CHAPTER 4: ELECTRONIC

Electronic

Understanding the uses of the CRO

Analysing logic gates

Understanding semiconductor diodes

Understanding

transistors

4.1 Understanding the uses of CRO

• Thermionic emission

•Properties of cathode rays

•Working principle of CRO

•Wave form using CRO

Introduction to Electronics

• The world is changed by electronics• Our communication is made easy by the

invention of many electronic devices such as computer and radar

• Inside the Motherboard of a computer you can see many electronic components.

• These electronic components help the computer to do a lot of work.

Can you recognize electronic devices in this motherboard???

4.1 Cathode Ray Oscilloscope

• Electrons are attracted to the nucleus of an atom

• There is a strong attractive force between the electrons and the positive charges of the nucleus.

• To move these electrons farther from the atom, energy is needed.

• This can be done by heating a metal using electric current

Thermionic emission

• Thermionic emission (Pancaran termion) is the emission of electrons (Pemancaran electron) from the hot metal surface in vacumm.

• A vacuum diode (Tiub Vakum) consists of a glass bulb containing two electrodes.

• One we called anode and the other is the cathode• The cathode made up of a tungsten filament• The cathode can be heated by a small current connected to the

filament• This filament when heated will release electrons from its surface• These electrons can be attracted to the anode when there is a

high potential difference applied between the anode and the cathode.

• The beam of electrons (Alur elektron) moving from the cathode to the anode is called cathode rays (sinar katod)

• Cathode rays consist of electrons that travel at high speed after being accelerated (menambah kelajuan) through a high potential difference.

Thermionic emission

Refer figure 4.1.1 (Thermionic diode)

Properties of cathode rays

1. Consist of electrons traveling at high speeds in a straight line

2. Are deflected (pemesongan) by a magnetic field

3. Are deflected by an electric field

4. Cause fluorescent material (Bahan berpendarfluor) to emit light

Cathode-Ray Oscilloscope (C.R.O)

Cathode-Ray Oscilloscope (C.R.O)

• The structure of the Cathode-Ray Oscilloscope (C.R.O) can be divided into three main sections:

1. The electron gun

2. The deflection system

3. The fluorescent screen

Uses of theCathode-Ray Oscilloscope (C.R.O)

1. To measure potential difference (menyukat beza keupayaan)

2. To measure short time interval (menyukat sela masa yang singkat)

3. Display waveform (memapar bentuk gelombang)

4.2 Understanding semiconductor

• Describe semiconductor•Differentiate between n-type & p-type of

semiconductor•Working principle & uses of diodes

•Describe the use of capacitor: 1. smoothing out output current2. Smoothing out output voltage

in rectifier

Understanding semiconductor Diodes

• Semiconductors have resistance between that of metals and insulators. Example: carbons and germanium

• In a pure semiconductor, the numbers of negative charge carriers (free electrons) and the positive charge carriers (holes) are the same.

When a semiconductor is doped (added an impurity) it becomes

a) A n-type which has more free electrons than holes. Impurity of valency 5, arsenic or phosphorus, is added

b) A p-type which has more holes than free electrons. Impurity of valency 3, indium or gallium, is added

Semiconductor diode consists of p-n junction as shown below

p n+ -

p-n junction

a) Structure

+ - + -

Band

b) Symbol c) Actual diode

An ideal diode

a) Allows current through when connected in forward bias. Its resistance = 0

+

+

Current

Forward bias (Pincang ke depan)

-

Refer experiment 4.4 in practical book

b) Does not allow current through when connected in reverse bias

Its resistance is infinite.

An ideal diode

+

+

-No Current

Reverse bias (Pincang Songsang)Refer experiment 4.4 in practical book

A diode is used as rectifier to convert a.c to d.c

a) Figure shows half-wave rectification. - Current only flows through the diode during the “+” half cycle.

- The voltage across the resistor, VR is direct voltage

+

a.c V

-

VD

VRR

V

VR

VDHalf-wave rectification

b) Figure shows a capacitor connected across the resistor to smoothen the voltage, VR

+

a.c V

-

VD

R

Smoothing capacitor

VR

Homework

• Draw full-wave rectification

• Send on Tuesday ( 17/7/2007)

4.3 Understanding transistors

• Characteristic of transistor’s terminal

•Working principle of transistor as a

1. current amplifier

2. Automatic switch

TRANSISTORS

• Transistor are solid state semiconductor devices that are used to amplify (mengawal) current and voltage.

• The transistor is the fundamental building block of the circuitry that governs the operation of computers, cellular phones, and all other modern electronics.

• Transistors may be packaged individually or as part of an integrated circuit, which may hold a billion or more transistors in a very small area.

The first transistor

Modern transistors

Types of semiconductor transistors

There are two types of semiconductor transistor

Collector (+)

PengeluarBase

Tapak

Emitter (-)

Pengeluar

N-P-N transistors

The n-p-n transistors has a thin layer of p-type silicon sandwiched between two

layers of n-type silicon

P-N-P transistors

Emitter (+)

Pengeluar

Collector (-)

Pengeluar

Base

Tapak

The p-n-p transistors has a thin layer of n-type silicon sandwiched between two

layers of p-type silicon

Collector, Based , Emitter

• The transistor has three leads (terminal) connected to the emitter, base and collector.

• The emitter emits or sends charge carriers through the thin base layer to be collected by the collector.

• In n-p-n transistor the emitter sends negative electrons to the collector.

• In p-n-p transistor the emitter sends positive holes to the collector

• The output current of a transistor flows between the emitter and the collector.

• The output current only flows when the transistor is “switched on”.

• The current in collector lead is called the collector current.

• The base current is used to control the collector current through the transistor.

• The base current can be used to switch the collector current on or off.

• In this way, the transistor can be used as a switch.• Transistor also can acts as a current amplifier.

Transistor as a switch

Transistor as a current amplifier

QUIZ

6 V4W

X

The figure shows a transistor circuit. Resistor W has a resistance of 4 kΩ. R is a fixed resistor and X is a variable resistor

a) Name the terminals B,C and E

b) What is the function of R?

c) In order to light the bulb, the potential difference across A R must be at least 4 V.

i) How much is the resistance of X when the bulb lights?

ii) What happens to the bulb if X has a resistance of 1 kΩ?

d) What must be done to the circuit so that the bulb is switched off in the bright light and on in the dark?

D

Solutiona) B = base , C = Collector and E = Emitterb) To limit the amount of current flowing into the base

terminal.c) i) Let the resistance of X = a

a / (4 + a) x 6 = 4 6a/ (4+ a) = 4 6 a = 4 (4 + a) 6a = 16 + 4a 2a = 16 a = 8 kΩ ii) The potential difference across AR 1/ (1+4) x 6 V 1.2 V Since the potential difference is 1.2 V, which is less than 4V,

the bulb does not light.

d) X is replaced with a light –dependent resistor (LDR)

Formula:-

V AR = RAR x Total Potential difference

RAR + RDA

4.4 Analysing logic gates

• Differentiate the logic gate baseon truth table & symbols

1. AND2. OR

3. NOT4. NAND5. NOR

• Build up truth table for logic gates ( two inputs)• Application of logic gate as control systems

Analysing Logic Gates

• LOGIC GATES1. Logic gates are electronic switches

with one or more inputs and one output.

Logic Operation

Input Output

Logic Gates

2. Input is data fed into a processor. The processor will process the inputs by using the operators of logic gates. The result of these operations are called the output.

3. The output depends on:-

i) the input

ii) the type of logic gate

4. Logic gates are operate on a binary input. This means each input or output either 0 or 1.

TRUTH TABLE (Jadual Kebenaran)

Input Output

A X

0

1

Input Output

A B X

0 0

0 1

1 0

1 1

The truth table shows the electrical state of the inputs and outputs in each case (remember 0 means low voltage and 1 means a high voltage). In a truth table, all possible inputs are included.

TYPES of Logic Gates

There are seven types of logic gates:

a) NOT gate TAK

b) AND gate DAN

c) OR gate ATAU

d) NAND gate TAKDAN

e) NOR gate TAKATAU

Analysing Logic Gates

• Logic gates are switching circuits in computers and other electronic devices.

• A logic gate has one or more inputs but only one output. The action of a logic gate is summarized by an equation in Boolean algebra or a truth table.

NOT logic gate

AND and NAND

logic gates

OR and NOR logic

gates

Get Logik

Types of Gates

Symbol Truth Table

Boolean Algebra

ANDA B X

0 0 0

0 1 0

1 0 0

1 1 1

X = A.B

ORA B X

0 0 0

0 1 1

1 0 1

1 1 1

X = A+B

NOT A X

0 1

1 0

X = A

A

B

X

A

B

X

A X

Get Logik

Types of Gates

Symbol Truth Table

Boolean Algebra

NANDA B X

0 0 1

0 1 1

1 0 1

1 1 0

X=A . B

NORA B X

0 0 1

0 1 0

1 0 0

1 1 0

X=A+B

A

B

X

A X

B

EXAMPLE

Q

C

D

A

B

A B C D Q

0 0 1 1 0

0 1 1 1 0

1 0 1 1 0

1 1 0 0 1

EXAMPLE

A B C D

0 0 0 0

1 0 0 1

0 1 0 1

1 1 1 1

C

D

A

B

Alat pengesan asap

Alat pengesan haba

Question

• Complete the truth table for the combination of logic gates shown in figure 8.