Industrial Automation component (diode)

1. What is diode?

A diode is a specialized electronic component with two electrodes called the anode and the cathode. Most diodes are made with semiconductor materials such as silicon, germanium, or selenium. 

2. Type of diode?
There are several types of diodes are available for use in electronics design,

Backward Diode

2.1This type of diode is also called the back diode, and it is not widely used. The backward diode is a PN-junction diode that is similar to the tunnel diode in its process. It finds a few special applications where its specific properties can be used.

2.2BARITT Diode

The short term of this diode Barrier Injection Transit Time diode is BARITT diode. It is applicable in microwave applications and allows many comparisons to the more widely used IMPATT diode

2.3Laser Diode

The laser diode is not the similar as the ordinary LED (light emitting diode) because it generates coherent light. These diodes are extensively used in many applications like DVDs, CD drives and laser light pointers for PPTs. Although these diodes are inexpensive than other types of laser generator, they are much more expensive than LEDs. They also have a partial life

2.4Light Emitting Diode

The term LED stands for light emitting diode, is one of the most standard types of the diode. When the diode is connected in forwarding bias, then the current flows through the junction and generates the light. There are also many new LED developments are changing they are LEDs and OLEDs

2.5Photodiode

The photodiode is used to detect light. It is found that when light strikes a PN-junction it can create electrons and holes. Typically, photodiodes operate under reverse bias condition where even a small amount of flow of current resulting from the light can be simply noticed. These diodes can also be used to produce electricity

2.6Schottky Diode

The Schottky diode has a lower forward voltage drop than ordinary Si PN-junction diodes. At low currents, the voltage drop may be between 0.15 & 0.4 volts as opposed to 0.6 volts for a Si diode. To attain this performance they are designed in a different way to compare with normal diodes having a metal to semiconductor contact. These diodes are extensively used in rectifier application, clamping diodes, and also in RF applications

2.7Zener Diode

The Zener diode is used to provide a stable reference voltage. As a result, it is used in vast amounts. It works under reverse bias condition and found that when a particular voltage is reached it breaks down. If the flow of current is limited by a resistor, it activates a stable voltage to be generated. This type of diode is widely used to offer a reference voltage power  supplies

3. Diode test and identify?

Test a Diode using a Digital Multimeter

Meter with a “Diode check” function displays the forward voltage drop of 0.548 volts instead of a low resistance.

Ohmmeter Mode Testing Procedure

4. Application of diode?

Radio demodulation :

The first use for the diode was the demodulation of amplitude modulated (AM) radio broadcasts. The history of this discovery is treated in depth in the radio article. In summary, an AM signal consists of alternating positive and negative peaks of voltage, whose amplitude or “envelope” is proportional to the original audio signal, but whose average value is zero. The diode (originally a crystal diode) rectifies the AM signal, leaving a signal whose average amplitude is the desired audio signal. The average value is extracted using a simple filter and fed into an audio transducer, which generates sound. 

Power conversion: Rectifiers are constructed from diodes, where they are used to convert alternating current (AC) electricity into direct current (DC). Automotive alternators are a common example, where the diode provides better performance than the commutator of earlier dynamo. Similarly, diodes are also used in Cockcroft–Walton voltage multipliers to convert AC into higher DC voltages. 

Over-voltage protection :Diodes are frequently used to conduct damaging high voltages away from sensitive electronic devices. They are usually reverse-biased (non-conducting) under normal circumstances. When the voltage rises above the normal range, the diodes become forward-biased (conducting). For example, diodes are used in ( stepper motor and H-bridge ) motor controller and relay circuits to de-energize coils rapidly without the damaging voltage spikes that would otherwise occur. (Any diode used in such an application is called a flyback diode). Many integrated circuits also incorporate diodes on the connection pins to prevent external voltages from damaging their sensitive transistors. Specialized diodes are used to protect from over-voltages at higher power 

Logic gates: Diodes can be combined with other components to construct AND and OR logic gates. This is referred to as diode logic.

 Ionising radiation detectors :In addition to light, mentioned above, semiconductor diodes are sensitive to more energetic radiation. In electronics, cosmic rays and other sources of ionising radiation cause noise pulses and single and multiple bit errors. This effect is sometimes exploited by particle detectors to detect radiation. A single particle of radiation, with thousands or millions of electron volts of energy, generates many charge carrier pairs, as its energy is deposited in the semiconductor material. If the depletion layer is large enough to catch the whole shower or to stop a heavy particle, a fairly accurate measurement of the particle’s energy can be made, simply by measuring the charge conducted and without the complexity of a magnetic spectrometer or etc. These semiconductor radiation detectors need efficient and uniform charge collection and low leakage current. They are often cooled by liquid nitrogen. For longer range (about a centimetre) particles they need a very large depletion depth and large area. For short range particles, they need any contact or un-depleted semiconductor on at least one surface to be very thin. The back-bias voltages are near breakdown (around a thousand volts per centimetre). Germanium and silicon are common materials. Some of these detectors sense position as well as energy. They have a finite life, especially when detecting heavy particles, because of radiation damage. Silicon and germanium are quite different in their ability to convert gamma rays to electron showers. Semiconductor detectors for high energy particles are used in large numbers. Because of energy loss fluctuations, accurate measurement of the energy deposited is of less use. 

Temperature measuring: A diode can be used as a temperature measuring device, since the forward voltage drop across the diode depends on temperature. From the Shockley ideal diode equation given above, it appears the voltage has a positive temperature coefficient (at a constant current)but depends on doping concentration and operating temperature. The temperature coefficient can be negative as in typical thermistors or positive for temperature sense diodes down to about 20 degrees Kelvin. 

Current steering :Diodes will prevent currents from flowing in unintended directions. To supply power to an electrical circuit during a power failure, the circuit can draw current from a battery. An Uninterruptible power supply built in this may use diodes to ensure that current is only drawn from the battery when necessary. Similarly, small boats typically have two circuits each with their own battery/batteries: one used for engine starting; one used for domestics. Normally both are charged from a single alternator, and a heavy duty split charge diode is used to prevent the higher charge battery (typically the engine battery) from discharging through the lower charged battery when the alternator is not running. 

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