The main purpose of rectifier diodes is voltage conversion. But this is not the only scope of these semiconductor elements. They are installed in switching and control circuits, used in cascade generators, etc. It will be interesting for beginner radio amateurs to learn how these semiconductor elements are arranged, as well as their principle of operation. Let's start with the general characteristics.
The main structural element is a semiconductor. This is a plate of a silicon or germanium crystal, which has two regions of p and n conductivity. Because of this design feature, it was called planar.
In the manufacture of a semiconductor, the crystal is processed as follows: to obtain a p-type surface, it is treated with molten phosphorus, and a p-type surface is treated with boron, indium or aluminum. During heat treatment, diffusion of these materials and the crystal occurs. As a result, a region with a p-n junction is formed between two surfaces with different electrical conductivity. The semiconductor obtained in this way is installed in the housing. This provides protection of the crystal from extraneous factors of influence and promotes heat dissipation.
Designations:
As already mentioned, silicon or germanium crystals are used as the basis of the p-n transition. The former are used much more often, this is due to the fact that in germanium cells the value of reverse currents is much higher, which significantly limits the permissible reverse voltage (it does not exceed 400 V). While for silicon semiconductors, this characteristic can reach up to 1500 V.
In addition, germanium cells have a much narrower operating temperature range, it varies from -60°C to 85°C. When the upper temperature threshold is exceeded, the reverse current sharply increases, which negatively affects the efficiency of the device. Silicon semiconductors have an upper threshold of about 125°C-150°C.
The power of the elements is determined by the maximum allowable direct current. In accordance with this characteristic, the following classification is adopted:
Below is a table describing the main parameters of rectifier diodes. These characteristics can be obtained from the datasheet (technical description of the element). As a rule, most radio amateurs turn to this information in cases where the element indicated in the diagram is not available, which requires finding a suitable analogue for it.
Note that in most cases, if you need to find an analogue of a particular diode, the first five parameters from the table will be enough. In this case, it is desirable to take into account the operating temperature range of the element and the frequency.
The easiest way to explain the principle of operation of rectifier diodes is with an example. To do this, we simulate a circuit of a simple half-wave rectifier (see 1 in Fig. 6), in which power is supplied from an alternating current source with voltage U IN (graph 2) and goes through VD to the load R.
Rice. 6. The principle of operation of a single diode rectifier During the positive half-cycle, the diode is in the open position and passes current through itself to the load. When the turn of the negative half-cycle arrives, the device is locked, and power is not supplied to the load. That is, it is as if the negative half-wave is cut off (in fact, this is not entirely true, since in this process there is always a reverse current, its value is determined by the characteristic I arr).
As a result, as can be seen from graph (3), at the output we get pulses consisting of positive half-cycles, that is, direct current. This is the principle of operation of rectifier semiconductor elements.
Note that the pulsed voltage at the output of such a rectifier is only suitable for powering low-noise loads, an example is a charger for an acid flashlight battery. In practice, such a scheme is used only by Chinese manufacturers, in order to make their products as cheap as possible. Actually, the simplicity of the design is its only pole.
The disadvantages of a single diode rectifier include:
Note that these shortcomings can be somewhat reduced; for this, it is enough to make a simple filter based on a high-capacity electrolyte (1 in Fig. 7).
Rice. 7. Even a simple filter can significantly reduce ripple The principle of operation of such a filter is quite simple. The electrolyte is charged during the positive half cycle and discharged when it is the negative half cycle. In this case, the capacitance must be sufficient to maintain the voltage on the load. In this case, the impulses will be somewhat smoothed out, approximately as shown in the graph (2).
The above solution will somewhat improve the situation, but not by much, if powered by such a half-wave rectifier, for example, active computer speakers, they will hear a characteristic background. To fix the problem, a more radical solution will be required, namely a diode bridge. Consider the principle of operation of this scheme.
The essential difference between such a circuit (from a single-half-wave) is that the voltage is applied to the load in each half-cycle. The switching circuit of semiconductor rectifier elements is shown below.
As can be seen from the above figure, the circuit involves four semiconductor rectifier elements, which are connected in such a way that only two of them work during each half-cycle. Let's describe in detail how the process takes place:
As can be seen from the result (graph 3), both half-cycles are involved in the process and no matter how the input voltage changes, it goes through the load in one direction. This principle of operation of the rectifier is called full-wave. Its advantages are obvious, we list them:
Interference from the bridge circuit is negligible, and becomes even less when using a filtering electrolytic tank. Due to this, such a solution can be used in power supplies for almost any amateur radio designs, including those that use sensitive electronics.
Note that it is not at all necessary to use four rectifying semiconductor elements; it is enough to take a ready-made assembly in a plastic case.
Such a package has four outputs, two for input and the same number for output. The legs to which AC voltage is connected are marked with a "~" sign or the letters "AC". At the output, the positive leg is marked with a “+” symbol, respectively, the negative leg is marked with a “-”.
On the circuit diagram, such an assembly is usually designated as a rhombus, with a graphic display of the diode located inside.
The question of what is better to use the assembly or individual diodes cannot be answered unambiguously. There is no difference in functionality between them. But the assembly is more compact. On the other hand, if it fails, only a complete replacement will help. If in this case separate elements are used, it is enough to replace the failed rectifier diode.
All these components differ in purpose, materials used, types of p-n junctions, design, power and other features and characteristics. Rectifier, pulse diodes, varicaps, Schottky diodes, trinistors, LEDs, and thyristors are widely used. Consider their main technical characteristics and general properties, although each type of these semiconductor components has many of its own purely individual parameters.
These are electronic devices with one p-n junction with one-sided conductivity and designed to convert AC voltage to DC. The frequency of the rectified voltage as a rule is not more than 20 kHz. Rectifier diodes also include Schottky diodes.
The main parameters of low power rectifier diodes at normal temperature are given in table 1 medium power rectifier diodes in table 2 and rectifier diodes of high power in table 3
A variety of rectifier diodes are . These devices on the reverse branch of the CVC have an avalanche characteristic similar to zener diodes. The presence of an avalanche characteristic allows them to be used as elements for protecting circuits from surges, including directly in the rectifier circuit.
In the latter case, rectifiers based on these diodes operate reliably under the conditions of switching overvoltages that occur in inductive circuits at the time of switching on or off the power supply or load. The main parameters of avalanche diodes at normal ambient temperature are given in
To rectify voltages above several kilovolts, rectifier poles have been developed, which are a set of rectifier diodes connected in series and assembled into a single structure with two terminals. These devices are characterized by the same parameters as rectifier diodes. The main parameters of rectifier poles at normal ambient temperature are given in
To reduce the overall dimensions of rectifiers and ease their installation, rectifier blocks(assemblies) having two, four or more diodes, electrically independent or connected in the form of a bridge and assembled in one housing. The main parameters of rectifier units and assemblies at normal ambient temperature are given in
Pulse diodes differ from rectifiers in a short reverse recovery time, or in a large magnitude of the pulsed current. Diodes of this group can be used in rectifiers at high frequency, for example, as a detector or modulators, converters, pulse shapers, limiters and other pulse devices, see reference tables 7
And 8
tunnel diodes perform the functions of active elements (devices capable of amplifying the signal in terms of power) of electronic circuits of amplifiers, generators, switches, mainly in the microwave ranges. Tunnel diodes have high speed, small overall dimensions and weight, are resistant to radiation, operate reliably in a wide temperature range, and are energy efficient.
The main parameters of tunnel and inverted diodes at normal ambient temperature are given in
- their principle of operation is based on the electrical (avalanche or tunnel) breakdown of the p-n junction, in which there is a sharp increase in the reverse current, and the reverse voltage changes very little. This property is used to stabilize the voltage in electrical circuits. Due to the fact that avalanche breakdown is typical for diodes made on the basis of a semiconductor with a large band gap, silicon is used as the starting material for zener diodes. In addition, silicon has a low thermal current and stable characteristics over a wide temperature range. For operation in zener diodes, a flat section of the I–V characteristic of the reverse current of the disd is used, within which sharp changes in the reverse current are accompanied by very small changes in the reverse voltage.
Zener parameters and stabistors low power are given in, zener diodes and high power stabistors - in, precision zener diodes -
The parameters of the voltage limiters are given in
Varicaps guide |
These are semiconductor diodes with electrically controlled junction barrier capacitance. The change in capacitance is achieved by changing the reverse voltage. As with other diodes, the base resistance of the varicap should be low. At the same time, to increase the value of the breakdown voltage, a high resistivity of the base layers adjacent to the junction is desirable. Based on this, the main part of the base - the substrate - is low-resistance, and the base layer adjacent to the transition is high-resistance. Varicaps are characterized by the following main parameters. The total capacitance of the varicap SB is the capacitance, including the barrier capacitance and the case capacitance, i.e., the capacitance measured between the terminals of the varicap at a given (nominal) reverse voltage.
Light-emitting diode It is a semiconductor device that converts electrical current directly into light radiation. It consists of one or more crystals placed in a housing with contact leads and an optical system (lens) that forms the light flux. The crystal radiation wavelength (color) depends on
These are the same LEDs only emitting light in the IR range.
This is the simplest semiconductor type laser, the design of which is based on a typical p-n junction. The principle of operation of the laser device is based on the fact that after free charge carriers are injected into the element, a population inversion is formed in the p-n junction zone.
A semiconductor voltage limiter is a diode that operates on the reverse branch of the I–V characteristic with avalanche breakdown. It is used for protective purposes against overvoltage of circuits of integrated and hybrid circuits, radio-electronic elements, etc. With the help of voltage limiters, you can protect the input and output circuits of various electronic components from the effects of short-term overvoltages.
The information in the guide is presented in the format of original PDF files, and for the convenience of downloading it is divided into collections in accordance with the English alphabet
Domestic Diodes Reference |
The reference book provides general information about domestic semiconductor diodes, namely, rectifiers, diode arrays, zener diodes and stabistors, varicaps, radiating and ultra-high semiconductor devices. It also tells about their classification and the system of symbols. Conventionally - graphic designations are given in accordance with GOST 2.730-73, and the terms and letter designations of parameters are in accordance with GOST 25529-82. Some information is given about the use of voltage limiters and the rules for mounting diodes. The application contains dimensional drawings of cases and an alphanumeric index for navigation
This database is nothing more than an electronic guide to semiconductor devices, including bridges and assemblies, and many radio components too.
There are more than 65,000 radio elements in the directory. There is information from all leading manufacturers as of December 2016. The guide has the following functions:
Sort by multiple characteristics in any directory order
filtering by almost all characteristics
editing directory data
viewing the documentation and drawing of the radio element body
reference view of data sheets in PDF format
The reference tables use the following conventions:
| U arr. max. | - | the maximum allowable constant reverse voltage of the diode; |
| U return and max. | - | the maximum allowable impulse reverse voltage of the diode; |
| I pr.max. | - | maximum average forward current for the period; |
| I e.i.max. | - | maximum pulse forward current for the period; |
| I prg. | - | rectifier diode overload current; |
| f max. | - | the maximum allowable switching frequency of the diode; |
| f working | - | diode operating frequency; |
| U pr at I pr | - | constant forward voltage of the diode at current I pr; |
| I arr. | - | constant diode reverse current; |
| T k.max. | - | the maximum allowable temperature of the diode case. |
| T p.max. | - | maximum allowable diode junction temperature. |
semiconductor diodes called single-junction (with one electrical junction) electrical converters with two external down conductors. The electrical junction can be an electron-hole junction, a metal-semiconductor contact, or a heterojunction. The figure schematically shows the device of a diode with an electron-hole junction 1, separating p-m p-regions (2 and 3) with different types of electrical conductivity.
Crystal 3 is provided with external current leads 4 and placed in a metal, glass, ceramic or plastic case 5, which protects the semiconductor from external influences (atmospheric, mechanical, etc.). Typically, semiconductor diodes have asymmetric electron-hole junctions. One region of the semiconductor (with a higher concentration of impurities) serves as an emitter, and the other (with a lower concentration) serves as a base. When an external voltage is directly connected to the diode, the injection of minority charge carriers mainly occurs from the heavily doped region of the emitter into the lightly doped region of the base.
The number of minority carriers passing in the opposite direction is much less than the injection from the emitter. Depending on the ratio of the linear dimensions of the transition and the characteristic length, planar and point diodes are distinguished. A diode is considered planar if its linear dimensions, which determine the junction area, are much larger than the characteristic length.
The characteristic length in the dictionary for diodes is the smallest of two values - the thickness of the base and the diffusion length of the minority carriers in the base. They determine the properties and characteristics of the diodes. Dot diodes include diodes with linear dimensions of the junction that are smaller than the characteristic length. The transition at the interface of regions with different types of conductivity has the properties of rectification (one-sided conduction) of the current; non-linearity of the current-voltage characteristic; the phenomenon of tunneling of charge carriers through the potential barrier in both reverse and forward bias; the phenomenon of impact ionization of semiconductor atoms at relatively high transition voltages; barrier capacitance, etc. These transition properties are used to create various types of semiconductor diodes.
According to the frequency range in which diodes can operate, they are divided into low-frequency (LF) and high-frequency (HF). By purpose, LF diodes are divided into rectifier, stabilizing, pulse, and HF diodes - into detector, mixing, modular, parametric, switching, etc. Sometimes diodes are distinguished into a special group that differ in basic physical processes: tunnel, avalanche-span, photo -, LEDs, etc.
According to the material of the main semiconductor crystal, germanium, silicon, gallium arsenide and other diodes are distinguished. To designate semiconductor diodes in the reference book, a six and seven-digit alphanumeric code is used (for example, KD215A, 2DS523G).
The first element - a letter (for devices of wide application) or a number (for devices used in a device for special purposes) - indicates the material on the basis of which the device is made: G or 1 - germanium; K or 2 - silicon and its compounds; A or 3 - gallium compounds (for example, gallium arsenide); And or 4 - indium compounds (for example, indium phosphide).
The second element is a letter indicating a subclass or group of devices: D - rectifier, pulse diodes; C - rectifier poles and blocks; B - varicaps; And - pulse tunnel diodes; A - microwave diodes; C - zener diodes.
The third element - a number - defines one of the main features that characterize the device (for example, purpose or principle of operation).
The fourth, fifth and sixth elements are a three-digit number indicating the serial number of the development of the technological type of the device.
The seventh element - the letter - conditionally determines the classification according to the parameters of devices manufactured using a single technology. Designation example: 2DS523G - a set of silicon impulse devices for special-purpose devices with a reverse resistance settling time from 150 to 500 ns; development number 23, group G. Development devices until 1973 in reference books. have three and four element notation systems.
Diodes with optimized self-capacitance and time required for the reverse resistance to recover are most suitable for switching power supplies. The achievement of the required indicator for the first parameter occurs with a decrease in the length and width of the p-n junction, which accordingly affects the decrease in the allowable dissipation power.
The value of the barrier capacitance of a pulse-type diode in most cases is less than 1 pF. The lifetime of minority carriers does not exceed 4 ns. Diodes of this type are characterized by the ability to transmit pulses with a duration of no more than a microsecond at currents with a wide amplitude. Ordinary diodes either do not work with the UPS at all, or they overheat and sharply degrade their parameters, so special high-frequency elements are needed - they are also "fast diodes". The following are their main types, names and characteristics sufficient for amateur radio practice.
