At present, power diodes have been created for currents over 1000 A and voltages over 1000 V.
When diodes are connected in series and in parallel, due to the mismatch of their I–V characteristics, uneven distributions of voltages or currents between individual diodes occur. On fig. 1.3 shows diagrams: serial (Fig. 1.3, a) and parallel (Fig. 1.3, 6) connection of two diodes. There are also direct (Fig. 1.3, d) and reverse (Fig. 1.3, c) branches of the I–V characteristics of the connected diodes. According to the given I–V characteristics, when diodes are connected in series, the reverse voltage U R applied to them at the same reverse currents I R is distributed unevenly between the diodes: voltage U R 1 is applied to the diode VD1, and voltage U R 2 is applied to the diode VD 2 (Fig. 1-3, c) . When the diodes are connected in parallel, the total current I F flowing through them with the same direct voltage drops U F is also unevenly distributed: the current I F 1 flows through the diode VD 1, and the current I F 2 (Fig. 1.3, d). To avoid failure of diodes due to overcurrent or overvoltages, special measures are taken to equalize the specified parameters between individual diodes. When diodes are connected in series, resistors connected in parallel with diodes are usually used to equalize voltages, and when connected in parallel, inductive dividers of various types are used.
Rice. 1.3. Series and parallel connection of diodes
A zener diode (Zener diode) is a semiconductor diode designed to maintain the voltage of a power source at a given level. Compared to conventional diodes, it has a fairly low regulated breakdown voltage (when reversed) and can maintain this voltage at a constant level with a significant change in the reverse current strength. The materials used to create the p-n junction of zener diodes have a high concentration of alloying elements (impurities). Therefore, at relatively small reverse voltages, a strong electric field arises in the junction, causing its electrical breakdown, which in this case is reversible (if thermal breakdown does not occur due to too much current). The operation of the zener diode is based on two mechanisms: Avalanche breakdown of the p-n junction
Tunneling breakdown of p-n junction (Zener effect in English literature). Despite the similar results of the action, these mechanisms are different, although they are present in any zener diode together, but only one of them prevails. For zener diodes up to a voltage of 5.6 volts, tunnel breakdown with a negative temperature coefficient predominates [source not specified 304 days], above 5.6 volts an avalanche breakdown with a positive temperature coefficient becomes dominant [source not specified 304 days]. At a voltage of 5.6 volts, both effects are balanced, so choosing this voltage is the best solution for devices with a wide temperature range of application [source not specified 321 days]. The breakdown mode is not related to the injection of minor charge carriers. Therefore, in the zener diode, injection phenomena associated with the accumulation and resorption of charge carriers during the transition from the breakdown region to the blocking region and vice versa are practically absent. This allows them to be used in pulse circuits as level clamps and limiters.
Types of zener diodes: precision- have increased stabilization voltage stability, for them additional standards are introduced for temporary voltage instability and voltage temperature coefficient (for example: 2S191, KS211, KS520); bilateral- provide stabilization and limitation of bipolar voltages, for them the absolute value of the asymmetry of the stabilization voltage is additionally normalized (for example: 2S170A, 2S182A); fast acting- have a reduced value of the barrier capacitance (tens of pF) and a short duration of the transient process (a few ns), which makes it possible to stabilize and limit short-term voltage pulses (for example: 2S175E, KS182E, 2S211E).
There are two-terminal linear voltage regulator microcircuits that have the same switching circuit as the zener diode, and often the same designation on electrical circuit diagrams.
Typical zener diode switching circuit 
Zener diode designation on circuit diagrams 
Designation of a two-anode zener diode on circuit diagrams 
Options. Stabilization voltage- the value of the voltage on the zener diode during the passage of a given stabilization current. The breakdown voltage of the diode, and hence the stabilization voltage of the zener diode, depends on the thickness of the p-n junction or on the resistivity of the diode base. Therefore, different zener diodes have different stabilization voltages (from 3 to 400 V). Temperature coefficient of stabilization voltage- the value determined by the ratio of the relative change in the ambient temperature at a constant stabilization current. The values of this parameter are different for different zener diodes. The coefficient can have both positive and negative values for high-voltage and low-voltage zener diodes, respectively. The change in sign corresponds to a stabilization voltage of about 6V. Differential resistance- the value determined by the ratio of the stabilization voltage increment to the small current increment that caused it in a given frequency range. Maximum allowable power dissipation- the maximum constant or average power dissipated on the zener diode, at which the specified reliability is ensured.
A zener diode is a special diode that is capable of operating under reverse bias conditions in the breakdown zone without any damage to itself.
The voltage-current curve for a zener diode is similar to the voltage-current curve for the P-N junction of a conventional diode.
When a zener diode is forward biased, then, as in any conventional diode, the current passing through it increases with increasing applied voltage. When the zener diode is reverse biased, the current is minimal until the applied voltage reaches the breakdown voltage value for a given diode. When this voltage is reached, there is a significant increase in the flowing current. However, unlike a conventional diode, the zener diode is designed to operate under reverse bias conditions in the breakdown zone.
The required voltage of the zener diode is the voltage at which breakdown occurs. In the process of manufacturing a zener diode, a certain amount of other materials, additives, are added to the main raw materials, so that during the operation of this device, breakdown occurs at a very specific voltage value.
If the voltage applied to the zener diode exceeds its breakdown voltage by a large enough amount, the heat that accompanies the passage of excessive current through the zener diode can cause serious damage. To prevent this kind of trouble, zener diode circuits usually have a resistor in series to limit the amount of current flowing through the zener diode. If the correct resistance value is selected, then the current in the circuit will not exceed the maximum current value for the zener diode.
If the applied voltage is less than that for which the zener diode is designed, then the resistance to current flow will be significant and this diode will remain basically in the open state, however, when the applied voltage becomes equal to or exceeds the rated voltage of the zener diode, then the current resistance will be overcome, and current will flow through the zener diode and through the circuit.
At various voltages above the zener voltage, the change in internal resistance results from changes in the depletion region of the device. As a result, the voltage drop across the zener diode will be relatively constant. The voltage drop must be kept close to the Zener voltage. The rest of the power supply voltage is lowered by the resistor connected in series.
Since the zener voltage is much higher than the zener voltage, the circuit we have just described can be used to supply a regulated voltage to a load. If the load is connected in parallel with the zener diode, then the voltage drop across the load will be equal to the voltage drop across the zener diode.
Many, many years ago, such a word as a zener diode did not exist at all. Especially in home appliances.
Let's try to imagine a bulky tube receiver of the middle of the twentieth century. Many sacrificed them to their own curiosity, when dad and mom got something new, and "Record" or "Neman" were given to be torn to pieces.
The tube receiver power supply was extremely simple: a powerful power transformer cube, which usually had only two secondary windings, a diode bridge or selenium rectifier, two electrolytic capacitors and a two-watt resistor between them.
The first winding fed the glow of all receiver lamps with alternating current and a voltage of 6.3V (volts), and about 240V came to a primitive rectifier to power the anodes of the lamps. There was no talk of any voltage stabilization. Based on the fact that the reception of radio stations was carried out on long, medium and short waves with a very narrow band and terrible quality, the presence or absence of stabilization of the supply voltage did not affect this quality at all, and there simply could not be a decent auto-tuning of the frequency on that element base.
Stabilizers at that time were used only in military receivers and transmitters, of course, also tube ones. For example: SG1P- gas-discharge stabilizer, finger-type. This continued until the advent of transistors. And then it turned out that circuits made on transistors are very sensitive to fluctuations in the supply voltage, and an ordinary simple rectifier is no longer enough. Using the physical principle inherent in gas-discharge devices, a semiconductor zener diode, less commonly called a Zener diode, was created.
Graphical representation of a zener diode on circuit diagrams.
Appearance of zener diodes. First on top in a surface mount package. The second from the top is in a DO-35 glass case and has a power of 0.5 W. The third one is 1 W (DO-41). Naturally, zener diodes are made in a variety of cases. Sometimes two elements are combined in one case.
First of all, we should not forget that the zener diode only works in DC circuits. The voltage is applied to it in reverse polarity, that is, a minus "-" will be applied to the anode of the zener diode. With this connection, a reverse current flows through it ( I arr) from the rectifier. The voltage from the rectifier output can change, the reverse current will also change, and the voltage at the zener diode and at the load will remain unchanged, that is, stable. The following figure shows the volt-ampere characteristic of a zener diode.
The zener diode works on the reverse branch of the I-V characteristic (Volt-Ampere Characteristic), as shown in the figure. Its main parameters are U st. (stabilization voltage) and I st. (stabilization current). These data are indicated in the passport for a specific type of zener diode. Moreover, the value of the maximum and minimum current is taken into account only when calculating stabilizers with a predicted large voltage change.
In order to choose the right zener diode, you need to understand the markings of semiconductor devices. Previously, all types of diodes, including zener diodes, were designated by the letter “D” and a number that determines what kind of device it is. Here is an example of a very popular zener diode D814 (A, B, C, D). The letter showed the stabilization voltage.
Next to the passport data of a modern zener diode ( 2C147A ), which was used in stabilizers to power circuits on the popular series of K155 and K133 microcircuits made using TTL technology and having a supply voltage of 5V.
To understand the markings and the main parameters of modern domestic semiconductor devices, you need to know a little about the symbols. They look like this: number 1 or letter G - germanium, number 2 or letter K - silicon, number 3 or letter A - gallium arsenide. This is the first sign. D - diode, T - transistor, C - zener diode, L - LED. This is the second sign. The third character is a group of numbers indicating the scope of the device. Hence: GT 313 (1T 313) - a high-frequency germanium transistor, 2S147 - a silicon zener diode with a nominal stabilization voltage of 4.7 volts, AL307 - a gallium arsenide LED.
Here is a diagram of a simple but reliable voltage regulator.
Between the collector of a powerful transistor and the case, a voltage is supplied from the rectifier and equal to 12 - 15 volts. From the emitter of the transistor, we remove 9V of a stabilized voltage, since we use a reliable D814B element as a zener diode VD1 (see table). Resistor R1 - 1 kOhm, transistor KT819 providing current up to 10 amperes.
The transistor must be placed on a heatsink. The only drawback of this circuit is the inability to adjust the output voltage. In more complex circuits, a tuning resistor, of course, is available. All laboratory and home amateur radio power supplies have the ability to adjust the output voltage from 0 to 20 - 25 volts.
The development of integrated microelectronics and the emergence of multifunctional circuits of medium and large degrees of integration, of course, also affected the problems associated with voltage stabilization. The domestic industry tensed up and launched the K142 series on the market of radio-electronic components, which was made up of just integral stabilizers. The full name of the product was KR142EN5A, but since the case was small and the name was not completely removed, they began to write KREN5A or B, and in conversation they were simply called “rolls”.
The series itself was quite large. Depending on the letter, the output voltage varied. For example, KREN3 gave out from 3 to 30 volts with the ability to adjust, and KREN15 was a fifteen-volt bipolar power source.
Connecting the integrated stabilizers of the K142 series was extremely simple. Two smoothing capacitors and the stabilizer itself. Take a look at the diagram.
If there is a need to get another stabilized voltage, then proceed as follows: let's say we use the KREN5A chip at 5V, but we need a different voltage. Then a zener diode is placed between the second output and the case in such a way that by adding the stabilization voltage of the microcircuit, and the zener diode, we would get the desired voltage. If we add a KS191 zener diode to V = 9.1 + 5V of the microcircuit, then we will get 14.1 volts at the output.
The simplest circuit for switching on a zener diode in the voltage stabilization mode is shown in fig. 18. In this mode, the voltage on the zener diode
remains practically constant, therefore, the voltage at the load is constant U H \u003d U st - const. In this case, the equation for the entire chain has the form: E \u003d U st + R st (I st - I H).
Most often, the zener diode operates in a mode where the voltage E is not stable, and R H is const. To maintain the stabilization mode, you must correctly select R CT. Usually, RCT is calculated for the midpoint A of the zener diode characteristic (Fig. 19). If we assume that E min E E max , then
If the voltage E changes in any direction, then the current of the zener diode will change, but the voltage on it U CT, and, consequently, on the load remains practically unchanged.
All voltage changes are absorbed by R CT , so the following condition must be met: 
The second stabilization mode: the input voltage is constant, and R H varies from R H min to R H max, in this case: 
,
;
.
Since R CT is constant, the voltage drop across it equal to E−U CT is also constant, so the current through R CT I CP +I H CP must be constant. This is possible when the stabilization current I CP and I H change to the same extent, but in opposite directions (i.e. the sum is constant).
It follows from the above expressions that in order to stabilize in a wider range of changes in the input voltage E, R CT must be increased, and in order to stabilize in the mode of changing the load current, R CT must be reduced (reducing R CT is not profitable, excess source energy is wasted).
If it is necessary to obtain a stable voltage lower than that given by the zener diode, it is possible to turn on additional resistance in series with the load (Fig. 20). The value of R ext is calculated according to Ohm's law. However, in this case, the load resistance R CT must be constant.
U H \u003d U CT ─I H R ext
To obtain higher stable voltages, zener diodes are connected in series, with the same stabilization currents (Fig. 21).
U CT =U CT 1 +U CT 2
To compensate for the temperature drift U CT in series with the zener diode, it is possible to turn on a thermo-dependent resistance R T , which has TKR T inverse according to the law TKU CT .
For zener diodes with TCU CT > 0, the p-n junction of an additional diode connected in the forward direction can be used as R T .
For stabilization with thermal compensation, special two-anode zener diodes are produced, which are included in the circuit arbitrarily, with one diode connected in the opposite direction - it provides stabilization mode, and the other in the forward direction - thermal compensation mode (Fig. 22).
The I-V characteristic of a stabistor differs little from the I-V characteristic of rectifier diodes.
However, in order to ensure the greatest steepness of the direct branch of the current-voltage characteristic, stabistors are made of highly alloyed semiconductors. This provides a small r b and a small value of R diff. Weak dependence of U PR on I PR on
working area (Fig. 23) allows the use of stabistors to stabilize small voltages of the order of 0.7V. By connecting the stabistors in series, you can select the required stabilization voltage.
The simplest circuit for switching on a zener diode in the voltage stabilization mode is shown in fig. 18. In this mode, the voltage on the zener diode
remains practically constant, therefore, the voltage at the load is constant U H \u003d U st - const. In this case, the equation for the entire chain has the form: E \u003d U st + R st (I st - I H).
Most often, the zener diode operates in a mode where the voltage E is not stable, and R H is const. To maintain the stabilization mode, you must correctly select R CT. Usually, RCT is calculated for the midpoint A of the zener diode characteristic (Fig. 19). If we assume that E min £ E £ E max , then
If the voltage E changes in any direction, then the current of the zener diode will change, but the voltage on it U CT, and, consequently, on the load remains practically unchanged.
All voltage changes are absorbed by R CT , so the following condition must be met: 
The second stabilization mode: the input voltage is constant, and R H varies from R H min to R H max, in this case: 
, 
; 
.
Since R CT is constant, the voltage drop across it equal to E−U CT is also constant, so the current through R CT I CP +I H CP must be constant. This is possible when the stabilization current I CP and I H change to the same extent, but in opposite directions (i.e. the sum is constant).
It follows from the above expressions that in order to stabilize in a wider range of changes in the input voltage E, R CT must be increased, and in order to stabilize in the mode of changing the load current, R CT must be reduced (reducing R CT is not profitable, excess source energy is wasted).
If it is necessary to obtain a stable voltage lower than that given by the zener diode, it is possible to turn on additional resistance in series with the load (Fig. 20). The value of R ext is calculated according to Ohm's law. However, in this case, the load resistance R CT must be constant.
U H \u003d U CT ─ I H R ext
To obtain higher stable voltages, zener diodes are connected in series, with the same stabilization currents (Fig. 21).
U CT =U CT 1 +U CT 2
To compensate for the temperature drift U CT in series with the zener diode, it is possible to turn on a thermo-dependent resistance R T , which has TKR T inverse according to the law TKU CT .
For zener diodes with TCU CT > 0, the p-n junction of an additional diode connected in the forward direction can be used as R T .
For stabilization with thermal compensation, special two-anode zener diodes are produced, which are included in the circuit arbitrarily, with one diode connected in the opposite direction - it provides stabilization mode, and the other in the forward direction - thermal compensation mode (Fig. 22).
Stabistors
The I-V characteristic of a stabistor differs little from the I-V characteristic of rectifier diodes.
However, in order to ensure the greatest steepness of the direct branch of the current-voltage characteristic, stabistors are made of highly alloyed semiconductors. This provides a small r b and a small value of R diff. Weak dependence of U PR on I PR on
working area (Fig. 23) allows the use of stabistors to stabilize small voltages of the order of 0.7V. By connecting the stabistors in series, you can select the required stabilization voltage.
tunnel diodes
Tunnel diodes are semiconductor devices, the CVC of which has a section with a negative differential resistance (Fig. 24).
Tunnel diodes are made from semiconductors with a high concentration of impurities. As a result, the thickness of the barrier layer of the p-n junction is very small (0.01–0.02 µm), which creates conditions for the tunnel effect.
The presence of a high concentration of impurities causes the splitting of impurity levels into bands and a strong curvature of the energy bands.
When a reverse voltage is applied, the current through the diode increases sharply (tunneling of electrons from the p to the n region). This is equivalent to a tunnel breakdown of a p-n junction.
When a forward bias is applied, the flux of electrons tunneled from the n region to the p region increases. As U pr increases, I pr increases, which reaches I max at U 1 (0 ¸ 1) (for germanium diodes U 1 = 40 ¸ 50 mV; for gallium arsenides - U 1 = 100 ¸ 150 mV). At these displacements, the diffusion current through the potential barrier is negligible, and I pr is determined only by the tunneling effect. With a further increase in U PR, I PR decreases (the overlap of energy bands decreases). When U PR \u003d U 2, the tunnel current is zero (1¸2).
This section of the I–V characteristic is characterized by a negative differential resistance 
because DI< 0.
In point 2, I PR \u003d I min is the usual direct diffusion current of the diode. (i.e. in point 2 the tunnel diode behaves like a normal diode), the tunnel effect is over.
With a further increase in U PR, I PR increases (2¸3) due to an increase in the diffusion current - overcoming the electrons of the potential barrier.
The main features of the CVC of tunnel diodes:
Plot with negative differential resistance R diff;
Large currents at reverse biases.
Main parameters:
Maximum current I max - corresponds to the peak of the current-voltage characteristic;
Minimum current I min - corresponds to the minimum CVC;
Peak voltage U 1 - corresponds to current I max;
Voltage U 2 - corresponds to I min;
Maximum I PR;
U PR corresponds to I PR max ;
Constant reverse voltage;
Diode capacitance.
Tunnel diodes are used in ultra-high-speed switching circuits (up to 1000 MHz).
A variety of tunnel diodes are inverted diodes. Their feature is the practical absence of a section with a negative differential resistance on the direct branch of the I–V characteristic (Fig. 25).
In terms of the shape of the I–V characteristic of a reversed diode, it represents an inverted I–V characteristic of a conventional diode.
The open state for such diodes corresponds to reverse bias. With reverse bias, the current through the diode is highly dependent on voltage. Advantage - diodes can operate at very low voltages.
They have good frequency properties, tk. tunneling is a fast-acting process, and the displacements are small, so there is practically no injection and accumulation of minority carriers.
Reversed diodes are used in the microwave range. The advantage of tunnel and inverted diodes is high radiation resistance, due to the high concentration of impurities.
Varicaps
A varicap is a semiconductor diode that is used as a voltage-controlled non-linear capacitance (pn junction capacitance is a function of applied voltage).
In varicaps, a barrier capacitance is used, because. diffusion is shunted by a small direct resistance of the p-n junction.
The varicap works with reverse biases at the p-n junction. Its capacitance varies over a wide range (10¸1000 pF) and is determined by the expression:
,
where C 0 is the capacitance at U D \u003d 0, U K is the value of the contact potential, U is the applied reverse voltage, n \u003d 2 - for sharp p-n transitions, n \u003d 3 - for smooth transitions. With increasing U arr, the capacitance decreases. The main characteristic of the varicap is the capacitance-voltage characteristic (CVC) (Fig. 26).
Main parameters:
Varicap capacitance C in - capacitance measured at a given U arr;
The capacitance overlap coefficient is the ratio of capacitances at two given U arr; ,
− loss resistance r П – total active resistance of the varicap;
− quality factor Q B is the ratio of reactive resistance at a given frequency Х С to loss resistance ;
TKS B - temperature coefficient C B.
Light emitting diodes
A light emitting diode is a semiconductor diode designed to display information. An LED (LED) is obtained on the basis of p-n or heterojunctions with a rectifying current-voltage characteristic (Fig. 27).
The radiation in the transition region is caused by the spontaneous recombination of charge carriers during the passage of a direct current. In this case, the recombining electron passes from the CD to the OT with the release of a light quantum with the energy hu » DW 33. To obtain visible light quanta, the width ∆W of the band gap must be DW 3 ³1.7 eV. At DW 3<1,7эВ излучение находятся в инфракрасном диапазоне.
Such a value of DW 33 is possessed by GaAsP semiconductor compounds with a different ratio of elements 1.4 In conventional planar junctions, light quanta are absorbed in the semiconductor crystal due to internal reflection. Therefore, a spherical crystal shape is used in LEDs, or a flat semiconductor crystal is fused into a spherical drop of glass or plastic, which reduces the effect of internal reflection (Fig. 28). Similar information.
Thematic materials:
