Correct circuit improvement of a pulse voltage stabilizer. Switching adjustable voltage stabilizer

For normal functioning of household appliances, a stable voltage is required. As a rule, various failures can occur on the network. The voltage from 220 V may deviate and the device may malfunction. Lamps are the first to get hit. If we consider household appliances in the house, televisions, audio equipment and other devices that operate from the mains may suffer.

In this situation, a pulse voltage stabilizer comes to the aid of people. He is fully capable of coping with the surges that occur daily. Many people are concerned about the question of how voltage drops occur and what they are connected with. They depend mainly on the load on the transformer. Today, the number of electrical appliances in residential buildings is constantly increasing. As a result, the demand for electricity is bound to increase.

It should also be taken into account that cables may be laid to a residential building that are already outdated. In turn, apartment wiring in most cases is not designed for heavy loads. To protect your equipment in the house, you should familiarize yourself in more detail with the design of voltage stabilizers, as well as the principle of their operation.

What functions does the stabilizer perform?

Mainly, a switching voltage stabilizer serves as a network controller. All jumps are monitored by him and eliminated. As a result, the equipment receives stable voltage. Electromagnetic interference is also taken into account by the stabilizer and cannot affect the operation of devices. Thus, the network gets rid of congestion, and cases are practically eliminated.

Simple stabilizer device

If we consider a standard pulse voltage, then only one transistor is installed in it. As a rule, they are used exclusively of the switching type, since today they are considered more efficient. As a result, the efficiency of the device can be greatly increased.

The second important element of a switching voltage stabilizer should be called diodes. In the usual scheme, you can find no more than three of them. They are connected to each other using a throttle. Filters are important for the normal operation of transistors. They are installed at the beginning and also at the end of the chain. In this case, the control unit is responsible for the operation of the capacitor. A resistor divider is considered to be an integral part of it.

How it works?

Depending on the type of device, the operating principle of a pulse voltage stabilizer may differ. Looking at the standard model, we can say that first current is applied to the transistor. At this stage, its transformation takes place. Next, diodes are switched on, whose responsibilities include transmitting the signal to the capacitor. With the help of filters, electromagnetic interference is eliminated. At this moment, the capacitor smoothes out voltage fluctuations and the current through the inductor through the resistive divider returns to the transistors for conversion.

Homemade devices

You can make a pulse voltage stabilizer with your own hands, but they will have low power. In this case, the most common resistors are installed. If you use more than one transistor in a device, you can achieve a high efficiency. An important task in this regard is the installation of filters. They influence the sensitivity of the device. In turn, the dimensions of the device are not at all important.

Stabilizers with one transistor

A switching DC voltage stabilizer of this type can boast an efficiency of 80%. As a rule, they operate in only one mode and can only cope with minor network interference.

Feedback in this case is completely absent. The transistor in the standard switching voltage stabilizer circuit operates without a collector. As a result, a large voltage is immediately applied to the capacitor. Another distinctive feature of devices of this type is a weak signal. Various amplifiers can solve this problem.

As a result, better performance of transistors can be achieved. The resistor of the device in the circuit must be located behind. In this case, it will be possible to achieve better operation of the device. As a regulator in the circuit, the pulsed constant voltage stabilizer has a control unit. This element is capable of weakening and also increasing the power of the transistor. This phenomenon occurs with the help of chokes that are connected to diodes in the system. The load on the regulator is controlled through filters.

Key type voltage stabilizers

Why install compensators?

In most cases, compensators play a secondary role in the stabilizer. It is connected with the regulation of impulses. Transistors mainly cope with this. However, compensators still have their advantages. In this case, much depends on which devices are connected to the power source.

If we talk about radio equipment, then a special approach is needed. It is associated with various vibrations, which are perceived differently by such a device. In this case, compensators can help transistors stabilize the voltage. Installing additional filters in the circuit, as a rule, does not improve the situation. At the same time, they greatly influence the efficiency.

Disadvantages of galvanic isolation

Galvanic isolations are installed to transmit signals between important system elements. Their main problem can be called incorrect estimation of the input voltage. This happens most often with outdated models of stabilizers. The controllers in them are not capable of quickly processing information and connecting capacitors to work. As a result, diodes suffer first of all. If the filtration system is installed behind resistors in the electrical circuit, then they simply burn out.

Making a power supply with your own hands makes sense not only for enthusiastic radio amateurs. A homemade power supply unit (PSU) will create convenience and save a considerable amount in the following cases:

• To power low-voltage power tools, to save the life of an expensive rechargeable battery;
• For electrification of premises that are particularly dangerous in terms of the degree of electric shock: basements, garages, sheds, etc. When powered by alternating current, a large amount of it in low-voltage wiring can create interference with household appliances and electronics;
• In design and creativity for precise, safe and waste-free cutting of foam plastic, foam rubber, low-melting plastics with heated nichrome;
• In lighting design, the use of special power supplies will extend the life of the LED strip and obtain stable lighting effects. Powering underwater illuminators, etc. from a household electrical network is generally unacceptable;
• For charging phones, smartphones, tablets, laptops away from stable power sources;
• For electroacupuncture;
• And many other purposes not directly related to electronics.

Acceptable simplifications

Professional power supplies are designed to power any kind of load, incl. reactive. Possible consumers include precision equipment. The pro-BP must maintain the specified voltage with the highest accuracy for an indefinitely long time, and its design, protection and automation must allow operation by unqualified personnel in difficult conditions, for example. biologists to power their instruments in a greenhouse or on an expedition.

An amateur laboratory power supply is free from these limitations and therefore can be significantly simplified while maintaining quality indicators sufficient for personal use. Further, through also simple improvements, it is possible to obtain a special-purpose power supply from it. What are we going to do now?

Abbreviations

1. KZ – short circuit.
2. XX – idle speed, i.e. sudden disconnection of the load (consumer) or a break in its circuit.
3. VS – voltage stabilization coefficient. It is equal to the ratio of the change in input voltage (in % or times) to the same output voltage at a constant current consumption. Eg. The network voltage dropped completely, from 245 to 185V. Relative to the norm of 220V, this will be 27%. If the VS of the power supply is 100, the output voltage will change by 0.27%, which, with its value of 12V, will give a drift of 0.033V. More than acceptable for amateur practice.
4. IPN is a source of unstabilized primary voltage. This can be an iron transformer with a rectifier or a pulsed network voltage inverter (VIN).
5. IIN - operate at a higher (8-100 kHz) frequency, which allows the use of lightweight compact ferrite transformers with windings of several to several dozen turns, but they are not without drawbacks, see below.
6. RE – regulating element of the voltage stabilizer (SV). Maintains the output at its specified value.
7. ION – reference voltage source. Sets its reference value, according to which, together with the OS feedback signals, the control device of the control unit influences the RE.
8. SNN – continuous voltage stabilizer; simply “analog”.
9. ISN – pulse voltage stabilizer.
10. UPS is a switching power supply.

Note: both SNN and ISN can operate both from an industrial frequency power supply with a transformer on iron, and from an electrical power supply.

About computer power supplies

UPSs are compact and economical. And in the pantry many people have a power supply from an old computer lying around, obsolete, but quite serviceable. So is it possible to adapt a switching power supply from a computer for amateur/working purposes? Unfortunately, a computer UPS is a rather highly specialized device and the possibilities of its use at home/at work are very limited:

It is perhaps advisable for the average amateur to use a UPS converted from a computer one only to power power tools; about this see below. The second case is if an amateur is engaged in PC repair and/or creation of logic circuits. But then he already knows how to adapt a power supply from a computer for this:

1. Load the main channels +5V and +12V (red and yellow wires) with nichrome spirals at 10-15% of the rated load;
2. The green soft start wire (low-voltage button on the front panel of the system unit) pc on is shorted to common, i.e. on any of the black wires;
3. On/off is performed mechanically, using a toggle switch on the rear panel of the power supply unit;
4. With mechanical (iron) I/O “on duty”, i.e. independent power supply of USB ports +5V will also be turned off.

Get to work!

Due to the shortcomings of UPSs, plus their fundamental and circuitry complexity, we will only look at a couple of them at the end, but simple and useful, and talk about the method of repairing the IPS. The main part of the material is devoted to SNN and IPN with industrial frequency transformers. They allow a person who has just picked up a soldering iron to build a power supply of very high quality. And having it on the farm, it will be easier to master “fine” techniques.

IPN

First, let's look at the IPN. We’ll leave pulse ones in more detail until the section on repairs, but they have something in common with “iron” ones: a power transformer, a rectifier and a ripple suppression filter. Together, they can be implemented in various ways depending on the purpose of the power supply.

Pos. 1 in Fig. 1 – half-wave (1P) rectifier. The voltage drop across the diode is the smallest, approx. 2B. But the pulsation of the rectified voltage is with a frequency of 50 Hz and is “ragged”, i.e. with intervals between pulses, so the pulsation filter capacitor Sf should be 4-6 times larger in capacity than in other circuits. The use of power transformer Tr for power is 50%, because Only 1 half-wave is rectified. For the same reason, a magnetic flux imbalance occurs in the Tr magnetic circuit and the network “sees” it not as an active load, but as inductance. Therefore, 1P rectifiers are used only for low power and where there is no other way, for example. in IIN on blocking generators and with a damper diode, see below.

Note: why 2V, and not 0.7V, at which the p-n junction in silicon opens? The reason is through current, which is discussed below.

Pos. 2 – 2-half-wave with midpoint (2PS). The diode losses are the same as before. case. The ripple is 100 Hz continuous, so the smallest possible Sf is needed. Use of Tr - 100% Disadvantage - double copper consumption on the secondary winding. At the time when rectifiers were made using kenotron lamps, this did not matter, but now it is decisive. Therefore, 2PS are used in low-voltage rectifiers, mainly at higher frequencies with Schottky diodes in UPSs, but 2PS have no fundamental limitations on power.

Pos. 3 – 2-half-wave bridge, 2RM. Losses on diodes are doubled compared to pos. 1 and 2. The rest is the same as 2PS, but the secondary copper is needed almost half as much. Almost - because several turns have to be wound to compensate for the losses on a pair of “extra” diodes. The most commonly used circuit is for voltages from 12V.

Pos. 3 – bipolar. The “bridge” is depicted conventionally, as is customary in circuit diagrams (get used to it!), and is rotated 90 degrees counterclockwise, but in fact it is a pair of 2PS connected in opposite polarities, as can be clearly seen further in Fig. 6. Copper consumption is the same as 2PS, diode losses are the same as 2PM, the rest is the same as both. It is built mainly to power analog devices that require voltage symmetry: Hi-Fi UMZCH, DAC/ADC, etc.

Pos. 4 – bipolar according to the parallel doubling scheme. Provides increased voltage symmetry without additional measures, because asymmetry of the secondary winding is excluded. Using Tr 100%, ripples 100 Hz, but torn, so Sf needs double capacity. Losses on the diodes are approximately 2.7V due to the mutual exchange of through currents, see below, and at a power of more than 15-20 W they increase sharply. They are built mainly as low-power auxiliary ones for independent power supply of operational amplifiers (op-amps) and other low-power, but demanding analog components in terms of power supply quality.

How to choose a transformer?

In a UPS, the entire circuit is most often clearly tied to the standard size (more precisely, to the volume and cross-sectional area Sc) of the transformer/transformers, because the use of fine processes in ferrite makes it possible to simplify the circuit while making it more reliable. Here, “somehow in your own way” comes down to strict adherence to the developer’s recommendations.

The iron-based transformer is selected taking into account the characteristics of the SNN, or is taken into account when calculating it. The voltage drop across the RE Ure should not be taken less than 3V, otherwise the VS will drop sharply. As Ure increases, the VS increases slightly, but the dissipated RE power grows much faster. Therefore, Ure is taken at 4-6 V. To it we add 2(4) V of losses on the diodes and the voltage drop on the secondary winding Tr U2; for a power range of 30-100 W and voltages of 12-60 V, we take it to 2.5 V. U2 arises primarily not from the ohmic resistance of the winding (it is generally negligible in powerful transformers), but due to losses due to magnetization reversal of the core and the creation of a stray field. Simply, part of the network energy, “pumped” by the primary winding into the magnetic circuit, evaporates into outer space, which is what the value of U2 takes into account.

So, we calculated, for example, for a bridge rectifier, 4 + 4 + 2.5 = 10.5 V extra. We add it to the required output voltage of the power supply unit; let it be 12V, and divide by 1.414, we get 22.5/1.414 = 15.9 or 16V, this will be the lowest permissible voltage of the secondary winding. If TP is factory-made, we take 18V from the standard range.

Now the secondary current comes into play, which, naturally, is equal to the maximum load current. Let us say we need 3A; multiply by 18V, it will be 54W. We have obtained the overall power Tr, Pg, and we will find the rated power P by dividing Pg by the efficiency Tr η, which depends on Pg:

• up to 10W, η = 0.6.
• 10-20 W, η = 0.7.
• 20-40 W, η = 0.75.
• 40-60 W, η = 0.8.
• 60-80 W, η = 0.85.
• 80-120 W, η = 0.9.
• from 120 W, η = 0.95.

In our case, there will be P = 54/0.8 = 67.5 W, but there is no such standard value, so you will have to take 80 W. In order to get 12Vx3A = 36W at the output. A steam locomotive, and that's all. It’s time to learn how to calculate and wind the “trances” yourself. Moreover, in the USSR, methods for calculating transformers on iron were developed that make it possible, without loss of reliability, to squeeze 600 W out of a core, which, when calculated according to amateur radio reference books, is capable of producing only 250 W. "Iron Trance" is not as stupid as it seems.

SNN

The rectified voltage needs to be stabilized and, most often, regulated. If the load is more powerful than 30-40 W, short-circuit protection is also necessary, otherwise a malfunction of the power supply may cause a network failure. SNN does all this together.

Simple reference

It is better for a beginner not to immediately go into high power, but to make a simple, highly stable 12V ELV for testing according to the circuit in Fig. 2. It can then be used as a source of reference voltage (its exact value is set by R5), for checking devices, or as a high-quality ELV ION. The maximum load current of this circuit is only 40mA, but the VSC on the antediluvian GT403 and the equally ancient K140UD1 is more than 1000, and when replacing VT1 with a medium-power silicon one and DA1 on any of the modern op-amps it will exceed 2000 and even 2500. The load current will also increase to 150 -200 mA, which is already useful.

0-30

The next stage is a power supply with voltage regulation. The previous one was done according to the so-called. compensation comparison circuit, but it is difficult to convert one to a high current. We will make a new SNN based on an emitter follower (EF), in which the RE and CU are combined in just one transistor. The KSN will be somewhere around 80-150, but this will be enough for an amateur. But the SNN on the ED allows, without any special tricks, to obtain an output current of up to 10A or more, as much as the Tr will give and the RE will withstand.

The circuit of a simple 0-30V power supply is shown in pos. 1 Fig. 3. IPN for it is a ready-made transformer such as TPP or TS for 40-60 W with a secondary winding for 2x24V. Rectifier type 2PS with diodes rated at 3-5A or more (KD202, KD213, D242, etc.). VT1 is installed on a radiator with an area of ​​50 square meters or more. cm; An old PC processor will work very well. Under such conditions, this ELV is not afraid of a short circuit, only VT1 and Tr will heat up, so a 0.5A fuse in the primary winding circuit of Tr is enough for protection.

Pos. Figure 2 shows how convenient a power supply on an electric power supply is for an amateur: there is a 5A power supply circuit with adjustment from 12 to 36 V. This power supply can supply 10A to the load if there is a 400W 36V Tr. Its first feature is the integrated SNN K142EN8 (preferably with index B) acts in an unusual role as a control unit: to its own 12V output is added, partially or completely, all 24V, the voltage from the ION to R1, R2, VD5, VD6. Capacitors C2 and C3 prevent excitation on HF DA1 operating in an unusual mode.

The next point is the short circuit protection device (PD) on R3, VT2, R4. If the voltage drop across R4 exceeds approximately 0.7V, VT2 will open, close the base circuit of VT1 to the common wire, it will close and disconnect the load from the voltage. R3 is needed so that the extra current does not damage DA1 when the ultrasound is triggered. There is no need to increase its denomination, because when the ultrasound is triggered, you need to securely lock VT1.

And the last thing is the seemingly excessive capacitance of the output filter capacitor C4. In this case it is safe, because The maximum collector current of VT1 of 25A ensures its charge when turned on. But this ELV can supply a current of up to 30A to the load within 50-70 ms, so this simple power supply is suitable for powering low-voltage power tools: its starting current does not exceed this value. You just need to make (at least from plexiglass) a contact block-shoe with a cable, put on the heel of the handle, and let the “Akumych” rest and save resources before leaving.

About cooling

Let's say in this circuit the output is 12V with a maximum of 5A. This is just the average power of a jigsaw, but, unlike a drill or screwdriver, it takes it all the time. At C1 it stays at about 45V, i.e. on RE VT1 it remains somewhere around 33V at a current of 5A. Power dissipation is more than 150 W, even more than 160, if you consider that VD1-VD4 also needs to be cooled. It is clear from this that any powerful adjustable power supply must be equipped with a very effective cooling system.

A finned/needle radiator using natural convection does not solve the problem: calculations show that a dissipating surface of 2000 sq. m. is needed. see and the thickness of the radiator body (the plate from which the fins or needles extend) is from 16 mm. To own this much aluminum in a shaped product was and remains a dream in a crystal castle for an amateur. A CPU cooler with airflow is also not suitable; it is designed for less power.

One of the options for the home craftsman is an aluminum plate with a thickness of 6 mm and dimensions of 150x250 mm with holes of increasing diameter drilled along the radii from the installation site of the cooled element in a checkerboard pattern. It will also serve as the rear wall of the power supply housing, as in Fig. 4.

An indispensable condition for the effectiveness of such a cooler is a weak, but continuous flow of air through the perforations from the outside to the inside. To do this, install a low-power exhaust fan in the housing (preferably at the top). A computer with a diameter of 76 mm or more is suitable, for example. add. HDD cooler or video card. It is connected to pins 2 and 8 of DA1, there is always 12V.

Note: In fact, a radical way to overcome this problem is a secondary winding Tr with taps for 18, 27 and 36V. The primary voltage is switched depending on which tool is being used.

And yet the UPS

The described power supply for the workshop is good and very reliable, but it’s hard to carry it with you on trips. This is where a computer power supply will fit in: the power tool is insensitive to most of its shortcomings. Some modification most often comes down to installing an output (closest to the load) electrolytic capacitor of large capacity for the purpose described above. There are a lot of recipes for converting computer power supplies for power tools (mainly screwdrivers, which are not very powerful, but very useful) in RuNet; one of the methods is shown in the video below, for a 12V tool.

Video: 12V power supply from a computer

With 18V tools it’s even easier: for the same power they consume less current. A much more affordable ignition device (ballast) from a 40 W or more energy saving lamp may be useful here; it can be completely placed in the case of a bad battery, and only the cable with the power plug will remain outside. How to make a power supply for an 18V screwdriver from ballast from a burnt housekeeper, see the following video.

Video: 18V power supply for a screwdriver

High class

But let’s return to SNN on ES; their capabilities are far from being exhausted. In Fig. 5 – bipolar powerful power supply with 0-30 V regulation, suitable for Hi-Fi audio equipment and other fastidious consumers. The output voltage is set using one knob (R8), and the symmetry of the channels is maintained automatically at any voltage value and any load current. A pedant-formalist may turn gray before his eyes when he sees this circuit, but the author has had such a power supply working properly for about 30 years.

The main stumbling block during its creation was δr = δu/δi, where δu and δi are small instantaneous increments of voltage and current, respectively. To develop and set up high-quality equipment, it is necessary that δr does not exceed 0.05-0.07 Ohm. Simply, δr determines the ability of the power supply to instantly respond to surges in current consumption.

For the SNN on the EP, δr is equal to that of the ION, i.e. zener diode divided by the current transfer coefficient β RE. But for powerful transistors, β drops significantly at a large collector current, and δr of a zener diode ranges from a few to tens of ohms. Here, in order to compensate for the voltage drop across the RE and reduce the temperature drift of the output voltage, we had to assemble a whole chain of them in half with diodes: VD8-VD10. Therefore, the reference voltage from the ION is removed through an additional ED on VT1, its β is multiplied by β RE.

The next feature of this design is short circuit protection. The simplest one, described above, does not fit into a bipolar circuit in any way, so the protection problem is solved according to the principle “there is no trick against scrap”: there is no protective module as such, but there is redundancy in the parameters of powerful elements - KT825 and KT827 at 25A and KD2997A at 30A. T2 is not capable of providing such a current, and while it warms up, FU1 and/or FU2 will have time to burn out.

Note: It is not necessary to indicate blown fuses on miniature incandescent lamps. It’s just that at that time LEDs were still quite scarce, and there were several handfuls of SMOKs in the stash.

It remains to protect the RE from the extra discharge currents of the pulsation filter C3, C4 during a short circuit. To do this, they are connected through low-resistance limiting resistors. In this case, pulsations may appear in the circuit with a period equal to the time constant R(3,4)C(3,4). They are prevented by C5, C6 of smaller capacity. Their extra currents are no longer dangerous for RE: the charge drains faster than the crystals of the powerful KT825/827 heat up.

Output symmetry is ensured by op-amp DA1. The RE of the negative channel VT2 is opened by current through R6. As soon as the minus of the output exceeds the plus in modulus, it will slightly open VT3, which will close VT2 and the absolute values ​​of the output voltages will be equal. Operational control over the symmetry of the output is carried out using a dial gauge with a zero in the middle of the scale P1 (its appearance is shown in the inset), and adjustment, if necessary, is carried out by R11.

The last highlight is the output filter C9-C12, L1, L2. This design is necessary to absorb possible HF interference from the load, so as not to rack your brain: the prototype is buggy or the power supply is “wobbly”. With electrolytic capacitors alone, shunted with ceramics, there is no complete certainty here; the large self-inductance of the “electrolytes” interferes. And chokes L1, L2 divide the “return” of the load across the spectrum, and to each their own.

This power supply unit, unlike the previous ones, requires some adjustment:

1. Connect a load of 1-2 A at 30V;
2. R8 is set to maximum, in the highest position according to the diagram;
3. Using a reference voltmeter (any digital multimeter will do now) and R11, the channel voltages are set to be equal in absolute value. Maybe, if the op-amp does not have the ability to balance, you will have to select R10 or R12;
4. Use the R14 trimmer to set P1 exactly to zero.

About power supply repair

PSUs fail more often than other electronic devices: they take the first blow of network surges, and they also get a lot from the load. Even if you do not intend to make your own power supply, a UPS can be found, in addition to a computer, in a microwave oven, washing machine, and other household appliances. The ability to diagnose a power supply and knowledge of the basics of electrical safety will make it possible, if not to fix the fault yourself, then to competently bargain on the price with repairmen. Therefore, let's look at how a power supply is diagnosed and repaired, especially with an IIN, because over 80% of failures are their share.

Saturation and draft

First of all, about some effects, without understanding which it is impossible to work with a UPS. The first of them is the saturation of ferromagnets. They are not capable of absorbing energies of more than a certain value, depending on the properties of the material. Hobbyists rarely encounter saturation on iron; it can be magnetized to several Tesla (Tesla, a unit of measurement of magnetic induction). When calculating iron transformers, the induction is taken to be 0.7-1.7 Tesla. Ferrites can withstand only 0.15-0.35 T, their hysteresis loop is “more rectangular”, and operate at higher frequencies, so their probability of “jumping into saturation” is orders of magnitude higher.

If the magnetic circuit is saturated, the induction in it no longer grows and the EMF of the secondary windings disappears, even if the primary has already melted (remember school physics?). Now turn off the primary current. The magnetic field in soft magnetic materials (hard magnetic materials are permanent magnets) cannot exist stationary, like an electric charge or water in a tank. It will begin to dissipate, the induction will drop, and an EMF of the opposite polarity relative to the original polarity will be induced in all windings. This effect is quite widely used in IIN.

Unlike saturation, through current in semiconductor devices (simply draft) is an absolutely harmful phenomenon. It arises due to the formation/resorption of space charges in the p and n regions; for bipolar transistors - mainly in the base. Field-effect transistors and Schottky diodes are practically free from drafts.

For example, when voltage is applied/removed to a diode, it conducts current in both directions until the charges are collected/dissolved. That is why the voltage loss on the diodes in rectifiers is more than 0.7V: at the moment of switching, part of the charge of the filter capacitor has time to flow through the winding. In a parallel doubling rectifier, the draft flows through both diodes at once.

A draft of transistors causes a voltage surge on the collector, which can damage the device or, if a load is connected, damage it through extra current. But even without that, a transistor draft increases dynamic energy losses, like a diode draft, and reduces the efficiency of the device. Powerful field-effect transistors are almost not susceptible to it, because do not accumulate charge in the base due to its absence, and therefore switch very quickly and smoothly. “Almost”, because their source-gate circuits are protected from reverse voltage by Schottky diodes, which are slightly, but through.

TIN types

UPS trace their origins to the blocking generator, pos. 1 in Fig. 6. When turned on, Uin VT1 is slightly opened by current through Rb, current flows through winding Wk. It cannot instantly grow to the limit (remember school physics again); an emf is induced in the base Wb and load winding Wn. From Wb, through Sb, it forces the unlocking of VT1. No current flows through Wn yet and VD1 does not start up.

When the magnetic circuit is saturated, the currents in Wb and Wn stop. Then, due to the dissipation (resorption) of energy, the induction drops, an EMF of the opposite polarity is induced in the windings, and the reverse voltage Wb instantly locks (blocks) VT1, saving it from overheating and thermal breakdown. Therefore, such a scheme is called a blocking generator, or simply blocking. Rk and Sk cut off HF interference, of which blocking produces more than enough. Now some useful power can be removed from Wn, but only through the 1P rectifier. This phase continues until the Sat is completely recharged or until the stored magnetic energy is exhausted.

This power, however, is small, up to 10W. If you try to take more, VT1 will burn out from a strong draft before it locks. Since Tp is saturated, the blocking efficiency is no good: more than half of the energy stored in the magnetic circuit flies away to warm other worlds. True, due to the same saturation, blocking to some extent stabilizes the duration and amplitude of its pulses, and its circuit is very simple. Therefore, blocking-based TINs are often used in cheap phone chargers.

Note: the value of Sb largely, but not completely, as they write in amateur reference books, determines the pulse repetition period. The value of its capacitance must be linked to the properties and dimensions of the magnetic circuit and the speed of the transistor.

Blocking at one time gave rise to line scan TVs with cathode ray tubes (CRT), and it gave birth to an INN with a damper diode, pos. 2. Here the control unit, based on signals from Wb and the DSP feedback circuit, forcibly opens/locks VT1 before Tr is saturated. When VT1 is locked, the reverse current Wk is closed through the same damper diode VD1. This is the working phase: already greater than in blocking, part of the energy is removed into the load. It’s big because when it’s completely saturated, all the extra energy flies away, but here there’s not enough of that extra. In this way it is possible to remove power up to several tens of watts. However, since the control device cannot operate until Tr has approached saturation, the transistor still shows through strongly, the dynamic losses are large and the efficiency of the circuit leaves much more to be desired.

The IIN with a damper is still alive in televisions and CRT displays, since in them the IIN and the horizontal scan output are combined: the power transistor and TP are common. This greatly reduces production costs. But, frankly speaking, an IIN with a damper is fundamentally stunted: the transistor and transformer are forced to work all the time on the verge of failure. The engineers who managed to bring this circuit to acceptable reliability deserve the deepest respect, but it is strongly not recommended to stick a soldering iron in there except for professionals who have undergone professional training and have the appropriate experience.

The push-pull INN with a separate feedback transformer is most widely used, because has the best quality indicators and reliability. However, in terms of RF interference, it also sins terribly in comparison with “analog” power supplies (with transformers on hardware and SNN). Currently, this scheme exists in many modifications; powerful bipolar transistors in it are almost completely replaced by field-effect ones controlled by special devices. IC, but the principle of operation remains unchanged. It is illustrated by the original diagram, pos. 3.

The limiting device (LD) limits the charging current of the capacitors of the input filter Sfvkh1(2). Their large size is an indispensable condition for the operation of the device, because During one operating cycle, a small fraction of the stored energy is taken from them. Roughly speaking, they play the role of a water tank or air receiver. When charging “short”, the extra charge current can exceed 100A for a time of up to 100 ms. Rc1 and Rc2 with a resistance of the order of MOhm are needed to balance the filter voltage, because the slightest imbalance of his shoulders is unacceptable.

When Sfvkh1(2) are charged, the ultrasonic trigger device generates a trigger pulse that opens one of the arms (which one does not matter) of the inverter VT1 VT2. A current flows through the winding Wk of a large power transformer Tr2 and the magnetic energy from its core through the winding Wn is almost completely spent on rectification and on the load.

A small part of the energy Tr2, determined by the value of Rogr, is removed from the winding Woc1 and supplied to the winding Woc2 of a small basic feedback transformer Tr1. It quickly saturates, the open arm closes and, due to dissipation in Tr2, the previously closed one opens, as described for blocking, and the cycle repeats.

In essence, a push-pull IIN is 2 blockers “pushing” each other. Since the powerful Tr2 is not saturated, the draft VT1 VT2 is small, completely “sinks” into the magnetic circuit Tr2 and ultimately goes into the load. Therefore, a two-stroke IPP can be built with a power of up to several kW.

It's worse if he ends up in XX mode. Then, during the half cycle, Tr2 will have time to saturate itself and a strong draft will burn both VT1 and VT2 at once. However, now there are power ferrites on sale for induction up to 0.6 Tesla, but they are expensive and degrade from accidental magnetization reversal. Ferrites with a capacity of more than 1 Tesla are being developed, but in order for IINs to achieve “iron” reliability, at least 2.5 Tesla is needed.

Diagnostic technique

When troubleshooting an “analog” power supply, if it is “stupidly silent,” first check the fuses, then the protection, RE and ION, if it has transistors. They ring normally - we move on element by element, as described below.

In the IIN, if it “starts up” and immediately “stalls out”, they first check the control unit. The current in it is limited by a powerful low-resistance resistor, then shunted by an optothyristor. If the “resistor” is apparently burnt, replace it and the optocoupler. Other elements of the control device fail extremely rarely.

If the IIN is “silent, like a fish on ice,” the diagnosis also begins with the OU (maybe the “rezik” has completely burned out). Then - ultrasound. Cheap models use transistors in avalanche breakdown mode, which is far from being very reliable.

The next stage in any power supply is electrolytes. Fracture of the housing and leakage of electrolyte are not nearly as common as they write on the RuNet, but loss of capacity occurs much more often than failure of active elements. Electrolytic capacitors are checked with a multimeter capable of measuring capacitance. Below the nominal value by 20% or more - we lower the “dead” into the sludge and install a new, good one.

Then there are the active elements. You probably know how to dial diodes and transistors. But there are 2 tricks here. The first is that if a Schottky diode or zener diode is called by a tester with a 12V battery, then the device may show a breakdown, although the diode is quite good. It is better to call these components using a pointer device with a 1.5-3 V battery.

The second is powerful field workers. Above (did you notice?) it is said that their I-Z are protected by diodes. Therefore, powerful field-effect transistors seem to sound like serviceable bipolar transistors, even if they are unusable if the channel is “burnt out” (degraded) not completely.

Here, the only way available at home is to replace them with known good ones, both at once. If there is a burnt one left in the circuit, it will immediately pull a new working one with it. Electronics engineers joke that powerful field workers cannot live without each other. Another prof. joke – “replacement gay couple.” This means that the transistors of the IIN arms must be strictly of the same type.

Finally, film and ceramic capacitors. They are characterized by internal breaks (found by the same tester that checks the “air conditioners”) and leakage or breakdown under voltage. To “catch” them, you need to assemble a simple circuit according to Fig. 7. Step-by-step testing of electrical capacitors for breakdown and leakage is carried out as follows:

• We set on the tester, without connecting it anywhere, the smallest limit for measuring direct voltage (most often 0.2V or 200mV), detect and record the device’s own error;
• We turn on the measurement limit of 20V;
• We connect the suspicious capacitor to points 3-4, the tester to 5-6, and to 1-2 we apply a constant voltage of 24-48 V;
• Switch the multimeter voltage limits down to the lowest;
• If on any tester it shows anything other than 0000.00 (at the very least - something other than its own error), the capacitor being tested is not suitable.

This is where the methodological part of the diagnosis ends and the creative part begins, where all the instructions are based on your own knowledge, experience and considerations.

A couple of impulses

UPSs are a special article due to their complexity and circuit diversity. Here, to begin with, we will look at a couple of samples using pulse width modulation (PWM), which allows us to obtain the best quality UPS. There are a lot of PWM circuits in RuNet, but PWM is not as scary as it is made out to be...

For lighting design

You can simply light the LED strip from any power supply described above, except for the one in Fig. 1, setting the required voltage. SNN with pos. 1 Fig. 3, it’s easy to make 3 of these, for channels R, G and B. But the durability and stability of the LEDs’ glow does not depend on the voltage applied to them, but on the current flowing through them. Therefore, a good power supply for LED strip should include a load current stabilizer; in technical terms - a stable current source (IST).

One of the schemes for stabilizing the light strip current, which can be repeated by amateurs, is shown in Fig. 8. It is assembled on an integrated timer 555 (domestic analogue - K1006VI1). Provides a stable tape current from a power supply voltage of 9-15 V. The amount of stable current is determined by the formula I = 1/(2R6); in this case - 0.7A. The powerful transistor VT3 is necessarily a field-effect transistor; from a draft, due to the base charge, a bipolar PWM simply will not form. Inductor L1 is wound on a ferrite ring 2000NM K20x4x6 with a 5xPE 0.2 mm harness. Number of turns – 50. Diodes VD1, VD2 – any silicon RF (KD104, KD106); VT1 and VT2 – KT3107 or analogues. With KT361, etc. The input voltage and brightness control ranges will decrease.

The circuit works like this: first, the time-setting capacitance C1 is charged through the R1VD1 circuit and discharged through VD2R3VT2, open, i.e. in saturation mode, through R1R5. The timer generates a sequence of pulses with the maximum frequency; more precisely - with a minimum duty cycle. The VT3 inertia-free switch generates powerful impulses, and its VD3C4C3L1 harness smooths them out to direct current.

Note: The duty cycle of a series of pulses is the ratio of their repetition period to the pulse duration. If, for example, the pulse duration is 10 μs, and the interval between them is 100 μs, then the duty cycle will be 11.

The current in the load increases, and the voltage drop across R6 opens VT1, i.e. transfers it from the cut-off (locking) mode to the active (reinforcing) mode. This creates a leakage circuit for the base of VT2 R2VT1+Upit and VT2 also goes into active mode. The discharge current C1 decreases, the discharge time increases, the duty cycle of the series increases and the average current value drops to the norm specified by R6. This is the essence of PWM. At minimum current, i.e. at maximum duty cycle, C1 is discharged through the VD2-R4-internal timer switch circuit.

In the original design, the ability to quickly adjust the current and, accordingly, the brightness of the glow is not provided; There are no 0.68 ohm potentiometers. The easiest way to adjust the brightness is by connecting, after adjustment, a 3.3-10 kOhm potentiometer R* into the gap between R3 and the VT2 emitter, highlighted in brown. By moving its engine down the circuit, we will increase the discharge time of C4, the duty cycle and reduce the current. Another way is to bypass the base junction of VT2 by turning on a potentiometer of approximately 1 MOhm at points a and b (highlighted in red), less preferable, because the adjustment will be deeper, but rougher and sharper.

Unfortunately, to set up this useful not only for IST light tapes, you need an oscilloscope:

1. The minimum +Upit is supplied to the circuit.
2. By selecting R1 (impulse) and R3 (pause) we achieve a duty cycle of 2, i.e. The pulse duration must be equal to the pause duration. You cannot give a duty cycle less than 2!
3. Serve maximum +Upit.
4. By selecting R4, the rated value of a stable current is achieved.

For charging

In Fig. 9 – diagram of the simplest ISN with PWM, suitable for charging a phone, smartphone, tablet (a laptop, unfortunately, will not work) from a homemade solar battery, wind generator, motorcycle or car battery, magneto flashlight “bug” and other low-power unstable random sources power supply See the diagram for the input voltage range, there is no error there. This ISN is indeed capable of producing an output voltage greater than the input. As in the previous one, here there is the effect of changing the polarity of the output relative to the input; this is generally a proprietary feature of PWM circuits. Let's hope that after reading the previous one carefully, you will understand the work of this tiny little thing yourself.

Incidentally, about charging and charging

Charging batteries is a very complex and delicate physical and chemical process, the violation of which reduces their service life several times or tens of times, i.e. number of charge-discharge cycles. The charger must, based on very small changes in battery voltage, calculate how much energy has been received and regulate the charging current accordingly according to a certain law. Therefore, the charger is by no means a power supply, and only batteries in devices with a built-in charge controller can be charged from ordinary power supplies: phones, smartphones, tablets, and certain models of digital cameras. And charging, which is a charger, is a subject for a separate discussion.

Question-remont.ru said:

There will be some sparking from the rectifier, but it's probably not a big deal. The point is the so-called. differential output impedance of the power supply. For alkaline batteries it is about mOhm (milliohms), for acid batteries it is even less. A trance with a bridge without smoothing has tenths and hundredths of an ohm, i.e. approx. 100 – 10 times more. And the starting current of a brushed DC motor can be 6-7 or even 20 times greater than the operating current. Yours is most likely closer to the latter - fast-accelerating motors are more compact and more economical, and the huge overload capacity of the batteries allows you to give the engine as much current as it can handle. for acceleration. A trans with a rectifier will not provide as much instantaneous current, and the engine accelerates more slowly than it was designed for, and with a large slip of the armature. From this, from the large slip, a spark arises, and then remains in operation due to self-induction in the windings.

What can I recommend here? First: take a closer look - how does it spark? You need to watch it in operation, under load, i.e. during sawing.

If sparks dance in certain places under the brushes, it’s okay. My powerful Konakovo drill sparkles so much from birth, and for goodness sake. In 24 years, I changed the brushes once, washed them with alcohol and polished the commutator - that’s all. If you connected an 18V instrument to a 24V output, then a little sparking is normal. Unwind the winding or extinguish the excess voltage with something like a welding rheostat (a resistor of approximately 0.2 Ohm for a power dissipation of 200 W or more), so that the motor operates at the rated voltage and, most likely, the spark will go away. If you connected it to 12 V, hoping that after rectification it would be 18, then in vain - the rectified voltage drops significantly under load. And the commutator electric motor, by the way, doesn’t care whether it is powered by direct current or alternating current.

Specifically: take 3-5 m of steel wire with a diameter of 2.5-3 mm. Roll into a spiral with a diameter of 100-200 mm so that the turns do not touch each other. Place on a fireproof dielectric pad. Clean the ends of the wire until shiny and fold them into “ears”. It is best to immediately lubricate with graphite lubricant to prevent oxidation. This rheostat is connected to the break in one of the wires leading to the instrument. It goes without saying that the contacts should be screws, tightened tightly, with washers. Connect the entire circuit to the 24V output without rectification. The spark is gone, but the power on the shaft has also dropped - the rheostat needs to be reduced, one of the contacts needs to be switched 1-2 turns closer to the other. It still sparks, but less - the rheostat is too small, you need to add more turns. It is better to immediately make the rheostat obviously large so as not to screw on additional sections. It’s worse if the fire is along the entire line of contact between the brushes and the commutator or spark tails trail behind them. Then the rectifier needs an anti-aliasing filter somewhere, according to your data, from 100,000 µF. Not a cheap pleasure. The “filter” in this case will be an energy storage device for accelerating the motor. But it may not help if the overall power of the transformer is not enough. Efficiency of brushed DC motors is approx. 0.55-0.65, i.e. trans is needed from 800-900 W. That is, if the filter is installed, but still sparks with fire under the entire brush (under both, of course), then the transformer is not up to the task. Yes, if you install a filter, then the diodes of the bridge must be rated for triple the operating current, otherwise they may fly out from the surge of charging current when connected to the network. And then the tool can be launched 5-10 seconds after being connected to the network, so that the “banks” have time to “pump up”.

And the worst thing is if the tails of sparks from the brushes reach or almost reach the opposite brush. This is called all-round fire. It very quickly burns out the collector to the point of complete disrepair. There can be several reasons for a circular fire. In your case, the most probable is that the motor was turned on at 12 V with rectification. Then, at a current of 30 A, the electrical power in the circuit is 360 W. The anchor slides more than 30 degrees per revolution, and this is necessarily a continuous all-round fire. It is also possible that the motor armature is wound with a simple (not double) wave. Such electric motors are better at overcoming instantaneous overloads, but they have a starting current - mother, don’t worry. I can’t say more precisely in absentia, and there’s no point in it – there’s hardly anything we can fix here with our own hands. Then it will probably be cheaper and easier to find and purchase new batteries. But first, try turning on the engine at a slightly higher voltage through the rheostat (see above). Almost always, in this way it is possible to shoot down a continuous all-round fire at the cost of a small (up to 10-15%) reduction in power on the shaft.

Circuits of homemade pulse DC-DC voltage converters using transistors, seven examples.

Due to their high efficiency, switching voltage stabilizers have recently become increasingly widespread, although they are usually more complex and contain a larger number of elements.

Since only a small fraction of the energy supplied to the switching stabilizer is converted into thermal energy, its output transistors heat up less, therefore, by reducing the area of ​​heat sinks, the weight and size of the device are reduced.

A noticeable disadvantage of switching stabilizers is the presence of high-frequency ripples at the output, which significantly narrows the scope of their practical use - most often switching stabilizers are used to power devices on digital microcircuits.

Step-down switching voltage stabilizer

A stabilizer with an output voltage lower than the input voltage can be assembled using three transistors (Fig. 1), two of which (VT1, VT2) form a key regulatory element, and the third (VT3) is an amplifier of the mismatch signal.

Rice. 1. Circuit of a pulse voltage stabilizer with an efficiency of 84%.

The device operates in self-oscillating mode. The positive feedback voltage from the collector of the composite transistor VT1 through capacitor C2 enters the base circuit of transistor VT2.

The comparison element and mismatch signal amplifier is a cascade based on the VTZ transistor. Its emitter is connected to the reference voltage source - zener diode VD2, and the base - to the output voltage divider R5 - R7.

In pulse stabilizers, the regulating element operates in switch mode, so the output voltage is regulated by changing the duty cycle of the switch.

Turning on/off transistor VT1 based on the signal from transistor VTZ is controlled by transistor VT2. At the moments when transistor VT1 is open, electromagnetic energy is stored in inductor L1, due to the flow of load current.

After the transistor closes, the stored energy is transferred to the load through the diode VD1. The ripples in the output voltage of the stabilizer are smoothed out by filter L1, SZ.

The characteristics of the stabilizer are entirely determined by the properties of the transistor VT1 and diode VD1, the speed of which should be maximum. With an input voltage of 24 V, output voltage of 15 V and a load current of 1 A, the measured efficiency value was 84%.

Choke L1 has 100 turns of wire with a diameter of 0.63 mm on a K26x16x12 ferrite ring with a magnetic permeability of 100. Its inductance at a bias current of 1 A is about 1 mH.

Step-down DC-DC voltage converter to +5V

The circuit of a simple switching stabilizer is shown in Fig. 2. Chokes L1 and L2 are wound on plastic frames placed in armored magnetic cores B22 made of M2000NM ferrite.

Choke L1 contains 18 turns of a harness of 7 wires PEV-1 0.35. A 0.8 mm thick gasket is inserted between the cups of its magnetic circuit.

The active resistance of the inductor winding L1 is 27 mOhm. Choke L2 has 9 turns of a harness of 10 wires PEV-1 0.35. The gap between its cups is 0.2 mm, the active resistance of the winding is 13 mOhm.

Gaskets can be made of rigid heat-resistant material - textolite, mica, electrical cardboard. The screw holding the magnetic circuit cups together must be made of non-magnetic material.

Rice. 2. Circuit of a simple key voltage stabilizer with an efficiency of 60%.

To set up the stabilizer, a load with a resistance of 5...7 Ohms and a power of 10 W is connected to its output. By selecting resistor R7, the rated output voltage is set, then the load current is increased to 3 A and, by selecting the size of capacitor C4, the generation frequency is set (approximately 18...20 kHz) at which high-frequency voltage surges on capacitor SZ are minimal.

The output voltage of the stabilizer can be increased to 8...10V by increasing the value of resistor R7 and setting a new operating frequency. In this case, the power dissipated by the VTZ transistor will also increase.

In switching stabilizer circuits, it is advisable to use electrolytic capacitors K52-1. The required capacitance value is obtained by connecting capacitors in parallel.

Main technical characteristics:

• Input voltage, V - 15...25.
• Output voltage, V - 5.
• Maximum load current, A - 4.
• Output voltage ripple at a load current of 4 A over the entire range of input voltages, mV, no more than 50.
• Efficiency, %, not lower than 60.
• Operating frequency at an input voltage of 20 b and a load current of 3A, kHz - 20.

An improved version of the +5V switching stabilizer

In comparison with the previous version of the pulse stabilizer, the new design of A. A. Mironov (Fig. 3) has improved and improved such characteristics as efficiency, stability of the output voltage, duration and nature of the transient process when exposed to a pulse load.

Rice. 3. Circuit of a pulse voltage stabilizer.

It turned out that when the prototype operates (Fig. 2), a so-called through current occurs through the composite switch transistor. This current appears at those moments when, based on a signal from the comparison node, the key transistor opens, but the switching diode has not yet had time to close. The presence of such a current causes additional heating losses of the transistor and diode and reduces the efficiency of the device.

Another drawback is the significant ripple of the output voltage at a load current close to the limit. To combat ripples, an additional output LC filter (L2, C5) was introduced into the stabilizer (Fig. 2).

The instability of the output voltage from changes in load current can only be reduced by reducing the active resistance of inductor L2.

Improving the dynamics of the transient process (in particular, reducing its duration) is associated with the need to reduce the inductance of the inductor, but this will inevitably increase the output voltage ripple.

Therefore, it turned out to be advisable to eliminate this output filter, and increase the capacitance of capacitor C2 by 5... 10 times (by parallel connecting several capacitors into a battery).

Circuit R2, C2 in the original stabilizer (Fig. 6.2) practically does not change the duration of the output current decline, so it can be removed (short circuit resistor R2), and the resistance of resistor R3 can be increased to 820 Ohms.

But then, when the input voltage increases from 15 6 to 25 6, the current flowing through resistor R3 (in the original device) will increase by 1.7 times, and the power dissipation will increase by 3 times (up to 0.7 W).

By connecting the lower output of resistor R3 (in the diagram of the modified stabilizer this is resistor R2) to the positive terminal of capacitor C2, this effect can be weakened, but at the same time the resistance of R2 (Fig. 3) should be reduced to 620 Ohms.

One of the effective ways to combat through current is to increase the rise time of the current through the opened key transistor.

Then, when the transistor is fully opened, the current through the diode VD1 will decrease to almost zero. This can be achieved if the shape of the current through the key transistor is close to triangular.

As calculations show, to obtain this current shape, the inductance of storage choke L1 should not exceed 30 μH.

Another way is to use a faster switching diode VD1, for example, KD219B (with a Schottky barrier). Such diodes have higher operating speed and lower voltage drop at the same value of forward current compared to conventional silicon high-frequency diodes. Capacitor C2 type K52-1.

Improved device parameters can also be obtained by changing the operating mode of the key transistor. The peculiarity of the operation of the powerful transistor VTZ in the original and improved stabilizers is that it operates in the active mode, and not in the saturated mode, and therefore has a high current transfer coefficient and closes quickly.

However, due to the increased voltage across it in the open state, the power dissipation is 1.5...2 times higher than the minimum achievable value.

You can reduce the voltage on the key transistor by applying a positive (relative to the positive power wire) bias voltage to the emitter of transistor VT2 (see Fig. 3).

The required value of the bias voltage is selected when setting up the stabilizer. If it is powered by a rectifier connected to a mains transformer, then a separate winding on the transformer can be provided to obtain the bias voltage. However, the bias voltage will change along with the network voltage.

Converter circuit with stable bias voltage

To obtain a stable bias voltage, the stabilizer must be modified (Fig. 4), and the inductor must be turned into transformer T1 by winding an additional winding II. When the key transistor is closed and the diode VD1 is open, the voltage on winding I is determined from the expression: U1=UBыx + U VD1.

Since the voltage at the output and at the diode changes slightly at this time, regardless of the value of the input voltage on winding II, the voltage is almost stable. After rectification, it is supplied to the emitter of transistor VT2 (and VT1).

Rice. 4. Scheme of a modified pulse voltage stabilizer.

Heating losses decreased in the first version of the modified stabilizer by 14.7%, and in the second - by 24.2%, which allows them to operate at a load current of up to 4 A without installing a key transistor on the heat sink.

In the stabilizer of option 1 (Fig. 3), the inductor L1 contains 11 turns, wound with a bundle of eight PEV-1 0.35 wires. The winding is placed in an armored magnetic core B22 made of 2000NM ferrite.

Between the cups you need to lay a 0.25 mm thick textolite gasket. In the stabilizer of option 2 (Fig. 4), transformer T1 is formed by winding two turns of PEV-1 0.35 wire over the inductor coil L1.

Instead of a germanium diode D310, you can use a silicon diode, for example, KD212A or KD212B, and the number of turns of winding II must be increased to three.

DC voltage stabilizer with PWM

A stabilizer with pulse-width control (Fig. 5) is close in principle to the stabilizer described in, but, unlike it, it has two feedback circuits connected in such a way that the key element closes when the load voltage exceeds or the current increases , consumed by the load.

When power is applied to the input of the device, the current flowing through resistor R3 opens the key element formed by transistors VT.1, VT2, as a result of which a current appears in the circuit transistor VT1 - inductor L1 - load - resistor R9. Capacitor C4 is charged and energy is accumulated in inductor L1.

If the load resistance is large enough, then the voltage across it reaches 12 B, and the zener diode VD4 opens. This leads to the opening of transistors VT5, VTZ and the closing of the key element, and thanks to the presence of the diode VD3, inductor L1 transfers the accumulated energy to the load.

Rice. 5. Stabilizer circuit with pulse-width control with efficiency up to 89%.

Stabilizer technical characteristics:

• Input voltage - 15...25 V.
• Output voltage - 12 V.
• Rated loading current is 1 A.
• Output voltage ripple at a load current of 1 A is 0.2 V. Efficiency (at UBX = 18 6, IN = 1 A) is 89%.
• Current consumption at UBX=18 V in load circuit closure mode is 0.4 A.
• Output short circuit current (at UBX =18 6) - 2.5 A.

As the current through the inductor decreases and capacitor C4 discharges, the voltage across the load will also decrease, which will lead to the closing of transistors VT5, VTZ and the opening of the key element. Next, the stabilizer operation process is repeated.

Capacitor C3, which reduces the frequency of the oscillatory process, increases the efficiency of the stabilizer.

With low load resistance, the oscillatory process in the stabilizer occurs differently. An increase in load current leads to an increase in the voltage drop across resistor R9, opening of transistor VT4 and closing of the key element.

In all operating modes of the stabilizer, the current it consumes is less than the load current. Transistor VT1 should be installed on a heat sink measuring 40x25 mm.

Choke L1 consists of 20 turns of a bundle of three PEV-2 0.47 wires, placed in a cup magnetic core B22 made of 1500NMZ ferrite. The magnetic core has a gap 0.5 mm thick made of non-magnetic material.

The stabilizer can be easily adjusted to a different output voltage and load current. The output voltage is set by choosing the type of zener diode VD4, and the maximum load current is set by a proportional change in the resistance of resistor R9 or by supplying a small current to the base of transistor VT4 from a separate parametric stabilizer through a variable resistor.

To reduce the level of output voltage ripple, it is advisable to use an LC filter similar to that used in the circuit in Fig. 2.

Switching voltage stabilizer with conversion efficiency 69...72%

The switching voltage stabilizer (Fig. 6) consists of a trigger unit (R3, VD1, VT1, VD2), a reference voltage source and a comparison device (DD1.1, R1), a direct current amplifier (VT2, DD1.2, VT5), a transistor switch (VTZ, VT4), an inductive energy storage device with a switching diode (VD3, L2) and filters - input (L1, C1, C2) and output (C4, C5, L3, C6). The switching frequency of the inductive energy storage device, depending on the load current, is in the range of 1.3...48 kHz.

Rice. 6. Circuit of a pulse voltage stabilizer with a conversion efficiency of 69...72%.

All inductors L1 - L3 are identical and are wound in B20 armored magnetic cores made of 2000NM ferrite with a gap between the cups of about 0.2 mm.

The rated output voltage is 5 V when the input voltage changes from 8 to 60 b and the conversion efficiency is 69...72%. Stabilization coefficient - 500.

The amplitude of the output voltage ripple at a load current of 0.7 A is no more than 5 mV. Output impedance - 20 mOhm. The maximum load current (without heat sinks for transistor VT4 and diode VD3) is 2 A.

Switching voltage stabilizer 12V

The switching voltage stabilizer (Fig. 6.7) with an input voltage of 20...25 V provides a stable output voltage of 12 V at a load current of 1.2 A.

Output ripple up to 2 mV. Due to its high efficiency, the device does not use heat sinks. The inductance of the inductor L1 is 470 μH.

Rice. 7. Circuit of a pulse voltage stabilizer with low ripple.

Transistor analogues: VS547 - KT3102A] VS548V - KT3102V. Approximate analogues of transistors BC807 - KT3107; BD244 - KT816.

The microcircuit being considered today is an adjustable DC-DC voltage converter, or simply a step-down adjustable current stabilizer of 40 volts at the input and from 1.2 to 35 V at the output. The LM2576 requires an input power of about 40-50 VDC. Since it can handle currents up to 3 amps, the LM2576 works as a switching regulator capable of driving a 3 amp load with a minimum number of components and a small heatsink. The price of the LM2576 chip is approximately 140 rubles.

Schematic diagram of the stabilizer

Features of the scheme

• Output adjustable voltage 1.2 - 35 V and low ripple
• Potentiometer for smooth adjustment of output voltage
• The board has an AC voltage bridge rectifier
• LED indication of input power
• PCB dimensions 70 x 63 mm

The circuit is intended for desktop power supplies, battery chargers, as an LED driver. Next are 2 design options - in standard and planar form:

Why can’t simple parametric stabilizers like LM317 be used in such stabilized power supplies? Because the power dissipation at a voltage of 30 V 3 A will be several tens of watts - a huge radiator and cooler will be required. But with pulse stabilization, the power released on the microcircuit is almost 10 times less. Therefore, with LM2576 we get a small and powerful, universal adjustable voltage regulator.