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Diode
Introduction
Invented in 1904 by John Ambrose Fleming. Was constructed with 2 electrodes in the form of
a vacuum tube. In 1906, Lee Dee Forest added a 3rd electrode
called a control grid and the triode, which is used as amplifier, switch..
The application of triode created a new era in broadcasting with the invention of the crystal radio sensor by Pickard, 1912.
Commonly used in DC power supply units as a rectifiers and voltage regulators, clipper, clamper circuit.
Comes in different shape and sizes
8.2 The construction and symbol of diode
The construction and symbol of diode
Made from a combination of 2 extrinsic semiconductors, P-type ad
N-type material.
The joint between the P-type and N-type material is called PN
junction.
Have 2 terminal( anode and cathode).
Produced from the silicon wafer
DEPLETION REGION AND
JUNCTION VOLTAGE
Near the PN junction the electrons diffuse into the vacant holes in the P material causing a depletion zone. This depletion zone acts like an insulator preventing other free electrons in the N-type silicon and holes in the P-type
silicon from combining.In addition this leaves a small electrical imbalance inside the crystal. Since
the N region is missing some electrons it has obtained a positive charge. And the extra electrons that filled the holes in the P region, have given it a negative charge. Unfortunately one cannot generate power from this
electrical imbalance. However the stage is set to see how the PN junction functions as a diode.
Depletion region and Junction Voltage
.
At the p-n junction, electrons from the n-type semiconductor will be attracted to the holes in the p-type semiconductor.
As a result, the holes and the electrons at the p-n junction disappear, forming a layer called “depletion layer”.
At the same time, the p-type semiconductor becomes more negative whereas the n-type semiconductor becomes more positive.
This will result a potential difference across the p-n junction. This potential difference is called the junction voltage (or the barrier voltage).
The junction voltage will prevent the charge carrier from flowing across the depletion layer.
REVERSE BIAS &
FORWARD BIAS
8.3 : The diode Operation (Reverse Bias & Forward Bias)
Reverse Bias & Forward Bias
The polarity of applied voltage which causes charge to flow through the diode is called Forward Bias. (all current, almost no volts)
The polarity of applied voltage which can't produce any current is called Reverse Bias.(all volts, almost no current)
I-V Characteristic Curve
8.4 I-V Characteristic Curve
Forward region: It is the operation region at which the potential applied to anode is more positive than that applied to the cathode.
Reverse Region: It is the operation region at which anode potential is more negative than cathode potential.
Saturation Region: Part of the reverse region where the diode impedance is very high, and causes very small drift current.
Break Down Region: The part of the reverse region where the diode impedance is very low, and the current passing through the diode is very high.
Threshold Voltage VT: It is also called the knee region. It can be determined on the I-V curve by the point at which diode starts to conduct current easily. It is also called the diode
barrier potential and is very near in amplitude to the diode build-in voltage.
Saturation Current: it is a very small current due to drift current in the diode in the reverse bias region. This current is very low (in the nano-amperes range) due to the high impedance of the depletion region.
Break Down Voltage: It is the maximum allowable voltage in the reverse bias region, at which diode resistance changed abruptly from very high impedance to very low impedance. If the reverse voltage applied on the diode exceeds this limit, a very high current in the reverse direction passes through the diode causing in burning it.
DIODES APPLICATION
Power diode
Rectifying power supply circuit (Rectifier = penerus)
Signal diode
• signal sensor in radar
Zener diode
• Voltage regulator in power supply circuit.• Voltage clipper in power supply circuit
LED
Indicator light in electronic circuit
Tunnel diode
• Oscillator circuit in an oscilloscope
Varactor diode
• Variable capacitor in a tune circuit
Photo diode
• Light sensor in a remote control unit
LASER diode
• Focused single colour light source in compact disc player
DIODE APPLICATION
i. DC Power Supply
ii. Rectifier
iii. Filter
iv. Voltage regulator
DC POWER SUPPLY
Contoh bekalan kuasa sebuah CPU
Contoh bekalan kuasa
DC POWER SUPPLY CIRCUIT
Waveform
RECTIFIER
RECTIFIER
2 types of rectifier
Half wave rectifier Full wave rectifier
Two diode
full wave rectifier
Bridge diode
full wave rectifier
HALF WAVE RECTIFIER
Half wave rectifier
Half wave rectifier
Half wave rectifier
Half wave rectifier
Full wave rectifier
Can produce ripple voltage during both
positive and negative input cycle.
There are 2 types of full wave rectifier:
I. Two diodes full wave rectifier
II. Bridge rectifier
TWO DIODES FULL WAVE RECTIFIER
Two diode full wave rectifier
Two diodes Full wave rectifier
Two diodes full waves rectifier
Two diode full waves rectifier
Two diodes full waves rectifier
Two diodes full waves rectifier
Two diodes full waves rectifier
FULL WAVE BRIDGE RECTIFIER
FILTER
Circuit that converts the pulsating AC
voltage to a DC voltage.
The main function of filter is to reduce the
ripple in the input waveform.
Capacitor filter is very popular because of
its low cost, small size, light weight and
good characteristics
Filter
Filter
Contoh
Types of filter
▪RC Filter
LC (T) Filter
LC (𝝿) Filter RLC Filter
VOLTAGE
REGULATOR
Function
Stabilize the output voltage.
Reduce the ripple at the output voltage of the filter circuit.
Zener Voltage regulator
IC VOLTAGE
REGULATOR
Commonly use 78xx series.
Provides a constant positive
output voltage.
The two final xx digits
designate the value of the
output voltage.