Adjustable electronic power supply. How to make an adjustable power supply with your own hands

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 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 feeding them alternating current its large value in low-voltage wiring can create interference 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 life LED strip and get 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 limitations and therefore can be significantly simplified while maintaining quality indicators sufficient for personal use. Further, through also simple improvements, you can get a power supply from it special purpose. 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 BP VSC is 100, 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 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 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 “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.

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 gaps between pulses, so the ripple filter capacitor Sph should be 4-6 times larger capacity than in other schemes. Usage power transformer TP for power – 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 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 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. 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 area cross section Sc) 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 smallest permissible voltage 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’s better for a beginner not to get involved right away. high power, and make a simple, highly stable 12V ELV for the sample according to the diagram 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 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 in this case it's 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. From here it is clear that any powerful adjustable power supply must be equipped with a very effective system cooling.

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. CPU cooler It is also not suitable for airflow; it is designed for less power.

One of the options for home handyman– 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: actually radical way To overcome this problem - the 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 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) on the 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 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 formalist pedant 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 high-power transistors β is large collector current drops significantly, and δr of the zener diode ranges from units 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 of parameters powerful elements– KT825 and KT827 at 25A and KD2997A at 30A. T2 is not capable of providing such a current, and while it warms up, FU1 and/or FU2 will have time to burn out.

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

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

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

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

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

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

About power supply repair

PSUs fail more often than others electronic devices: they take the first blow of the network throws, they 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 they 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 back 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 birth to line-scan TVs with cathode ray tubes(CRT), and she is 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 transferred to 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.

IIN with damper is still alive in TVs and CRT displays, since in them IIN and output line scan combined: powerful 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 they are almost completely replaced by field, controlled special forces. 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 the 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 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. These components are better called 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 check 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 pair 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 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 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.

When doing something regularly, people strive to make their work easier by creating various devices and devices. This fully applies to the radio business. When assembling electronic devices with one of important issues, the question of nutrition remains. Therefore, one of the first devices that a novice radio amateur often assembles is this.

Important Features power supply, are its power, stabilization of the output voltage, the absence of ripple, which can manifest itself, for example, when assembling and powering an amplifier, from this power supply in the form of background or hum. And finally, it is important for us that the power supply is universal so that it can be used to power many devices. And for this it is necessary that it can produce different output voltages.

A partial solution to the problem may be Chinese adapter with output voltage switching. But such a power supply does not have the ability to be smoothly adjusted and does not have voltage stabilization. In other words, the voltage at its output “jumps” depending on the supply voltage of 220 volts, which often sags in the evenings, especially if you live in a private house. Also, the voltage at the output of the power supply unit (PSU) may decrease when a more powerful load is connected. The power supply proposed in this article, with stabilization and regulation of the output voltage, does not have all these shortcomings. By rotating the variable resistor knob, we can set any voltage in the range from 0 to 10.3 volts, with the possibility of smooth adjustment. We set the voltage at the output of the power supply according to the readings of the multimeter in voltmeter mode, D.C.(DCV).

This can come in handy more than once, for example, when testing LEDs, which, as you know, do not like being supplied with a voltage that is too high compared to the rated voltage. As a result, their service life can be sharply reduced, and in particularly severe cases, the LED can burn out immediately. Below is a diagram of this power supply:

The design of this RBP is standard and has not undergone significant changes since the 70s of the last century. The first versions of the schemes were using germanium transistors, later versions were using modern element base. This block power supply is capable of delivering power up to 800 - 900 milliamps, in the presence of a transformer providing the required power.

The limitation in the circuit is the diode bridge used, which allows currents of a maximum of 1 ampere. If you need to increase the power of this power supply, you need to take a more powerful transformer, a diode bridge and increase the radiator area, or if the dimensions of the case do not allow this, you can use active cooling(cooler). Below is a list of parts required for assembly:

This power supply uses the domestic high-power transistor KT805AM. In the photo below you can see it appearance. The adjacent figure shows its pinout:

This transistor will need to be attached to the radiator. In the case of attaching the radiator to the metal body of the power supply, for example, as I did, you will need to place a mica gasket between the radiator and the metal plate of the transistor, to which the radiator should be adjacent. To improve heat transfer from the transistor to the radiator, you need to use thermal paste. In principle, any one used for application to a PC processor will do, for example the same KPT-8.

The transformer should produce a voltage of 13 volts on the secondary winding, but in principle a voltage within 12-14 volts is acceptable. The power supply contains a filter electrolytic capacitor, with a capacity of 2200 microfarads (more is possible, less is undesirable), for a voltage of 25 volts. You can take a capacitor designed for a higher voltage, but remember that such capacitors are usually larger in size. The figure below shows a printed circuit board for the sprint-layout program, which can be downloaded from general archive, attached archive.

I assembled the power supply not exactly using this board, since my transformer with a diode bridge and a filter capacitor were on a separate board, but this does not change the essence.

Variable resistor and a powerful transistor, in my version they are connected by hanging mounting, on wiring. The contacts of the variable resistor R2 are marked on the board, R2.1 - R2.3, R2.1 is the left contact of the variable resistor, the rest are counted from it. If, nevertheless, during connection the left and right contacts of the potentiometer were confused, and the adjustment is carried out not from the left - minimum, to the right - maximum, you need to swap the wires going to the extreme terminals of the variable resistor. The circuit provides a power-on indication on the LED. Switching on and off is carried out using a toggle switch, by switching the 220 volt power supplied to primary winding transformer. This is what the power supply looked like at the assembly stage:

Power is supplied to the power supply through the native power supply connector ATX computer, using a standard detachable cable. This solution allows you to avoid the tangle of wires that often appears on a radio amateur’s desk.

The voltage at the output of the power supply is removed from laboratory clamps, under which any wire can be clamped. You can also connect standard multimeter probes with crocodiles at the ends to these clamps, by inserting them on top, for more convenient supply of voltage to the assembled circuit.

Although if you want to save money, you can limit yourself simple wiring at the ends with alligator clips, clamped using laboratory clamps. If using a metal housing, place a suitable size casing on the clamp securing screw to prevent the clamp from shorting to the housing. I have been using this type of power supply for at least 6 years now, and it has proven the feasibility of its assembly and ease of use in the daily practice of a radio amateur. Happy assembly everyone! Especially for the site " Electronic circuits "AKV.

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 not 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 analogs 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 music center with two series-connected windings of 13.5V 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, for the KT819 transistor the legs are located like ECB, and for the MJE13009 transistor it’s like BCE, so it’s best to connect the transistors to the board with small pieces of wire and then you won’t have problems with correct installation 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 control the output characteristics, it is advisable to install a universal Chinese meter(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 large size of the toroidal transformer from the music center, the fan had to be placed outside, but this technical specifications The power supply doesn't really affect it.

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!

For radio amateurs, and in general modern man, an indispensable thing in the house is a power supply unit (PSU), because it has a very useful function - voltage and current regulation.

At the same time, few people know that it is quite possible to make such a device with due diligence and knowledge of radio electronics with your own hands. For any radio amateur who likes to tinker with electronics at home, homemade laboratory power supplies will allow him to practice his hobby without restrictions. Our article will tell you how to make an adjustable power supply with your own hands.

What you need to know

A power supply with current and voltage regulation is a must-have item in a modern home. This device, thanks to its special device, can convert the voltage and current available in the network to the level that a particular electronic device can consume. Here approximate diagram work on which you can make a similar device with your own hands.

But ready-made power supplies are quite expensive to buy for specific needs. Therefore, today very often converters for voltage and current are made by hand.

Pay attention! Homemade laboratory power supplies can have different dimensions, power ratings and other characteristics. It all depends on what kind of converter you need and for what purpose.

Professionals can easily make a powerful power supply, while beginners and amateurs can start with a simple type of device. In this case, depending on the complexity, a very different scheme can be used.

What to consider

The regulated power supply is a universal converter that can be used to connect any household or computing equipment. Without it, not a single home appliance will be able to function normally.
Such a power supply consists of the following components:

• transformer;
• converter;
• indicator (voltmeter and ammeter).
• transistors and other parts necessary to create a high-quality electrical network.

The diagram above shows all the components of the device.
Besides this, this type The power supply must have protection for high and low current. Otherwise, any abnormal situation may lead to the fact that the converter and connected to it electrical appliance it will just burn out. This result can also be caused by improper soldering of board components, incorrect connection or installation.
If you are a beginner, then in order to make an adjustable type of power supply with your own hands, it is better to choose a simple assembly option. One of the simple types of converter is a 0-15V power supply. It has protection against excess current in the connected load. The diagram for its assembly is located below.

Simple assembly diagram

This is, so to speak, universal type assemblies. The diagram here is understandable to anyone who has held a soldering iron at least once in their hands. The advantages of this scheme include the following points:

• it consists of simple and affordable parts that can be found either on the radio market or in specialized radio electronics stores;
• simple type of assembly and further configuration;
• here the lower limit for voltage is 0.05 volts;
• dual-range protection for current indicator (at 0.05 and 1A);
• wide range for output voltages;
• high stability in the functioning of the converter.

Diode bridge

In this situation, the transformer will provide a voltage that is 3V higher than the maximum required output voltage. It follows from this that a power supply capable of regulating voltage up to 20V requires a transformer of at least 23 V.

Pay attention! The diode bridge should be selected based on the maximum current, which will be limited by the available protection.

A 4700 µF filter capacitor will allow equipment sensitive to power supply noise to avoid background noise. To do this, you will need a compensation stabilizer with a suppression coefficient for ripples of more than 1000.
Now that we have understood the basic aspects of assembly, we need to pay attention to the requirements.

Device requirements

To create a simple, but at the same time high-quality and powerful power supply with the ability to regulate voltage and current with your own hands, you need to know what requirements exist for this type of converter.
These technical requirements look like this:

• adjustable stabilized output for 3–24 V. In this case, the current load must be at least 2 A;
• unregulated 12/24 V output. This assumes heavy load by current.

To fulfill the first requirement, you should use an integral stabilizer. In the second case, the output must be made after the diode bridge, so to speak, bypassing the stabilizer.

Let's start assembling

Transformer TS-150–1

Once you have determined the requirements that your permanent regulated power supply must meet, and the appropriate circuit has been selected, you can begin the assembly itself. But first of all, let's stock up on the parts we need.
For assembly you will need:

• powerful transformer. For example, TS-150–1. It is capable of delivering voltages of 12 and 24 V;
• capacitor. You can use a 10000 µF 50 V model;
• chip for stabilizer;
• strapping;
• details of the circuit (in our case, the circuit shown above).

After this, according to the diagram, we assemble an adjustable power supply with our own hands in strict accordance with all the recommendations. The sequence of actions must be followed.

Ready power supply

The following parts are used to assemble the power supply:

• germanium transistors (mostly). If you want to replace them with more modern silicon elements, then the lower MP37 should definitely remain germanium. MP36, MP37, MP38 transistors are used here;
• A current-limiting unit is assembled on the transistor. It provides monitoring of the voltage drop across the resistor.
• Zener diode D814. It determines the regulation of the maximum output voltage. It absorbs half of the output voltage;

Pay attention! Since the D814 zener diode takes exactly half the output voltage, it should be selected to create a 0-25V output voltage of approximately 13V.

• lower limit in assembled block power supply has a voltage indicator of only 0.05 V. This indicator is rare for more complex circuits converter assemblies;
• dial indicators display current and voltage indicators.

Assembly parts

To accommodate all the parts, you must choose a steel case. It will be able to shield the transformer and power supply board. As a result, you will avoid situations of various types of interference for sensitive equipment.

The resulting converter can be safely used to power any household equipment, as well as experiments and tests carried out in a home laboratory. Also, such a device can be used to assess the performance of a car generator.

Conclusion

Using simple circuits to assemble an adjustable type of power supply, you will be able to get your hands on and in the future make more complex models with your own hands. You should not take on backbreaking work, as in the end you may not get the desired result, and a homemade converter will work ineffectively, which in a negative way may affect both the device itself and the functionality of electrical equipment connected to it.
If you do everything correctly, then at the end you will get great block voltage-regulated power supply for your home laboratory or other everyday situations.

Selecting a street motion sensor to turn on the lights

Good day, forum users and site guests. Radio circuits! Wanting to collect a decent, but not too expensive and cool block food, so that it has everything and it doesn’t cost anything in terms of money. In the end, I chose the best, in my opinion, circuit with current and voltage regulation, which consists of only five transistors, not counting a couple of dozen resistors and capacitors. Nevertheless, it works reliably and is highly repeatable. This scheme has already been reviewed on the site, but with the help of colleagues we managed to improve it somewhat.

I assembled this circuit in its original form and encountered one unpleasant problem. When adjusting the current, I can’t set it to 0.1 A - at least 1.5 A at R6 0.22 Ohm. When I increased the resistance of R6 to 1.2 Ohms, the current during a short circuit turned out to be at least 0.5 A. But now R6 began to heat up quickly and strongly. Then I used a small modification and got a much wider current adjustment. Approximately 16 mA to maximum. You can also make it from 120 mA if you transfer the end of the resistor R8 to the T4 base. The bottom line is that before the resistor voltage drops, a drop is added B-E transition and this additional voltage allows you to open T5 earlier, and as a result, limit the current earlier.

Based on this proposal, I conducted successful tests and eventually received a simple laboratory power supply. I am posting a photo of my laboratory power supply with three outputs, where:

• 1-output 0-22v
• 2-output 0-22v
• 3-output +/- 16V

Also, in addition to the output voltage regulation board, the device was supplemented with a power filter board with a fuse block. What happened in the end - see below.