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|17.2||Electronic Components and Switching|
In these revision notes for Electronic Components and Switching, we cover the following key points:
An electronic component is a basic element that contributes for the development of an idea into a circuit for execution. Each component has a few basic properties and it behaves accordingly. Some electronic components that are used in different electronic circuits include resistors, capacitors, diodes, LEDs, transistors, integrated circuits and relays.
The components in an electric circuit are classified into two categories: input and output components (devices). Some examples of input components include: pressure switches, reed switch, variable resistors or rheostats, thermistor, LDR (light-dependent resistor), microphone, etc. As for the output components, we can mention: LED (light emitting diode), bulb, buzzer, loudspeaker, relay, electric heater, electric bell, electric motor, etc.
The input devices are also known as transducers, i.e. devices that convert electric signals into other forms or vice-versa.
Electronic devices such as diodes and transistors are made from special materials called semiconductors. A semiconductor is a solid substance that has a conductivity between that of an insulator and that of most metals, either due to the addition of an impurity or because of temperature effects. Silicon (Si) and Germanium (Ge) [mainly Silicon] are the two most notorious examples of semiconductors used in electronics. Devices made of semiconductors, are essential components of most electronic circuits.
There are two types of impurities added to a semiconductor: donors and acceptors. The difference between donor and acceptor impurities is that a donor impurity donates charges to the semiconductor while an acceptor impurity accepts the charges from the semiconductor material. The process of adding impurities to a semiconductor to increase its electricity conducting ability is known as "doping".
Semiconductors come in two primary types: intrinsic and extrinsic. Intrinsic semiconductors are semiconductors that are pure, i.e. they don't contain any doping agents added, whereas the extrinsic semiconductors do.
Extrinsic semiconductors are divided into two types: P-Type and N-Type. The P-Type semiconductors carry a positive charge, while the N-type ones carry a negative charge.
Some of the advantages of semiconductors in electric circuit when compared to conductors include:
Diode is an electronic device used to change the current from AC to DC. This process is known as rectification. A diode lets the current flow in the forwards direction but blocks the backward one.
Potential divider is an arrangement used to deliver only a portion of the input potential difference produced by the source.
Reed switch is a type of switch controlled through a magnetic field.
Transistor is a semiconductor device with three connections, capable of amplification in addition to rectification. There are essentially two basic types of point-contact transistors, the N-P-N transistor and the P-N-P transistor, where the N and N stand for negative and positive, respectively. The only difference between the two is the arrangement of bias voltages.
Another way of switching a small lamp or a LED besides the traditional switching is by using a transistor. This method is called electronic switching. There are two main methods of electronic switching:
This is a kind of switch that is controlled through the light intensity. A light sensitive resistor (LDR) is connected in the section of circuit's potential divider. The resistance of this LDR decreases when light falls on it. As a result, the current or voltage can be controlled by changing the resistance in the circuit.
The same effect is obtained by constructing a circuit containing a thermistor, which is a special type of resistor sensitive to temperature, i.e. a resistor whose resistance falls when the temperature rises. Again, the current or voltage can be controlled by changing the resistance in the circuit.
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