Adjustable stabilizer with short-circuit protection. Stabilizer short circuit protection

Coursework

Communication, communication, radio electronics and digital devices

When the stabilizer input is overloaded, the full input voltage will be applied to the emitter-collector section of the control transistors. Therefore, to increase the reliability of this circuit, the maximum permissible voltage of the transistors used should be at least 1.5 times...

Introduction

It seems that everything has been written about continuous voltage stabilizers. However, the development of a reliable and not too complex (no more than three or four transistors) stabilizer, especially with an increased load current, is quite a serious task, because one of the first places is the requirement for reliable protection of control transistors from overload. In this case, it is desirable that after eliminating the cause of the overload, normal operation of the stabilizer is restored automatically. The desire to meet these requirements often leads to a significant complication of the stabilizer circuit and a noticeable decrease in its efficiency. In this work I will try to find the optimal solution.

1. Object of study

The object of the study is a voltage stabilizer circuit with an output current of up to 3A, which uses short-circuit protection (Fig. 1). This transistor stabilizer is designed to power radio-electronic circuits with a current of up to 3A.

Fig.1. Transistor stabilizer circuit with short circuit protection

The stabilizer provides an adjustable voltage to the load from 15 to 27V at a rated input voltage from the rectifier of 30V. Load current up to 3A. The stabilization coefficient is not less than 300, the amplitude of the output voltage ripple is not more than 10 mV.

Using variable resistor R7, the load voltage can be changed in the range from 15 to 27V, and using variable resistor R3, the protection operation current can be changed in the range from 0.15 to 3A.

Zener diode VD1 with direct connection of the p-n junction reduces the temperature drift of the device’s output voltage. Resistor R4 increases the reliability of the stabilizer at elevated temperatures. Transistor VT1 is mounted on a radiator in the form of a duralumin plate measuring 100x100x5mm. It should have the lowest possible initial current (it is advisable to use a silicon transistor). The input voltage is supplied to the stabilizer from a rectifier via a single-phase bridge circuit made using diodes.

When the stabilizer input is overloaded, the full input voltage will be applied to the emitter-collector section of the control transistors. Therefore, to increase the reliability of this circuit, the maximum permissible voltage of the transistors used must be at least 1.5 times greater than the effective value of the voltage of the secondary winding of the power transformer used in the rectifier.

Some tips from the source for optimizing the circuit:

1. If the stabilizer does not work well at low load currents, you need to reduce the resistance of the voltage divider R6, R7, R8 or load the output of the stabilizer with a constant resistor, but this reduces its efficiency. Therefore, it is better to replace transistor VT1 with another one with a lower gain value.
2. Sometimes it is useful to connect a constant resistor with a resistance of 2.2-10 kOhm between the collector and emitter of this transistor. In this case, the stabilizer reliably returns to operating mode, and the stabilization coefficient decreases slightly.
3. If the stabilizer does not return to operating mode after an overload even when the load is disconnected (this phenomenon is often observed at the value of the set protection current, that is, at the maximum resistance of resistor R3), it is necessary:
4. or reduce the resistance of resistor R3;
5. or briefly connect a resistor with a resistance of 300-510 Ohms between the collector and the emitter of transistor VT1.

2. Terms of reference

Transistor stabilizer with short circuit protection with load current from 3A

1. Purpose and goals of modernization of the facility

Purpose

Power supply for radio-electronic circuits. The stabilizer provides an adjustable voltage to the load from 15 to 27V at a rated input voltage from the rectifier of 30V. Load current up to 3A.

Purpose of modernization

Improve the electrical parameters of the device (reduce ripple voltage), replace the circuit element base with a modern one, provide protection from interference, moisture and overheating.

2. Characteristics of the modernized facility

Brief information about the object being modernized or links to documents containing such information

1. Load type: active-reactive;
2. Maximum load current: 3, A;
3. Ripple voltage at maximum load current:< 10, мВ;
4. Stabilization coefficient: > 300;
5. Output voltage: 15 - 27, V;
6. Protection current: 0.15 - 3, A

Information about the operating conditions of the automation object and environmental characteristics

Air temperature

1. working: from -50 to +50 ºС;
2. limit: from -50 to +65 ºС;

Relative air humidity: no more than 80% at 20 ºС;

Impact

rain: up to 3 mm/min;

salt fog: droplet dispersion up to 10 microns, water content up to 3 g/m3;

Beats

1. single: up to 75 g at D no more than 10 ms;
2. multiple: up to 5 g with D no more than 10 ms;

Vibrations: up to 120 Hz at 4...6 g.

3. System requirements

Object requirements

The object must comply with the characteristics specified in paragraph 2.

The facility must provide

1. power supply of equipment with voltage from 15 to 27V and current up to 3 A;
2. protection of electronic equipment from short circuits.

Requirements for types of collateral

Technical: provide a set of technical means necessary for each stage of device modernization.

Informational: provide the most complete information:

1. about the standards and design methods used in the process of modernizing the facility;
2. about the object being modernized and its components.

4. Development sources

GOST 15150-69. Design for different climatic regions

S. B. Shmakov. How to create your own power supplies

3. Transistor voltage stabilizers with overload protection

Before looking for the optimal solution, let's analyze the load characteristics Uout = f(Iout) of voltage stabilizers made according to the most common circuits. With some types of stabilizers, when overloaded, the output voltage Uout quickly drops to zero. However, the current does not decrease and may be sufficient to damage the load, and the power dissipated by the control transistor sometimes exceeds the permissible limit. In other versions, the stabilizer is supplemented with trigger protection. When overloaded, not only the output voltage decreases, but also the current. However, the protection is not effective enough, since it operates only after a drop in the output voltage and, under some conditions, does not eliminate the thermal overload of the control transistor. To return such a stabilizer to operating mode, it is necessary to almost completely turn off the load, and this is not always acceptable, especially for a stabilizer that serves as an integral part of a more complex device.

Fig.2. Transistor stabilizer circuit

Protection of the stabilizer, the diagram of which is shown in Fig. 2, triggers already with a slight decrease in the output voltage caused by an overload.

The ratings of the circuit elements are given for an output voltage of 12V in two versions: without brackets if VD1 is D814B, and in brackets if it is KS139E.

Its good parameters are explained by the fact that all the necessary signals are formed from a stabilized output voltage, and both transistors (regulating VT1 and controlling VT2) operate in voltage amplification mode.

Fig.3. Load characteristics

The experimentally measured load characteristics of this stabilizer are shown in Fig. 3 (curves 3 and 4).

If the output voltage deviates from the nominal value, its increment through the zener diode VD1 is transmitted almost completely to the emitter of transistor VT2. If we do not take into account the differential resistance of the zener diode, ∆ Uе˜ ∆Uout. This is a negative feedback signal. But the device also has a positive side.

It is created by part of the output voltage increment supplied to the base of the transistor through the voltage divider R2R3:The total feedback in the stabilization mode is negative, the error signal is the valuewhich in absolute value is greater, the smaller R3 is compared to R2. Reducing this ratio has a beneficial effect on the stabilization coefficient and the output resistance of the stabilizer. Considering thatZener diode VD1 should be selected for the maximum possible, but lower output stabilization voltage.

If you replace resistor R3 with two diodes connected in the forward direction and connected in series, the parameters of the stabilizer will improve, since the place of R3 in the expressions for ∆Ub and ∆Ube will be taken by the small differential resistance of open diodes. However, such a replacement leads to some problems when the stabilizer goes into protective mode. We will dwell on them below, but for now we will leave resistor R3 in the same place.

In stabilization mode, the voltage drop across resistor R1 remains virtually unchanged. The current flowing through this resistor is the sum of the zener diode current VD1 and the emitter current of transistor VT2, which is almost equal to the base current of transistor VT1.

As the load resistance decreases, the last component of the current flowing through R1 increases, and the first (zener diode current) decreases down to zero, after which the increase in output voltage is no longer transmitted to the emitter of transistor VT2 through the zener diode.

As a result, the negative feedback circuit is broken, and the positive feedback loop, which continues to operate, leads to an avalanche-like closing of both transistors and cut-off of the load current. Load current, above whichprotection is triggered, can be estimated using the formula:

where h21E current transfer coefficient by transistor VT1. Unfortunately, h21E has a large scatter from transistor instance to transistor instance, depending on current and temperature.

Therefore, resistor R1 often has to be selected during setup. In a stabilizer designed for high load current, the resistance of resistor R1 is small. As a result, the current through the zener diode VD1 increases so much when the load current decreases that it is necessary to use a zener diode of increased power.

The presence in the load characteristics (see curves 3 and 4 in Fig. 3) of relatively extended transition sections between the operating and protective modes (note that these sections are the heaviest from the point of view of the thermal regime of the transistor VT1) is explained mainly by the fact that the development of the switching process prevented by local negative feedback through resistor R1. The lower the stabilization voltage of the zener diode VD1, the higher, other things being equal, the value of resistor R1 and the more “delayed” the transition from the operating to the protective mode of the stabilizer is.

This, as well as the previously made, conclusion about the advisability of using a zener diode VD1 with the highest possible stabilization voltage is confirmed experimentally. The output voltage of the stabilizer according to the circuit shown in Fig. 2, with zener diode D814B (U C.T. = 9 V), compared to a similar zener diode KS139E (U C.T. = 3.9 V), depends much less on the load and it more “steeply” goes into protective mode when overloaded.

Fig.4. Stabilizer circuit with additional transistor VT 3

It is possible to reduce and even completely eliminate the transition section of the load characteristic of the stabilizer by adding an additional transistor VT3 to it, as shown in Fig. 4.

In operating mode, this transistor is in saturation and has virtually no effect on the operation of the stabilizer, only slightly worsening the temperature stability of the output voltage.

When, as a result of an overload, the zener diode current VD1 tends to zero, transistor VT3 goes into the active state and then closes, creating conditions for quickly turning on the protection. In this case, there is no smooth transition section of the load characteristic (see curve 1 in Fig. 3).

Diodes VD2 and VD3 in operating mode stabilize the voltage based on transistor VT2, which helps improve the basic parameters of the stabilizer. However, without an additional transistor VT3, this negatively affects the protection, as it weakens the positive component of the OS. Switching to the protective mode in this case is very delayed and occurs only after the load voltage has decreased to a value close to that supported by diodes VD2 and VD3 based on transistor VT2 (see curve 2 in Fig. 3).

The stabilizers considered have a significant drawback for many applications: they remain in a protective state after eliminating the cause of the overload, and often do not go into operating mode when the supply voltage is applied with a connected load. There are various ways to start them, for example, using an additional resistor installed parallel to the collector-emitter section of transistor VT1, or by “feeding” the base of transistor VT2. The problem is solved by a compromise between the reliability of starting under load and the magnitude of the short circuit current, which is not always acceptable.

A less common, but interesting way to remove the stabilizer from the protective mode is that a specially designed pulse generator periodically forcibly opens the control transistor, transferring the stabilizer to the operating mode for some time. If the cause of the overload is eliminated, at the end of the next impulse the protection will not work again and the stabilizer will continue to operate normally. The average power dissipated by the control transistor during overload increases slightly.

Fig.5. Stabilizer circuit with output from protective mode

In Fig. Figure 5 shows a diagram of one of the possible options for a stabilizer operating on this principle.

When overloaded, the stabilizer goes into oscillatory mode due to the positive feedback loop, which is closed through capacitor C1. Resistor R3 limits the charging current of the capacitor, and R4 serves as a generator load when the external load is closed.

In the absence of an overload after the supply voltage is applied, the stabilizer starts up thanks to resistor R2. Since capacitor C1 is shunted by a series-connected open diode VD2 and resistors R3 R5, the self-excitation conditions are not met and the device operates similarly to that discussed earlier (see Fig. 2). During the transition of the stabilizer to protective mode, capacitor C1 acts as a booster, accelerating the development of the process.

Fig.6. Equivalent circuit of the stabilizer in protective mode

The equivalent circuit of the stabilizer in protective mode is shown in Fig. 6. With load resistance R H equal to zero, the positive terminal of capacitor C1 is connected through resistor R4 to the common wire (minus of the input voltage source).

The voltage to which the capacitor was charged in stabilization mode is applied to the base of transistor VT2 in negative polarity and keeps the transistor closed.

The capacitor is discharged by current i1 flowing through resistors R3R5 and open diode VD2. When the voltage at the base of VT1 exceeds -0.7V, diode VD2 will close, but recharging of the capacitor will continue with current i2 flowing through resistor R2.

Upon reaching a small positive voltage at the base of transistor VT2, the latter, and with it VT1, will begin to open. Due to the positive feedback through capacitor C1, both transistors will open completely and remain in this state for some time until the capacitor is charged with current i3 almost to the voltage Uin, after which the transistors will close and the cycle will repeat.

With those indicated in the diagram in Fig. 6 element ratings, the duration of the generated pulses is units of milliseconds, the repetition period is 100...200 ms. The amplitude of the output current pulses in protective mode is approximately equal to the protection operation current. The average value of the short circuit current, measured with a dial milliammeter, is approximately 30 mA.

With increasing load resistance R H there comes a moment when, with transistors VT1 and VT2 open, the negative feedback “outweighs” the positive one and the generator again turns into a voltage stabilizer. R value H , at which the mode change occurs, depends mainly on the resistance of resistor R3. If its values ​​are too small (less than 5 Ohms), hysteresis appears in the load characteristic, and with zero resistance R3, voltage stabilization is restored only with a load resistance of more than 200 Ohms. An excessive increase in the resistance of resistor R3 leads to a transition section appearing in the load characteristic.

The amplitude of negative polarity pulses based on transistor VT2 reaches 10V, which can lead to electrical breakdown of the base-emitter section of this transistor. However, the breakdown is reversible, and its current is limited by resistors R1 and R3. It does not interfere with the operation of the generator. When choosing transistor VT2, it is also necessary to take into account that the voltage applied to its collector-base section reaches the sum of the input and output voltages of the stabilizer.

In operating equipment, the output of the voltage stabilizer is usually shunted by a capacitor (C2, shown in Fig. 5 with a dashed line). Its capacity should not exceed 200 μF. The limitation is due to the fact that during an overload that is not accompanied by a complete short circuit of the output, this capacitor enters the positive feedback circuit of the generator. In practice, this is expressed in the fact that the generator “starts up” only with significant overload, and hysteresis appears in the load characteristic.

The resistance of resistor R4 must be such that the voltage drop across it during the pulse is sufficient to open transistor VT2 (> 1 V) and ensure that the conditions for self-generation are met at zero load resistance. Unfortunately, in stabilization mode this resistor only reduces the efficiency of the device.

For accurate operation of the protection, it is necessary that, at any permissible load current, the minimum (including ripple) input voltage of the stabilizer remains sufficient for its normal operation. When testing all the stabilizers discussed above with a rated output voltage of 12V, the power source was a 14V bridge diode rectifier with a 10,000 µF capacitor at the output. The ripple voltage at the rectifier output, measured with a VZ-38 millivoltmeter, did not exceed 0.6 V.

If necessary, the pulse nature of the protection can be used to indicate the status of the stabilizer, including sound. In the latter case, when overloaded, clicks will be heard at a pulse repetition rate.

Fig.7. Stabilizer circuit with pulse protection

In Fig. Figure 7 shows a diagram of a more complex stabilizer with pulse protection, which is largely devoid of the disadvantages of the one discussed earlier (see Fig. 5).

Its output voltage is 12V, output resistance 0.08 Ohm, stabilization factor 250, maximum operating current 3A, protection threshold 3.2A, average load current in protective mode 60 mA.

The presence of an amplifier on transistor VT2 allows, if necessary, to significantly increase the operating current by replacing transistor VT1 with a more powerful composite one. The protection algorithm for this stabilizer differs little from that previously described.

There is no series resistor in the output circuit of the stabilizer (similar to R4, see Fig. 5) that degrades the efficiency; resistor R1 serves as the generator load. The purpose of diodes VD1, VD2 and transistor VT4 is similar to elements VD2, VD3 and VT3 in the stabilizer according to the circuit shown in Fig. 4.

The value of the limiting resistor R4 can range from tens of ohms to 51 kOhms. The output of the stabilizer can be bypassed with a capacitor with a capacity of up to 1000 μF, which, however, leads to the appearance of hysteresis in the load characteristic: at a protection threshold of 3.2 A, the measured value of the return current to stabilization mode is 1.9 A.

To clearly switch modes, it is necessary that, with a decrease in load resistance, the current through the zener diode VD3 stops before the transistor VT2 enters saturation.

Therefore, the value of resistor R1 is chosen in such a way that before the protection operates, a voltage of at least 2...3 V remains between the collector and emitter of this transistor. In protective mode, transistor VT2 enters saturation, as a result, the amplitude of the load current pulses can be 1.2. .. 1.5 times the protection operation current. It should be taken into account that with a significant decrease in resistance R1, the power dissipated by transistor VT2 significantly increases.

The presence of capacitor C1 can theoretically lead to an increase in the ripple of the output voltage of the stabilizer. The output stabilized voltage is equal to the sum of the voltage drops across the diodes VD1 and VD2, the base-emitter section of transistor VT4 and the stabilization voltage of the zener diode VD3 minus the voltage drop at the base-emitter section of transistor VT3 approximately 1.4 V greater than the stabilization voltage of the zener diode. The protection trip current is calculatedaccording to the formula

Thanks to the additional amplifier on transistor VT2, the current flowing through resistor R3 is relatively small, even with significant calculated load currents.

This, on the one hand, improves the efficiency of the stabilizer, but on the other hand, it forces the use of a zener diode capable of operating at low currents as VD3. The minimum stabilization current of the KS211Zh zener diode shown in the diagram (see Fig. 7) is 0.5 mA.

Such a stabilizer, in addition to its intended purpose, can serve as a battery discharge limiter. To do this, the output voltage is set so that if the battery voltage is less than the permissible value, the protection will operate, preventing further discharge. In this case, it is advisable to increase the value of resistor R6 to 10 kOhm. As a result, the current consumed by the device in operating mode will decrease from 12 to 2.5 mA. It should be borne in mind that on the verge of tripping the protection, this current increases to approximately 60 mA, but with the start of the pulse generator, the average value of the battery discharge current drops to 4...6 mA.

Using the considered principle of pulse protection, it is possible to build not only voltage stabilizers, but also self-healing electronic “fuses” installed between the power source and the load. Unlike fuse links, such fuses can be used repeatedly without worrying about restoration after eliminating the cause of the trip.

The electronic fuse must withstand both short-term and long-term, full or partial load faults. The latter often occurs with long connecting wires, the resistance of which is a significant part of the payload. This case is most severe for the switching element of the fuse.

Fig.8. Scheme of a self-resetting electronic fuse with pulse protection

In Fig. Figure 8 shows a diagram of a simple self-resetting electronic fuse with pulse protection. The principle of its operation is close to the voltage stabilizer described above (see Fig. 5), but before the protection is triggered, transistors VT1 and VT2 are in a state of saturation and the output voltage is almost equal to the input. If the load current exceeds the permissible value, transistor VT1 comes out of saturation and the output voltage begins to decrease.

Its increment through capacitor C1 goes to the base of transistor VT2, closing the latter, and with it VT1. The output voltage decreases even more, and as a result of an avalanche-like process, transistors VT1 and VT2 are completely closed. After some time, depending on the time constant of the R1C1 circuit, they will open again, however, if the overload remains, they will close again. This cycle is repeated until the overload is eliminated.

The frequency of the generated pulses is approximately 20 Hz with a load slightly exceeding the permissible load, and 200 Hz with a full load. The duty cycle of the pulses in the latter case is more than 100. When the load resistance increases to an acceptable value, the transistor VT1 will enter saturation and the generation of pulses will stop. The tripping current of the "fuse" can be approximately determined by the formula

The coefficient of 0.25, selected experimentally, takes into account that at the moment of transition of transistor VT1 from saturation to active mode, its current transfer coefficient is significantly less than the nominal one.

The measured protection trip current at an input voltage of 12V 0.35A, the amplitude of the load current pulses when it is closed 1.3 A.

Hysteresis (the difference between the currents of protection operation and restoration of the operating mode) was not detected. If necessary, blocking capacitors with a total capacity of no more than 200 μF can be connected to the “fuse” output, which will increase the operating current to approximately 0.5 A.

If it is necessary to limit the amplitude of load current pulses, a resistor of several tens of ohms should be included in the emitter circuit of transistor VT2 and the value of resistor R3 should be slightly increased.

If the load is not fully closed, an electrical breakdown of the base-emitter section of transistor VT2 is possible. This has little effect on the operation of the generator, and does not pose a danger to the transistor, since the charge accumulated in capacitor C1 before breakdown is relatively small.

Fig.9. Fuse diagram without efficiency reduction

The disadvantages of the “fuse” assembled according to the considered circuit (Fig. 8) are low efficiency due to the resistor R3 connected in series to the load circuit and the base current of the transistor VT1, which is independent of the load.

The latter is also typical for other similar devices. Both reasons that reduce efficiency are eliminated in a more powerful “fuse” with a maximum load current of 5A, the circuit of which is shown in Fig. 9.

Its efficiency exceeds 90% over a more than tenfold range of load current changes. Current consumption when there is no load is less than 0.5 mA.

To reduce the voltage drop across the “fuse”, a germanium transistor is used as VT4. When the load current is less than permissible, this transistor is on the verge of saturation. This state is maintained by a negative feedback loop, which, when transistor VT2 is open and saturated, is formed by transistors VT1 and VT3. The voltage drop in the collector-emitter section of transistor VT4 does not exceed 0.5 V at a load current of 1 A and 0.6 V at 5 A.

When the load current is less than the protection response current, transistor VT3 is in active mode and the voltage between its collector and emitter is sufficient to open transistor VT6, which ensures the saturated state of transistor VT2 and, ultimately, the conducting state of switch VT4. With an increase in load current, the base current of VT3 under the influence of negative feedback increases, and the voltage at its collector decreases until transistor VT6 closes. At this moment the protection is triggered. The operation current can be estimated using the formula

where Req is the total resistance of resistors R4, R6 and R8 connected in parallel.

Coefficient 0.5, as in the previous case, is experimental. When the load is closed, the amplitude of the output current pulses is approximately twice as large as the protection operation current.

Thanks to the action of the positive OS, which closes through capacitor C2, transistor VT6, and with it VT2VT4, are completely closed, and VT5 opens. The transistors remain in the indicated states until capacitor C2 is charged by the current flowing through the base-emitter section of transistor VT5 and resistors R7, R9, R11, R12. Since R12 has the largest value of the listed resistors, it determines the repetition period of the generated pulses, approximately 2.5 s.

After charging of capacitor C2 is complete, transistor VT5 will close, VT6 and VT2VT4 will open. Capacitor C2 will discharge in approximately 0.06 s through transistor VT6, diode VD1 and resistor R11. With a closed load, the collector current of transistor VT4 at this time reaches 8... 10A. Then the cycle will repeat. However, during the first pulse after eliminating the overload, transistor VT3 will not go into saturation and the “fuse” will return to operating mode.

It is interesting that during the pulse, transistor VT6 does not open completely. This is prevented by the negative feedback loop formed by transistors VT2, VT3, VT6. With the value of resistor R9 (51 kOhm) indicated in the diagram (Fig. 9), the voltage at the collector of transistor VT6 does not fall below 0.3Uin..

The most unfavorable load for the “fuse” is a powerful incandescent lamp, whose resistance of the cold filament is several times less than that of the heated filament. A test carried out with a 12V 32 + 6 W car lamp showed that 0.06 s for warming up is quite enough and the “fuse”, after turning it on, reliably enters the operating mode. But for more inertial lamps, the duration and repetition period of the pulses may have to be increased by installing a capacitor C2 of a higher rating (but not an oxide one).

The duty cycle of the generated pulses as a result of such a replacement will remain the same. It was not chosen by chance to be equal to 40. In this case, both at the maximum load current (5 A) and when the “fuse” output is closed, approximately the same and safe power is dissipated on transistor VT4.

The GT806A transistor can be replaced with another from the same series or a powerful germanium transistor, for example, P210, with any letter index. If germanium transistors are not available or it is necessary to operate at elevated temperatures, you can also use silicon transistors with h21e>40, for example, KT818 or KT8101 with any letter indices, increasing the value of resistor R5 to 10 kOhm. After such a replacement, the voltage measured between the collector and emitter of transistor VT4 did not exceed 0.8V at a load current of 5A.

When making a “fuse,” the VT4 transistor must be mounted on a heat sink, for example, an aluminum plate with dimensions of 80 x 50 x 5 mm. A heat sink with an area of ​​1.5...2 cm² is also needed for the VT3 transistor,

Turn on the device for the first time without a load, and first of all, check the voltage between the collector and emitter of transistor VT4, which should be approximately 0.5 V. Then a wire-wound variable resistor with a resistance of 10...20 Ohms and a power of 100 W is connected to the output through an ammeter.

4. Simulation

Rice. 10. Transistor stabilizer circuit

Initially, the circuit was assembled using ideal elements, after which they were replaced with real ones. The circuit elements have been replaced with analogues from the database Multisim.

Fig. 11. Oscillogram of device operation

Red line signal from the input of the circuit, blue from the output.

We offer to order in our online store popular stabilizing devices with an energy-saving control mode and a fully automatic system for eliminating emergency situations in the electrical network. The main objectives of these Energia and Voltron brands are: fail-safe protection against short circuits, high-speed equalization of high and low power supplies in household and industrial consumer networks and solving problems associated with unpredictable short-term overloads. The official manufacturer of Russian recommended equipment for 220V, 380V electrical networks is the ETK Energy company. The stabilization accuracy of some household rulers is only ±3% and ±5%, thanks to which they will work ideally even with high-precision medical devices. You can buy a voltage stabilizer with short circuit protection in Moscow, St. Petersburg and the region. Many domestic single-phase and three-phase brands Energia and Voltron offered for purchase are excellent for simple and highly sensitive modern electrical equipment also because they have smooth automatic adjustment of dangerous input surges and sags. The best Russian-made electrical appliances at the moment are considered to be new, improved models with a pure sinusoidal waveform, namely: Energy Hybrid, Classic and Ultra. It is also worth noting that during the operation of these lines there is absolutely no flickering of light bulbs. The universal housing of automatic devices Energia Classic, Ultra, Hybrid U and Voltron RSN provides, in addition to standard floor operation, compact wall installation.

Single-phase and three-phase voltage stabilizers with short-circuit protection, widely presented on our website today, are in great consumer demand for highly efficient and durable protection of various individual low-power equipment and the entire home, apartment, office, country house, educational, entertainment and medical institutions, industrial and other facilities where problems often arise in a 1-phase or 3-phase network. The model range consists of mid- and premium-class devices with maximum capacities provided by the manufacturer for 1, 2, 3, 5, 8, 10, 15, 20 and 30 kW (kVA). Therefore, with us you can choose such electrical equipment even for the safety of the largest cottage or industrial premises with a large number of consumers in use. You can buy a voltage stabilizer with short-circuit protection in Moscow, St. Petersburg from us at an affordable price. According to the type of equalization of low-quality power supply in the household electrical network, there are relay, electronic (thyristor) and electromechanical Russian network devices. Almost all series have high technical characteristics and are additionally equipped with a self-diagnostic system for carefully monitoring the state of the power supply at the input and output. For continuous use in conditions of negative external temperatures (up to -20, -30 degrees Celsius) there are special frost-resistant models. A digital display allows you to monitor important parameters on the network. With us you can choose high-quality and very reliable low-noise and absolutely silent network equipment with multi-level protection against emergency failures. Warranty 1-3 years. The manufacturer's stated service life for most of our certified electrical appliances is at least 10 years. All devices can be used 24 hours a day.

Currently, stabilization devices made on microcircuits are widely used in electronics. An integrated voltage stabilizer is a device in which all the elements included in the design are arranged on a silicon chip in such a way that the sequence of these connections and components constitutes a stabilizer circuit.

Such stabilizers can be found in different types of electronic equipment: in amplifiers, in power supplies of televisions, telephones, and audio systems.

Types of stabilizers

Two types of integrated stabilizers are widely used in electronics:

• semiconductor (solid-state);
• hybrid-film (with elements made from films).

Semiconductor stabilizers, in turn, are divided into several groups:

1. having adjustable output voltage - require the connection of additional elements;
2. having a fixed voltage supplied to the output - they are a ready-to-use product that does not require additional connections to the circuit;
3. bipolar – used for devices requiring bipolar output voltage.

Characteristics

A typical integrated stabilizer circuit consists of the following elements:

• reference voltage source;
• error amplifier;
• adjustment elements connected between the source and the load;
• circuit for turning off the device when a signal is supplied from the outside;
• transistor for protection against short circuit or overload.

Integrated stabilizer chips are functionally complete devices and have only three external pins: input, output and ground. These microcircuits are manufactured for fixed voltage values ​​from 5 to 24 V and loads up to 1 A.

Stabilization devices on the IC are provided with built-in circuits that limit the output current, as well as an overload protection circuit for temperature.

The value of ION in the stabilizer circuit

The reference voltage source is one of the key elements, since it performs the task of maintaining a stable voltage at the nominal value at the output when the input voltage changes. The simplest version of this source is a parametric stabilizer based on a zener diode. With their help you can get a voltage of 2.5 V.

If it is necessary to obtain lower reference voltage values, series connections of silicon diodes are used.

Also, integrated stabilizers can use voltage as a source
emitter junction of bipolar transistors.

Advantages and disadvantages

The advantages of integrated linear voltage stabilizers include:

1. high stabilizing coefficient;
2. high smoothing coefficient of the load voltage value;
3. low output impedance;
4. do not produce their own interference.

However, the efficiency of such stabilizers is low and decreases at low output voltages. An increase in efficiency is possible by increasing the size and dimensions of the device, which is not always a convenient and profitable option.

Voltage stabilizer 12 Volt

In situations where using a full-fledged 12-Volt power supply is pointless, it is much easier to lower the main voltage of the circuit locally in some part of it; an integrated 12-Volt voltage stabilizer is used. Such stabilizers are produced on the basis of the domestic KR142EN series or popular microcircuits of the 78XX line.

Such stabilizers are equipped with current and overheat protection, which makes power supplies using them virtually invulnerable. These properties make the stabilizer useful for a number of electronic devices:

• household electrical appliances;
• measuring, laboratory equipment;
• radio electronics, etc.

The stabilizer has such characteristics as the presence of an internal thermal regulation system, a protection circuit for the output transistor, and self-protection against short-circuit pulses. The output current of the device is 1 A - 1.5 A, the maximum voltage value is 30 - 35 V.

Stabilizer 12 V 5 A

An integrated voltage stabilizer 12 Volt 5 Ampere can be based on the LM 338 chip and have the following characteristics:

1. input voltage – from 3 to 35 Volts;
2. output voltage – from 1.2 to 32 Volts;
3. output current – ​​5 Amperes;
4. permissible temperature range – from 0 to 125 degrees Celsius;
5. output voltage error is no more than 0.1%.

Such an imported integrated stabilizer is a universal microcircuit, on the basis of which it is possible to obtain high-quality power circuits by connecting it in various ways.

Foreign integrated stabilizers

The well-known 78XX line of positive voltage compensation devices was successfully created by specialists from Texas Instruments. These stabilizers are provided with protection against short-circuit currents, against exceeding the operating temperature of the crystal, as well as against the operating point crossing the boundaries of the operating mode acceptable for safe operation.

In addition to fixed voltage stabilizers, adjustable modifications of integrated stabilization devices are also produced abroad. Prominent representatives of such devices are considered to be the “317” line of microcircuits. The voltage supplied to the output of these microcircuits is determined by a divider on two resistors.

Important points

When using imported integrated voltage stabilizers, it is worth considering some features:

• A capacitor with a capacity of 47 - 220 nF should be connected to the input and output of the device to prevent self-excitation;
• If the capacitor connected to the output has a large capacity and the load current is low, a diode must be connected between the input and output. This will ensure a rapid decrease in the output voltage to the input value;
• for stable operation of the device, the input voltage value must be selected higher than the output voltage by at least 3V;
• devices of the “law-drop” line, characterized by a small voltage difference from input to output, for stable stabilization must be provided with an input voltage that exceeds the output voltage by 0.1 - 0.5 V.

In transistor stabilizers, three types of protection are most often used: from increasing the output voltage, from decreasing the output voltage, from overcurrent or short circuit in the load.

Overcurrent protection in stabilizers can be limited to a constant level of I K.Z. exceeding the value of I NOM or with a sharp decrease in current consumption to I K.Z.0 in short circuit mode. In the first case, the overcurrent mode is characterized by greater power allocated to the control transistor. Therefore, in such cases, the supply voltage at the stabilizer input is usually turned off. In the second case, the power dissipated by the transistor during a short circuit is significantly less than the power at the rated load current. Therefore, turning off the power in such a circuit is not necessary.

Traditional transistor stabilizers often have unreliable overload protection. Inertia-free protection systems falsely trigger even from short-term overloads when connecting a capacitive load. Inertial protection means do not have time to operate in the event of a strong current pulse, for example, in the event of a short circuit leading to breakdown of transistors. Devices with an output current limiter are inertia-free; they do not have a trigger effect, but in the event of a short circuit, a large amount of power is dissipated on the control transistor, which requires the use of an appropriate heat sink .

The only way out in this situation is the simultaneous use of means for limiting the output current and inertial protection of the control transistor from overload, which will provide it with two to three times less power and heat sink dimensions. But this leads to an increase in the number of elements, design dimensions and complicates the repeatability of the device in amateur conditions.

A schematic diagram of a stabilizer, the number of elements in which is minimal, is shown in Fig. 1. The source of the reference voltage is a thermally stabilized zener diode VD1.

To eliminate the influence of the input voltage of the stabilizer on the mode of the zener diode, its current is set by a stable current generator (GCT), built on a field-effect transistor VT1. Thermal stabilization and stabilization of the Zener diode current increase the output voltage stabilization coefficient.

The reference voltage is supplied to the left (according to the circuit) input of the differential amplifier on transistors VT2.2 and VT2.3 of the K125NT1 microassembly and resistor R7, where it is compared with the feedback voltage taken from the output voltage divider R8R9. The voltage difference at the inputs of a differential amplifier changes the balance of the collector currents of its transistors.

The regulating transistor VT4, controlled by the collector current of the transistor VT2.2, has a large base current transfer coefficient. This increases the depth of feedback and increases the stabilization coefficient of the device, and also reduces the power dissipated by the differential amplifier transistors.

Let's look at the operation of the device in more detail.

Let us assume that in steady state, with an increase in the load current, the output voltage will decrease slightly, which will also cause a decrease in the voltage at the emitter junction of transistor VT3.2. At the same time, the collector current will also decrease. This will lead to an increase in the current of transistor VT2.2, since the sum of the output currents of the differential amplifier transistors is equal to the current flowing through resistor R7, and practically does not depend on the operating mode of its transistors.

In turn, the growing current of transistor VT2.2 causes an increase in the collector current of the regulating transistor VT4, proportional to its base current transfer coefficient, increasing the output voltage to the original level and allows it to be maintained unchanged regardless of the load current.

For short-term protection of the device with its return to its original state, a collector current limiter of the regulating transistor is introduced, made on transistor VT3 and resistors R1, R2.

Resistor P1 performs the function of a current sensor flowing through the regulating transistor VT4. If the current of this transistor exceeds the maximum value (about 0.5 A), the voltage drop across resistor R1 will reach 0.6 V, i.e. the threshold voltage for opening transistor VT3. Opening, it shunts the emitter junction of the control transistor, thereby limiting its current to approximately up to 0.5 A.

Thus, when the load current briefly exceeds the maximum value, transistors VT3 and VT4 operate in the GTS mode, which causes a drop in the output voltage without tripping the overcurrent protection. After some time, proportional to the time constant of circuit R5C1, this leads to the opening of transistor VT2.1 and the further opening of transistor VT3, which closes transistor VT4. This state of the transistors is stable, therefore, after eliminating the short circuit or de-energizing the load, it is necessary to disconnect the device from the network and turn it on again after discharging capacitor C1.

The considered continuous compensation voltage stabilizer reduces the maximum power dissipated by the control transistor in short-circuit mode. The electrical circuit diagram of the stabilizer is shown in Fig. 5.

Current limit mode

Resistor R 1 is a current sensor. In case of overcurrent on R 1 a voltage arises, which through a resistor R 2 supplied to the base-emitter junction of the transistor VT3 , which opens slightly. As a result, base and collector currents appear VT3 , which reduce the base current of the transistor VT2 , the collector currents of the transistors decrease accordingly VT2 And VT1 , which leads to limiting the output current of the voltage regulator.

Short circuit protection

For protection, 2 resistors are used - R 2 And R 3 and during normal operation

transistor emitter voltage VT1 equals output. During a short circuit, the output voltage is zero, and accordingly the voltage at the emitter of the transistor VT1

is also zero and the entire input voltage is applied to the resistors R 2 And R 3 . Voltage at

R 2 increases and the voltage drop is added to it R 1 , which leads to the discovery

Rice. 5. Circuit diagram of the voltage stabilizer

on an op-amp with a variable current limit level

and with short circuit protection

transistor VT3 . Resistors R 2 And R 3 designed so that the collector current VT3 in short circuit mode was approximately 80% of the base current VT2 . Accordingly, the base current VT2 decreases by about 5 times, which leads to a decrease in the collector current VT1 also 5 times. Thus the transistor VT1 protected against overload in case of short circuit.

Output voltage stabilization

If in normal operation for some reason the output voltage of the stabilizer changes, then the voltage created by the divider also changes R 6 , R 7 , R 8 at point A. Operational amplifier D.A.1 amplifies the difference between the reference voltage () and the voltage at point A (), which can be calculated using the formula

If the voltage at the output of the stabilizer has decreased, then the difference will be positive and increases, which leads to a decrease in the current passing through the zener diode VD3 , which is part of the current passing through R 4 .The other part goes to the base of the transistor VT2 and to the output of the operational amplifier D.A.1 . Accordingly, if it decreases, then the currents increase, and, and, accordingly, increases. When increasing, the stabilization circuit works along a similar chain (reducing the deviation.

Zener diode VD3 turns on so that the operational amplifier D.A.1 worked in active mode, in which it should be approximately half the operational amplifier supply voltage (+U). The output voltage of the stabilizer itself () can be significantly higher. Transistor based VT2 voltage is higher than 2. Accordingly, the difference between and the voltage at the base VT2 is a certain value, which is compensated using a zener diode VD3