Semiconductor diodes are widely used inelectronics and electronics industry. They are used both independently and as a pn-junction transistors and many other devices. As a discrete component, diodes are a key part of many electronic circuits. They find many uses ranging from low power applications to current rectifiers.
What is a diode?
Translated from the Greek name of thisAn electronic item literally means “two pins”. They are called the anode and cathode. In the circuit, the current passes from the anode to the cathode. The semiconductor diode is a one-way element, and the movement of current in the opposite direction is blocked.
Operating principle
The device of semiconductor diodes is very different.This is the reason that there are many types of them, which differ both in nominal value and in the functions they perform. However, in most cases, the basic principle of operation of semiconductor diodes is the same. They contain a pn-transition, which provides their basic functionality.
This term is commonly used in relation tostandard diode form. In fact, it is applicable to almost any type of them. Diodes form the basis of the modern electronics industry. Everything - from simple elements and transistors to modern microprocessors - is based on semiconductors. The principle of operation of a semiconductor diode is based on the properties of semiconductors. The technology is based on a group of materials, the introduction of impurities into the crystal lattice of which allows to obtain areas in which charge carriers are holes and electrons.
Pn junction
The pn-type diode got its name becauseIt uses a pn-junction, which allows current to flow only in one direction. The element has other properties that are also widely used. Semiconductor diodes, for example, are able to emit and record light, change capacitance and regulate voltage.
Pn-junction is a base semiconductorstructure. As the name implies, it represents the connection between the p- and n-type regions. The transition allows charge carriers to move only in one direction, which, for example, makes it possible to convert alternating current into direct current.
Standard diodes are usually made from silicon, although germanium and other semiconductor materials are also used, mainly for special purposes.
Volt-ampere characteristics
The diode is characterized by a current-voltage curve,which can be divided into 2 branches: direct and inverse. In the opposite direction, the leakage current is close to 0, but as the voltage increases, it slowly increases and, when the breakdown voltage is reached, it begins to increase sharply. In the forward direction, the current quickly increases with an increase in the applied voltage above the conduction threshold, which is 0.7 V for diodes made of silicon and 0.4 V for germanium. Elements that use other materials have different current-voltage characteristics and voltages of the conductivity and breakdown threshold.
Diode with pn-junction can be considered asbaseline device. It is widely used in many applications - from signal circuits and detectors to limiters or transient suppressors in induction or relay coils and high power rectifiers.
Characteristics and parameters
Diode specifications provide high volumedata. However, accurate explanations of what they are are not always available. Below are detailed information about the various characteristics and parameters of the diode, which are given in the specifications.
Semiconductor material
Материал, используемый в р-n-переходах, имеет paramount because it affects many of the main characteristics of semiconductor diodes. The most widely used silicon, because it is characterized by high efficiency and low production costs. Another commonly used element is germanium. Other materials, as a rule, are used in special-purpose diodes. The choice of semiconductor material is important because the conductivity threshold depends on it - about 0.6 V for silicon and 0.3 V for germanium.
Voltage drop in direct current mode (U pr.)
Any electrical circuit through which it passescurrent causes a voltage drop, and this parameter of a semiconductor diode is of great importance, especially for rectification, when power losses are proportional to U pr. In addition, electronic elements often have to provide a small voltage drop, since the signals may be weak, but they still need to be overcome him.
This happens for two reasons.The first is in the nature of the pn-junction itself and is the result of the voltage of the conductivity threshold, which allows the current to overcome the depleted layer. The second component is normal resistive loss.
The indicator is of great importance for the rectifier diodes, which can pass large currents.
Peak reverse voltage (U sample max)
This is the greatest reverse voltage thatsemiconductor diode can withstand. It can not be exceeded, otherwise the element may fail. This is not just the rms voltage of the incoming signal. Each circuit should be considered essentially, but for a simple rectifier with one half-wave with a smoothing capacitor, it should be remembered that the capacitor will hold the voltage equal to the peak of the input signal. Then the diode will be exposed to the peak of the incoming signal in the opposite direction, and therefore in these conditions there will be a maximum reverse voltage equal to the peak value of the wave.
Maximum Forward Current (U Ave. Max)
When designing an electrical circuit is necessaryensure that the maximum current levels of the diode are not exceeded. As the current increases, additional heat is generated, which needs to be removed.
Leakage current (I sample)
In an ideal diode reverse current should not be.But in real pn-junctions it is due to the presence of minority carriers in the semiconductor. The leakage current depends on three factors. Obviously, the most significant of these is the reverse voltage. Also, the leakage current depends on the temperature - with its growth, it increases significantly. In addition, it strongly depends on the type of semiconductor material. In this respect, silicon is much better than germanium.
The leakage current is determined at a certain reverse voltage and a specific temperature. It is usually specified in micro amperes (μA) or pico amperes (pA).
Transfer capacity
All semiconductor diodes have a capacitytransition. The depleted zone is a dielectric barrier between two plates that form at the edge of the depleted section and the area with the main charge carriers. The actual value of the capacitance depends on the reverse voltage, which leads to a change in the transition zone. Its increase expands the depleted zone and, therefore, reduces capacity. This fact is used in varactors or varicaps, but for other applications, especially radio frequency, this effect should be minimized. The parameter is usually specified in pF at a given voltage. For many radio frequency applications, special low-impedance diodes are available.
Type of shell
Depending on the destination semiconductorDiodes are manufactured in different types and shapes. In some cases, especially when used in signal processing circuits, the housing is a key element in determining the overall characteristics of this electronic element. In power circuits, in which heat dissipation is important, a housing can determine many common parameters of a diode. High power devices need to be able to be attached to the radiator. Small items can be made in lead shells or as surface mount devices.
Types of diodes
Sometimes it is useful to familiarize yourself with the classification of semiconductor diodes. However, some elements may fall into several categories.
Reversed diode.Although it is not so widely used, it is a kind of pn-type element, which in its action is very similar to a tunnel one. It has a low voltage drop in the open state. It is used in detectors, rectifiers and high-frequency switches.
Injection diode. It has much in common with the more common avalanche span. Used in microwave generators and alarm systems.
Diode Gunn. Not related to pn-type, but is a semiconductor device with two terminals. It is commonly used to generate and convert microwave signals in the 1-100 GHz range.
Light emitting or LED is one of the mostpopular types of electronic items. With forward bias, the current flowing through the junction causes light to emit. They use compound semiconductors (for example, gallium arsenide, gallium phosphide, indium phosphide), and they can glow in different colors, although initially limited to only red. There are many new developments that change the way that displays function and produce, of which OLED LEDs are an example.
Photodiode. Used to detect light.When a photon hits a pn-junction, it can create electrons and holes. Photodiodes usually operate under reverse bias conditions, under which even a small current resulting from the action of light can be easily detected. Photodiodes can be used to generate electricity. Sometimes pin-type elements are used as photodetectors.
Pin diode.The name of the electronic element well describes the device of a semiconductor diode. It has standard p- and n-type regions, but between them there is an internal region without impurities. It has the effect of increasing the depletion area, which can be useful for switching, as well as in photodiodes, etc.
A standard pn-junction can be thought of asordinary or standard type of diode that is used today. They can be used in radio frequency or other low-voltage devices, as well as in high-voltage and high-power rectifiers.
Schottky diodes.They have a lower forward voltage drop than standard pn-type silicon semiconductors. At low currents, it can be from 0.15 to 0.4 V, and not 0.6 V, as in silicon diodes. To do this, they are not made as usual - they use metal-semiconductor contact. They are widely used as limiters, rectifiers and in radio equipment.
Diode with accumulation of charge.It is a type of microwave diode used to generate and form pulses at very high frequencies. Its operation is based on a very fast trip characteristic.
Лазерный диод.It differs from conventional light emitting, as it produces coherent light. Laser diodes are used in many devices - from DVD and CD-drives to laser pointers. They are much cheaper than other forms of lasers, but much more expensive than LEDs. Differ in the limited term of operation.
Tunnel diodeAlthough today it is not widely used, it was previously used in amplifiers, oscillators and switching devices, oscillograph synchronization circuits, when it was more efficient than other elements.
Varaktor or varicap.Used in many radio frequency devices. With this diode, the reverse bias changes the width of the depletion layer as a function of the applied voltage. In this configuration, it acts as a capacitor with a depletion region acting as an insulating dielectric, and plates formed by conductive regions. Used in voltage controlled oscillators and radio frequency filters.
Стабилитрон.It is a very useful type of diode because it provides a stable reference voltage. Due to this, the zener diode is used in large quantities. It works under reverse bias and breaks through when a certain potential difference is reached. If the current is limited by a resistor, then this provides a stable voltage. Widely used to stabilize power supplies. There are 2 types of reverse breakdown in Zener diodes: Zener decomposition and impact ionization.
Таким образом, различные типы полупроводниковых The diodes include elements for low-power and high-power applications that emit and detect light, with low direct voltage drops and variable capacitance. In addition to this, there are a number of varieties that are used in microwave technology.
