According to Christensson (2016, par 1), a diode is an electrical component that is designed for unidirectional conduction of electric current. A diode has two terminals with each end having an electrode that bears a different charge. One side of the terminal referred to as, an anode, has a positive charge while the other end, the cathode, is negatively charged. The electrical current naturally flows from the positive anode terminal to the negative cathode terminal. The figure below represents a unidirectional diode (Christensson, 2018)
The diodes serve as switches since they prevent or allow current flow. For example, the current flowing through a conductor can be stopped by doing a reversal of the diode in action inside the circuit. When the same diode is flipped back to its previous position it will allow the current flow through the same circuit. In other circumstances and appliances, multiple diodes are used as logic gates to perform OR and AND functions.
While conventionally the current is unidirectional in diodes, in some specific cases the current flow can be reversed. If the applied negative voltage on a diode far exceeds its break down voltage, the current will start to flow in its opposite direction. The breakdown voltage of any diode falls within the range of -50 to -100 volts although the range can be higher or less depending on the materials and the design of the diodes (Christensson 2016, par 3). However, some diodes can be damaged by the application of the reverse current flow, while other diodes are made in such a way that current can flow in bi-directionally. For example, Zener diodes are made with a particular break down voltages for diverse industry applications.
The light emitting diode (LED) is another common diode type. They generate visible light when current is allowed between the cathode and anode through the p-n junction (Britannica 2018, par 3). The current electrical charge produces light that comes in different colors depending on the materials and charge applied in the diode design.
Zener Diode
According to Oskay (2012), Zener diode is a special electrical device that operates in the region of Zener breakdown. This diode type acts like the normal p-n junction diodes operating under forwarding biased condition. When the Zener diode receives forward biased voltage, it allows large electric current amounts and then only block a small current flow. The Zener diode is doped heavily than the other normal p-n junction diodes and it is for this reason that it has a thin depletion region. Therefore, the Zener diodes permit more current flow than the normal diodes with p-n junction characteristics.
The Zener diodes permit current flow in the forward direction like normal diodes do, but also they allow current flow in the other reverse directions if the reverse voltage value is greater than the reading of Zener voltage itself. The Zener diode is conventionally connected in the reverse direction since its design is for it to work and operate in a reverse mode.
There are two type of reverse breakdown Zener diode regions. The Avalanche break occurs in both Zener and normal diodes at reverse voltages. The p-n junction diode is applied with high reverse voltage causing the free election, representing the minority carries, gain energy and then accelerate at high velocities.
The high-speed free electrons collide with atoms and this knocks of many more electrons. The electrons accelerate and then collide with other atoms. As a result of the high-velocity collision, an avalanche of free electrons are made. This results in rapid increase in the electric current flowing through the diodes. The increased current cannot destroy the avalanche diodes because they are made to operate in the region of avalanche breakdown.
On the other hand, Zener breakdown happens in a doped p-n junction as a result of the narrow and small depletion region. When the diode is increasingly applied with a biased voltage, the narrow depletion region produces an electric field.
Transistors
According to Chandler (2018, par 2), transistor devices control electrons movement and consequently electric current flow. The transistor is like a switch as it can either turn a current on and off. There are diverse types of transistors with the bipolar junction transistor being the most common type. The figure below shows an example of a bipolar transistor.
The bipolar junction transistor has three pins, the Base, Collector, and Emitter. The figure below shows the symbol of the diode.
The transistor has a semiconducting material. The electric current flows from the base to the other side, emitter and this then opens the flow of the electric current from collector to the emitter. In a standard NPN transistor, a voltage of about 0.7V is needed between the emitter and the base for there to be a current flow between the emitter and the base (Dahl 2014, par 4). In case a 0.7V is applied from the base to the emitter, the transistor will turn on and then there will be electric current flow from the collector side to the emitter.
In the figure above, a 9V battery is connected to a resistor and an LED. However, the connection is done through the transistor. This implies that there will be no flow of current in the circuit up to the time the transistor will turn on. In order for the transistor to turn on, one needs to apply 0.7V from the side of the emitter to the transistor. In this scenario, when the 0.7V is applied, there is electric current flow registered from the collector to the emitter. The current flow then turns on the light emitting diode on.
Amplifier
According to Britannica (2018), an amplifier is a circuit that increases its input signal. However, all amplifiers are not same as they are classified in accordance with their operations methods and configurations. In most of the electronics, small amplifiers are used in many devices since they possess the ability to amplify small input signals.
There are other classifications of amplifiers. These include operational amplifiers, small signal, power amplifier and large signals. The classification itself depends on the size of the signal whether small or large, input processing, physical configuration and the relationship between electric current flow and the signal input. An ideal signal amplifier has certain characteristics. These include input resistance, output resistance, and the gain. The figure below shows an ideal amplifier (Harris 2018, par 5).
The amplified difference between output and input signal represents the Gain of the amplifier. The Gain is the measure of the extent to which the amplifier ‘amplifies’ the signal. For example, if the input signal registered 1V with an output generation of 50V, the gain for this amplifier would be ‘50’. The gain is a simple ratio of the output by the input. It does not have units and commonly represented by the symbol, ‘A’.
References
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Chandler, N., 2018. How Transistors Work. [Online]
Available at: https://electronics.howstuffworks.com/transistor1.htm
[Accessed 14 March 2018].
Christensson, Per. "Diode Definition." TechTerms. (March 15, 2016). Accessed Mar 13, 2018. https://techterms.com/definition/diode.
Dahl, Ø. N., n.d. How Transistors Work – A Simple Explanation. [Online]
Available at: https://www.build-electronic-circuits.com/how-transistors-work/
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Oskay, W., n.d. Basics: Introduction to Zener Diodes. [Online]
Available at: https://www.evilmadscientist.com/2012/basics-introduction-to-zener-diodes/
[Accessed 12 January 2012].
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Available at: https://electronics.howstuffworks.com/amplifier.htm
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