode (LED)
The Light Emitting Diode (LED)
Applications
The Photodiode
• The photodiode is a pn junction device
that operates in reverse bias
The Photodiode
The Photodiode operation
The Photodiode Applications
The diode data sheet
TROUBLESHOOTING
Homework
• Basic problems
– 1, 6, 12,16
12
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