Engineering & Technology

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Overview

Almost all electrical products in the home contain electronic circuits and electronic components. A brief overview of some components is shown below:

Component name Basic function Applications
Resistor Restricts the flow of current through electrical and electronic circuits. All electronic circuits.
Restricting current flow.
Capacitor Stores electrical charge. Smoothing the output of rectifiers.
Power factor correction.
Timer and oscillator circuits.
Thermistor A type of resistor whose resistance is dependent upon its temperature. Temperature measurement.
Light dependent resistor (LDR) A type of resistor whose resistance is dependent upon the brightness of the light it is exmposed to. Autotmatic light switches that activate lamps when it gets dark.
Smoke detectors.
Signal diode A device that allows current to flow in one direction only. Used for shaping small electrical signals and low power rectification (converting ac to dc).
Rectifier diode Has the same function as a signal diode but can withstand much higher currents. AC to DC power supplies and battery chargers.
Protecting transistors in relay circuits.
Zener diode A type of diode that will allow current to flow in the opposite direction once a specific voltage has been reached. Regulating voltages in power supplies and battery chargers to specific levels.
Light emiting diode (LED) Emits light when when current flows through it. Like any other diode it conducts in one direction only. Used for indication and graphical displays.
Energy saving lamps.
Car indicators and headlamps.
Photodiode A type of diode that produces a voltage dependent upon the brightness of the light it is exposed to. Television remote controls.
Smoke detectors.
Fibreoptic communications.
Transistor A device that has the ability to amplifiy voltages and currents and control the flow of current. Pretty much any electronic device.
Diac Operates in a similar fashion to a diode but will only conduct once a specific voltage has been reached. Light dimmers.
Motor speed control.
Industrial heating control.
Triac A device that is capable of switching alternating currents. Light dimmers.
Motor speed control.
Industrial heating control.
Resistors

Resistors are manufactured to have specific resistances. They are used extensively in electronics and will be found in most circuits. 

Carbon film and metal film resistors

Film resistors are made by depositing a thin layer of either carbon or aluminium onto a ceramic cylinder. The physical dimension of the layer determines its resistance. They are low power devices commonly having a power rating of typically between 1/8 Watt and 1/2 Watt.
Due to their small size they usually labeled using a colour code.

Wirewound resistors

Wire wound resistors are used in high power circuits. They are much more robust that film resistors and can be manufactured to withstand hundreds of Watts. The resistive element in this type of resistor is a length of nichrome wire, the length and cross-sectional area determining its resistance.

Resistors on a circuit board

SMD resistors are tiny resistors designed to sit on the surface of a circuit board rather than having leads which are pushed through holes. They are positioned by robots and sescured using a process called reflow soldering.

In the image below they are the brown rectangles with silver ends.

Capacitors

Essentially a capacitor is made by sandwiching an insulating material (dielectric) between two metal plates of foil. Their basic function is to store electrical charge and are found in most electronic circuits. 

Electrolytic Capacitors

The image below shows an  electrolytic capacitor. Capacitors are used in 

Wirewound resistors

Wire wound resistors are used in high power circuits. They are much more robust that film resistors and can be manufactured to withstand hundreds of Watts. The resistive element in this type of resistor is a length of nichrome wire, the length and cross-sectional area determining its resistance.

Resistors on a circuit board

SMD resistors are tiny resistors designed to sit on the surface of a circuit board rather than having leads which are pushed through holes. They are positioned by robots and sescured using a process called reflow soldering.

In the image below they are the brown rectangles with silver ends.

Thermistors

A thermistor is a type of resistor whose resitance varies depending on temperature. They are used in thermostats, boilers and heaters to regulate temperature. There are two types:

* The resistance of a negative temperature co-efficient thermistor (NTC) reduces with increasing  temperature.

* The resistance of a positive temperature co-efficient thermistor (PTC) increases with increasing temperature.

Light dependent resistors

A light dependent resistor (also known as an LDR) is a type of resistors whose resistance is dependent on the brightness of light that shines on it.

When it is dark the LDR has a high resistance. With increasing brightness the resistance drops.


LDRs are used in smoke detectors and outside lights that switch on when it becomes dark.