In this article we will look at a stabilized power supply with continuously adjustable output voltage 0...24 volts and a current of 3 amperes. The power supply protection is implemented on the principle of limiting the maximum current at the source output. The current limit threshold is adjusted using resistor R8. The output voltage is regulated by variable resistor R3.

Schematic diagram power supply is shown in Figure 1.

List of elements:

R1........................180R 0.5W
R2, R4............. 6K8 0.5W
R3......................10k (4k7 – 22k) reostat
R5........................7k5 0.5W
R6........................0.22R not less than 5W (0.15-0.47R)
R7......................20k 0.5W
R8.........................100R (47R – 330R)
C1, C2............1000 x35v (2200 x50v)
C3......................1 x35v
C4......................470 x 35v
C5...................100n ceramic (0.01-0.47)
F1...................5A
T1...................KT816 (BD140)
T2...................BC548 (BC547)
T3...................KT815 (BD139)
T4...................KT819 (KT805,2N3055)
T5...................KT815 (BD139)
VD1-4............KD202 (50v 3-5A)
VD5...................BZX27 (KS527)
VD6...................AL307B, K (RED LED)

Let's start in order:

Step-down transformer such power is selected so that it is capable of delivering current to the load of the required value for a long time, and the voltage on the secondary winding is 2...4 volts greater than the maximum voltage at the output of the power supply. Accordingly, the rectifier bridge is selected with a current reserve, so that later the bridge diodes or the diode assembly do not have to be molded onto the radiator.

How to estimate the power of a transformer? For example: on the secondary there should be 25 volts at a current of 3 amperes, which means we have 25 * 3 = 75 watts. So that the transformer can supply 3 amperes to the load for a long time, increase this percentage value by 20... 30, i.e. 75 + 30% = 97.5 W. It follows that you need to choose a 100 watt transformer.

The maximum voltage at the output of the power supply depends on the zener diode VD5, located in the collector circuit of transistor T1. For example: when using a KS168 zener diode, we get a maximum voltage of about 5 volts at the output, and if we install a KS527, we get a maximum output voltage of 25 volts. Information on zener diodes can be found in the article:

What rating should the filter container be?, standing after the diode bridge? In our case, according to the diagram, there are two parallel tanks C1 and C2 of 1000 microfarads each. In general, the capacitance of this capacitor is selected at the rate of about 1000 microfarads per 1 ampere of output current.
The C4 electrolyte located at the output of the power supply is selected in the region of 200 microfarads per 1 ampere of output current.

At what voltage should electrolytes C1, C2 and C4 be set? If you don’t go into abstruse calculations, you can use the formula: ~Uin:3×4, i.e. the amount of voltage produced by the secondary winding of the step-down transformer must be divided by 3 and multiplied by 4. For example: on the secondary we have 25 volts of alternating time, hence 25:3*4 = 33.33, so capacitors C1, C2 and C4 are selected at Uwork = 35 volts. You can supply containers with a higher operating voltage, but not less than the calculated value. Of course, such a calculation is crude, but nevertheless...

A current limiter is assembled on T5. The limiting threshold depends on the value of resistor R6 and the position of variable resistor R8. In principle, the R8 variable can not be installed, but the limit threshold can be made fixed. To do this, connect the base of transistor T5 to the emitter T4 directly, and select the resistor R6 to set the required threshold. For example: with R6=0.39 Ohm the limitation will be about 3 amperes.

Limit current adjustment. Without load, set potentiometer R3 Uout to about 5 volts. Connect an ammeter and a 1 Ohm resistor connected in series to the power supply output (resistor power 10 watts). Adjust R8 to the required limiting current. We check: we gradually turn R3 to the maximum, while the readings of the control ammeter should not change.

During operation, transistor T1 heats up slightly, place it on a small radiator, but T4 heats up thoroughly, considerable power is dissipated on it, you can’t do without a radiator of an impressive size, or even better, adapt a cooler from a computer to this radiator.

How to estimate the dissipation power of T1? For example: the voltage after the diode bridge is 28 volts, and at the output 12 volts. The difference is 16 volts. Let's estimate the power dissipation at a maximum current of 3 amperes, i.e. 12*3 = 36 Watt. If we set the output voltage to 5 volts at a current of 3 amperes, then the power dissipated on the transistor is (28 - 5) * 3 = 69 Watts. Therefore, when choosing a T4 transistor, do not be lazy to look into the transistor reference book, look at what dissipation power it is designed for (column in the table Pk max). For reference material on the transistor, see the figure below (click on the image to enlarge the picture):

The power supply circuit board is shown in the following figure:

What size fuse should I use? In this circuit there are two fuses: along the primary winding of the transformer (selected 0.5...1 ampere more than the maximum current of the primary winding), and the second in front of the rectifier bridge (selected 1 ampere more than the maximum limiting current of the power supply).

You can squeeze out much more than 3 amperes from this circuit; for this you need to have a trans-r capable of delivering the required current, install a diode bridge with a current reserve, count the filter capacitances, reinforce the paths on the board through which a large current will flow with a thick wire, and Apply a parallel connection of transistors as T4 as shown in the following figure. Transistors are also placed on a radiator with forced ventilation by a fan.

If you are going to use this power supply as a charger for car battery, set no load (battery not connected) with a voltage regulator of about 14.6 volts at the output and connect the battery. As the battery charges, the density of the electrolyte increases, the resistance increases, and accordingly the current will drop. When the battery is charged and there is 14.6 volts at its terminals, the charging current will stop.

Appearance printed circuit board And assembled block nutrition see below:

A voltage converter is useful in many cases. Firstly, this device is useful for obtaining 28 V voltage when powering a gigabyte Internet ADC switch, as well as when connecting a Macintosh G4s unit from a standard ATX computer power supply. Moreover, there are many cases when you will need a voltage different from the standard one.

You may even need to connect 12 V electrical equipment to the 6 V power supply of a travel trailer or motorcycle. You can also use a converter to power a computer cooler from 24 V when the usual fan speed of 12 V is not enough. In what cases do you need to increase the speed of the cooler , you can find out from other articles. It would be especially useful to read a story about how to assemble a homemade, powerful heater for a car.

The proposed voltage converter circuit is used to power the fluorescent lamp in a flatbed scanner.

Explanations for the diagram.

Transformer must be assembled on a ferrite core. The converter will work great on a 30mm diameter toroidal core, which looks like a miniature donut. If you use an armored ferrite magnetic core, the converter will work too. In addition, a core consisting of two W-shaped halves is easier to find and it is easier to wind wire on it. An armored ferrite magnetic core can be found, for example: in a broken computer power supply, in the base of a burnt compact fluorescent lamp(CFL or economy lamp).

You don’t have to wind a lot of winding wire onto the transformer core, so the turns can even be wound with a thin wire in polyvinyl insulation. The primary winding of a step-up transformer consists of only 4 turns, the two secondary windings are wound with 13 turns each.

Don't make a mistake and assemble the transformer correctly. The primary winding is wound in the opposite direction than the secondary windings, which are wound in the same direction. The beginning of one secondary winding is connected to the end of the other. In the diagram, the dots near the “spirals” indicate the beginning of the transformer windings.

Transistors Bipolar converter switches are needed. Since, for the above purposes of using our converter, the output current cannot exceed 500 mA, you can use common transistors: 2N3904, 2N4401, PN2222, MPS2222, C945, NTE123AP. If you are going to run a plasma monitor from the converter, then you need to take two more powerful transistors, such as D965, which are installed in the camera flash. If you need to connect a load with a power of more than 5 A to the converter, then install switches on composite transistors, for example TIP120 or TIP3055. But then don’t forget to change the diodes in the circuit to ones that can withstand currents over 10 A, and the transistors themselves will need to be mounted on radiators.

Diodes install not just any that you find, but those that can close with reverse current polarity in 35 nanoseconds or less. Excellent, according to this indicator, diodes 1N914 and 1N4148 are suitable for the converter, but they can withstand a forward current of no more than 4 A. When connecting a load with a lower resistance than the cooler to the converter, you need to install rectifiers SUF30J, UF510, UF540, which can operate at currents of 15 – 20 A.

Capacitors can be chosen with an insulating lining, either polyester or polypropylene. The 100 pF and 470 pF capacitors are not electrolytic, but non-polar, they are needed to filter high frequencies. The output capacitor, having a capacity of 1.5 mF, is electrolytic. In terms of voltage, choose capacitors that are twice as high as the voltage that acts in the circuit.

Coil needed for an inductance value of about 1 mH. There are a lot of such coils in radio and television equipment, as well as in the same economical lamps.

Resistors Be sure to choose according to power with a reserve. Resistors of 0.5 W are optimal for this circuit. When the output voltage is doubled, the resistance of the resistors must also be doubled.

As previously mentioned, the above circuit is primarily designed to power a computer fan with an input voltage that is twice as high. And you can, by changing the ratio of turns on the transformer, change the input voltage within other limits. A smart head and skillful hands will help you with this.

Wind generator based asynchronous motor What to do if the differential circuit breaker constantly trips

The article explains how to convert a regular computer power supply to 24 volts.

In some cases, there is a need for powerful power supplies for various equipment designed for 24 volts.

In this article I will tell you how you can convert a regular computer power supply, both ATX and AT, to 24 V. Also, from several such blocks you can assemble any voltage to power all kinds of devices.

For example, to power the local automatic telephone exchange UATSK 50/200M, designed for a voltage of 60 V and a power of about 600 Watts, the author of the article replaced the usual huge transformer blocks for three small computer power supplies that fit neatly on the wall next to the power switch and create almost no noise.

The modification consists of adding two power diodes, an inductor and a capacitor. The circuit is similar to the +12V power bus after the pulse transformer, only the diodes and capacitor polarity are reversed, as shown in the figure (filter capacitors are not shown).

The beauty of this modification is that the protection and voltage stabilization circuits remain untouched and continue to operate as before. It is possible to obtain a voltage other than 24 volts (for example, 20 or 30), but to do this you will have to change the parameters of the reference voltage divider of the control chip and change or disable the protection circuit, which is more difficult to do.

Additional diodes D1 and D2 are mounted through insulation on the same radiator as the others, in any convenient location but ensuring full contact patch with the radiator.

Choke L1 can be mounted in any accessible place on the board (can be glued), but it should be noted that in various models and brands of power supplies, it will heat up differently, perhaps even more than the one already in the + L2 circuit (depending on the quality of the power supply). In this case, you need to either select the inductance (which should not be less than standard L2) or attach it directly to the body (through insulation) to remove heat.

You can check the unit at full load or at the load at which you will operate it. In this case, the housing must be completely closed (as expected). When checking, you should monitor whether the radiators on which the semiconductors and the additionally installed choke along the -12V circuit are overheating. For example, a power supply designed for 300 watts can be loaded with a current of 10-13A at a voltage of 24V. It would be a good idea to check the output voltage ripple with an oscilloscope.

It is also very important to note that if you have two or more blocks connected in series working together, then the case (ground) of the circuit must be DISCONNECTED from the metal case of the power supply (I did this by simply cutting the tracks at the points where the board is attached to the chassis). Otherwise you will get short circuit either through the grounding wire of the power cords or through the touching of the housings to each other. To demonstrate the correct operation of the unit, you can display a light bulb or LED outside.

The difference between the conversion of AT and ATX standards is only in the launch of the block. The AT starts working immediately after being connected to a 220 V network, and the ATX must either be started with a PS-ON signal, as is done on a computer, or the wire of this signal must be grounded (usually it goes to the control leg of the microcircuit). In this case, the block will also start when connected to the network.

DIY mirror heating

WITHwinter cold snaps, I decided to do self-heated rear view mirrors, because last winter I got tired of scraping them off frozen ice and snow before each trip. And besides, after these actions I noticed that I scratched the mirrors themselves with a brush, even if the scratches are small and they are not very visible, it is still unpleasant. And besides, it’s very good in the rain, the drops that fall on the mirror dry immediately and the mirror is always dry!

DIY steering wheel heating

DIY steering wheel heating

It’s not very comfortable in winter, especially in cool areas, when everything in the car is at minus temperatures, including the steering wheel, so sometimes you have to drive with gloves. This problem has been resolved make your own steering wheel heating.

From several options I chose the best one in my opinion. Using carbon tape (12mm*0.6mm).

Electronic cooling fan relay

DIY electronic relay for turning on the cooling fan.

In hot weather, the temperature sensor that controls the radiator cooling fan has to be changed very often. And the switching temperature cannot be adjusted. All these shortcomings can be solved simply DIY electronic relay. What kind of car you will use it in is not a fundamental question, VAZ, GAZ, UAZ and other brands.

DIY police siren

DIY police siren

I’ll go straight to what it is and what kind of sounds we get. This homemade police siren made on a microcontroller PIC16F628. If you want to assemble a police quack with your own hands, it won’t take much effort. This assembly has two sounds, the first is a siren, the second when you press a button is a kind of police “quack”. Let's move from theory to practice.

DIY stroboscopes

Do-it-yourself stroboscopes for cars

I think it’s clear from the picture what stroboscopes are, and I think they know what visually we see when they work without any explanation. I found a solution how to do it simple do-it-yourself strobe lights.

How to connect a 12 volt fan to 24 volts

How to connect a 12 volt fan to 24 volts

Each owner of a heavy vehicle (truck, bus, etc.) with on-board voltage 24 volts at least once I encountered a problem when it was necessary connect a 12 Volt consumer.

One of the simplest solutions to this is to connect this consumer (cassette player, radio station, kettle or something else) to one of the batteries, which in such machines are connected in series. But this solution has one very big drawback: the battery to which the 12 volt consumer is connected will always be undercharged, and the second battery may be overcharged. >Both of these cases will lead to reduced battery life. The second most the right way connecting 12-volt consumers to a 24-volt network is to use a 24 to 12 volt voltage converter.

Simple DIY converter 12-220 Volt

DIY converter 12-220V

IN lately more and more people are interested in assembly DIY inverters (converters). The proposed assembly is capable of delivering power up to 300W.

The good old multivibrator is used as a master oscillator. Of course, this solution is much inferior to modern high-precision generators on microcircuits, but let's not forget that I tried to simplify the circuit as much as possible so that the result would be an inverter that would be available to the general public. A multivibrator is not bad, it works more reliably than some microcircuits, is not so critical to input voltages, and works in harsh weather conditions (remember the TL494, which needs to be heated at sub-zero temperatures).

The transformer used is a ready-made one from UPS; the core dimensions allow for 300 watts of output power. The transformer has two primary windings of 7 Volts (each arm) and a mains winding of 220 Volts. In theory, any transformers from uninterruptible power supplies will do.

The diameter of the primary winding wire is about 2.5 mm, just what is needed.

Car battery charger

Car battery charger

In this article I want to give a simple assembly of DIY car battery charger. Even very simple, it does not contain anything superfluous. After all, by often complicating a circuit we reduce its reliability. In general, here we will consider a couple of options for such simple car chargers that can be soldered by anyone who has ever repaired a coffee grinder or changed a switch in the hallway. A long time ago I had the idea of ​​collecting the simplest charger for the battery of your motorcycle, since the generator sometimes simply cannot cope with charging the latter, it is especially difficult for him on a winter morning when you need to start it from the starter. Of course, many will say that with a kick starter it is much easier, but then the battery can be thrown out altogether.

car battery charger

DIY car battery charger

IN winter time years, more and more often we pay attention to car battery charging, due to its discharge, and poor performance. But the prices for battery chargers are not very small, and sometimes it’s easier to do DIY charger, which will be discussed further.

The proposed scheme is of very high quality will charge your battery, and it will extend its service life.

Stroboscope for setting the ignition timing with your own hands

Do-it-yourself strobe light for setting up the OZ

When replacing a distributor, or repairs related to ignition of the mixture, be it a carburetor change, we are faced with the need to adjust the ignition timing.

What is the ignition timing angle (IAF) -the angle of rotation of the crank from the moment at which voltage begins to be applied to the spark plug to break down the spark gap until the piston reaches TDC.

To configure the OZ, most masters use the so-called car strobe light, which flashes at the moment when a spark runs through the spark plug. You can see details on how to use a strobe to set up the VOS on the Internet. The same article provides simple circuit car strobe light, which with your own hands Can be assembled by almost any beginning radio amateur.

From 24 to 12 volts, and now let's study the 12-24 V boost converter. This DC-DC converter assembled on the basis of a specialized chip manufactured by Texas Instruments. The circuit was needed for use in a car (in particular, for charging a laptop at 20 V) and was chosen for its extreme simplicity, requiring a minimum number of external components. The switching element is a transistor, integrated inside the regulator, and is capable of withstanding a maximum current of 3A and 60V voltage. The switching frequency is determined by the parameters of the internal oscillator and is fixed at 100 kHz. Additional functions - diagram soft start to eliminate current surges during startup and internal current limiting. Maintaining output voltage accuracy is 4% depending on the load.

12-24 V converter circuit

Converter Specifications

• Vin 10-15V DC
• Vout 24V
• Iout 1A
• frequency 100 kHz

The input capacitor and diode should be located close enough to the regulator to minimize inductance. The elements IC1, L1, D1, C1, C2, C5, C6 are the main parts used in the voltage converter. When installed, capacitor C3 should be located as close as possible to IC1. Choose low ESR capacitors with low DC resistance.

At maximum output power, significant heat generation is noticeable, for this reason the chip is mounted directly on the common ground of the board.

Inverter operating schedules

The last graph shows the ripple of the output voltage and inductive current. We see that the output voltage ripple is about 0.6 Vpp and the peak current is 2.4 A. The inductor in the design is used at 5 A DC, so it can easily withstand this current and without heating the coil much.