Power unit. DIY power supply Schematic diagram of a 12 volt power supply

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. compensating 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 power supply. 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 absolute value, 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 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 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.

Evgeniy said:

Need more cuts. So that all the text is made up of abbreviations. Fuck that no one understands, but you don’t have to write the same word that is repeated THREE times in the text.

By clicking the “Add comment” button, I agree with the site.

Currently, feeding block systems are the main part of lighting devices. It is the 12-volt feeding device that allows you to save electrical energy. Making the device is not difficult. In our article we will try to answer the question of how to do it.

Types of power supplies

It is customary to divide feeding systems into several types. The first group includes secondary power sources, of which there are a large number. In the second - transformer or network. The third group includes pulsed sources. Each power supply has its own characteristics, its positive and negative sides.

The main part of the lighting devices is the recharge system. It is the 12-volt feeding device that allows you to save electrical energy. Making the device is not difficult. In our article we will try to answer the question of how to make a power supply with your own hands.

The most common is the second type of feeding system, which we will assemble today.

Components of the device

The mechanism we are assembling today consists of three parts:

• step-down transformer, which is the most important and integral part;
• a capacitor, with the help of which the current voltage is stabilized to optimal readings;
• diodes that are necessary to assemble a diode bridge with your own hands.

Each part is very important. If an error is made in any of them during assembly, this will lead to the fact that the assembled unit and the household electrical appliance connected to the system will not work correctly. And also the assembled device may not turn on at all. Let's look at each of the components of the mechanism in more detail.

Transformer selection

The voltage converting device is one of the main transformer components. Here the alternating 220-volt voltage is converted into something similar to itself, but with a slightly reduced amplitude.

Using simple calculations, we will find out how many revolutions the secondary winding has made around its axis. Having found out the number of revolutions (usually the voltage indicator in this case is 6.3), you should divide the voltage indicator by the number of turns.

A conventional step-down device, necessary to reduce the voltage from the usual 220-volt to 12-volt, can be used as a transformer-type machine.

It is optimal to use a 470 μF capacitor with a 25-volt voltage for the device. Why would this be the best option? This is due to the fact that when the voltage leaves the unit, it becomes higher than the standard voltage of 12V. When the mechanism starts working, the voltage returns to standard values ​​(12 V).

How to make a rectifier

A device that operates on semiconductor diodes is called a rectifier, which is one of the important elements of the power supply circuit. With the help of a rectifier, the values ​​of alternating current are converted and brought closer to their constant values.

It is not difficult to assemble a 12 volt power supply with your own hands. First of all, you should understand that a capacitor has two outputs: one is positive, the other is negative.

How can you figure out which one is which? If the diode has a positive value, then there is a special strip on it; if there is no strip, then the diode has a negative value. The diode components are connected in series:

Schematic connection of 2 elements: the device with a minus must be connected to a diode with a positive value.

The connection of 2 other diodes is carried out in a similar way (the device with a minus value must be connected to a diode with a positive value). Connecting paired structures to each other, in this case it is necessary to connect diodes in pairs (negative with negative indicator, and positive with positive).

It is important to ensure that the connection is correct, otherwise it will lead to problems in the operation of the mechanism.

After creating a diode bridge with 4 connecting points:

• two with a plus-minus circuit;
• one plus-plus;
• One minus or minus - you can start assembling the mechanism. It is important to check the quality of contact between the diode systems.

Assembly of filtration blocks

Before connecting the 12 volt power supply, it is recommended to install special filters that will help the operation of household appliances connected to the device. To power household appliances, an LC circuit is usually used. Where the rectifier with the plus value comes out of the device, a choke must be connected. Electric current must pass through it.

At the second stage of filtration, work is carried out with an electrolytic capacitor with a large capacity, which should be connected to the inductor on the side with a positive value.

The connection of the second pin goes to the common electrical wire with a minus value. An electrolytic capacitor helps stabilize the electric current. How does this happen? We will look at this issue in a little more detail.

How to stabilize the output voltage

To stabilize the output voltage, you can use a 12-volt Zener diode. Even if you install more powerful stabilizers, the output will be the same 12 Volts.

Where does the remaining amount go? The rest is converted into thermal energy, so this component is usually mounted on the surface of the radiator.

Regulatory process

It is common practice to use regulated power supplies. When installing the stabilizer, it is necessary to mount a special wire to which a variable resistor should be connected.

The variable resistor and output of the assembly have 220-ohm resistance values. A semiconductor diode is installed at the input and output of the stabilizing device.

The regulator allows you to stabilize current indicators to optimal values ​​and prevents burnout of the mechanism. To enhance the safety of the assembled unit, you can install an electronic voltmeter at the output of the system, which will help monitor the current voltage in the system.

Assembling a 12 Volt power supply is not difficult even for a person with minimal knowledge in the field of assembling any devices. To do this, you can use step-by-step instructions with photos at each stage. Having the necessary parts and step-by-step instructions, you can assemble any mechanism.

When connecting to electrical appliances, you must consult with a master electrician, who will check the correct assembly, which will prevent problems with the operation of the device.

Photo of 12 volt power supplies

We all know that power supplies today are an integral part of a large number of electrical appliances and lighting systems. Without them, our life is unrealistic, especially since energy savings contribute to the operation of these devices. Basically, power supplies have an output voltage of 12 to 36 volts. In this article I would like to answer one question: is it possible to make a 12V power supply with your own hands? In principle, no problems, because this device actually has a simple design.

What can you assemble a power supply from?

So, what parts and devices are needed to assemble a homemade power supply? The design is based on only three components:

• Transformer.
• Capacitor.
• Diodes, from which you will have to assemble a diode bridge with your own hands.

As a transformer, you will have to use a regular step-down device, which will reduce the voltage from 220 V to 12 V. Such devices are sold in stores today, you can use an old unit, you can convert, for example, a transformer with a step-down to 36 volts into a device with a step-down to 12 volt. In general, there are options, use any.

As for the capacitor, the best option for a homemade unit is a capacitor with a capacity of 470 μF with a voltage of 25V. Why exactly with this voltage? The thing is that the output voltage will be higher than planned, that is, more than 12 volts. And this is normal, because under load the voltage will drop to 12V.

Assembling a diode bridge

Now here’s a very important point, which concerns the question of how to make a 12V power supply with your own hands. First, let's start with the fact that a diode is a bipolar element, like, in principle, a capacitor. That is, he has two outputs: one is minus, the other is plus. So, the plus on the diode is indicated by a stripe, which means that without a stripe it is a minus. Diode connection sequence:

• First, two elements are connected to each other according to a plus-minus scheme.
• The other two diodes are connected in the same way.
• After that, the two paired structures must be connected to each other according to the scheme plus with plus and minus with minus. The main thing here is not to make a mistake.

In the end you should have a closed structure, which is called a diode bridge. It has four connecting points: two “plus-minus”, one “plus-plus” and another “minus-minus”. You can connect elements on any board of the required device. The main requirement here is high-quality contact between the diodes.

Secondly, a diode bridge is, in fact, a regular rectifier that rectifies the alternating current coming from the secondary winding of the transformer.

Complete assembly of the device

Everything is ready, we can proceed to assembling the final product of our idea. First you need to connect the transformer leads to the diode bridge. They are connected to the plus-minus connection points, the remaining points remain free.

Now you need to connect the capacitor. Please note that there are also marks on it that determine the polarity of the device. Only on it everything is the opposite than on diodes. That is, the capacitor is usually marked with a negative terminal, which is connected to the minus-minus point of the diode bridge, and the opposite pole (positive) is connected to the minus-minus point.

All that remains is to connect the two power wires. For this, it is best to choose colored wires, although this is not necessary. You can use single-color ones, but on the condition that they have to be marked in some way, for example, make a knot on one of them or wrap the end of the wire with electrical tape.

So, the power wires are connected. We connect one of them to the plus-plus point on the diode bridge, the other to the minus-minus point. That's it, the 12-volt step-down power supply is ready, you can test it. In idle mode, it usually shows a voltage of around 16 volts. But as soon as a load is applied to it, the voltage will drop to 12 volts. If there is a need to set the exact voltage, you will have to connect a stabilizer to the homemade device. As you can see, making a power supply with your own hands is not very difficult.

Of course, this is the simplest scheme; power supplies can have different parameters, with two main ones:

As an addition, a function can be used that distinguishes power supply models into regulated (switching) and unregulated (stabilized). The first are indicated by the ability to change the output voltage in the range from 3 to 12 volts. That is, the more complex the designs, the more capabilities the units as a whole have.

And one last thing. Homemade power supplies are not entirely safe devices. So when testing them, it is recommended to move some distance away and only after that connect them to a 220-volt network. If you calculate something inaccurately, for example, choose the wrong capacitor, then there is a high probability that this element will simply explode. It is filled with electrolyte, which during an explosion will spray over a considerable distance. In addition, you should not make replacements or soldering while the power supply is turned on. A lot of voltage collects on the transformer, so don't play with fire. All modifications must be carried out only with the device turned off.