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.