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CHAPTER 17
DIODES AND APPLICATIONS
Typical Diode package
Diode symbol
Diode Approximations

The ideal diode model
การป้ อนไฟให้ Diode

Forward bias:
ให้ ศักย์ ไฟฟ้ าด้ าน Anode ( P ) สูงกว่ า Cathode ( N )
 VF > VB (VB (Si ) = 0.7 V;
VB (Ge ) = 0.3 V )
 ป้ อนไฟให้ กระแสไหลในทิศตามลูกศร ของสัญลักษณ์ ไดโอด
 Diode จะทาตัวเหมือน switch ปิ ด ยอมให้ กระแสผ่ านได้

Diode Approximations

The complex diode model
DIODE CHARACTERISTICS

Diode Characteristic
Curve

Reverse bias


As the voltage (VR)
increases to the
left, the current
remains near zero
until the
breakdown voltage
(VBR) is reached
When breakdown
occurs, there is a
large reverse
current that can
destroy the diode
การป้ อนไฟให้ Diode

Reverse bias:
ให้ ศักย์ ไฟฟ้ าด้ าน Anode ( P ) ต่ากว่ า Kathode ( N )
 ป้ อนไฟให้ กระแสไหลในทิศย้ อนลูกศร ของสัญลักษณ์ ไดโอด
 Diode จะทาตัวเหมือน switch เปิ ด ทาให้ กระแสผ่ านไม่ ได้

Breakdown Voltage (VBR)

Reverse bias สูงมาก จนกระทั่ง


Depletion region ขยายจนเต็มพืน้ ที่ N และ P
Avalanche Effect



Free e- ฝั่ ง P มีพลังงานสูงมากจนกระทั่ง ชน valence e- ใน P กลายเป็ น Free eทาให้ จานวน Free e- เกิดเป็ นจานวนเท่ าทวีคูณ ( rapid multiplication )
ทาให้ เกิด Free e- ในฝั่ ง P จานวนมาก ไหลผ่ านรอยต่ อได้

กลายเป็ นกระแสไหลในทิศย้ อนกลับ
Diode Testing

Working diode

Forward bias:


Voltmeter:
2.5 – 3.5 v
(internal meter voltage)
Open diode


0.7 v
Reverse bias:


Voltmeter:
Forward & Reverse bias

Voltmeter:
2.5-3.5 v

Ohm meter:
High resistance
Shorted diode

Forward & Reverse bias


Voltmenter:
Ohm meter:
0v
Low resistance
การใช้ งาน diode


กาหนดทิศการไหลของกระแสในวงจร
ตัวอย่ างวงจรที่ใช้ งาน diode

วงจร rectifier ใน DC Power Supply

กระแสสลับ (AC) 2 ขัว้ (+/-) ให้ เป็ น กระแสตรง ( DC) (ขัว้ เดียว)
วงจร Diode Limiter (จากัดความต่ างศักย์ ของสัญญาณ AC)
 วงจร Diode Clamper (ยกระดับความต่ างศักย์ ของสัญญาณ AC)

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 reverse-biased
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 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
Center-Tapped Full-Wave Rectifier
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
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 Voltages for half-wave and
full-wave
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
Surge Current in the Capacitor-Input
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 =

∆VOUT
∆VIN
100%
Load regulation

Specifies how much change occurs in the output
voltage over a certain range of load current value
VNL- VFL
Load regulation =
100%
VFL
Diode Limiter

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
ชนิ ดของ Diode
Regular diode
 Zener diode
 Varactor diode
 Light-Emitting diode (LED)
 Photo diode

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 diode

Avalanche


also occurs in the rectifier diode (regular 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
Regulator: ตัวคงค่าควา
I ZK  I zener  I ZM
Zener Equivalent Circuit
Regulator: ตัวคงค่าความต่างศ ักย ์
Zener diode impedance

The ratio of ∆Vz to ∆Iz is the zener
diode impedance
Zz =
∆VZ
∆IZ


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
I ZK  I zener  I ZM
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
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
VARACTOR DIODES
A
C
d
VARACTOR DIODES
VARACTOR DIODE APPLICATIONS
fr 
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 ntype 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)
symbol
electroluminescence
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