The simplest circuit for switching on a zener diode in voltage stabilization mode is shown in Fig. 18. In this mode, the voltage on the zener diode

remains practically constant, therefore the voltage on the load is constant U Н = U st – const. In this case, the equation for the entire chain has the form: E = 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 select R ST correctly. Typically, RST is calculated for the midpoint A of the zener diode characteristics (Fig. 19). If we assume that E min  E  E max , then

If the voltage E changes in any direction, then the zener diode current 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, then 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).

From the above expressions it follows that in order to stabilize in a wider range of changes in the input voltage E, R CT must be increased, and 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 provided by the zener diode, it is possible to include an additional resistance in series with the load (Fig. 20). The R ext value is calculated using Ohm's law. However, in this case the load resistance R CT must be constant.

U Н =U CT ─I Н 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, it is possible to switch on a temperature-dependent resistance R T in series with the zener diode, having TKR T inverse according to the law TKU CT.

For zener diodes with TKU CT >0, the p-n junction of an additional diode connected in the forward direction can be used as R T.

For stabilization with temperature compensation, special two-anode zener diodes are produced, which are connected to the circuit arbitrarily, with one diode connected in the reverse direction - providing stabilization mode, and the other in forward direction - temperature compensation mode (Fig. 22).

1.10.2. Stabilizers

The current-voltage characteristic of a stabistor differs little from the current-voltage 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 doped semiconductors. This ensures a small r b and a small value of R diff. Weak dependence of U PR on I PR at

working area (Fig. 23) allows the use of stabistors to stabilize low voltages of the order of 0.7V. By connecting stabistors in series, you can select the required stabilization voltage.

The simplest parallel stabilizer consists of a ballast resistor connected in series between the power source and the load, and a zener diode that shunts the load to a common wire (“to ground”). It can be thought of as a voltage divider that uses a zener diode as the low side. The difference between the supply voltage and the breakdown voltage of the zener diode drops across the ballast resistor, and the supply current flowing through it branches into the load current and the zener diode current. Stabilizers of this kind are called parametric: they stabilize the voltage due to the nonlinearity of the current-voltage characteristic of the zener diode, and do not use feedback circuits.

The calculation of a parametric stabilizer on semiconductor zener diodes is similar to the calculation of a stabilizer on gas-filled devices, with one significant difference: gas-filled zener diodes are characterized by threshold voltage hysteresis. When there is a capacitive load, the gas-filled zener diode is self-excited, so the designs of such stabilizers usually do not contain capacitive filters, and the designer does not need to take into account transient processes in these filters. In stabilizers based on semiconductor zener diodes, there is no hysteresis; filter capacitors are connected directly to the terminals of the zener diode and the load - as a result, the designer must take into account the surge current of the charge (discharge) of these capacitors when turning the power on (off). The worst cases in which the stabilizer elements are likely to fail or stabilization to fail are:

• Supplying the maximum possible supply voltage to the stabilizer input in the event of a short circuit of the stabilizer output to the common wire - for example, while charging a discharged capacitor connected directly to the stabilizer output, or in the event of a catastrophic failure of the zener diode. The permissible power dissipation of the ballast resistor must be sufficient to withstand such a short circuit. Otherwise, the ballast resistor is likely to be destroyed.
• Supplying the maximum possible supply voltage to the stabilizer input when the load is disconnected from the stabilizer output. The permissible current of the zener diode must exceed the calculated current through the ballast resistor, determined by Ohm's law. Otherwise, when the zener diode crystal is heated above +175 °C, the zener diode is destroyed. Compliance with the safety data sheet is just as important for zener diodes as for transistors.
• The load selects the maximum possible current when the minimum possible supply voltage is supplied to the stabilizer input. The resistance of the ballast resistor must be small enough so that, even under these conditions, the current through the resistor exceeds the load current by an amount equal to the minimum permissible current of the zener diode. Otherwise, the zener diode current is interrupted and stabilization stops.

In practice, it often turns out that it is impossible to meet all three conditions, both for reasons of the cost of components and because of the limited range of operating currents of the zener diode. First of all, you can sacrifice the condition of short circuit protection, entrusting it to fuses or thyristor protection circuits, or rely on the internal resistance of the power supply, which will not allow it to produce both the maximum voltage and maximum current at the same time.

Series and parallel connection

In the documentation for foreign-made zener diodes, the possibility of their serial or parallel connection is usually not considered. In the documentation for Soviet zener diodes there are two formulations:

• for low and medium power devices, “serial or parallel connection of any number of zener diodes” [of the same series] is allowed;
• for medium and high power devices, “a series connection of any number of zener diodes [of the same series] is allowed.” Parallel connection is permitted provided that the total power dissipation on all parallel-connected zener diodes does not exceed the maximum permissible power for one zener diode."

Series connection of zener diodes different series is possible provided that the operating currents of the series chain fall within the rated stabilization current ranges each used series. There is no need to shunt zener diodes with high-resistance equalizing resistors, as is done in rectifier columns. “Any number” of zener diodes connected in series is possible, but in practice is limited by technical conditions for the electrical safety of high-voltage devices. Subject to these conditions, when selecting zener diodes according to TKN and their thermostatting, it is possible to construct precision high-voltage voltage standards. For example, in the 1990s, the zener diode standard of 1 million V, built by the Russian company Megavolt-Metrology for the Canadian energy institute IREQ, had the best stability indicators in the world. The main error of this installation did not exceed 20 ppm, and the temperature instability was no more than 2.5 ppm over the entire operating temperature range.

Composite Zener diode

If the circuit requires greater currents and powers to be removed from the zener diode than is permissible according to technical conditions, then a DC buffer amplifier is connected between the zener diode and the load. In a “composite zener diode” circuit, the collector junction of the single current-amplifying transistor is connected in parallel with the zener diode, and the emitter junction is in series with the zener diode. The resistance that sets the bias of the transistor is selected so that the transistor smoothly turns on at a zener diode current approximately equal to its rated stabilization current. For example, with I degree no. =5 mA and U be.min. =500 mV resistance R=500 mV/5 mA=100 Ohm, and the voltage on the “composite zener diode” is equal to the sum of U st.nom. and U be.min. . At high currents, the transistor opens and shunts the zener diode, and the zener diode current increases slightly - by an amount equal to the base current of the transistor, therefore, to a first approximation, the differential resistance of the circuit decreases by a factor (- current gain of the transistor). The TKN of the circuit is equal to the algebraic sum of the TKN of the zener diode at I st.nom. and TKN of a forward biased diode (approximately -2 mV/°C), and its area of ​​safe operation in practice is limited by the OBR of the transistor used.

The compound zener circuit is not designed for "forward current" operation, but is easily converted to double-ended ("two-node zener") using a diode bridge.

Basic circuit of a series regulator

The simplest circuit of a series stabilizer also contains only a zener diode, a transistor and a ballast resistance, but the transistor in it is connected according to a circuit with a common collector (emitter follower). The temperature coefficient of such a stabilizer is equal to the algebraic difference U st.nom. Zener diode and U be.min. transistor; to neutralize the influence of U boe.min. in practical circuits, a directly connected diode VD2 is connected in series with the zener diode. The minimum voltage drop across the control transistor can be reduced by replacing the ballast resistor with a transistor current source.

Stabilization voltage multiplication

To stabilize a voltage that exceeds the maximum voltage of typical small-sized zener diodes, you can assemble a composite “high-voltage zener diode”, for example, dial a voltage of 200 V from series-connected zener diodes of 90, 90 and 20 V. But at the same time, the noise voltage and instability of such a circuit may be unacceptable are high, and filtering the noise of the high-voltage circuit will require expensive, massive capacitors. Significantly better characteristics have a circuit that multiplies the voltage of a single low-noise low-voltage zener diode by a voltage of 5...7 V. In this circuit, as well as in a conventional temperature-compensated zener diode, the reference voltage is equal to the sum of the breakdown voltage of the zener diode and the base-emitter junction voltage of the bipolar transistor. The reference voltage multiplication factor is determined by the divider R2-R3. The actual multiplication factor is slightly larger than the calculated one due to the current branching into the base of the transistor.

For reasons of safety and ease of installation, it is more convenient to use a PNP transistor in a positive voltage stabilizer, and an NPN transistor in a negative voltage stabilizer. In these configurations, the power transistor collector is electrically connected to common and can be mounted directly to the chassis without insulating pads. For reasons of availability and cost, it is easier and cheaper to use NPN transistors in stabilizers of any polarity. At voltages and currents typical of tube amplifiers, the capacitance of the capacitor shunting the zener diode should be several thousand microfarads. Moreover, it not only filters the low-frequency noise of the zener diode, but also ensures a smooth increase in voltage when the circuit starts up. As a result, when the power is turned on, the thermal load on the series resistance R1 increases.

ION on a temperature-compensated zener diode

Temperature-compensated zener diodes are usually supplied with direct current from a transistor or integrated current source. Using a basic circuit with a ballast resistor does not make sense, since even when the circuit is powered with a stabilized voltage, the current instability will be unacceptably high. Low-current zener diodes for a current of 1 mA are usually powered from current sources based on bipolar transistors, field-effect transistors with a p-n junction, zener diodes for a current of 10 mA are usually powered from current sources based on MOS transistors with a built-in channel in depletion mode. The integrated current sources of the LM134/LM334 family allow currents up to 10 mA, but are not recommended for use in circuits with currents greater than 1 mA due to high temperature instability (+0.336%/°C).

High-resistance loads with a constant, relatively thermally stable resistance can be connected directly to the zener diode terminals. In other cases, a buffer amplifier using a precision operational amplifier or discrete bipolar transistors is connected between the zener diode and the load. In well-designed circuits of this kind, which have undergone long-term electrical and thermal training, instability during long-term operation is about 100 ppm per month - significantly higher than the same indicator for precision integral IONs.

Zener diode white noise generator

The intrinsic noise of the avalanche breakdown zener diode has a spectrum close to the spectrum of white noise. In 9...12 V zener diodes, the noise level is high enough that it can be used for targeted noise generation. The frequency range of such a generator is determined by the bandwidth of the voltage amplifier and can extend to hundreds of MHz. The illustrations above show two possible designs of amplifiers: in the first case, the upper limit frequency of the amplifier (1 MHz) is set by the capacitance C2, in the second it is determined by the bandwidth of the integrated amplifiers (900 MHz) and the quality of installation.

The noise level of a particular zener diode is hardly predictable and can only be determined experimentally. Some early series of zener diodes were characterized by particularly high noise levels, but as technology improved they were replaced by low-noise devices. Therefore, in serial products it is more justified to use not zener diodes, but high-frequency bipolar transistors in reverse connection, for example, the 2N918 transistor developed back in the 1960s - its noise spectrum extends to 1 GHz.

Programmable jumpers on zener diodes

A zener diode based on a reverse-biased emitter junction of an integral planar npn transistor (“surface zener diode”) differs from discrete zener diodes in its low maximum stabilization current. The maximum reverse current allowed in a typical emitter structure with aluminum metallization does not exceed 100 μA. At high currents, a visible flash occurs in the surface layer and an aluminum jumper appears under the oxide layer, forever turning the dead zener diode into a resistor with a resistance of about 1 Ohm.

This disadvantage of integrated zener diodes is widely used in the production of analog integrated circuits to fine-tune their parameters. In technology burning out zener diodes(English) zener zapping) in parallel with the switched resistances, elementary zener diode cells are formed. If it is necessary to adjust the value of the circuit resistance or the voltage divider coefficient, unnecessary zener diode cells are burned with current pulses of 5 ms duration and a force of 0.3-1.8 A, short-circuiting the corresponding resistors. The same technique can be used in digital ICs with aluminum metallization.

6. Generalized classification of power plants according to various criteria, transformative power plants and power plants for obtaining control actions.

7. Controlled control systems, generalized block diagram of a technological object with controlled control systems.

22. Characteristics of thyristor turn-off, turn-off time (recovery).

8. Classification of executive power plants.

9. Classification of converter power plants.

10. Simple and combined converters and their block diagrams.

17. Determination of the main losses in valves at low frequencies.

11. The role of computers and microprocessor technology in the development of power plants.

12. Types of conversion of electrical energy parameters, examples of the use of converter power plants.

13. The main passive components used in power plants: resistors, capacitors, inductors, main parameters and design features.

14. Power semiconductor devices (SPD), general information, directions of development and classification according to the degree of controllability.

15. Power diodes (valves), physical basis and design, system of designations and markings, system of parameters and characteristics, special groups of parameters.

16. Equivalent thermal circuit of a power diode, internal and total steady-state thermal resistance.

18. Components of additional losses in controlled and uncontrolled SPP.

19. Serial and parallel connection of power diodes, calculation of equalizing elements.

20. Power zener diodes and voltage limiters, symbol, main parameters and voltage, areas of use.

23. System of thyristor parameters for current and voltage.

24. System of dynamic parameters of a thyristor.

21. Thyristors, block diagram, two-transistor model and thyristor voltage-voltage, switching conditions and characteristics.

34. Principles of constructing modern power bipolar transistors, basic parameters.

25. Characteristics of the thyristor control transition and control circuit parameters.

26. Dependence of thyristor parameters on temperature, thyristor notation and marking system.

27. Basic structure, designation, voltage and parameters of a triac, areas of use of a triac.

29. Basic structures and operating principles of a turn-off thyristor and a combined turn-off thyristor.

28. Structure, designation and parameters of thyristor optocouplers, areas of their use.

33. Basic circuits of thyristor locking devices, determination of the circuit recovery time of thyristors.

30. Structure and voltage-voltage of a thyristor-diode.

32. Requirements for thyristor control pulses, operating modes of control pulse generators.

36. Construction of powerful switching elements based on pt. Advantages and disadvantages of pt.

38. Timing diagrams for turning off igbt and the dependence of the open transistor voltage on temperature.

37. Structure, equivalent circuit and graphical symbols of insulated gate bipolar transistors (IGBT), operating principle, advantages and disadvantages.

39. Structure of construction and circuits of power semiconductor modules (SPM), areas of use.

41. Structure and design features of turn-off thyristors of the gct and igbt types, principles of operation, parameters and areas of use.

42. Operating modes of self-propelled control systems in power plants and their characteristics.

44. Executive control systems, classification, areas of use.

45. Switching power amplifiers, basic circuits, operating features, calculation of elements.

54. Transformative power plants, classification, areas of use.

46. ​​Methods for generating control actions, the structure of control circuits for power amplifiers.

51. Pulse-width regulators (pulse-width) of direct current, classification, basic circuits and their features.

52. Adjustment characteristics of successive widths, calculation of basic elements.

53. Adjustment characteristics of parallel widths, calculation of the main elements.

55. Rectifiers for single and three-phase power supply, structure, classification, main operational parameters and characteristics.

56. Basic circuits of single-phase power supply rectifiers, time diagrams of their operation for various types of loads, calculation of basic parameters and characteristics.

1. Half-wave rectification circuit

2. Full-wave rectification circuit with zero point output

3. Single-phase bridge rectification circuit

57. Basic circuits of three-phase power supply rectifiers, timing diagrams of operation for various types of loads, calculation of basic parameters and characteristics.

59. Time diagrams of operation of adjustable three-phase power supply rectifiers for various types of loads, adjustment characteristics.

61. Block diagrams of control systems for adjustable rectifiers and integrated circuits, main components and their implementation.

63. Autonomous current inverters (ACI), classification, basic circuits, timing diagrams of operation, calculation of basic parameters and characteristics, examples of use in control systems.

62. Autonomous inverters (AI), definition, purpose, classification, areas of use.

63. Autonomous current inverters (ACI), classification, basic circuits, timing diagrams of operation, calculation of basic parameters and characteristics, examples of use in control systems.

65. Autonomous resonant inverters (air), definition, classification, physical processes and operating features.

66. Basic air circuits without counter diodes, timing diagram of operation, calculation of main parameters and characteristics, advantages and disadvantages.

67. Basic air circuits with built-in diodes and frequency doubling, timing diagrams of operation, calculation of basic parameters and characteristics.

68. Use of air with counter diodes and frequency doubling in control systems of electrical technological installations.

40. Power intelligent devices (SIP), structure, classification, features and protective functions of SIP.

72. Structure of high-speed protection systems for power plants during emergency conditions, main elements and requirements for them.

19. Serial and parallel connection of power diodes, calculation of equalizing elements.

Currently, 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 current-voltage characteristics, uneven distributions of voltages or currents arise between individual diodes. In Fig. Figure 1.3 shows the following diagrams: serial (Fig. 1.3, a) and parallel (Fig. 1.3, 6) connections of two diodes. The forward (Fig. 1.3, d) and reverse (Fig. 1.3, c) branches of the current-voltage characteristics of the connected diodes are also presented there. According to the given current-voltage 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 diode VD1, and voltage U R 2 is applied to diode VD 2 (Fig. 1-3, c) . When diodes are connected in parallel, the total current I F flowing through them at equal forward voltage drops U F is also distributed unevenly: current I F 1 flows through diode VD 1, and current I F 2 flows through diode VD2 (Fig. 1.3d). To prevent failure of diodes due to overcurrent or overvoltage, special measures are taken to equalize the specified parameters between individual diodes. When diodes are connected in series, resistors connected in parallel to the diodes are usually used to equalize the voltages, and inductive dividers of various types are used when connected in parallel.

Rice. 1.3. Series and parallel connection of diodes

20. Power zener diodes and voltage limiters, symbol, main parameters and voltage, areas of use.

Zener diode (Zener diode) is a semiconductor diode designed to maintain the voltage of the power source at a given level. Compared to conventional diodes, it has a fairly low regulated breakdown voltage (when turned on in reverse) and can maintain this voltage at a constant level even 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

Tunnel breakdown of a p-n junction (Zener effect in English literature). Despite the similar results of action, these mechanisms are different, although they are present together in any zener diode, but only one of them predominates. 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 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 optimal solution for devices with a wide temperature range of use [source not specified 321 days]. The breakdown mode is not associated with the injection of minority charge carriers. Therefore, in a 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 back are practically absent. This allows them to be used in pulse circuits as level clamps and limiters.

Types of zener diodes: precision- have increased stability of stabilization voltage, for which additional standards are introduced for temporary voltage instability and temperature coefficient of voltage (for example: 2S191, KS211, KS520); bilateral- provide stabilization and limitation of bipolar voltages, for which the absolute value of the stabilization voltage asymmetry is additionally normalized (for example: 2S170A, 2S182A); fast-acting- have a reduced barrier capacitance value (tens of pF) and a short duration of the transient process (units ns), which makes it possible to stabilize and limit short-term voltage pulses (for example: 2S175E, KS182E, 2S211E).

There are microcircuits of linear voltage regulators with two terminals, which have the same connection circuit as the zener diode, and often the same designation on electrical circuit diagrams.

Typical circuit for switching on a zener diode

Designation of a zener diode on circuit diagrams

Designation of a two-anode zener diode on circuit diagrams

Options. Stabilization voltage- the voltage value on the zener diode during the passage of a given stabilization current. The breakdown voltage of the diode, and therefore 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 voltage stabilization- a value determined by the ratio of the relative change in 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- a value determined by the ratio of the stabilization voltage increment to the small current increment that caused it in a given frequency range. Maximum permissible power dissipation- maximum constant or average power dissipated on the zener diode, at which the specified reliability is ensured.

The very name of this device “zener diode” is consonant with the word stability or constancy of something or in something. Stability is very important in a person’s life, stability in salary, prices in the store, etc. In electronics, supply voltage stability is a very important, basic parameter that is checked first when setting up or repairing electronic equipment. The voltage in the electrical network can change depending on the overall load, the quality of the power supply networks, and many other factors, but the supply voltage of electronic devices must remain constant at a certain specified value.

So, what is a zener diode?

Wikipedia will give you this definition:

"A semiconductor zener diode, or Zener diode, is a semiconductor diode that operates under reverse bias in the breakdown mode. Before breakdown occurs, minor leakage currents flow through the zener diode..."

Everything is correct, but too abstruse.

I'll try to put it more simply

A zener diode is a semiconductor device that stabilizes voltage.

I think that at first this definition is enough (and I will tell you below how it stabilizes the voltage)

The principle of operation of a zener diode

Dear reader, this figure shows the operating principle of a zener diode.

Imagine that water is poured into a certain container, the water level in the container must be strictly defined, so that the container does not overflow, an overflow pipe is made in it through which water exceeding a given level will pour out of the container.

Now from “plumbing” let’s move on to electronics.

The designation of the zener diode on the circuit diagram is the same as that of the diode, the difference between the “dash” of the cathode is depicted as the letter G.

Designation of the zener diode in the diagram

The zener diode operates only in a direct current circuit, and passes voltage in the forward anode-cathode direction in the same way as a diode. Unlike a diode, a zener diode has one feature: if current is applied in the reverse direction to the cathode - anode, no current will flow through the zener diode, but current will not flow in the opposite direction only until the voltage exceeds the specified value.

What is the voltage reference value for a zener diode?

The zener diode has its own parameters - stabilization voltage and current. The voltage parameter indicates at what voltage the zener diode will pass current in the opposite direction, the current parameter specifies the current strength at which the zener diode can operate without being damaged.

Zener diodes are made to stabilize voltages of various values, for example, a zener diode with the designation V6.8 will stabilize the voltage within 6.8 Volts.

Table of operating parameters of zener diodes.

The table shows the main parameters - stabilization voltage and stabilization current. There are other parameters, but you don't need them yet. The main thing is to understand the essence of how a zener diode works and learn how to choose the one you need for your circuits and for repairing radio electronics.

Let's consider a circuit diagram explaining the principle of operation of a zener diode.

Let's take the zener diode as a parameter - the stabilization voltage is 12 Volts. In order for current to flow through the zener diode in the opposite direction from the cathode to the anode, the input voltage must be higher than the stabilization voltage of the zener diode (with a margin). For example, if a zener diode is designed for a stabilization voltage of 12V, the input voltage must be at least 15V. Ballast resistor Rb limits the current that will pass through the zener diode to the nominal value.As you can see, at a voltage exceeding the stabilization current of the zener diode, it begins to dump the excess voltage through itself to minus. In other words, the zener diode acts as an overflow pipe; the greater the water pressure or the magnitude of the electric current, the more the zener diode opens, and vice versa, as the voltage decreases, the zener diode begins to close, reducing the flow of current through itself.

These changes can occur either smoothly or with great speed in short time intervals, which makes it possible to achieve a high voltage stabilization coefficient.

If the voltage at the input of the stabilizer is less than 12 Volts, the zener diode will “close” and the voltage at the output of the stabilizer will “float” in the same way as at the input, but there will be no voltage stability. That is why the input voltage must be greater than the required output voltage (with a margin).The given diagram is calledparametric stabilizer. Who If he wants a complete breakdown of how to calculate a parametric stabilizer, let him visit Google, for us beginners it’s enough for the first time, let’s not bother ourselves with formulas.

Now let's move on to the labs (laboratory work:).

In front of you is a mock-up of a parametric stabilizer; there are voltmeters at the input and output of the mock-up. Now the voltmeter at the INPUT of the stabilizer shows 6 volts at the OUTPUT of the stabilizer, almost the same voltage. As I already said, the zener diode of the prototype has a stabilization voltage of 8 and 2 volts, a voltage of 6 volts at the INPUT of the stabilizer does not exceed the stabilization voltage of the zener diode, so the zener diode is closed.

Now I increase the voltage at the input of the stabilizer to 15 Volts, the voltage at the input of the stabilizer exceeded the stabilization voltage of the zener diode and at the output of the stabilizer it reached the specified stabilization voltage of 8.2 Volts, and so it remains, practically unchanged, even with sudden surges in voltage, the zener diode works instantly, maintaining voltage stability . I repeat again - “In order for a parametric stabilizer to work correctly, there must always be a voltage at the input that exceeds the stabilization voltage of the zener diode, i.e., with a margin of approximately 15-25%”

Since the stabilization current of such a parametric stabilizer is too small, the parametric stabilizer is usually used in power supplies as a stabilizing element of the circuit, where, in addition to the stabilizer itself, there are voltage regulation elements and powerful transistors.

An example is a circuit of an adjustable stabilizer (power supply).

In modern electronics, parametric stabilizers are used less and less, mainly using special microcircuits, which are quite powerful stabilizers with a very good stabilization coefficient, they are compact and easy to use.

But we'll talk about them next time. However, parametric stabilizers can be found in many different electronic circuits, so you need to know them and understand a basic operating principle.

How to check zener diode

To check the zener diode, you need to know how to use a multimeter and use the technique for testing a semiconductor diode. If possible, you can assemble a parametric stabilizer circuit and check the zener diode in operation, as described in this article. If you have a zener diode and you don’t know its parameters (the inscription on the body of the stub has been erased), by assembling a circuit of a parametric stabilizer, you can determine what stabilization voltage this unidentified stub operates at.

A zener diode, also known as a Zener diode, is named after the discoverer of tunnel breakdown, Clarence Zener, and is designated in the diagrams as follows.

But unlike a rectifier diode, current can flow through it in both directions.

To better understand its operation, you can imagine it as two diodes connected back-to-back, but with different voltage drops.

For any zener diode, the voltage drop across one of its diodes is approximately 0.7 volts, and the voltage drop across the other depends on the chosen zener diode, since different zener diodes have different stabilization voltages (from 3 to 400 volts). For example, for the BZX55C3V3, the forward voltage drop is 0.7 volts, and the breakdown voltage, by our analogy, the voltage drop across the second diode is 3.3 volts.

What is described above becomes more clear if you look at the volt-ampere characteristic (VAC) of the zener diode.

The right branch of the current-voltage characteristic is similar to the current-voltage characteristic of a diode, and the left branch is responsible for the same tunnel breakdown. Until the reverse voltage reaches the breakdown voltage, practically no current flows through the zener diode, apart from leakage. With a further increase in the reverse voltage, at a certain moment a breakdown begins, it is characterized by a bend in the current-voltage characteristic. A further increase in the reverse voltage leads to a tunnel breakdown; in this state, the current through the zener diode increases, but the voltage does not.

A distinctive feature of tunnel breakdown is its reversibility, that is, after removing the applied voltage, the zener diode will return to its original state. If the maximum permissible current is exceeded and a thermal breakdown occurs, the zener diode will fail.

The simplest circuit of a zener diode stabilizer looks like this.

Let's assemble it by connecting an oscilloscope instead of a load and applying a triangular signal with an amplitude of 10 volts to the input. The generator voltage is the first channel, the voltage on the zener diode is the second channel.

The oscillogram shows that the voltage at the zener diode varies from -0.88 to 3.04 volts.

In order to understand why this happens, let's replace the diagram above with two equivalent ones.
When the zener diode is switched on directly, when there is a plus on the anode, there is a minus on the cathode.

When the zener diode is switched back on, when there is a minus on the anode, there is a plus on the cathode.

Before this, we did not take into account the load resistance. Before considering how the circuit behaves under load, it is necessary to familiarize yourself with the basic characteristics of the zener diode.

• Vz - stabilization voltage, usually the minimum and maximum values ​​are indicated
• Iz and Zz - minimum stabilization current and zener diode resistance
• Izk and Zzk- current and resistance at the point where the “break” of the characteristic begins
• Ir and Vr- reverse current and voltage at a given temperature
• Tc- temperature coefficient
• Izrm- maximum stabilization current

What happens when we connect the load?
The current flowing through the zener diode will decrease, since part of it will flow through the load. The question is how much it will decrease if the current through the zener diode becomes less minimum stabilization current The zener diode will no longer stabilize the voltage and the entire supply voltage will be applied to the load. From this we can conclude that when the load is disconnected, the current through the zener diode must be equal to the sum of 2 currents, the minimum stabilization current and the load current.
This sum of currents is set using a quenching resistor, in our circuit its nominal value is 1K.

The formula for calculating it is as follows