Voltage stabilizers are an essential part of all electronic circuits; they provide continuous, stable power to system components, ensuring the stability of its parameters and protection in case of faults in the circuit or in the primary voltage source. 12 volts DC voltage is the most popular, used to power many devices used separately or built into various structures.
Classic stabilizer
Most power systems are built using a 12-volt linear voltage regulator circuit, which can have several options:
- Parallel – adjustment using a parallel control element;
- Sequential – activation of the adjustment element in series with the load.
The simplest voltage stabilizer is a zener diode, also called a Zener diode - this is a diode that operates constantly in breakdown mode. The voltage at which breakdown occurs is the stabilization voltage, the main parameter of the zener diode. When the load is connected in parallel, an elementary voltage stabilizer is obtained, approximately equal to the stabilization voltage.
The ballast resistance R determines the zener diode current specified in the specification. This solution is characterized by a low stabilization coefficient, temperature dependence and is used at low load currents to power individual components of the main circuit. It is possible to significantly increase the output current if a powerful transistor is installed in series with the load.
In this circuit, the transistor is connected in series with the load as an emitter follower, all the current flows through its junction. The level on the base is controlled by a zener diode: as the current at the output increases, more voltage is applied to the base, the conductivity of the transistor increases, and the output voltage is restored. The power of such a stabilizer is determined by the type of transistor and can reach tens of watts.
It is important to note! In this form, the stabilizer is not protected from overload and short circuit, in which it instantly fails. For practical use, the circuit becomes significantly more complicated: current limiting elements and various protective functions are introduced.
Integral stabilizer
A 12 volt voltage stabilizer can easily be implemented by using a specialized integrated linear stabilizer from the 78XX series with a fixed output voltage. For an output voltage of 12 volts, 7812 microcircuits are produced; from different manufacturers they are called LM7812, L7812, K7812, etc.
The domestic analogue is KR142EN8B. Manufactured in TO – 220, TO – 3, D2PAK packages with three terminals. These microcircuits can be found in power supplies of any equipment; they have practically replaced stabilizers based on discrete elements.
Main characteristics of the stabilizer in a widely used housingTO – 220:
- Output stabilized voltage – from 11.5 to 12.5 V;
- Input voltage – up to 30 V;
- Output current – up to 1A;
- Built-in overload and short circuit protection.
The input voltage must exceed the output voltage (12 volts) by at least 3 volts over the entire output current range. For an output current of up to 100 mA, a variant of the –78L12 microcircuit is available. A typical connection circuit allows you to assemble a reliable 12-volt voltage stabilizer with your own hands with characteristics suitable for many tasks.
The circuit has stabilization parameters similar to the used microcircuit.
In some cases, it is advisable to use 1083/84/85 series microcircuits. These are integrated stabilizers with an output current of 3.5 and 7.5 amperes. The devices are of the Low Dropout type - for them the difference between the input and output voltage can be 1 volt. The connection circuit is fully consistent with 7812 type microcircuits.
Video
The circuit of a 12-volt power supply is very simple, since to stabilize the voltage and filter out noise well, an integrated stabilizer is used on the KR142EN8B microcircuit. A powerful bipolar transistor is used to increase the output current TIP3055
, the voltage drop across the transistor within 0.5 volts is compensated by the VD2 diode connected to the circuit of the middle leg of the stabilizer, thereby raising the voltage at the output of the microcircuit to the half volt we need.
An important element of a 12-volt power supply is a step-down transformer, since the circuit is designed for high current, it must have parameters not lower than the following: voltage on the secondary winding from 12 to 18 volts and an output current of at least 10 Amps. The microcircuit can be replaced with L7812ABV, MC7812BT or LM7812CT, the transistor can be installed of any brand, with a collector current of at least 15 Amps. The capacitors used in the circuit are designed for a voltage of 25 V, the diode bridge for a current of at least 10 Amps, VD2 can be replaced with almost any silicon diode.
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cxema.org - Powerful switching power supply 12V 40A
I recently ordered such a device from a local store. The device is designed to power a stand with 30 car radios at once. It’s clear, if you estimate, then one radio will consume about 1 Ampere of current, this is just if it is turned on, but if you run it at full volume, then the consumption of one radio will be around 7-8 Amps. 30 radios of 1 A each is already 30 Amperes, and at a voltage of 12 Volts, the power of the power supply should be at least 350-400 watts. Since finances were limited, it was extremely unprofitable to assemble such a thing with a 400-watt network transformer, so I decided to create a pulse circuit. One of the simplest options is built on a high-voltage half-bridge driver IR2153, despite the ease of assembly, such a power supply can provide the specified power.
The cost of components does not exceed $10, and the block turned out to be of minimal size.
A surge protector and fuse are built at the power input. The thermistor protects the field switches from voltage surges during power supply. The diode bridge is built on 4 1N5408 rectifiers, this is a 3 Amp diode with a reverse voltage of 1000 Volts. Capacitors 200V 470uF - removed from the computer power supply. By replacing the capacitance, you can increase or decrease the power of the power supply as a whole. Despite the fact that I loaded the power supply almost to the maximum, the keys were completely cold after 3 minutes of operation. The keys themselves are secured through insulation to a common heat sink of small dimensions. Venting is carried out by a cooler, which powers a separate 3-watt power supply; this unit was removed from an LED lamp. This decision is due to the fact that if the cooler is powered from a common 12 Volt bus, a background may form, and this in turn leads to distortion if a car radio is connected to the unit.
The transformer had to be wound from scratch.
The core was taken from a computer power supply. All industrial windings need to be removed and your own wound. The network winding consists of 40 turns of 0.8 mm wire. The secondary winding is wound with a bar of 7 cores of 0.8 mm wire, the winding consists of 2x3 turns. At the output there is a dual 2x30A Schottky diode; the power supply housing serves as a heat sink for it, and the housing itself was taken from a computer power supply.
The limiting resistor for powering the microcircuit needs a powerful one (2 watts) during operation it may overheat a little, the value may deviate in one direction or another by 10%.
The result is a very powerful power supply, which has been powering the stand with car radios for a week now, working 12 hours a day without breaks.
Sincerely - AKA KASYAN
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How to make a 12V power supply with your own hands
The 12 volt DC power supply consists of three main parts:
- A step-down transformer from a conventional input alternating voltage of 220 V. At its output there will be the same sinusoidal voltage, only reduced to approximately 16 volts at idle - without load.
- Rectifier in the form of a diode bridge. It “cuts off” the lower half-sine waves and puts them up, that is, the resulting voltage varies from 0 to the same 16 volts, but in the positive region.
- A high-capacity electrolytic capacitor that smooths out the half-sine voltage, making it approach a straight line at 16 volts. This smoothing is better, the larger the capacitor capacity.
The simplest thing you need to obtain a constant voltage capable of powering devices designed for 12 volts - light bulbs, LED strips and other low-voltage equipment.
A step-down transformer can be taken from an old computer power supply or simply bought in a store so as not to bother with windings and rewinding. However, in order to ultimately reach the desired 12 volts of voltage with a working load, you need to take a transformer that lowers the volts to 16.
For the bridge, you can take four 1N4001 rectifier diodes, designed for the voltage range we need or similar.
The capacitor must have a capacity of at least 480 µF. For good output voltage quality, you can use more, 1,000 µF or higher, but this is not at all necessary to power lighting devices. The operating voltage range of the capacitor is needed, say, up to 25 volts.
Device layout
If we want to make a decent device that we won’t be ashamed to attach later as a permanent power supply, say, for a chain of LEDs, we need to start with a transformer, a board for mounting electronic components and a box where all this will be fixed and connected. When choosing a box, it is important to consider that the electrical circuits heat up during operation. Therefore, it is good to find a box that is suitable in size and with holes for ventilation. You can buy it in a store or take a case from a computer power supply. The latter option may be cumbersome, but as a simplification you can leave the existing transformer in it, even along with the cooling fan.
Power supply housing
Power supply housing
On the transformer we are interested in the low-voltage winding. If it reduces the voltage from 220 V to 16 V, this is an ideal case. If not, you'll have to rewind it. After rewinding and checking the voltage at the output of the transformer, it can be mounted on the circuit board. And immediately think about how the circuit board will be attached inside the box. It has mounting holes for this.
Low voltage winding
Circuit board
Further installation steps will take place on this mounting board, which means that it must be sufficient in area, length and allow the possible installation of radiators on diodes, transistors or a microcircuit, which must still fit into the selected box.
Diode bridge
We assemble the diode bridge on the circuit board, you should get such a diamond of four diodes. Moreover, the left and right pairs consist equally of diodes connected in series, and both pairs are parallel to each other. One end of each diode is marked with a stripe - this is indicated by a plus. First we solder the diodes in pairs to each other. In series - this means the plus of the first is connected to the minus of the second. The free ends of the pair will also turn out - plus and minus. Connecting pairs in parallel means soldering both pluses of the pairs and both minuses. Now we have the output contacts of the bridge - plus and minus. Or they can be called poles - upper and lower.
Diode bridge circuit
The remaining two poles - left and right - are used as input contacts, they are supplied with alternating voltage from the secondary winding of the step-down transformer. And the diodes will supply a pulsating voltage of constant sign to the bridge outputs.
If you now connect a capacitor in parallel with the output of the bridge, observing the polarity - to the plus of the bridge - plus of the capacitor, it will begin to smooth out the voltage, and as well as its capacitance is large. 1,000 uF will be enough, and even 470 uF is used.
Attention! An electrolytic capacitor is an unsafe device. If it is connected incorrectly, if voltage is applied to it outside the operating range, or if it is overheated, it may explode. At the same time, all its internal contents scatter around the area - tatters of the case, metal foil and splashes of electrolyte. Which is very dangerous.
Well, here we have the simplest (if not primitive) power supply for devices with a voltage of 12 V DC, that is, direct current.
Problems with a simple power supply with a load
The resistance drawn on the diagram is the equivalent of the load. The load must be such that the current supplying it, with an applied voltage of 12 V, does not exceed 1 A. You can calculate the load power and resistance using the formulas.
Where does the resistance R = 12 Ohm, and the power P = 12 watts come from? This means that if the power is more than 12 watts and the resistance is less than 12 ohms, then our circuit will begin to work with overload, will get very hot and will quickly burn out. There are several ways to solve the problem:
- Stabilize the output voltage so that when the load resistance changes, the current does not exceed the maximum permissible value or when there are sudden current surges in the load network - for example, when some devices are turned on - the peak current values are cut to the nominal value. Such phenomena occur when the power supply powers radio-electronic devices - radios, etc.
- Use special protection circuits that would turn off the power supply if the load current exceeds.
- Use more powerful power supplies or power supplies with more power reserves.
Power supply with stabilizer on a chip
The figure below shows the development of the previous simple circuit by including a 12-volt stabilizer LM7812 at the output of the microcircuit.
Power supply with stabilizer on a chip
This is already better, but the maximum load current of such a stabilized power supply unit should still not exceed 1 A.
High Power Power Supply
The power supply can be made more powerful by adding several powerful stages using TIP2955 Darlington transistors to the circuit. One stage will provide an increase in load current of 5 A, six composite transistors connected in parallel will provide a load current of 30 A.
Darlington transistors type TIP2955
A circuit with this kind of power output requires adequate cooling. Transistors must be provided with heat sinks. You may also need an additional cooling fan. In addition, you can protect yourself with fuses (not shown in the diagram).
The figure shows the connection of one composite Darlington transistor, which makes it possible to increase the output current to 5 amperes. You can increase it further by connecting new cascades in parallel with the specified one.
Connecting one composite Darlington transistor
Attention! One of the main disasters in electrical circuits is a sudden short circuit in the load. In this case, as a rule, a current of gigantic power arises, which burns everything in its path. In this case, it is difficult to come up with such a powerful power supply that can withstand this. Then protection circuits are used, ranging from fuses to complex circuits with automatic shutdown on integrated circuits.
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Power supply 12 Volt, 20 Ampere and 240 Watt with passive cooling
There’s no point in describing why I like to tinker with power supplies, but I’ll write about why it’s 12 Volts.
It just so happens, but power supplies with an output voltage of 12 Volts are among the most popular, along with 5 Volts and 19 Volts.
5 Volts is used to power small devices, but what added more popularity is that the same voltage is provided by the USB port, which is why such power supplies began to “proliferate”.
19 Volts are used in laptops, and such power supplies are also used by amateur radio enthusiasts for various kinds of soldering stations and amplifiers, mainly due to their acceptable power and compactness.
Well, 12 Volts is just a safe voltage for starters and at the same time allows you to transmit quite a lot of power. Of course, in my opinion, it is often possible (and sometimes necessary) at 24 Volts, but this voltage is more used in industrial devices.
In everyday life, 12 Volts can be used to power LED strips that have become widespread for decorative lighting and lighting; 12 Volts also power video surveillance systems, sometimes small computers, as well as various engravers, 3D printers, etc.
In general, I have plans to make several reviews of similar power supplies, but with different powers, and today a 240-watt power supply with a passive cooling system landed on my desk.
At the moment, common fanless power supplies have a power of up to 240-300 Watts, and the latter are much less common and I would rather say that 240 Watts is almost the maximum.
With this I will end the brief introduction and move on to the subject of the review.
A power supply in a familiar metal case, I think many have seen similar solutions on sale.
It was packed in a regular white box, it wasn’t included in the photo, and there’s not much to look at. 
The input and output are connected to one large terminal block; there is a sticker on top indicating the purpose of the contacts, but they are glued with a shift, which can confuse an inexperienced user. 
The terminal block has a protective cover, and it opens 90 degrees, which is, although small, a plus, since there are options where the cover does not open completely. 
To the right of the terminal block there is a trimming resistor and an LED indicating the power supply is turned on.
The declared parameters are 12 Volt 20 Ampere, the real manufacturer is unknown, the marking is standard for many inexpensive power supplies - S-240-12
On the side there is a 110/200 Volt input voltage switch; it is better to check that it is in the correct position before turning it on for the first time.
The release date is the end of 2016, so the power supply can be said to be fresh. 
First, we measure what is configured at the output of the power supply.
Set to 12.3 Volts, adjustment range 10-14.5 Volts. After checking I set it to something close to 12 Volts. 
There is nothing more to inspect externally, so we remove the top cover and see what’s inside. 
And inside the power supply is no different from other similar inexpensive units.
It immediately reminded me of a 48 Volt 240 Watt power supply, I would even say that they are the same.
It’s probably not even true, in fact it’s the same power supply, just for a different voltage, which is why I wrote at the very beginning that the real manufacturer is unknown. 
Classic inspection of the filling.
1. The input filter is present, although not in full, there is no capacitor after the inductor and a varistor. Unfortunately, this is a feature of the vast majority of Chinese power supplies.
2. Interference suppression capacitors in a dangerous circuit - Y1, in a less dangerous one, an ordinary high-voltage one, we can say that it’s normal.
3. The input diode bridge is installed with a reserve, 8 Amps 1000 Volts, but there is no radiator. In the previous version, the diode bridge was rated at 20 Amps.
Also visible nearby are two thermistors connected in parallel.
4. Rubicon input capacitors g I'd like to use the Rubicon, if only the parameters corresponded to the declared ones, but more on that later.
5. A pair of high-voltage transistors pressed against an aluminum case, which acts as a radiator.
6. The power transformer is clearly marked as 240 Watts 12 Volts. It looks quite good, traces of varnish impregnation are visible. 
Chinese manufacturers continue to produce their power supplies based on the classic element base. I won’t say that this is bad, but more famous manufacturers are much less likely to make power supplies based on the TL494.
In its own way, this has its advantages: repairing such a power supply is quite simple, components are available everywhere, and there is a lot of documentation on them. 
As in the 48 Volt version, a reinforced version of the radiator is also used here; the output diode assembly is pressed against a finned radiator, which already transfers some of the heat to the case. If in the 48 Volt version this was not particularly necessary, then with currents of 20 Amps such a solution is not superfluous. 
1. The output choke, with quite normal dimensions, is wound with only two wires, and the cross-section of the wire is comparable to that used in a 48 Volt power supply.
2. The output capacitors have a declared capacity of 2200 µF, the manufacturer is also unknown, however, I did not expect to see capacitors from Nichicon or at least Samwha here.
3.4. But I checked the moment with the clamping of the power elements separately, since last time I had big complaints about the fastening of the diode assembly. In this case, everything is basically fine. You can find fault a little with the clamping of the transistors (on the left), but practice has shown that everything is in order. 
We take the board out of the case and look at the quality of the soldering and look for the manufacturer’s “jambs”. 
High-voltage transistors are used with a reserve, there is no need to worry. In addition, the TO247 case in which they are made improves heat dissipation to the radiator.
The MBR30200 output diode assembly consists of two high-voltage Schottky diodes. I am a little skeptical about the use of high-voltage Schottky diodes, since they no longer have an advantage over conventional ones in terms of voltage drop, but there remains an advantage in higher switching speed, i.e. dynamic losses are less. 
General view of the printed circuit board from below. 
The soldering looks quite normal, in this part of the power supply everything is fine, even clean. 
The power tracks are additionally covered with solder to increase the cross-section; there are no particular complaints here either, although in some places there is not enough solder in my opinion. 
But I still found one unpleasant moment. One of the power contacts is not soldered very well. You can, of course, say that there are three contacts per pole, but it could happen that it ends up being loaded. Sobs
www.kirich.blog
HOMEMADE 12V POWER SUPPLY
Hello to all radio amateurs, in this article I would like to introduce you to a power supply with voltage regulation from 0 to 12 volts. It is very easy to set the desired voltage, even in millivolts. The diagram does not contain any purchased parts - all this can be pulled out of old equipment, both imported and Soviet.
Schematic diagram of power supply unit (reduced)
The case is made of wood, in the middle there is a 12 volt transformer, a 1000 uF x 25 volt capacitor and a board that regulates the voltage.
Capacitor C2 must be taken with a large capacity, for example, to connect an amplifier to the power supply and so that the voltage does not drop at low frequencies.
It is better to install transistor VT2 on a small radiator. Because during prolonged operation it can heat up and burn out; I already burned out 2 of them until I installed a decent-sized radiator.
Resistor R1 can be set constant; it does not play a big role. On top of the case there is a variable resistor that regulates the voltage, and a red LED that shows whether there is voltage at the power supply output.
At the output of the device, in order not to constantly screw the wires to something, I soldered alligator clips - they are very convenient. The circuit does not require any settings and works reliably and stably; any radio amateur can really do it. Thank you for your attention, good luck everyone! .
Forum on simple power supply circuits
Discuss the article HOMEMADE 12V POWER SUPPLY
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| The article presents a circuit of a fairly simple, but also powerful power supply, quite suitable not only for charging 12-volt car batteries, but also for powering and testing many home-made circuits that require a powerful stabilized voltage. An irreplaceable item in a car enthusiast's garage. The required voltage at the output of the device can be smoothly changed in the range of 0 - 12 volts. The output load can be up to 20 amperes. The collectors of the power transistors are interconnected and can be installed on one aluminum finned heat sink with a cooled surface area of at least 200 sq.cm. The transformer will be suitable from old Soviet TVs, for example, TS-270; even higher power will be quite suitable, but at the same time the overall dimensions of the unit will increase. All secondary windings are removed and a winding of 14 - 16 volts is wound over the mains with a copper enameled wire with a diameter of 2 mm. The turns should be distributed evenly across the entire width of the transformer frame. The circuit is easy to repeat and does not require special skills in amateur radio, does not require settings or adjustments, and works immediately if the parts are in good condition and assembled correctly. |
LED lighting is increasingly being introduced into our lives. Capricious light bulbs fail and beauty immediately fades. And all because LEDs cannot work simply by being plugged into the mains. They must be connected through stabilizers (drivers). The latter prevent voltage drops, component failure, overheating, etc. This article and how to assemble a simple circuit with your own hands will be discussed.
Stabilizer selection
In the on-board network of the car, the operating power is approximately 13 V, while most LEDs are suitable for 12 V. Therefore, they usually install a voltage stabilizer, the output of which is 12 V. Thus, normal conditions are provided for the operation of lighting equipment without emergency situations and premature failure.
At this stage, amateurs are faced with the problem of choice: many designs have been published, but not all work well. You need to choose one that is worthy of your favorite vehicle and, in addition:
- will actually work;
- will ensure the safety and security of lighting equipment.
The simplest DIY voltage stabilizer
If you have no desire to buy a ready-made device, then it’s worth learning how to make a simple stabilizer yourself. It is difficult to make a pulse stabilizer in a car with your own hands. That is why it is worth taking a closer look at the selection of amateur circuits and designs of linear voltage stabilizers. The simplest and most common version of a stabilizer consists of a ready-made microcircuit and a resistor (resistance).
The easiest way to make a current stabilizer for LEDs with your own hands is on a microcircuit. The assembly of parts (see figure below) is carried out on a perforated panel or a universal printed circuit board.
Scheme of a 5 ampere power supply with a voltage regulator from 1.5 to 12 V.
To assemble such a device yourself, you will need the following parts:
- plateau size 35*20 mm ;
- chip LD1084;
- RS407 diode bridge or any small diode for reverse current;
- a power supply consisting of a transistor and two resistances. Designed to turn off the rings when the high or low beam is turned on.
In this case, the LEDs (3 pcs.) are connected in series with a current-limiting resistor that equalizes the current. This set, in turn, is connected in parallel to the next similar set of LEDs.
Stabilizer for LEDs on the L7812 chip in cars
The current stabilizer for LEDs can be assembled on the basis of a 3-pin DC voltage regulator (L7812 series). The mounted device is perfect for powering both LED strips and individual light bulbs in a car.
Required components to assemble such a circuit:
- chip L7812;
- capacitor 330 uF 16 V;
- capacitor 100 uF 16 V;
- 1 ampere rectifier diode (1N4001, for example, or a similar Schottky diode);
- wires;
- heat shrink 3 mm.
There can actually be many options.
Connection diagram based on LM2940CT-12.0
The stabilizer body can be made of almost any material except wood. When using more than ten LEDs, it is recommended to attach an aluminum radiator to the stabilizer.
Maybe someone has tried it and will say that you can easily do without unnecessary troubles by directly connecting the LEDs. But in this case, the latter will be in unfavorable conditions most of the time, and therefore will not last long or will burn out altogether. But tuning expensive cars results in a fairly large sum.
As for the described schemes, their main advantage is simplicity. Manufacturing does not require any special skills or abilities. However, if the circuit is too complex, then assembling it with your own hands becomes unreasonable.
Conclusion
The ideal option for connecting LEDs is via. The device balances network fluctuations; with its use, current surges will no longer be a problem. In this case, it is necessary to comply with the power supply requirements. This will allow you to adjust your stabilizer to the network.
The device must provide maximum reliability, stability and stability, preferably for many years. The cost of the assembled devices depends on where all the necessary parts will be purchased.
In the video - for LEDs.
24.06.2015We present a powerful stabilized 12 V power supply. It is built on an LM7812 stabilizer chip and TIP2955 transistors, which provides a current of up to 30 A. Each transistor can provide a current of up to 5 A, respectively, 6 transistors will provide a current of up to 30 A. You can change the number of transistors and get desired current value. The microcircuit produces a current of about 800 mA.
A 1 A fuse is installed at its output to protect against large transient currents. It is necessary to ensure good heat dissipation from transistors and the microcircuit. When the current through the load is large, the power dissipated by each transistor also increases, so that excess heat can cause the transistor to fail.
In this case, a very large radiator or fan will be required for cooling. 100 ohm resistors are used for stability and to prevent saturation as... the gain factors have some scatter for the same type of transistors. The bridge diodes are designed for at least 100 A.
Notes
The most expensive element of the entire design is perhaps the input transformer. Instead, it is possible to use two series-connected car batteries. The voltage at the input of the stabilizer must be a few volts higher than the required output (12V) so that it can maintain a stable output. If a transformer is used, the diodes must be able to withstand a fairly large peak forward current, typically 100A or more.
No more than 1 A will pass through LM 7812, the rest is provided by transistors. Since the circuit is designed for a load of up to 30 A, six transistors are connected in parallel. The power dissipated by each of them is 1/6 of the total load, but it is still necessary to ensure sufficient heat dissipation. Maximum load current will result in maximum dissipation and will require a large heatsink.
To effectively remove heat from the radiator, it may be a good idea to use a fan or water-cooled radiator. If the power supply is loaded to its maximum load, and the power transistors fail, then all the current will pass through the chip, which will lead to a catastrophic result. To prevent breakdown of the microcircuit, there is a 1 A fuse at its output. The 400 MOhm load is for testing only and is not included in the final circuit.
Computations
This diagram is an excellent demonstration of Kirchhoff's laws. The sum of currents entering a node must be equal to the sum of currents leaving this node, and the sum of the voltage drops on all branches of any closed circuit circuit must be equal to zero. In our circuit, the input voltage is 24 volts, of which 4V drops across R7 and 20 V at the input of LM 7812, i.e. 24 -4 -20 = 0. At the output, the total load current is 30A, the regulator supplies 0.866A and 4.855A each 6 transistors: 30 = 6 * 4.855 + 0.866.
The base current is about 138 mA per transistor, to get a collector current of about 4.86A, the DC gain for each transistor must be at least 35.
TIP2955 meets these requirements. The voltage drop across R7 = 100 Ohm at maximum load will be 4V. The power dissipated on it is calculated by the formula P= (4 * 4) / 100, i.e. 0.16 W. It is desirable that this resistor be 0.5 W.
The input current of the microcircuit comes through a resistor in the emitter circuit and the B-E junction of the transistors. Let's apply Kirchhoff's laws once again. The regulator input current consists of 871 mA current flowing through the base circuit and 40.3 mA through R = 100 Ohms.
871.18 = 40.3 + 830. 88. The input current of the stabilizer must always be greater than the output current. We can see that it only consumes about 5 mA and should barely get warm.
Testing and Bugs
During the first test, there is no need to connect the load. First, we measure the output voltage with a voltmeter; it should be 12 volts, or a value not very different. Then we connect a resistance of about 100 Ohms, 3 W as a load. The voltmeter readings should not change. If you do not see 12 V, then, after turning off the power, you should check the correctness of installation and the quality of soldering.
One of the readers received 35 V at the output, instead of the stabilized 12 V. This was caused by a short circuit in the power transistor. If there is a short circuit in any of the transistors, you will have to unsolder all 6 to check the collector-emitter transitions with a multimeter.
At 1-2 amperes, but it is already problematic to obtain a higher current. Here we will describe a high-power power supply with a standard voltage of 13.8 (12) volts. The circuit is 10 amperes, but this value can be increased further. There is nothing special in the circuit of the proposed power supply, except that, as tests have shown, it is capable of delivering a current of up to 20 Amps for a short time or 10A continuously. To further increase power, use a larger transformer, diode bridge rectifier, higher capacitor capacity and number of transistors. For convenience, the power supply circuit is shown in several figures. The transistors do not have to be exactly the ones in the circuit. We used 2N3771 (50V, 20A, 200W) because there are many of them in stock.
The voltage regulator operates within small limits, from 11 V to 13.8 at full load. With an open circuit voltage value of 13.8V (nominal battery voltage is 12V), the output will drop to 13.5 for about 1.5A, and 12.8V for about 13A.
The output transistors are connected in parallel, with 0.1 ohm 5 watt wirewound resistors in the emitter circuits. The more transistors you use, the higher the peak current that can be drawn from the circuit.
The LEDs will show incorrect polarity, and the relay will block the power supply stabilizer from the rectifiers. High power thyristor BT152-400 opens when overvoltage occurs and takes on the current, causing the fuse to blow. Don't think that the triac will burn out first, the BT152-400R can withstand up to 200A for 10ms. This power source can also serve as a charger for car batteries, but to avoid incidents, no need to leave the battery connected for a long time unattended.
