DIODES AND APPLICATIONS

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DIODES AND APPLICATIONS
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
Average Value of the Half-wave output voltage VAVG=Vp (out) /  Figure 17-2

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) 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

Average Value of the Full-wave rectified output voltage
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)

Full-Wave Bridge Rectifier

Bridge Output Voltage

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 : 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 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 Load regulation ∆VOUT
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 Line regulation = ∆VIN VNL- VFL Load regulation = VFL

Diode Limiting and Clamping Circuits
Diode Limiters Diode limiters (clipper) cut off above or below specified levels

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 Normally, ZZ is specified at IZT ZZ is approximately constant over the full range of reverse-current values ∆VOUT Zz = ∆VIN

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 Load 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

VARACTOR DIODES

VARACTOR DIODES

VARACTOR DIODE APPLICATIONS

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)
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

Homework Basic problems 1, 6, 12,16 12 16