MODULE 5

ELECTRONICS

Learning Outcomes:

Outline the behaviour of diode and transistor
Distinguish between half wave and full wave rectifiers
Discuss forward bias and reverse bias
Understand the logic gates and digital electronics

5.1 Diodes

Semiconductor

A semiconductor is a material that has electrical conductivity in between that of a conductor and that of an insulator.

Two practically important semiconductors are germanium (Ge) and silicon (Si).

Intrinsic Semiconductor

A pure semiconductor which is free of impurities and defects is called an intrinsic semiconductor.

At 0 K intrinsic semiconductor behaves as an insulator. At room temperature conduction is possible.

Extrinsic Semiconductor

A semiconductor doped with suitable impurity atoms is called extrinsic semiconductor.

Doping

The process of deliberately introducing a controlled amount of suitable replacement atoms as impurities into the semiconductor is called doping.

n-type Semiconductor

If a small amount of Group V impurity atoms such as arsenic (As) is added to a pure Si or Ge crystal, n-type semiconductor is obtained.

The As atom is known as donor impurity.

In n-type semiconductor, the negative charge carriers (electrons) greatly outnumber the positive charge carriers (holes).

p-type Semiconductor

If Group III impurity atoms such as boron (B) are added to a pure Si or Ge crystal, p-type semiconductor is obtained.

The B atom is known as acceptor impurity.

In n-type semiconductor, the positive charge carriers greatly outnumber the negative charge carriers.

p-n Junction Diode

A p-n junction diode is basically a p-n junction with metallic contacts provided at the ends for the application of an external voltage. It permits the easy flow of electric current in one direction but restrains the flow in the opposite direction.

Forward Bias

If the positive terminal of a battery is connected to the p-side and the negative terminal to the n-side, then the p-n junction is said to be forward biased.

Reverse Bias

If the positive terminal of a battery is connected to the n-side and the negative terminal to the p-side, then the p-n junction is said to be reverse biased.

A diode conducts when forward biased and does not conduct when reverse biased.

Diodes are non-linear devices.

Characteristic Curve

The current-voltage graph for a device is called its I-V characteristics.

When the diode is forward biased, the current first increases very slowly till the voltage across the diode crosses a certain value called the threshold voltage. After this voltage the diode current increases rapidly.

When the diode is reverse biased, a very small current called reverse saturation current Io flows which remains almost constant with change in the reverse bias voltage.

At a very high reverse bias, called the avalanche or breakdown voltage, the current suddenly increases so greatly that a p-n junction diode will be destroyed.

Half wave rectifier

A rectifier that converts ac into dc during the half of the input cycle is called a half wave rectifier.

Half wave rectifier

A rectifier that converts ac into dc during the half of the input cycle is called a half wave rectifier.

Full wave rectifier

A rectifier that converts ac into dc during the whole input circuit is called a full wave rectifier.

A full wave rectifier consists of a centre-tap transformer, two diodes and a load resistor.

A full wave rectifier is more efficient for getting rectified voltage or current than the half wave rectifier.

Light Emitting Diode

A light emitting diode is a heavily doped p-n junction that emits optical radiation (infrared, visible or UV) under forward-biased conditions. The diode is encapsulated in a transparent package so that emitted light can emerge out.

When a p-n junction is forward biased, the majority carriers (holes in p-region and electrons in n-region) are injected across the junction and become minority carriers. Recombination of minority carriers with majority carriers takes place. When the recombination rate is equal to the injection rate, a steady-state carrier distribution is established in the diode.

Each time an electron recombines with a hole, it falls into a lower energy level and the difference in energy is emitted in the form of a photon of light with a frequency characteristic of the semiconductor material.

The wavelength range of visible light is from about 380 nm to 750 nm.

Advantages of LEDs over Incandescent and Fluorescent Devices

Low power requirement
High efficiency
Long useful life
Fast switching time
Fast on-off capability
Ruggedness

5.2 Transistors

A transistor is a three-terminal semiconductor device which works as an amplifier.

Two types of transistor are (i) n-p-n transistor and (ii) p-n-p transistor.

Three portions of a transistor are:

1. Emitter (E). The emitter supplies a large number of majority carriers for current flow through the transistor. It is of moderate size and heavily doped.

2. Base (B). The middle portion which forms two p-n junctions with the emitter and collector is called the base. It is very thin and lightly doped. The base controls the flow of majority carriers from emitter to collector.

3. Collector (C). The portion that collects most of the majority carriers supplied by the emitter is called the collector. It is moderately doped and slightly larger in size compared to the emitter.

In normal operation, the two types of transistors are biased as shown below.

Forward bias of the emitter-base junction forces majority carriers in the emitter to enter the base, resulting in IE .

The thin and lightly doped base allows almost all the injected carriers to diffuse into the collector. A small fraction of this that recombines in the base and a small number of majority carriers crossing into the emitter gives rise to IB .

The remaining emitter injected carriers which have diffused across the base-collector junction are strongly attracted by the reverse bias to yield IC .

The input circuit (emitter-base junction) has low resistance because of forward bias, whereas the output circuit (collector-base junction) has high resistance due to reverse bias.

Sign convention

The three currents IE , IC and IB are taken positive when they flow into the transistor.
The three voltages VBE, VCB and VCE are taken positive if the terminal indicated by the first subscript is positive with respect to the terminal indicated by the second subscript.

5.3 Digital Electronics

A signal (current or voltage) which varies continuously with time is called an analogue signal.

A signal which has only two possible discrete values is called a digital signal. Such signals are conveniently represented by binary numbers which has only two digits 0 (low) or 1 (high).

1. Introduction to Digital Electronics

Digital electronics is a branch of electronics that deals with circuits operating using discrete voltage levels (typically 0 and 1), unlike analog electronics, which use continuous signals. Digital systems form the backbone of modern navigation, communication, and ship automation.

For a Deck Officer Class III, understanding digital electronics is essential because many ship systems, including electronic navigation instruments (ECDIS, GPS, AIS), communication systems, and automated control systems, rely on digital technology.

2. Basic Concepts in Digital Electronics

Digital electronics work on binary numbers (0s and 1s), which represent electrical ON/OFF states. The main elements include:

Bit (Binary Digit) – The smallest unit of digital data (either 0 or 1).
Byte – A group of 8 bits.
Logic Gates – Basic digital circuits that perform logical operations.
Integrated Circuits (ICs) – Electronic chips that contain multiple logic gates or circuits.

4. Logic Gates in Digital Electronics

Logic gates are fundamental building blocks in digital circuits. They process binary inputs (0s and 1s) and generate corresponding outputs.

5.3.1 Logic Gates

Logic gates are digital circuits that follows certain logical relationship between the input and output voltages. The basic logic gates are (i) OR (ii) AND (iii) NOT (iv) NAND and (v) NOR.

A table that shows all possible input combinations and the corresponding outputs for a logic gate is called truth table.

Importance of Logic Gates in Ship Systems

AND, OR, and NOT gates are used in automation and decision-making circuits.
XOR gates are applied in error detection systems in communication equipment like AIS and VHF radio.
NAND and NOR gates form the basis of memory storage in electronic chart display systems.

5. Flip-Flops & Memory in Ship Systems

Flip-flops are circuits used for data storage, signal synchronization, and system control. They are crucial in:
✅ Navigation data logging (storing past positions in GPS).
✅ Radar processing (storing and updating ship movements).
✅ Engine automation (controlling sequential operations in machinery).

Types of Flip-Flops

SR Flip-Flop – Basic storage unit.
D Flip-Flop – Used in counters and registers.
JK Flip-Flop – Advanced control systems.

6. Digital Counters and Timers in Maritime Operations

Counters and timers are used in digital electronic circuits for:
✅ Autopilot systems – Maintaining preset routes.
✅ Engine maintenance schedules – Tracking operating hours.
✅ Alarm systems – Timed alerts for safety warnings (e.g., fire alarms, bilge alarms).

Types of Counters:

Synchronous Counters – Used in GPS data processing.
Asynchronous Counters – Used in automatic power control in ship generators.

7. Digital Communication in Maritime Systems

Digital electronics play a vital role in modern maritime communication systems:

AIS (Automatic Identification System) – Uses digital signal processing (DSP) for ship tracking.
GMDSS (Global Maritime Distress and Safety System) – Uses digital encoding for emergency communications.
ECDIS (Electronic Chart Display & Information System) – Uses digital storage and processing of navigational charts.
Radar Systems – Convert analog radar waves into digital signals for precise imaging.

Importance:
✅ Improves accuracy of ship position tracking.
✅ Enhances safety with real-time alerts.
✅ Reduces errors in distress signaling and navigation.

8. Microcontrollers and Automation in Ships

Microcontrollers are embedded in ship systems for automation and control. They are used in:
✅ Engine Room Monitoring Systems – Automatic temperature and pressure control.
✅ Fire Detection and Suppression Systems – Automated alarms and fire extinguishers.
✅ Autopilot Systems – Computer-controlled course maintenance.

9. Importance of Digital Electronics for Deck Officers

Digital electronics are a key part of modern ships, making it essential for Deck Officers to understand their principles. A Deck Officer Class III should be familiar with:

Digital circuits used in ship automation.
Basic troubleshooting of digital navigation systems.
Understanding data storage in ECDIS and AIS.
How digital counters and timers are used in ship operations.
Digital communication for effective maritime distress signaling.

By mastering digital electronics, a Deck Officer can efficiently operate, maintain, and troubleshoot shipboard electronic systems.

Digital electronics is a critical supporting subject for Deck Officers in Class III certification. From navigation systems like ECDIS and GPS to automated control systems in the engine room, digital circuits and logic play an essential role in modern shipping. Understanding logic gates, memory units, counters, and communication systems helps Deck Officers enhance safety, improve navigation accuracy, and comply with IMO digital standards.

Digital Communication System

Digital Communication is the transfer of data or information using digital technologies and platforms. A basic digital communication system involves the transmission and reception of signal through electronic devices and networks.

Input Transducer

An input transducer is a device that converts the input signal to an electrical signal.

(Example: microphone).

Source Encoder

The source encoder is used to compresses the data into minimum number of bits. This process helps in reducing the bandwidth needed for transmission.

Channel Encoder

The signal may get altered due to noise during the transmission. The channel encoder eliminates the errors and adds some redundant bits to the transmitted data.

Digital Modulator

Digital Modulator convert the signal into a format that can be easily transmitted through the channel or in a medium.

Channel

The channel or a medium helps the signal to transmit from the transmitter end to the receiver end.

Digital Demodulator

Once the signal has reached the receiver end, the received signal is demodulated. The signal gets reconstructed here.

Channel Decoder

the Channel Decoder is used for correction of errors at the receiver end.

The distortions which might occur during the transmission, are corrected by adding some redundant bits.

Source Decoder

The source encoder works oppositely as that of the source encoder. The resultant signal is once again digitized and the pure digital output is obtained without the loss of information. The source decoder recreates the source output.

Output Transducer

The output transducer converts the signal into the original physical form.

Page updated

Google Sites

Report abuse