In the actual world, diodes cannot attain zero or infinite resistance. However, a diode will have very low resistance in one direction and very high resistance in the other direction to prevent the current flow. The most common type of diode is a semiconductor diode. Only when a specified threshold voltage is present in the forward direction do these diodes, they begin to conduct electricity. When current flows in this direction, the diodes are said to be forward biased. The diode is considered to be reverse biased when it is linked in the opposite direction within a circuit. Here we will discuss working, types, applications and symbol of diode.
What is diode?
A diode is a simplest form of semiconductor diodes that functions as a current one-way switch. It permits current to flow freely in one direction while drastically restricting current flow in the other. Because they convert alternating current (ac) to pulsing direct current (dc), diodes are also known as rectifiers (dc).
A diode is an electrical component with two terminals that conducts electricity mostly in one direction. As the name indicates; di-ode; two terminals. Diodes are used to limit the voltage in circuits as well as to convert AC to DC. To get the most out of diodes, semiconductors like silicon and germanium are used. Despite the fact that they both transfer electricity in the same direction, the manner in which they do so, differs. Diodes come in a variety of shapes and sizes, each with its own set of applications.
Anode and cathode establish the polarity of a diode. When positive voltage is given to the anode, most diodes enable current to flow. When a current travels through a light-emitting diode, its p-n junction emits light. A rectifier can be made by connecting many p-n junction diodes in series. Zener diodes have a well-defined breakdown voltage below which current flows in the opposite direction and a steady voltage can be maintained despite voltage or current changes. Varactor diodes change their capacitance when the bias voltage changes; these diodes have a wide range of applications in signal transmission and are widely employed in the radio and television industries.
Silicon and germanium are the two semiconductor materials that can be used to make diodes. The diode is considered to be forward-biased when the anode voltage is greater than the cathode voltage, and it conducts readily with a minimal voltage drop. The diode is considered to be reverse-biased when the cathode voltage is higher than the anode voltage. When a diode conducts, the arrow in the symbol depicts the direction of conventional current flow.
Symbol of diode
The arrow in the symbol of the diode points in the opposite direction to the electron flow. The symbol shows that current is flowing from the positive to the negative side of the voltage source. Thus, the arrow shows the direction of conventional current, against the direction of electron flow. The symbol of diode is shown
The sign for a typical diode can be seen. There are two terminals known as anode and cathode. The anode symbolizes the conventional current flow in the forward biased situation. The arrowhead is the anode and the cathode is on the other end.
Types of diode
Here are some common types of diodes.
- Light Emitting Diode: Also known as LED. When current passes through the electrodes, light is produced by it. It works in forward bias region. LEDs are available in variety of colors even there are tricolor LED (which can emit 3 different colors at same time). The emitted light color is dependent on the band gap of the semiconductor material.
- Laser diode: A type of diode which gives coherent light as output. They have short lifetime but have many applications in CD drives and DVDs.
- Tunnel diode: Due to the quantum mechanical process known as tunneling, a tunnel diode exhibits practically negative resistance.
- Avalanche diode: It is very sensitive diode that operates in reverse bias region under avalanche effect. They are used in photo-detection.
- Zener diode: A diode that works in reverse bias region and provides stable reference voltage. It is used in power supplies to get reference voltage.
- Varactor diode: A Varactor Diode is a p-n junction diode that behaves as a variable capacitor when the reverse bias voltage across its terminals is varied. It is also known as a Varactor Diode since it is a diode that can function as a variable capacitor.
- Schottky diode: Main purpose of this diode is rectification. It has low forward voltage than ordinary diodes.
- Photodiode: A diode that outputs current when light is incident on it. It operates in reverse bias region and are used in solar cells and light detection instruments. Symbol of Diode is shown below:
What is PN junction diode?
PN junction diodes or rectifiers are the diodes that are used to rectify an AC signal. They are made up of 2 types of semiconductor materials; p-type and N-type. Combination of two such semiconductor layers form PN junction. They only allow the current in forward direction.
Characteristics of diode
Forward voltage VF and forward current IF, as well as reverse voltage and current VR and IR, are the basic characteristics of diodes.
Biasing of diode
A forward-biased diode allows electricity to pass through it. When a diode is reverse-biased, it functions as an insulator, preventing current from flowing through it. The characteristics of diode are given below:
- Forward biasing: A biasing in which P-type side is connected to positive terminal and N-type is connected to negative terminal of battery. The voltage drop in this biasing, across the diode is very small. It behaves as short circuit when forward biased.
- Reverse biasing: It means the biasing in which the voltage is completely dropped across diode. The polarity of battery is reversed i.e. negative terminal with p-type and positive terminal with N-type. It behaves as open circuit when reverse biased.
- Zero biased diode: A condition when potential across diode is zero.
What is reverse breakdown voltage?
When a diode is reverse biased and the reverse voltage is within a certain range, it simply blocks current. The reverse barrier is broken if that range is exceeded. The reverse breakdown voltage is the voltage at which this breakdown occurs. The diode can conduct in the opposite way if the circuit voltage is higher than the reverse breakdown voltage. This is why, in practice, diodes have a high reverse resistance rather than an infinite resistance.
Working of diode
The interaction between n-type and p-type semiconductors is essential to the operation of a diode. There are a lot of free electrons in an n-type semiconductor. In other words, in an n-type semiconductor, the concentration of free electrons is large while the concentration of holes is quite low. The majority charge carriers in an n-type semiconductor are free electrons, and the minority charge carriers are holes in an n-type semiconductor.
A p-type semiconductor contains a large number of holes and a small number of free electrons. In a p-type semiconductor, holes are the majority charge carriers, whereas free electrons are the minority charge carriers. When the two junctions come into contact with each other, carriers spread from one side to the other. Because the p-type region has a high concentration of holes and the n-type region has a low concentration, the holes start diffusing from the p-type region to the n-type region. Similarly, free electrons from the n-type zone will drift towards the p-type zone, where they will recombine with holes to form uncovered negative ions. Along the junction line, there will be a layer of negative ions on the p-type side and a layer of positive ions on the n-type side. Because all of the charge carriers are recombined in this region, the layers of uncovered positive ions and uncovered negative ions generate an area in the center of the diode where no charge carrier resides. This portion is called depletion region.
There is no more charge carrier diffusion from one side to the other in the diode after the formation of the depletion region. It is because the electric field has formed across the depletion region that will prevent charge carriers from migrating from one side to the other. When diode is forward biased then depletion region width decreases and current increases due to the flow of charges. In this situation, diode is said to be short circuit diode. When reverse voltage is applied across diode then the width of depletion region increases thus preventing the electron flow. So in reverse mode, current decreases and it is said to be open circuit diode.
Diode works on AC or DC?
Diodes conduct only when they are forward biased. Since, AC reverses it direction periodically, a diode can conduct only in half cycles and insulates during the negative cycles. This property of a diode is used in rectification of AC into DC.
Application of diode
Diodes are being used in variety of fields, some of which are discussed here. Diodes can be used as rectifiers. They are also utilized in logic gates, voltage multipliers, clamping and clipping circuits etc.