DIY adjustable power supply. Regulated high-power power supply or charger

Those beginners who are just starting to study electronics are in a hurry to build something supernatural, like microbugs for wiretapping, a laser cutter from a DVD drive, and so on... and so on... What about assembling a power supply with an adjustable output voltage? This power supply is an essential item in every electronics enthusiast's workshop.

Where to start assembling the power supply?

First, you need to decide on the required characteristics that the future power supply will satisfy. The main parameters of the power supply are the maximum current ( Imax), which it can supply to the load (powered device) and the output voltage ( U out), which will be at the output of the power supply. It’s also worth deciding what kind of power supply we need: adjustable or unregulated.

Regulated power supply is a power supply whose output voltage can be changed, for example, from 3 to 12 volts. If we need 5 volts - we turned the regulator knob - we got 5 volts at the output, we need 3 volts - we turned it again - we got 3 volts at the output.

Not adjustable block The power supply is a power supply with a fixed output voltage - it cannot be changed. For example, the well-known and widely used “Electronics” power supply D2-27 is unregulated and has an output voltage of 12 volts. Also unregulated power supplies are all kinds of chargers for cell phones, adapters for modems and routers. All of them, as a rule, are designed for one output voltage: 5, 9, 10 or 12 volts.

It is clear that for a novice radio amateur it is the regulated power supply that is of greatest interest. They can power a huge amount of both homemade and industrial devices, designed for different supply voltages.

Next you need to decide on the power supply circuit. The circuit should be simple, easy to repeat by beginning radio amateurs. Here it is better to stick to a circuit with a conventional power transformer. Why? Because it is quite easy to find a suitable transformer both in the radio markets and in the old consumer electronics. Making a switching power supply is more difficult. For a switching power supply, it is necessary to produce quite a lot of winding parts, such as a high-frequency transformer, filter chokes, etc. Also, switching power supplies contain more electronic components than conventional power supplies with a power transformer.

So, the circuit of the regulated power supply proposed for repetition is shown in the picture (click to enlarge).

Power supply parameters:

Output voltage ( U out) – from 3.3...9 V;

Maximum load current ( Imax) – 0.5 A;

The maximum amplitude of output voltage ripple is 30 mV;

Overcurrent protection;

Protection against overvoltage at the output;

High efficiency.

It is possible to modify the power supply to increase the output voltage.

The circuit diagram of the power supply consists of three parts: a transformer, a rectifier and a stabilizer.

Transformer. Transformer T1 reduces the alternating mains voltage (220-250 volts), which is supplied to the primary winding of the transformer (I), to a voltage of 12-20 volts, which is removed from the secondary winding of the transformer (II). Also, “part-time”, the transformer serves as a galvanic isolation between the electrical network and the powered device. This is a very important function. If the transformer suddenly fails for any reason (voltage surge, etc.), then the mains voltage will not be able to reach the secondary winding and, therefore, the powered device. As you know, the primary and secondary windings of a transformer are reliably isolated from each other. This circumstance reduces the risk of electric shock.

Rectifier. From the secondary winding power transformer T1, a reduced alternating voltage of 12-20 volts is supplied to the rectifier. This is already a classic. The rectifier consists of a diode bridge VD1, which rectifies alternating voltage from the secondary winding of the transformer (II). To smooth out voltage ripples, after the rectifier bridge there is an electrolytic capacitor C3 with a capacity of 2200 microfarads.

Adjustable pulse stabilizer.

The pulse stabilizer circuit is assembled on a fairly well-known and accessible DC/DC converter microcircuit - MC34063.

To make it clear. The MC34063 chip is a specialized PWM controller designed for pulsed DC/DC converters. This chip is the core of the adjustable switching regulator used in this power supply.

The MC34063 chip is equipped with a protection unit against overload and short circuit in the load circuit. The output transistor built into the microcircuit is capable of delivering up to 1.5 amperes of current to the load. At the base specialized chip MC34063 can be assembled as step-up ( Step-Up), and downward ( Step-Down) DC/DC converters. It is also possible to build adjustable pulse stabilizers.

Features of pulse stabilizers.

By the way, switching stabilizers have higher efficiency compared to stabilizers based on KR142EN series microcircuits ( CRANKS), LM78xx, LM317, etc. And although power supplies based on these chips are very simple to assemble, they are less economical and require the installation of a cooling radiator.

The MC34063 chip does not require a cooling radiator. It is worth noting that this chip can often be found in devices that operate autonomously or use backup power. The use of a switching stabilizer increases the efficiency of the device, and, consequently, reduces power consumption from the battery or battery. Due to this it increases offline time operation of the device from a backup power source.

I think it’s now clear why a pulse stabilizer is good.

Parts and electronic components.

Now a little about the parts that will be required to assemble the power supply.

Power transformers TS-10-3M1 and TP114-163M

A TS-10-3M1 transformer with an output voltage of about 15 volts is also suitable. You can find a suitable transformer in radio parts stores and radio markets, the main thing is that it meets the specified parameters.

Chip MC34063 . The MC34063 is available in DIP-8 (PDIP-8) for conventional through-hole mount and SO-8 (SOIC-8) for surface mount. Naturally, in the SOIC-8 package the chip is smaller in size, and the distance between the pins is about 1.27 mm. Therefore, it is more difficult to make a printed circuit board for a microcircuit in the SOIC-8 package, especially for those who have only recently begun to master printed circuit board manufacturing technology. Therefore, it is better to take the MC34063 chip in a DIP package, which is larger in size, and the distance between the pins in such a package is 2.5 mm. It will be easier to make a printed circuit board for a DIP-8 package.

Chokes. Chokes L1 and L2 can be made independently. To do this, you will need two ring magnetic cores made of 2000HM ferrite, size K17.5 x 8.2 x 5 mm. The standard size is deciphered as follows: 17.5 mm. – outer diameter of the ring; 8.2 mm. - internal diameter; a 5 mm. – height of the ring magnetic circuit. To wind the inductor you will need a PEV-2 wire with a cross section of 0.56 mm. 40 turns of such wire must be wound on each ring. The turns of the wire should be distributed evenly over the ferrite ring. Before winding, the ferrite rings must be wrapped in varnished cloth. If you don’t have varnished fabric at hand, you can wrap the ring with three layers of tape. It is worth remembering that ferrite rings may already be painted - covered with a layer of paint. In this case, there is no need to wrap the rings with varnished cloth.

In addition to homemade chokes, you can also use ready-made ones. In this case, the process of assembling the power supply will speed up. For example, as chokes L1, L2 you can use the following surface-mount inductors (SMD - inductor).

As you can see, on the top of their case the inductance value is indicated - 331, which stands for 330 microhenry (330 μH). Also, ready-made chokes with radial leads for conventional installation in holes are suitable as L1, L2. This is what they look like.

The inductance value on them is marked either color code, or numeric. For the power supply, inductances marked 331 (i.e. 330 μH) are suitable. Taking into account the tolerance of ±20%, which is allowed for elements of household electrical equipment, chokes with an inductance of 264 - 396 μH are also suitable. Any inductor or inductor is designed for a certain direct current. As a rule, it maximum value (I DC max) is indicated in the datasheet for the throttle itself. But this value is not indicated on the body itself. In this case, you can approximately determine the value of the maximum permissible current through the inductor based on the cross-section of the wire with which it is wound. As already mentioned, for self-made chokes L1, L2 require a wire with a cross section of 0.56 mm.

Throttle L3 is homemade. To make it, you need a magnetic core made of ferrite. 400HH or 600HH with a diameter of 10 mm. You can find this in antique radios. There it is used as a magnetic antenna. You need to break off a piece 11 mm long from the magnetic circuit. This is quite easy to do; ferrite breaks easily. You can simply tightly clamp the required section with pliers and break off the excess magnetic circuit. You can also clamp the magnetic core in a vice, and then sharply hit the magnetic core. If you fail to carefully break the magnetic circuit the first time, you can repeat the operation.

Then the resulting piece of magnetic circuit must be wrapped with a layer of paper tape or varnished cloth. Next, we wind 6 turns of PEV-2 wire folded in half with a cross-section of 0.56 mm onto the magnetic circuit. To prevent the wire from unwinding, wrap it with tape on top. Those wire leads from which winding of the inductor began are subsequently soldered into the circuit in the place where the points are shown in image L3. These points indicate the beginning of winding the coils with wire.

Additions.

Depending on your needs, you can make certain changes to the design.

For example, instead of a VD3 zener diode type 1N5348 (stabilization voltage - 11 volts), you can install a protective diode - a suppressor - in the circuit 1.5KE10CA.

A suppressor is a powerful protective diode, its functions are similar to a zener diode, however, its main role is in electronic circuits– protective. The purpose of the suppressor is to suppress high-voltage pulse noise. The suppressor has a high speed and is able to extinguish powerful impulses.

Unlike the 1N5348 zener diode, the 1.5KE10CA suppressor has a high response speed, which will undoubtedly affect the performance of the protection.

In technical literature and among radio amateurs, a suppressor can be called differently: protective diode, limiting zener diode, TVS diode, voltage limiter, limiting diode. Suppressors can often be found in switching power supplies - there they serve as protection against overvoltage of the powered circuit in the event of faults in the switching power supply.

About the purpose and parameters protective diodes You can learn from the article about the suppressor.

Suppressor 1.5KE10 C A has the letter WITH in the name and is bidirectional - the polarity of its installation in the circuit does not matter.

If there is a need for a power supply with a fixed output voltage, then the variable resistor R2 is not installed, but replaced with a wire jumper. The required output voltage is selected using a constant resistor R3. Its resistance is calculated using the formula:

Uout = 1.25 * (1+R4/R3)

After the transformations, we obtain a formula that is more convenient for calculations:

R3 = (1.25 * R4)/(U out – 1.25)

If you use this formula, then for U out = 12 volts you will need a resistor R3 with a resistance of about 0.42 kOhm (420 Ohm). When calculating, the value of R4 is taken in kilo-ohms (3.6 kOhm). The result for resistor R3 is also obtained in kilo-ohms.

To more accurately set the output voltage U out, you can install a trimming resistor instead of R2 and set the required voltage using the voltmeter more accurately.

It should be taken into account that a zener diode or suppressor should be installed with a stabilization voltage 1...2 volts higher than the calculated output voltage ( U out) power supply. So, for a power supply with a maximum output voltage equal to, for example, 5 volts, a 1.5KE suppressor should be installed 6V8 CA or similar.

Manufacturing of printed circuit board.

A printed circuit board for a power supply can be made in different ways. Two methods for making printed circuit boards at home have already been discussed on the pages of the site.

The fastest and most comfortable way is to make a printed circuit board using a printed circuit board marker. Marker used Edding 792. He showed himself at his best. By the way, the signet for this power supply was made with just this marker.

The second method is suitable for those who have a lot of patience and a steady hand. This is a technology for making a printed circuit board using a correction pencil. This is quite simple and accessible technology will be useful for those who could not find a marker for printed circuit boards, but do not know how to make boards with LUT or do not have a suitable printer.

The third method is similar to the second, only it uses tsaponlak - How to make a printed circuit board using tsaponlak?

In general, there is plenty to choose from.

Setting up and checking the power supply.

To check the functionality of the power supply, you first need to turn it on, of course. If there are no sparks, smoke or pops (this is quite possible), then the power supply is most likely working. At first, keep some distance from him. If you made a mistake when installing electrolytic capacitors or set them to a lower operating voltage, they can “pop” and explode. This is accompanied by electrolyte splashing in all directions through the protective valve on the body. So take your time. You can read more about electrolytic capacitors. Don’t be lazy to read this – it will come in handy more than once.

Attention! The power transformer is under high voltage during operation! Don't put your fingers near it! Don't forget about safety rules. If you need to change something in the circuit, then first completely disconnect the power supply from the mains, and then do it. There is no other way - be careful!

At the end of this whole story, I want to show you a finished power supply that I made with my own hands.

Yes, it does not yet have a housing, a voltmeter and other “goodies” that make it easier to work with such a device. But, despite this, it works and has already managed to burn out an awesome three-color flashing LED because of its stupid owner, who loves to recklessly twist the voltage regulator. I wish you, novice radio amateurs, to collect something similar!

Single-phase alternating voltage of 220 V is supplied to private houses and apartments. It is ideal for operating incandescent light bulbs that illuminate the home. However, household appliances require power from DC and with much less stress.

General concepts about the network

Everyone knows that in order for a TV or computer to work, you need to connect it to electrical outlet. However, not everyone knows that TV blocks and units cannot be switched on directly from a 220V power supply.

And there are two reasons for this:

• The outlet contains alternating current, but the TV components require direct current;
• Various components and circuits of the TV use voltages of different values ​​for their operation. And for this you will need several lines with different indicators.

For example, for a radio to operate it is necessary constant voltage 9B. And for a computer 5V and 12V.

In order to obtain the required voltage, there are power supplies that are located in the housing of household appliances.

What is a power supply?

The power supply is called electronic device, converting alternating voltage to direct voltage. It provides individual components with the required current and voltage.

The power supply is the source of electricity for all components of the device.

Is it possible to do without a power supply? It is possible, but not always.

Instead of BP you can use accumulators or batteries.

This principle is acceptable in laptops, receivers or players, where the power consumption is not too high.

For a desktop computer or TV, such inclusion is impractical.

IN household appliances two types are used:

• Transformer;
• Pulse.

Each of these blocks is ideal for certain electronic devices, according to the specified technical characteristics.

It is impossible to single out the best or worst type. They have their advantages and disadvantages and successfully solve the task assigned to them.

The transformer power supply consists of a step-down transformer with a primary winding for mains voltage. And the secondary winding based on the required voltage and current.

AC voltage conversion In constant operation it is carried out using a rectifier. The ripple voltage is then smoothed out using large capacitors. To the diagram transformer block may include filters against high-frequency interference, short-circuit protection, current and voltage stabilizers.

Transformer power supplies are distinguished by their simplicity of design, high reliability, availability of the element base and low level of self-interference. They are assembled according to simple schemes.

However, such power supplies have a large weight and dimensions, and a low efficiency.

Switching power supplies are based on the principle of initial rectification of the incoming voltage, followed by conversion into pulses of increased frequency.

In pulse blocks with galvanic isolation, the network power is supplied to a transformer (with much smaller dimensions than in a transformer power supply).

If galvanic isolation from the supply network is not needed, then the pulses are immediately fed to the low-frequency output filter.

Thanks to the use of negative feedback, switching power supplies provide stable characteristics regardless of fluctuations in input voltage and load size.

Switching power supplies have relatively small dimensions and weight. They cover a wide range of input voltage and frequency and are characterized by a high efficiency.

The disadvantages include the high-frequency level of interference caused by the operating principle of switching power supplies.

Typically, power supplies already built into the equipment, and there is no need to change anything about it. However, in some cases it becomes necessary to have a separate power supply for a certain voltage.

For example: the radio receiver is designed to operate on batteries and does not have a built-in control device. It is reasonable to use a separate power supply unit. This will save you the hassle of frequently replacing batteries.

In the case where a radio amateur is engaged in the manufacture or repair of a radio electronic devices, he has to work with equipment that uses different supply voltages. Then a power supply with adjustable output voltage will be useful.

Of course, such a device can buy at an electronics store. However, it is much more pleasant for a creative person to make such a device with his own hands. Moreover, there may not be a power supply on sale with the characteristics required by the master.

In radio magazines and on the Internet you can find a huge number of various schemes for regulated power supplies.

But in amateur radio practice it is quite enough to have a simple adjustable power supply from 0 to 12V. Both an experienced and a novice radio amateur can make such a device with his own hands.

Advantages of the power supply

Scheme of a simple but reliable power supply with smooth regulation consists of two parts:

• The main part (the power supply itself);
• Transistor circuit for output voltage regulator.

The main part includes:

• Step-down transformer with power up to 30W. A transformer is required with a primary winding designed for alternating current 220V and a secondary winding with an output voltage of 15V and a current of 2-3 amperes;
• A rectifier assembled on four KD202 diodes (or similar) to convert DC voltage from AC;
• An electrolytic capacitor with a capacity of at least 1000 microfarads. Due to its ability to accumulate and release voltage, it serves as a smoothing filter. The higher the capacitor rating, the smaller the voltage surges.

IN transistor circuit includes:

• Parametric stabilizer consisting of a resistor and a zener diode. A constant value with a small deviation coefficient is formed at the zener diode;
• A variable resistor that smoothly changes the output voltage;
• An emitter follower consisting of two transistors operating in current amplification mode.

When installed correctly, the device begins to work immediately, without any settings in the circuit.

Checking it at work

Connect a voltmeter to the output of the power supply. Turn the voltage regulator to minimum. The voltmeter reading should be zero. Smoothly move the regulator to the right position. The voltmeter readings should increase smoothly up to a maximum of +12V.

In parallel with the voltmeter we turn on half ampere load. The output voltage drop should be minimal.

Despite the simplicity of the design, the power supply produces good characteristics and parameters.

Small do-it-yourself modifications will improve the design. For example, you can install an overload protection unit, or install an internal voltmeter.

Hello dear friends. Now I will tell you about a good and cheap power source (also a charger for a car), which you can assemble with your own hands. To assemble this circuit, you will need a list of parts, now I will list them for you: a power step-down transformer, a diode bridge, a high-capacity electrolyte capacitor and a smaller capacitor, two resistors (one variable and the other constant), microcircuit bank and three powerful transistors. The most important thing is that all these parts can be found in an old tube TV; in general, you don’t need to spend money on buying scarce radio components - this is a big plus of this scheme. The second significant advantage is that such a simple circuit is capable of delivering current up to 22 Amperes at 13 volts. You can see for yourself what great advantages it is: both lightweight and at low cost. cash, and turn such a mono circuit into a laboratory power supply, a power supply for experiments (regulated), for powering powerful devices, and so on. See the power supply-charger diagram below.

Now I’ll tell you about each detail in more detail. Let's start with the power transformer. The power transformer is designed to convert voltage of one frequency. They can be up or down. A step-up transformer increases the voltage, and a step-down transformer lowers it, which means that since our transformer lowers the voltage according to the circuit, it is a step-down transformer. The transformer consists of a primary, secondary winding and magnetic circuit. The magnetic core consists of individual pressed sheets of electrical steel. The primary winding consists of many turns with a smaller cross-section of wire and is characterized by high resistance in relation to the secondary winding (when you are looking for a 220 volt winding, measure the resistance; where there is more, that is the mains winding).

The secondary consists of the least number of turns and the cross-section of the wire is larger - this is necessary in order to remove more current. Beginners may ask why pins 15, 13 and 10,11 are connected to secondary ones. This must be done for a higher output voltage of the transformer. You can simply wind more wire on the point - the voltage will rise. And if your transformer does not have enough voltage, then you can connect two transformers to the network and connect the secondary ones in series, but then it is better to take transformers of the same power, since a transformer of lower power will heat up more. You can independently rewind the transformer to the voltage and current you need - but more on that in another article. In general, this is what the transformer looks like, as described above. You can get it from a tube TV, it will be 150 watts. 150/10=15 A, at 10 volts such a transformer will give you 15 amperes, and at 150 volts - 150./150=1 only one ampere. Calculate for yourself what current you need.

The diode bridge is assembled using a bridge circuit. A diode bridge using a bridge circuit is twice as good at removing network ripples as a single half-wave rectifier, so diode bridges are installed in power supplies using a bridge circuit so that the equipment that powers the network through the diode bridge does not fail, even if the ULF produces a characteristic sound. Any capacitors, but with a current of at least 15-20 Amps, or buy a diode bridge on the market and a current of at least 20 Amps. A 47,000 microfarad capacitor electrolyte removes ripples just like a diode bridge, only the capacitor removes these ripples better and, accordingly, the larger the capacitance of the capacitor, the more ripples it can remove. You can make electrolytic capacitors yourself: take a half-liter jar and pour electrolyte, lower 2 plates (one copper and the other iron), you get an anode and a cathode and can be connected to the network. The capacitance of the capacitor will directly depend on the amount of electrolyte (or rather, charged electrolyte) and the size of the plates (or rather, how quickly we can charge the electrolyte and discharge it, because with a larger area of ​​the plates we will charge the liquid faster). By the way, with a very large capacitance, you can dispense with the stabilizer, since the capacitor will actually act as a voltage stabilizer and filter.

Chip KREN8b will stabilize the current to 1 Ampere. This chip in this power supply can be compared with preamplifier in ULF, since the main amplification occurs in transistors T1, T2, T3. We must place all transistors on radiators. With resistor R1 we regulate the current (up to 1 Ampere), which is stabilized by the microcircuit and supplied to the base of the transistor. Accordingly, we regulate the gain of all three transistors at once (the maximum current to the base of one transistor is 0.33 A, since 1/3 = 0.333333 A). The positive charge is amplified both through the microcircuit (to control the gain of the transistors) and through the transistors (we supply the transistors with a positive charge, and control the gain from the microcircuit).

If we connect three more transistors in parallel with these three and connect another one in parallel with the KRNE microcircuit, then we can get a current twice as high as with this working standard circuit. I recommend it if you need high currents, but the transformer must be powerful enough. With my method, the output current should be 40 A at 13 volts, which means 40 * 13 = 520 watts. The transformer should have a capacity of half a kilowatt. Resistor R2 is needed to limit the current to prevent a short circuit. Then we next install an electrolyte capacitor to smooth out the pulsations at the final stage, and it would not hurt to also install a capacitor of a smaller capacity in order to smooth out the pulsations of higher frequencies. Also, if you have a lot of interference in your network, then I recommend installing a throttle, which will remove all high-frequency RF interference. Install the throttle in series, in the open circuit in front of the microcircuit, to the plus, of course.

Making a power supply with your own hands makes sense not only for enthusiastic radio amateurs. Homemade block power supply (PS) will create convenience and save a considerable amount also in the following cases:

• To power low-voltage power tools, to save expensive resources battery(battery);
• For electrification of premises that are particularly dangerous in terms of the degree of electric shock: basements, garages, sheds, etc. When feeding them alternating current its large value in low-voltage wiring can interfere 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 professional power supply must maintain the specified voltage indefinitely with the highest accuracy for a 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 restrictions 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 shutdown load (consumer) or an open circuit 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 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 work both from IPN industrial frequency with a transformer on iron, and from IIN.

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, computer UPS a fairly 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 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 USB power+5V ports will also turn 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 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 unit.

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. Usage of Tr – 100% Disadvantage – double consumption of copper 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 rotated 90 degrees counterclockwise, but in fact this 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. Built primarily for food analog devices, requiring 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. Built primarily as low-power auxiliary units for independent power supply operational amplifiers(O-Amp) and other low-power analog nodes that are demanding on the quality of power supply.

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 scheme of comparison, but remake this one on high current difficult. 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 VT1 base circuit to common, 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. It's just average power jigsaw, but, unlike a drill or screwdriver, he takes it constantly. 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. This might be much more useful here. available device ignition (ballast) from an economy lamp of 40 W or more; 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 block power supply with regulation 0-30 V, 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 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 P1 scale (in the inset - its appearance), and adjustment if necessary - 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 up 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 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 televisions with cathode ray tubes (CRT), and it gave rise 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 unit 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 in 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 put the “dead guy” in 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, and 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 voltage limits of the multimeter 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 consider a couple of samples using pulse width modulation (PWM), which allows us to obtain 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. That's why good block The power supply for the LED strip must include a load current stabilizer; technically - 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 charge of the base, 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 maximum frequency; more precisely - with a minimum duty cycle. The inertia-free switch VT3 generates powerful impulses, and its harness VD3C4C3L1 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 current leakage circuit of the base 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 inserting a 3.3-10 kOhm potentiometer R* into the gap between R3 and the VT2 emitter after adjustment, 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 of a bug flashlight and other low-power unstable random power sources. 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.

Everyone has long known that without a normal regulated power supply it is not possible to start a single device made by yourself. After all, the power supply is the basis of an amateur radio laboratory, so in this article I will tell you how to make a simple adjustable power supply from available parts using only two transistors. This figure shows an easy-to-make regulated power supply circuit.

This circuit is very unpretentious in radio components; therefore, every beginning radio amateur can assemble it practically from what is at hand. The Br1 diode bridge will work with almost any one with a current of at least 3A. If there is no diode bridge, replace it with suitable diodes. Capacitor C1 can be replaced with anything from 1000 µF to 10,000 µF. Variable resistor P1 from 5 to 10 kOhm. Transistor T1 KT815, BD137, BD139 transistor T2 KT805, KT819, TIP41, MJE13009 and many other Soviet and foreign analogues are selected according to the required load and power of the power source.

Diode D1 with a current of at least 3A can be replaced with a jumper; it protects capacitor C2 from reverse polarity when connected to the battery power supply. The power source for this circuit can be any transformer from 12 to 30 volts. For my power supply, I used a toroidal transformer from a music center with two series-connected 13.5V windings and a current of 3.5A. After rectifying the voltage, the output turned out to be 30 volts.

As always, I posted all the details of the power supply on printed circuit board measuring 6.5 by 4.5 cm. When installing transistors, pay attention to the pinout. For example, the KT819 transistor has legs arranged like ECB, and the MJE13009 transistor has BCE legs, so it’s best to connect the transistors to the board with small pieces of wire and then you won’t have problems with the correct installation of the transistors on the radiator.

Install two transistors on one radiator without insulating gaskets because the collectors of the transistors in the circuit are connected together. Don’t forget to lubricate the transistor mounting points with thermal paste. It is advisable to mount the diode assembly on a small radiator; it also does not heat up slightly. To monitor the output characteristics, it is advisable to install a universal Chinese measuring instrument (UKIP) indicated in the diagram V/A1.

I placed all the components of the power supply in a standard case from a computer power supply. Only because of the large size of the toroidal transformer from the music center, the fan had to be placed outside, but this does not particularly affect the technical characteristics of the power supply.

Featuring a powerful 3.5 amp toroidal transformer, I use this versatile, regulated power supply to power a variety of DIY projects and as a charger for small batteries.

Friends, I wish you good luck and good mood! See you in new articles!