There are many devices designed to convert electric current, and rectifier diodes are one of them.
The rectifier diode is an AC to DC current converter. It is one of the types of semiconductors. Received wide application due to the main characteristic - the transfer of electric current strictly in one direction.
Operating principle
The desired effect during the operation of the device is created features p-n transition. They consist in the fact that next to the junction of two semiconductors a layer is built in, which is characterized by two points: high resistance and the absence of charge carriers. Further, when this blocking layer is exposed to an alternating voltage from the outside, its thickness decreases and subsequently disappears. The current that increases during this is the direct current that passes from the anode to the cathode. In the case of a change in the polarity of the external alternating voltage, the blocking layer will be larger, and the resistance will inevitably increase.
The I-V characteristic of the rectifier diode (volt-ampere characteristic) also gives an idea of the specifics of the operation of the rectifier and is non-linear. It looks like this: there are two branches - direct and reverse. The first reflects the highest conductivity of the semiconductor when a direct potential difference occurs. The second indicates the value of low conductivity at the inverse potential difference.
The current-voltage characteristics of the rectifier are directly proportional to the temperature, with an increase in which the potential difference is reduced. Electric current will not pass through the device in case of low conductivity, but an avalanche breakdown occurs in the case of a reverse voltage that has risen to a certain level.
Assembly usage
When operating a rectifier semiconductor diode, only half of the AC waves are useful, respectively, more than half of the input voltage is irretrievably lost.
In order to improve the quality of AC to DC conversion, an assembly of four devices is used - a diode bridge. Favorably differs in that it passes current throughout each half-cycle. Diode bridges are produced in the form of a kit enclosed in a plastic case.
circuit diagram diode bridge Physical and technical parameters
The main parameters of rectifier diodes are based on the following values:
- the maximum allowable value of the potential difference when rectifying the current, at which the device will not fail;
- the highest average rectified current;
- the highest reverse voltage.
The industry produces rectifiers with different physical characteristics. Accordingly, the devices have a different shape and method of installation. They are divided into three groups:
- Rectifier Diodes high power. They are characterized by a current carrying capacity of up to 400 A and are high-voltage. High-voltage rectifier diodes are produced in two types of cases - pin, where the case is sealed and glass, and tablet, where the case is made of ceramic.
- Medium power rectifier diodes. They have a capacity from 300 mA to 10A.
- Low power rectifier diodes. The maximum allowable current value is up to 300 mA.
Selection of Rectifier Diodes
When purchasing a device, you must be guided by the following parameters:
- values of the current-voltage characteristics of the maximum reverse and peak current;
- the maximum allowable reverse and forward voltage;
- average strength of the rectified current;
- device material and type of installation.
Depending on the physical characteristics, an appropriate designation is applied to the body of the device. The catalog with the marking of rectifier diodes is presented in a specialized guide. You need to know that the labeling of imported analogues differs from domestic ones.
It is also worth paying attention to the fact that rectifier circuits differ in the number of phases:
- Single-phase. Widely used for household electrical appliances. There are automotive diodes and for electric arc welding.
- Multiphase. Indispensable for industrial equipment, public and special transport.
Schottky diode
A separate position is occupied by the Schottky diode. It was invented in connection with the growing needs in the developing industry of radio electronics. Its main difference from other diodes is that its design contains a semiconductor metal as p-n alternative transition. Accordingly, the Schottky diode has its own unique properties that silicon rectifier diodes cannot boast of. Some of them:
- operational renewability of the charge due to its low value;
- minimum voltage drop across the junction with direct connection;
- leakage current is high.
In the manufacture of the Schottky diode, materials such as silicon and gallium arsenide are used, but sometimes germanium is also used. Material properties are slightly different, but in any case, the maximum allowable reverse voltage for a Schottky rectifier is no more than 1200 V.
In contrast to all the advantages, this type of design also has disadvantages. For example, in the bridge assembly, the device categorically does not perceive the excess of reverse current. Violation of the condition leads to the breakdown of the rectifier. Also, a small voltage drop occurs at a low voltage of about 60-70 V. If the value exceeds this figure, then the device turns into an ordinary rectifier.
It is worth noting that the advantages of a powerful rectifier Schottky diode significantly exceed the disadvantages.
zener diode
To stabilize the voltage, a special device is used that can operate in breakdown mode - a zener diode, the foreign name of which is “Zener diode”. The device performs its function by operating in the breakdown mode at a reverse bias voltage. The increase in current occurs at the moment of breakdown, at the same time the differential value drops to a minimum, as a result of which the voltage is stable and covers a fairly serious range of reverse currents.
Practical use of rectifier diode
In connection with the unstoppable development of scientific and technological progress, the use of rectifiers has affected all spheres of human life. Power rectifier diodes are used in such units and mechanisms:
- in power supplies of the main engines of vehicles (land, air and water), industrial machines and equipment, drilling rigs;
- in the configuration of the diode bridge for welding machines;
- in rectifying plants for electroplating baths used to produce non-ferrous metals or apply a protective coating to a part or product;
- in rectifying plants for water and air purification, filters of various kinds;
- for the transmission of electricity over long distances through a high-voltage power line.
AT Everyday life Rectifiers are used in various transistor circuits. Mostly low-power devices are used both in the form of a half-wave rectifier and in the form of a diode bridge. For example, generator rectifier diodes are well known to motorists.
Wah-wah-wah ... Usually these words are used when telling jokes about Caucasians))) Caucasians, please do not be offended - I respect the Caucasus. But, as they say, you can’t throw words out of a song. And in our case, this word has a different meaning. And it's not even a word, but an abbreviation.
VAC is the volt-ampere characteristic. Well, in this section we are interested in current-voltage characteristic of a semiconductor diode.
The I–V curve of the diode is shown in fig. 6.
Rice. 6. CVC of a semiconductor diode.
The graph shows the I–V characteristics for forward and reverse switching on of the diode. They also say that the direct and reverse branch of the current-voltage characteristic. The direct branch (Ipr and Upr) displays the characteristics of the diode during direct connection (that is, when a "plus" is applied to the anode). The reverse branch (Iobr and Uobr) displays the characteristics of the diode when it is turned back on (that is, when a "minus" is applied to the anode).
On fig. 6, the blue thick line is the characteristic of the germanium diode (Ge), and the black thin line is the characteristic of the silicon (Si) diode. The figure does not indicate the units for the current and voltage axes, since they depend on the specific brand of the diode.
What do we see on the chart? Well, for starters, let's define, as for any flat coordinate system, four coordinate angles (quadrants). Let me remind you that the first quadrant is considered, which is located at the top right (that is, where we have the letters Ge and Si). Next, the quadrants are counted counterclockwise.
So, the II and IV quadrants are empty. This is because we can only turn on the diode in two ways - forward or reverse. A situation is impossible when, for example, a diode flows through reverse current and at the same time it is switched on in the forward direction, or, in other words, it is impossible to apply both "plus" and "minus" to one output at the same time. More precisely, it is possible, but then it will be a short circuit))). It remains to consider only two cases - direct connection of the diode and reverse diode switching.
The direct connection graph is drawn in the first quadrant. This shows that the higher the voltage, the greater the current. Moreover, up to a certain point, the voltage grows faster than the current. But then a fracture occurs, and the voltage almost does not change, and the current begins to grow. For most diodes, this break occurs in the range of 0.5 ... 1 V. It is this voltage that is said to "drop" on the diode. That is, if you connect the light bulb according to the first circuit in fig. 3, and you will have a battery voltage of 9 V, then not 9 V will fall on the bulb, but 8.5 or even 8 (depending on the type of diode). These 0.5 ... 1 V is the voltage drop across the diode. A slow increase in current to a voltage of 0.5 ... 1V means that in this section the current through the diode practically does not flow even in the forward direction.
The reversal graph is drawn in the third quadrant. From this it can be seen that in a significant area the current almost does not change, and then increases like an avalanche. What does it mean? If you turn on the light bulb according to the second circuit in fig. 3, then it will not glow, because the diode does not pass current in the opposite direction (more precisely, it passes, as can be seen on the graph, but this current is so small that the lamp will not glow). But a diode cannot hold the voltage indefinitely. If you increase the voltage, for example, to several hundred volts, then this high voltage The diode will “break through” (see the inflection on the reverse branch of the graph) and the current will flow through the diode. That's just a "breakdown" - this is an irreversible process (for diodes). That is, such a “breakdown” will lead to the burnout of the diode and it will either completely stop passing current in any direction, or vice versa - it will pass current in all directions.
The characteristics of specific diodes always indicate the maximum reverse voltage - that is, the voltage that the diode can withstand without “breakdown” when turned on in the opposite direction. This must be taken into account when designing devices where diodes are used.
Comparing the characteristics of silicon and germanium diodes, we can conclude that in the p-n junctions of a silicon diode, the forward and reverse currents are less than in a germanium diode (at the same voltage values at the terminals). This is due to the fact that silicon has a larger band gap and for the transition of electrons from the valence band to the conduction band, they need to impart a large additional energy.
RESISTORS, CAPACITORS
BRIEF THEORETICAL INFORMATION
Resistors
Resistors are among the most common parts of electronic equipment. They account for from 20 to 50%, i.e., up to half of the total number of radio components in the device. The principle of operation of resistors is based on the use of the property of materials to resist the flowing current. Resistors are characterized by the following main parameters:
Rated resistance value. It is measured in ohms (Ohm), kiloohms (kOhm), megaohms (MΩ). ,
The nominal resistance values indicate on the resistor case. The nominal resistance value corresponds to the value from standard rows resistances given in Appendix 1.
Tolerance the actual resistance of the resistor from its nominal value. This deviation is measured as a percentage, it is normalized and determined by the accuracy class. Three accuracy classes are most widely used: I - allowing deviation of resistance from the nominal value by ± 5%, II - by ± 10%, III - by ± 20%. In modern electronic equipment, resistors with increased resistance accuracy are often used, they are produced with tolerances (%): ± 2; ±1; ±0.5; ±0.2; ±0.1; ±0.05; ±0.02; ±0.01 etc.
Rated power dissipation resistor Rnom. This parameter is measured in watts (W). This is the maximum power of direct or alternating current, during the flow of which through a resistor it can work for a long time without damage. Power Рnom, current I flowing through the resistor, voltage drop U across the resistor and its resistance R are related by the dependence: P=UI U=IR. In most REA devices, resistors with a rated power dissipation from 0.125 to 2 W are used.
Temperature coefficient of resistance (TCR) of the resistor. Characterizes the relative change in the resistance of the resistor when the ambient temperature changes by 1 ° C and is expressed as a percentage. In resistors, TCR is insignificant and averages tenths - units of a percent.
Electromotive force (EMF) of own noise. The inherent noise of the resistor arises due to the disordered movement of a part of the electrons when a voltage is applied to it. Noise EMF (Esh) is measured in microvolts per volt of applied voltage (µV/V). This value for resistors is also insignificant and amounts to a few microvolts per volt.
Intrinsic inductance and capacitance of resistors. They are determined by the overall dimensions, design and affect the frequency range of resistors.
Resistors are used to limit the current strength in circuits, to create the necessary voltage drops in certain sections of the circuits, for various adjustments (volume, timbres, etc.), and in many other cases.
Conditional graphic designation of resistors and connection diagrams
According to GOST2.728-74, the UGO of a constant wire resistor has the following form:
Rice. 1. UGO wirewound resistor
There are two main types of resistor connection circuits - series connection of resistors and parallel.
When resistors are connected in series, their equivalent resistance will be equal to the sum of all individual resistances
When resistors are connected in parallel, their equivalent resistance can be calculated by the formula
.
Capacitors
electrical capacitor called devices designed to accumulate an electric charge.
The principle of operation of a capacitor is based on the accumulation of an electric charge between two closely spaced conductors. Such conductors are also called plates. Depending on the type of dielectric that separates the plates, there are types of capacitors.
The main parameters of the capacitor include:
Electrical rated capacitance- the ability of a capacitor to accumulate electric charges on the plates under the influence of an electric field. The nominal capacity is indicated on the capacitor or in the accompanying documentation, is selected in accordance with the installed number. It is measured in farads [F], however, 1F is a rather large value, so the value of conventional capacitors is used with the prefixes nano- (10 -9), micro- (10 -6), miles - (10 -3).
Tolerance the actual capacitance of the capacitor from its nominal value. This deviation is measured as a percentage, it is normalized and determined by the accuracy class.
Temperature Coefficient of Capacitance (TKE)- the relative change in the capacitance of the capacitor under the influence of temperature. Under the influence of temperature, the capacitor plates change their geometric dimensions, the distance between them and the value of the dielectric constant of the dielectric change, therefore, the value of the capacitance of the capacitor also changes. For all capacitors this dependency non-linear, however, depending on the type of dielectric, for some it approaches linear.
Rated voltage U- the maximum allowable value of the direct voltage (or the sum of the constant component and the amplitude of the variable component) at which the capacitor can operate during the entire guaranteed service life at normal temperature.
Conditional graphic designation of capacitors and connection diagrams
According to GOST2.728-74, it is fundamentally electrical diagrams capacitors are marked:
Rice. 2. UGO capacitor
There are two main types of capacitor circuits - series and parallel.
When capacitors are connected in parallel, their capacitance is added according to the formula
.
When capacitors are connected in series, their equivalent capacitance can be calculated by the formula
.
Marking resistors and capacitors
Resistor marking
According to GOST 28883-90 - industrially produced resistors, the following marking systems are used:
Letter full
The parameters and characteristics included in the full symbol of the resistor are indicated in the following sequence: rated power dissipation, nominal resistance and letter designation of the unit of measure, permissible resistance deviation in percent (%), functional characteristic, designation of the end of the shaft and the length of the protruding part of the shaft.
An example of a complete symbol for a permanent non-wire resistor with registration number 4, rated power dissipation 0.5 W, nominal resistance 10 kOhm, with a tolerance of ± 1%, noise level group A, TKS group - B, all climatic modification C.
Р1-4‑0.5‑10kOhm±1% A-B-V OZHO.467.157 TU
Letter abbreviations
Due to the fact that the full symbol occupies a significant place on the resistor case, its use is not always possible and convenient, therefore, an abbreviated letter designation was introduced, which includes the designation of the nominal resistance and the permissible deviation. The nominal resistance is indicated as a code. The coded designation of the nominal resistance consists of three or four characters, including two or three digits and a letter of the Latin alphabet. The letter of the code from the Russian or Latin alphabet indicates the multiplier that makes up the resistance, and determines the position of the decimal point. The letters R, K, M, G, T denote the factors 1, 10 3 , 10 6 , 10 9 , 10 12 respectively. Examples of coded designations for nominal resistance are as follows: 215 Ohm - 215R, 150 kOhm - 150K,2.2 MΩ - 2M2.6.8 GΩ - 6G8.1 TΩ - 1T0 The coded designation of the tolerance consists of a letter corresponding to the deviation in%. The meaning of the encoding letters is given in Appendix 2.
In addition to the coding described above, commercially available resistors use color coding.
Capacitor marking
A short letter marking of a capacitor is carried out according to the same rules as the marking of resistors. The nominal capacitance of a capacitor is expressed using 3-4 numbers and a multiplier code. It is customary to use the following letters p, n, μ, m, corresponding to the multipliers pico-, nano-, micro-, mi- farad.
An example of marking a capacitor: p10 - 0.1pF; 1μ5 - 1.5μF.
SEMICONDUCTOR DIODES:
VAC OF THE RECTIFIER DIODE
Comparing the characteristic of a real diode with the characteristic perfect p-n transition.
It is known that the static CVC of an idealized semiconductor diode is described by the expression:
,
where I is the diode current; U- the voltage applied to it; Is- saturation current, determined parameters p-n transition; kT/q– thermal potential ( kT/q\u003d 0.0259 V at T \u003d 300K).
The type of characteristic described by this expression is shown in fig. 3.
Rice. 3. CVC of an ideal p-n junction.
When displaying the CVC, the scale along the axes of forward and reverse voltages is chosen differently, since these values differ by orders of magnitude. Different scales give the impression of a break in the characteristic at the zero point, but in reality the I–V characteristic is differentially smooth. On the direct branch of the characteristic, the dependence of current on voltage is exponential, and after passing the voltage through the threshold value U A further change in voltage by tenths of a volt causes a significant change in current through the diode.
The only CVC parameter associated with the physical and structural parameters and geometric dimensions of the active region of the diode is the saturation current I s.
where q is the electron charge; n i is the intrinsic concentration of charge carriers in the semiconductor; N db and L pb is the diffusion coefficient and diffusion length of minority carriers in it; W b is the thickness of the base; F – p-n area transition.
The CVC of a real diode differs from the characteristics of an ideal p-n junction for a number of reasons:
Recombination and generation of holes and electrons in the transition SCR
Voltage drop across the volumetric base resistance
・Appearance effects high level high current injection
The presence of leakage currents through the p-n junction
The beginning of the breakdown on the reverse branch of the current-voltage characteristic
Inhomogeneous base alloying
Warming up the p-n junction with the allocated power
These effects lead to the fact that the CVC of the diode is described only qualitatively.
The reverse branch of the CVC is formed by the sum of three components:
saturation current I s, thermal generation current in the SCR p-n junction I G and leakage current I ut. The ratio between these components for diodes from different semiconductor materials is different
The thermal generation current in the p-n junction is described by the formula
where δ - p-n-junction width; τpn is the effective lifetime characterizing the rate of generation of electron-hole pairs in the transition SCR. The current depends on the applied reverse voltage through the dependence δ (U).
The leakage current is due to conductive channels inside the p-n junction and on the surface of the crystal. It depends on the area and perimeter of the junction and a number of other factors and has an approximately linear dependence on the reverse voltage.
The forward branch of the current-voltage characteristic of a real diode retains the exponential dependence of current on voltage, so it can be described by expressions like:
where I 0 and m are the parameters of the characteristic, which can vary in different parts of the CVC.
Comparison of the characteristics of diodes from various
materials
The diodes studied in the work are made of various semiconductor materials, but have approximately the same physical and structural parameters. The difference in their characteristics is due to the difference in the parameters:
bandgap width
Mobility of charge carriers
The lifetime of charge carriers, etc.
Biggest Influence the difference in the parameters is affected by the difference in the values of the band gap E g. It determines the intrinsic concentration of charge carriers n i which is included in the expression of the CVC parameters.
Gap value E g and n i are given in Appendix 3.
The saturation currents of all diodes, except for germanium, are very small and amount to a few nanoamperes, so the main component of the reverse current of these diodes is the leakage current. The main difference between the direct branches of the I–V characteristics of various diodes is the different value of the saturation current. Appendix 3 gives the values U OL obtained theoretically for real diodes, it can differ for a number of reasons, mainly due to the drop in the volume resistance of the base.
WORK PROCEDURE
To study the current-voltage characteristics of a real diode, students need to assemble the experimental circuit
Rice. 4. Scheme of the experiment
A digital oscilloscope or digital multimeters can be used as a miliammeter and voltmeter. The controlled voltage source on the NI ELVIS training stand is used as a source. In order to ensure the uninterrupted operation of the bench generator, it is necessary to include a limiting resistance R in the circuit, the value of which the students need to calculate using the bench parameters.
After assembling the circuit and checking it by the teacher, students need to make a series of experiments. By adjusting the voltage value at the output from the generator and recording the instrument readings in a table.
To control the direction of the electric current, it is necessary to use different radio and electrical parts. In particular, modern electronics uses a semiconductor diode for this purpose, its use ensures a smooth current.
Device
A semiconductor electric diode or diode valve is a device that is made of semiconductor materials (usually silicon) and operates only with a one-way flow of charged particles. The main component is a crystalline part, with a p-n junction, which is connected to two electrical contacts. Vacuum diode tubes have two electrodes: a plate (anode) and a heated cathode.
Photo - semiconductor diodeTo create semiconductor diodes, germanium and selenium are used, as they were more than 100 years ago. Their structure allows the use of parts to improve electronic circuits, convert AC and DC to unidirectional pulsating, and to improve various devices. On the diagram, it looks like this:
Photo - diode designation Exist different types semiconductor diodes, their classification depends on the material, principle of operation and field of use: zener diodes, pulsed, alloy, point, varicaps, laser and other types. Quite often, analogues of bridges are used - these are planar and polycrystalline rectifiers. Their message is also made with the help of two contacts.
The main advantages of a semiconductor diode:
- Complete interchangeability;
- Excellent throughput parameters;
- Availability. They can be bought at any electrical goods store or removed for free from old circuits. The price starts from 50 rubles. In our stores, both domestic brands (KD102, KD103, etc.) and foreign ones are presented.
Marking
The marking of a semiconductor diode is an abbreviation for the main parameters of the device. For example, KD196V is a silicon diode with a breakdown voltage of up to 0.3 V, a voltage of 9.6, a model of the third development.
Based on this:
- The first letter identifies the material from which the device is made;
- Device name;
- The number that determines the purpose;
- Device voltage;
- A number that defines other parameters (depends on the type of part).
Video: the use of diodes
Principle of operation
Semiconductor or rectifier diodes have a fairly simple principle of operation. As we have already said, the diode is made of silicon in such a way that one of its ends is p-type and the other end is n-type. This means that both contacts have different characteristics. One has an excess of electrons, while the other has an excess of holes. Naturally, there is a region in the device in which all the electrons fill certain gaps. This means that there are no external charges. Due to the fact that this region is depleted of charge carriers and is known as the unifying region.
Photo - the principle of operation Despite the fact that the connecting section is very small (often its size is a few thousandths of a millimeter), the current cannot flow in it in the usual way. If a voltage is applied such that the p-type area becomes positive and the n-type area, respectively, negative, the holes go to the negative pole and help the electrons pass through the pooling area. In the same way, electrons move to the positive contact and, as it were, bypass the unifying one. Despite the fact that all particles move with different charges in different directions, in the end they form a unidirectional current, which helps to rectify the signal and prevent voltage surges at the diode contacts.
If voltage is applied to a semiconductor diode in the opposite direction, no current will flow through it. The reason is that the holes are attracted by the negative potential, which is in the p-type region. Similarly, electrons are attracted to a positive potential that is applied to the n-type region. This causes the merging area to increase in size, making the flow of directional particles impossible.
Photo - characteristics of semiconductors IV-characteristics
The current-voltage characteristic of a semiconductor diode depends on the material from which it is made and some parameters. For example, an ideal semiconductor rectifier or diode has the following parameters:
- Direct connection resistance - 0 ohm;
- Thermal potential - VG \u003d + -0.1 V .;
- In the straight section, RD > rD, i.e., the direct resistance is greater than the differential one.
If all parameters match, then the following graph is obtained:
Photo - CVC of an ideal diode Such a diode is used in digital electrical engineering, the laser industry, and it is also used in the development of medical equipment. It is necessary for high demands on logic functions. Examples are laser diode, photodiode.
In practice, these parameters are very different from the real ones. Many devices are simply not capable of working with such high accuracy, or such requirements are not needed. The equivalent circuit characteristic of a real semiconductor demonstrates that it has serious drawbacks:
Photo - CVC in a real semiconductor diode This IV characteristic of a semiconductor diode indicates that during direct switching, the contacts must reach the maximum voltage. Then the semiconductor will open to the passage of electronic charged particles. These properties also demonstrate that the current will flow normally and without interruption. But until all parameters are matched, the diode does not conduct current. At the same time, for a silicon rectifier, the voltage varies within 0.7, and for a germanium one - 0.3 Volts.
The operation of the device is very dependent on the level of maximum forward current that can pass through the diode. On the diagram, it is defined by ID_MAX. The device is designed in such a way that when switched on in a direct way, it can only withstand electricity limited strength. Otherwise, the rectifier will overheat and burn out like a normal LED. Various types of devices are used to control temperature. Naturally, some of them affect the conductivity, but they prolong the performance of the diode.
Another disadvantage is that when passing AC current, the diode is not an ideal isolating device. It only works in one direction, but leakage current must always be taken into account. Its formula depends on the remaining parameters of the diode used. Most often, schemes designate it as I OP. A study by independent experts found that germanium passes up to 200 µA, and silicon up to 30 µA. At the same time, many imported models are limited to a leakage of 0.5 µA.
Photo - domestic diodes All types of diodes are susceptible to voltage breakdown. This is a property of the network, which is characterized by limited voltage. Any stabilizing device must withstand it (zener diode, transistor, thyristor, diode bridge and capacitor). When the external potential difference of the contacts of a rectifier semiconductor diode is significantly higher than the limited voltage, then the diode becomes a conductor, reducing the resistance to a minimum in one second. The purpose of the device does not allow it to do such jumps, otherwise it will distort the VAC.
A semiconductor diode is a semiconductor device with one p-n junction and two terminals.
According to the functional purpose, they distinguish:
1) Rectifier diodes.
2) Zener diodes.
3) Pulse and high-frequency diodes.
4) Tunnel diodes.
5) Varicaps.
Rectifier Diodes designed to rectify alternating current with a frequency of 50 Hz into direct current. The main property of the electron-hole transition is used - one-way conduction.
It is one p-n junction in a sealed housing with two leads. The positive terminal is called the anode, the negative terminal is called the cathode.
Figure 19 shows the structure of a rectifier diode.
Figure 19 - The structure of the rectifier diode
The diode in electrical circuits is designated in accordance with Figure 20.
Figure 20 - Image of a diode in electrical circuits
The graph of the relationship between current and voltage is called the current-voltage characteristic (VAC). The rectifier diode has a non-linear IV characteristic.
The characteristic for the direct connection of the diode initially has a significant non-linearity, since as the forward voltage increases, the resistance of the barrier layer increases gradually. At a certain voltage, the barrier layer practically disappears, and then the characteristic becomes almost linear.
When turned on again, the current increases sharply. This happens due to sharp increase potential barrier to p-n junction, the diffusion current sharply decreases, and the drift current increases. However, with a further increase in the reverse voltage, the increase in current is insignificant.
Figure 21 shows the current-voltage characteristic of a rectifier diode.
Figure 21 - IV characteristic of a rectifier diode
The parameters of rectifier diodes are a value that characterizes the most significant properties of the device.
There are: static and limiting parameters.
Static: Determined by static characteristics (see figure 22).
Figure 22 - Additional constructions for determining the static parameters of the rectifier diode
1. The steepness of the current-voltage characteristic:
S = DI / DU , mA / V
where DI is the current increment;
DU - voltage increment.
The slope of the current-voltage characteristic shows how many milliamps the current will change with an increase in voltage by 1 volt.
2. Internal resistance of the diode to alternating current.
Ri \u003d DU / DI, Ohm
3. Diode DC resistance.
R 0 \u003d U / I, Ohm
Limit Mode Options:
Exceeding them leads to the failure of the device. Taking into account these parameters, an electrical circuit is built.
1. I PR.DOP - admissible value of direct current;
2. U OBR.DOP - allowable value of the reverse voltage;
3. R RASS - allowable power dissipation.
The main disadvantage of all semiconductor devices is the dependence of their parameters on temperature. As the temperature increases, the concentration of charge carriers increases and the conductivity of the transition increases. The reverse current is greatly increased. With an increase in temperature, electrical breakdown occurs earlier. Figure 23 shows the effect of temperature on the CVC.
Figure 23 - Effect of temperature on the CVC of the diode
On the basis of a rectifier diode, you can build a simple half-wave rectifier circuit (see Figure 24).
Figure 24 - Scheme of the simplest rectifier
The circuit consists of a transformer T, which serves to convert the initial voltage into a voltage of the desired value; Rectifier diode VD, which serves to rectify alternating current, capacitor C, which serves to smooth out ripples and load R n.
