chapter 4 electronics
TRANSCRIPT
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CHAPTER 4: ELECTRONIC
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Electronic
Understanding the uses of the CRO
Analysing logic gates
Understanding semiconductor diodes
Understanding
transistors
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4.1 Understanding the uses of CRO
• Thermionic emission •Properties of cathode rays•Working principle of CRO
•Wave form using CRO
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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.
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Can you recognize electronic devices in this motherboard???
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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
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Thermionic emission
• Thermionic emission (Pancaran termion) is the emission of electrons (Pemancaran electron) from the hot metal surface in vacumm.
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• 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)
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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 field4. Cause fluorescent material (Bahan
berpendarfluor) to emit light
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Cathode-Ray Oscilloscope (C.R.O)
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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 gun2. The deflection system3. The fluorescent screen
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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)
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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
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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.
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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
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Semiconductor diode consists of p-n junction as shown below
p n+ -
p-n junction
a) Structure
+ - + -
Band
b) Symbol c) Actual diode
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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
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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
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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
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b) Figure shows a capacitor connected across the resistor to smoothen the voltage, VR
+
a.c V
-
VD
R
Smoothing capacitor
VR
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Homework
• Draw full-wave rectification
• Send on Tuesday ( 17/7/2007)
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4.3 Understanding transistors
• Characteristic of transistor’s terminal•Working principle of transistor as a
1. current amplifier2. Automatic switch
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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.
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The first transistor
Modern transistors
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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
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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
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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
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• 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.
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Transistor as a switch
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Transistor as a current amplifier
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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
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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
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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
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Analysing Logic Gates
• LOGIC GATES1. Logic gates are electronic switches
with one or more inputs and one output.
Logic Operation
Input Output
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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 gate4. Logic gates are operate on a binary input. This
means each input or output either 0 or 1.
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TRUTH TABLE (Jadual Kebenaran)
Input OutputA X01
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.
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TYPES of Logic Gates
There are seven types of logic gates:a) NOT gate TAKb) AND gate DANc) OR gate ATAUd) NAND gate TAKDANe) NOR gate TAKATAU
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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.
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NOT logic gate
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AND and NAND
logic gates
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OR and NOR logic
gates
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Get Logik
Types of Gates
Symbol Truth Table
Boolean Algebra
ANDA B X0 0 00 1 01 0 01 1 1
X = A.B
ORA B X0 0 00 1 11 0 11 1 1
X = A+B
NOT A X0 11 0
X = A
A
B
X
A
B
X
A X
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Get Logik
Types of Gates
Symbol Truth Table
Boolean Algebra
NANDA B X0 0 10 1 11 0 11 1 0
X=A . B
NORA B X0 0 10 1 01 0 01 1 0
X=A+B
A
B
X
A X
B
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EXAMPLE
Q
C
D
A
B
A B C D Q0 0 1 1 00 1 1 1 01 0 1 1 01 1 0 0 1
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EXAMPLE
A B C D0 0 0 01 0 0 10 1 0 11 1 1 1
C
D
A
B
Alat pengesan asap
Alat pengesan haba
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Question
• Complete the truth table for the combination of logic gates shown in figure 8.