1.
CHAPTER 17
DIODES AND APPLICATIONS

2.
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

3.
Power supply
Figure 17-1

4.
The Half-Wave Rectifier
Figure 17-2 Average Value of
the Half-wave
output voltage
VAVG=Vp (out) / 

5.
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

6.
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 reverse-
biased
Figure 17-7

7.
• 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
FULL-WAVE RECTIFIERS
Figure 17-9
Average Value of the Full-wave rectified output voltage
VAVG= 2Vp (out) / 

8.
Center-Tapped Full-Wave Rectifier
• Using two diode connected to the secondary of a center-
tapped 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

9.
Center-Tapped Full-Wave Rectifier

10.
Effect of the Turn Ratio on Full-
Wave 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

11.
Peak Inverse Voltage (full-wave
rectifier)
(sec)
p
(sec)
p
(sec)
p
)
out
(
p
(sec)
p
(sec)
p
(sec)
p
2
D
V
2
2
V
2
V
V
V
2
V
2
V
V














)
out
(
p
(sec)
p V
2
V
PIV 


12.
Full-Wave Bridge Rectifier

13.
Bridge Output Voltage
)
out
(
p
(sec)
p V
V
PIV 


14.
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”

15.
Ripple Factor (r)
• Ripple factor is the
ratio of the Vr to VDC,
expressed as :
%
100
V
V
r
DC
r


NOTE: the frequency in the full-wave rectifier is
twice of the half-wave rectifier

16.
Ripple Voltages for half-wave and
full-wave

17.
Surge Current in the Capacitor-
Input Filter

18.
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

19.
IC Regulators

20.
Basic regulated power supply

21.
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
∆VOUT
∆VIN
%
100

Line regulation =
VNL- VFL
VFL
%
100

Load regulation =

22.
Diode Limiting and Clamping
Circuits
• Diode Limiters
– Diode limiters (clipper) cut off above or below
specified levels
in
L
S
L
out V
R
R
R
V 










23.
Diode Limiting and Clamping
Circuits
• Diode Limiters
– Adjustment of the limiting level

24.
Diode Clampers
• Diode clamper known as a dc restorer
– Add a dc level to an ac signal

25.
Diode Clampers

26.
ZENER DIODES
• The zener diode is a
silicon pn junction device
and operate in the
reverse breakdown
region
symbol

27.
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

28.
Breakdown Characteristic

29.
Zener Equivalent Circuit

30.
Zener diode impedance
• The ration of ∆Vz to ∆Iz is the zener diode
impedance
• Normally, ZZ is specified at IZT
• ZZ is approximately constant over the full
range of reverse-current values
∆VOUT
∆VIN
Zz =

31.
Zener Voltage Regulation
• Zener diodes can be used for voltage
regulation in noncritical low-current
applications

32.
• As the input voltage varies, the zener
diode hole the constant voltage across the
output terminals
Zener Voltage Regulation

33.
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

34.
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

35.
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
dielectric constant
A
C
d





36.
VARACTOR DIODES

37.
VARACTOR DIODES

38.
VARACTOR DIODE APPLICATIONS
LC
fr

2
1


39.
LEDs and PHOTODIODES
• There are two types of optoelectronic
devices
– The Light Emitting Diode (LED)
– The photodiode (light detector)

40.
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

41.
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

42.
The Light Emitting Diode (LED)
symbol
electroluminescence

43.
The Light Emitting Diode (LED)

44.
The Light Emitting Diode (LED)
Applications

45.
The Photodiode
• The photodiode is a pn junction device
that operates in reverse bias

46.
The Photodiode

47.
The Photodiode operation

48.
The Photodiode Applications

49.
The diode data sheet

50.
TROUBLESHOOTING

51.
Homework
• Basic problems
– 1, 6, 12,16
12
16