Currently, there are many power tools that operate on rechargeable batteries. However, after a certain time, the battery life gradually decreases and does not provide the tool with the required power. In such cases, even more frequent charging does not help, so you have to decide what to do next: abandon the unit altogether or switch it to power from the general network. Since a new battery can be compared in price to the tool itself, you can make your own power supply from an electronic transformer, which will cost much less.
Converting an electronic transformer into a switching power supply is not as simple as it turns out to be in practice. In addition to the transformer, you will need to install a rectifier bridge at the output and a smoothing capacitor. If necessary, also connect the load.
It must be taken into account that the converter cannot be started without a load or with insufficient load. This can be easily checked using an LED connected to the output of the rectifier using a limiting resistor. As a result, the whole thing will end with just one flash of the LED light source at the moment of switching on.
In order for another flash to appear, the converter must first be turned off and then turned on again. It is possible to achieve a constant glow instead of flashes by connecting the rectifier to an additional load, which extracts useful power and releases heat. This circuit can only be used with a constant load controlled through the primary circuit.
If the load requires more than 12 volts supplied by the electronic transformer, it is necessary to rewind the output transformer. There is another option to solve this problem, more effective and less expensive.
The manufacture of such a power supply is carried out in accordance with the presented diagram. It is based on an electronic transformer with a power of 105 watts. In addition, converting an electronic transformer into a power supply will require the use of additional elements - a rectifier bridge VD1-VD4, an output inductor L2, a matching transformer T1 and a mains filter.
To make a T1 transformer, you will need a ferrite ring with dimensions K30x18x7. The wire in the primary winding is doubled, twisted into a bundle and wound in this form in the amount of 10 turns. A wire with a diameter of 0.8 mm, for example, PEV-2, is best suited. The secondary winding consists of the same wire with the same laying, wound in 2x22 turns. The result is a double symmetrical winding with a common midpoint obtained by connecting the beginning of one winding to the end of the other.
Throttle L2 is also made by hand. It consists of the same ferrite ring as the transformer. For the windings, similar PEV-2 wires are used, wound in 10 turns. The rectifier bridge is assembled using KD213 or KD2997 diodes, which can operate at a minimum operating frequency of 100 kHz. If you use other elements, for example, KD242, they will only heat up, but will not provide the required voltage. The radiator area for installing diodes must be at least 0.6-0.7 m2. The radiator is used together with insulating gaskets.
The chain of electrolytic capacitors C4, C5 includes three 2200 μF elements connected in parallel. This option is used by all switching power supplies in order to reduce the overall inductance of electrolytic capacitors. In some circuits, ceramic capacitors of 0.33-0.5 μF can be connected in parallel with them to smooth out high-frequency oscillations.
The surge protector is installed at the input of the power supply, although the entire system can function without it. The input filter is equipped with a ready-made choke of the DF50GTs brand, which can be taken from the TV. All components and elements of the block are mounted on a common board using the surface-mounting method. Insulating material is used for the board, and the entire finished structure is placed in a brass or tin case with ventilation holes.
If the power supply is correctly assembled, no further adjustment is required, since the device immediately begins to function normally. However, it is still necessary to check the functionality. For this purpose, 240 Ohm resistors and a minimum power of 5 watts are connected at the output of the power supply as a load.
Quite often situations arise when application becomes problematic due to specific operating conditions. This may be too little current consumption or its change over a wide range, as a result, the power supply simply does not start. A typical example is a chandelier in which LED lamps are installed instead of halogen lamps, despite the fact that the lighting device has a built-in electronic transformer. A simplified diagram of this transformer, shown in the figure, will help solve this problem.
In this diagram, the winding of control transformer T1, marked in red, serves to provide current feedback. That is, when the current does not flow through the load or passes in very small quantities, the transformer simply will not turn on. This means that the device will not work if a 2.5 W light bulb is connected to it.
This circuit can be modified, which will allow the device to operate without any load at all. The device will be protected from short circuits. How to do all this in practice is shown in the following figure.
Operation of an electronic transformer with minimal or no load is ensured by replacing current feedback with voltage feedback. For this purpose, the current feedback winding is removed, and in its place a wire jumper is soldered into the board without affecting the ferrite ring.
Then, on the control transformer TR1, installed on a small ring, a winding consisting of 2-3 turns should be wound. Another turn is wound on the output transformer, after which both additional windings are connected. If the device does not start to function, it is recommended to change the phase arrangement on any winding.
The resistor installed in the feedback circuit must have a resistance in the range from 3 to 10 ohms. With its help, the depth of feedback is determined, which determines the value of the current at which generation fails. This will be the response current against a short circuit, depending on the resistance of the resistor.
Today, electromechanics rarely repair electronic transformers. In most cases, I myself don’t really bother with working on resuscitating such devices, simply because, usually, buying a new electronic transformer is much cheaper than repairing an old one. However, in the opposite situation, why not work hard to save money. In addition, not everyone has the opportunity to get to a specialized store to find a replacement there, or go to a workshop. For this reason, any radio amateur needs to be able to and know how to check and repair pulse (electronic) transformers at home, what ambiguous issues may arise and how to resolve them.
Due to the fact that not everyone has an extensive amount of knowledge on the topic, I will try to present all available information as accessible as possible.
Fig.1: Transformer.
Before proceeding to the main part, I will give a short reminder about what an electronic transformer is and what it is intended for. A transformer is used to convert one variable voltage to another (for example, 220 volts to 12 volts). This property of an electronic transformer is very widely used in radio electronics. There are single-phase (current flows through two wires - phase and “0”) and three-phase (current flows through four wires - three phases and “0”) transformers. The main significant point when using an electronic transformer is that as the voltage decreases, the current in the transformer increases.
A transformer has at least one primary and one secondary winding. The supply voltage is connected to the primary winding, a load is connected to the secondary winding, or the output voltage is removed. In step-down transformers, the primary winding wire always has a smaller cross-section than the secondary wire. This allows you to increase the number of turns of the primary winding and, as a result, its resistance. That is, when checked with a multimeter, the primary winding shows a resistance many times greater than the secondary. If for some reason the diameter of the secondary winding wire is small, then, according to the Joule-Lance law, the secondary winding will overheat and burn the entire transformer. A transformer malfunction may consist of a break or short circuit (short circuit) of the windings. If there is a break, the multimeter shows one on the resistance.
In fact, to figure out the cause of the breakdown, you don’t need to have a huge amount of knowledge; it’s enough to have a multimeter on hand (standard Chinese, as in Figure 2) and know what numbers each component (capacitor, diode, etc.) should produce at the output. d.).
Figure 2: Multimeter.
The multimeter can measure DC, AC voltage and resistance. It can also work in dialing mode. It is advisable that the multimeter probe be wrapped with tape (as in Figure No. 2), this will protect it from breaks.
In order to correctly test the various elements of the transformer, I recommend desoldering them (many try to do without this) and examining them separately, since otherwise the readings may be inaccurate.
We must not forget that diodes only ring in one direction. To do this, set the multimeter to continuity mode, the red probe is applied to the plus, the black probe to the minus. If everything is normal, the device makes a characteristic sound. When the probes are applied to opposite poles, nothing should happen at all, and if this is not the case, then a breakdown of the diode can be diagnosed.
When checking transistors, they also need to be unsoldered and the base-emitter, base-collector junctions must be wired, identifying their permeability in one direction and the other. Typically, the role of a collector in a transistor is performed by the rear iron part.
We must not forget to check the winding, both primary and secondary. If you have problems determining where the primary winding is and where the secondary winding is, then remember that the primary winding gives more resistance.
The capacitance of a capacitor is measured in farads (picofarads, microfarads). To study it, a multimeter is also used, on which the resistance is set to 2000 kOhm. The positive probe is applied to the minus of the capacitor, the negative to the plus. Increasing numbers should appear on the screen up to almost two thousand, which are replaced by one, which stands for infinite resistance. This may indicate the health of the capacitor, but only in relation to its ability to accumulate charge.
One more point: if during the dialing process there is confusion about where the “input” is located and where the “output” of the transformer is located, then you just need to turn the board over and on the back side at one end of the board you will see a small marking “SEC” (second), which indicates the output, and on the other “PRI” (first) the input.
And also, do not forget that electronic transformers cannot be started without loading! It is very important.
The opportunity to practice repairing a transformer presented itself not so long ago, when they brought me an electronic transformer from a ceiling chandelier (voltage - 12 volts). The chandelier is designed for 9 bulbs, each 20 watts (180 watts in total). On the packaging of the transformer it also said: 180 watts. But the mark on the board said: 160 watts. The country of origin is, of course, China. A similar electronic transformer costs no more than $3, and this is actually quite a bit when compared with the cost of the other components of the device in which it was used.
In the electronic transformer I received, a pair of switches on bipolar transistors burned out (model: 13009).
The operating circuit is a standard push-pull, in place of the output transistor is a TOP inverter, whose secondary winding consists of 6 turns, and the alternating current is immediately redirected to the output, that is, to the lamps.
Such power supplies have a very significant drawback: there is no protection against short circuit at the output. Even with a short-circuit of the output winding, you can expect a very impressive explosion of the circuit. Therefore, it is highly not recommended to take risks in this way and short-circuit the secondary winding. In general, it is for this reason that radio amateurs do not really like to mess with electronic transformers of this type. However, some, on the contrary, try to modify them on their own, which, in my opinion, is quite good.
But let's get back to the point: since there was a darkening of the board right under the keys, there was no doubt that they failed precisely because of overheating. Moreover, the radiators do not actively cool the case box filled with many parts, and they are also covered with cardboard. Although, judging by the initial data, there was also an overload of 20 watts.
Due to the fact that the load exceeds the capabilities of the power supply, reaching the rated power is almost equivalent to failure. Moreover, ideally, with a view to long-term operation, the power of the power supply should be not less, but twice as much as necessary. This is what Chinese electronics is like. It was not possible to reduce the load level by removing several light bulbs. Therefore, the only suitable option, in my opinion, to correct the situation was to increase the heat sinks.
To confirm (or refute) my version, I launched the board directly on the table and applied the load using two halogen pair lamps. When everything was connected, I dripped a little paraffin onto the radiators. The calculation was as follows: if the paraffin melts and evaporates, then we can guarantee that the electronic transformer (fortunately, if only it is itself) will burn out in less than half an hour of operation due to overheating. After 5 minutes of operation, the wax still did not melt, it turned out that the main problem is related precisely to poor ventilation, and not to a malfunction of the radiator. The most elegant solution to the problem is to simply fit another larger housing under the electronic transformer, which will provide sufficient ventilation. But I preferred to connect a heat sink in the form of an aluminum strip. Actually, this turned out to be quite enough to correct the situation.
As another example of repairing an electronic transformer, I would like to talk about repairing a device that reduces the voltage from 220 to 12 Volts. It was used for 12 Volt halogen lamps (power - 50 Watt).
The copy in question stopped working without any special effects. Before I got it into my hands, several craftsmen refused to work with it: some could not find a solution to the problem, others, as mentioned above, decided that it was not economically feasible.
To clear my conscience, I checked all the elements and traces on the board and found no breaks anywhere.
Then I decided to check the capacitors. The diagnostics with a multimeter seemed to be successful, however, taking into account the fact that the charge accumulated for as long as 10 seconds (this is a lot for capacitors of this type), a suspicion arose that the problem was in it. I replaced the capacitor with a new one.
A small digression is needed here: on the body of the electronic transformer in question there was a designation: 35-105 VA. These readings indicate at what load the device can be turned on. It is impossible to turn it on without a load at all (or, in human terms, without a lamp), as mentioned earlier. Therefore, I connected a 50 Watt lamp to the electronic transformer (that is, the value that fits between the lower and upper limits of the permissible load).
Rice. 4: 50W halogen lamp (package).
After connection, no changes occurred in the performance of the transformer. Then I completely examined the design again and realized that during the first check I did not pay attention to the thermal fuse (in this case, model L33, limited to 130C). If in the continuity mode this element gives one, then we can talk about its malfunction and an open circuit. Initially, the thermal fuse was not tested for the reason that it is attached tightly to the transistor using heat shrink. That is, to fully check the element, you will have to get rid of the heat shrinkage, and this is very labor-intensive.
Fig. 5: Thermal fuse attached by heat shrink to the transistor (the white element pointed to by the handle).
However, to analyze the operation of the circuit without this element, it is enough to short-circuit its “legs” on the reverse side. Which is what I did. The electronic transformer immediately started working, and the earlier replacement of the capacitor turned out to be not superfluous, since the capacity of the previously installed element did not meet the declared one. The reason was probably that it was simply worn out.
As a result, I replaced the thermal fuse, and at this point the repair of the electronic transformer could be considered complete.
Write comments, additions to the article, maybe I missed something. Take a look at, I will be glad if you find anything else useful on mine.
The device has a fairly simple circuit. A simple push-pull self-oscillator, which is made using a half-bridge circuit, the operating frequency is about 30 kHz, but this indicator strongly depends on the output load.
The circuit of such a power supply is very unstable, it does not have any protection against short circuits at the output of the transformer, perhaps precisely because of this, the circuit has not yet found widespread use in amateur radio circles. Although recently there has been a promotion of this topic on various forums. People offer various options for modifying such transformers. Today I will try to combine all these improvements in one article and offer options not only for improvements, but also for strengthening the ET.
We won’t go into the basics of how the circuit works, but let’s get down to business right away.
We will try to refine and increase the power of the Chinese Taschibra electric vehicle by 105 watts.
To begin with, I want to explain why I decided to take on the powering and alteration of such transformers. The fact is that recently a neighbor asked me to make him a custom-made charger for a car battery that would be compact and lightweight. I didn’t want to assemble it, but later I came across interesting articles that discussed remaking an electronic transformer. This gave me the idea - why not try it?
Thus, several ETs from 50 to 150 Watts were purchased, but experiments with conversion were not always completed successfully; of all, only the 105 Watt ET survived. The disadvantage of such a block is that its transformer is not ring-shaped, and therefore it is inconvenient to unwind or rewind the turns. But there was no other choice and this particular block had to be remade.
As we know, these units do not turn on without load; this is not always an advantage. I plan to get a reliable device that can be freely used for any purpose without fear that the power supply may burn out or fail during a short circuit.
Improvement No. 1
The essence of the idea is to add short-circuit protection and also eliminate the above-mentioned drawback (activation of a circuit without an output load or with a low-power load).
Looking at the unit itself, we can see the simplest UPS circuit; I would say that the circuit has not been fully developed by the manufacturer. As we know, if you short-circuit the secondary winding of a transformer, the circuit will fail in less than a second. The current in the circuit increases sharply, the switches instantly fail, and sometimes even the basic limiters. Thus, repairing the circuit will cost more than the cost (the price of such an ET is about $2.5).
The feedback transformer consists of three separate windings. Two of these windings power the base switch circuits.
First, remove the communication winding on the OS transformer and install a jumper. This winding is connected in series with the primary winding of the pulse transformer.
Then we wind only 2 turns on the power transformer and one turn on the ring (OS transformer). For winding, you can use a wire with a diameter of 0.4-0.8 mm.
Next, you need to select a resistor for the OS, in my case it is 6.2 ohms, but a resistor can be selected with a resistance of 3-12 ohms, the higher the resistance of this resistor, the lower the short-circuit protection current. In my case, the resistor is a wirewound one, which I do not recommend doing. We select the power of this resistor to be 3-5 watts (you can use from 1 to 10 watts).
During a short circuit on the output winding of a pulse transformer, the current in the secondary winding drops (in standard ET circuits, during a short circuit, the current increases, disabling the switches). This leads to a decrease in the current on the OS winding. Thus, generation stops and the keys themselves are locked.
The only drawback of this solution is that in the event of a long-term short circuit at the output, the circuit fails because the switches heat up quite strongly. Do not expose the output winding to a short circuit lasting more than 5-8 seconds.
The circuit will now start without load; in a word, we have a full-fledged UPS with short-circuit protection.
Improvement No. 2
Now we will try to smooth out the mains voltage from the rectifier to some extent. For this we will use chokes and a smoothing capacitor. In my case, a ready-made inductor with two independent windings was used. This inductor was removed from the UPS of the DVD player, although homemade inductors can also be used.
After the bridge, an electrolyte with a capacity of 200 μF should be connected with a voltage of at least 400 Volts. The capacitor capacity is selected based on the power of the power supply 1 μF per 1 watt of power. But as you remember, our power supply is designed for 105 Watts, why is the capacitor used at 200 μF? You will understand this very soon.
Improvement No. 3
Now about the main thing - increasing the power of the electronic transformer and is it real? In fact, there is only one reliable way to power it up without much modification.
For powering up, it is convenient to use an ET with a ring transformer, since it will be necessary to rewind the secondary winding; it is for this reason that we will replace our transformer.
The network winding is stretched across the entire ring and contains 90 turns of wire 0.5-0.65 mm. The winding is wound on two folded ferrite rings, which were removed from an ET with a power of 150 watts. The secondary winding is wound based on needs, in our case it is designed for 12 Volts.
It is planned to increase the power to 200 watts. That is why an electrolyte with a reserve, which was mentioned above, was needed.
We replace the half-bridge capacitors with 0.5 μF; in the standard circuit they have a capacity of 0.22 μF. Bipolar keys MJE13007 are replaced with MJE13009.
The power winding of the transformer contains 8 turns, the winding was done with 5 strands of 0.7 mm wire, so we have a wire in the primary with a total cross-section of 3.5 mm.
Go ahead. Before and after the chokes we place film capacitors with a capacity of 0.22-0.47 μF with a voltage of at least 400 Volts (I used exactly those capacitors that were on the ET board and which had to be replaced to increase the power).
Next, replace the diode rectifier. In standard circuits, conventional rectifier diodes of the 1N4007 series are used. The current of the diodes is 1 Ampere, our circuit consumes a lot of current, so the diodes should be replaced with more powerful ones in order to avoid unpleasant results after the first turn on of the circuit. You can use literally any rectifier diodes with a current of 1.5-2 Amps, a reverse voltage of at least 400 Volts.
All components except the generator board are mounted on a breadboard. The keys were secured to the heat sink through insulating gaskets.
We continue our modification of the electronic transformer, adding a rectifier and filter to the circuit.
The chokes are wound on rings made of powdered iron (removed from a computer power supply unit) and consist of 5-8 turns. It is convenient to wind it using 5 strands of wire with a diameter of 0.4-0.6 mm each.
Electronic transformers for halogen lamps (HT)- a topic that is not losing relevance among both experienced and very mediocre radio amateurs. And this is not surprising, because they are very simple, reliable, compact, easy to modify and improve, which significantly expands their scope of application. And due to the massive transition of lighting technology to LED technology, ETs have become obsolete and have fallen greatly in price, which, in my opinion, has become almost their main advantage in amateur radio practice.
There is a lot of different information about ET regarding the advantages and disadvantages, design, principle of operation, modification, modernization, etc. But finding the right circuit, especially high-quality devices, or purchasing a unit with the required configuration can be very problematic. Therefore, in this article I decided to present photos, sketched diagrams with wire data and brief reviews of those devices that came (will fall) into my hands, and in the next article I plan to describe several options for alterations of specific ETs from this topic.
For clarity, I conditionally divide all ET into three groups:
Now let's move on to the ETs themselves. For convenience, they are sorted by power output in ascending order.
1. ET with power up to 60 W.
1.1. L&B
1.2. Tashibra
The two ETs mentioned above are typical representatives of the cheapest China. The scheme, as you can see, is typical and widespread on the Internet.
1.3. Horoz HL370
Factory China. Holds the rated load well and doesn't get too hot.
1.4. Relco Minifox 60 PFS-RN1362
But here is a representative of a good ET made in Italy, equipped with a modest input filter and protection against overload, overvoltage and overheating. Power transistors are selected with a power reserve, so they do not require radiators.
2. ET with a power of 105 W.
2.1. Horoz HL371
Similar to the above model Horoz HL370 (item 1.3.) factory made in China.
2.2. Feron TRA110-105W
There are two versions in the photo: on the left is the older one (2010 onwards) – factory made in China, on the right is the newer one (2013 onwards), reduced in price to typical China.
2.3. Feron ET105
Similar Feron TRA110-105W (item 2.2.) factory China. The photo of the original board was not saved, so instead I’m posting a photo of the Feron ET150, the board of which is very similar in appearance and similar in element base.
2.4. Brilux BZE-105
Similar Relco Minifox 60 PFS-RN1362 (item 1.4.) is a good ET.
3. ET with a power of 150 W.
3.1. Buko BK452
An electric vehicle reduced in price to a factory price in China, into which an overload protection module (SC) was not soldered. And so, the block is quite good in form and content.
3.2. Horoz HL375 (HL376, HL377)
And here is a representative of high-quality ETs with a very rich set of equipment. What immediately catches your eye is the chic two-stage input filter, powerful paired power switches with a volumetric radiator, protection against overload (short circuit), overheating and double overvoltage protection. This model is also significant in that it is the flagship for the subsequent ones: HL376 (200W) and HL377 (250W). The differences are marked in red on the diagram.
3.3. Vossloh Schwabe EST 150/12.645
Very high quality ET from the world famous German manufacturer. Compact, well-designed, powerful unit with element base from the best European companies.
3.4. Vossloh Schwabe EST 150/12.622
No less high-quality, newer version of the previous model (EST 150/12.645), characterized by greater compactness and some circuit solutions.
3.5. Brilux BZ-150B (Kengo Lighting SET150CS)
One of the highest quality ETs I've come across. A very well thought out block with a very rich element base. It differs from a similar model Kengo Lighting SET150CS only in the communication transformer, which is slightly smaller in size (10x6x4mm) with the number of turns 8+8+1. The uniqueness of these ETs is their two-stage overload protection (SC), the first of which is self-healing, configured for a smooth start of halogen lamps and light overload (up to 30-50%), and the second is blocking, triggered when an overload exceeds 60% and requires a unit reboot (short-term shutdown followed by switching on). Also notable is the rather large power transformer, the overall power of which allows you to squeeze out up to 400-500 W from it.
I personally didn’t come across them, but I saw similar models in the photo in the same case and with the same set of elements for 210W and 250W.
4. ET with a power of 200-210 W.
4.1. Feron TRA110-200W (250W)
Similar Feron TRA110-105W (item 2.2.) factory China. Probably the best unit in its class, designed with a large power reserve, and therefore is the flagship model for the absolutely identical Feron TRA110-250W, made in the same housing.
4.2. Delux ELTR-210W
A maximally cheap, slightly clumsy ET with many unsoldered parts and heat dissipation of power switches to a common radiator through pieces of electrical cardboard, which can be classified as good only because of the presence of overload protection.
4.3. Light kit EK210
According to the electronic filling, similar to the previous Delux ELTR-210W (clause 4.2.), a good ET with power switches in a TO-247 housing and two-stage overload protection (SC), despite which it ended up burnt out, almost completely, along with the protection modules ( why are there no photos? After complete recovery, when connecting a load close to the maximum, it burned out again. Therefore, I can’t say anything sensible about this ET. Possibly a marriage, or perhaps poorly thought out.
4.4. Kanlux SET210-N
Without further ado, a pretty high-quality, well-designed and very compact ET.
ET with a power of 200W can also be found in paragraph 3.2.
5. ET with a power of 250 W or more.
5.1. Lemanso TRA25 250W
Typical China. The same well-known Tashibra or a pitiful semblance of Feron TRA110-200W (section 4.1.). Even despite the powerful paired keys, it hardly maintains the declared characteristics. The board was received crippled, without a case, so there is no photo of it.
5.2. Asia Elex GD-9928 250W
Essentially the TRA110-200W model improved to a good ET (clause 4.1.). Up to half of the housing is filled with a thermally conductive compound, which significantly complicates its disassembly. If you come across one and need to disassemble it, put it in the freezer for several hours, and then quickly break off the frozen compound piece by piece until it warms up and becomes viscous again.
The next most powerful model, Asia Elex GD-9928 300W, has an identical body and circuit.
ET with a power of 250W can also be found in paragraph 3.2. and clause 4.1.
Well, that’s probably all ET for today. In conclusion, I will describe some nuances, features and give a couple of tips.
Many manufacturers, especially cheap electric vehicles, produce these products under different names (brands, types) using the same circuit (case). Therefore, when searching for a circuit, you should pay more attention to its similarity than to the name (type) of the device.
It is almost impossible to determine the quality of an ET based on the body, since, as can be seen in some photos, the model may be understaffed (with missing parts).
The cases of good and high-quality models are usually made of high-quality plastic and can be disassembled quite easily. Cheap ones are often held together with rivets, and sometimes glued together.
If, after disassembling, it is difficult to determine the quality of an electronic device, pay attention to the printed circuit board - cheap ones are usually mounted on getinax, high-quality ones are mounted on PCB, good ones, as a rule, are also mounted on PCB, but there are rare exceptions. The quantity (volume, density) of radio components will tell you a lot. Inductive filters are always absent in cheap ETs.
Also, in cheap ETs, the heat sink of power transistors is either completely absent, or is placed on the housing (metal) through electrical cardboard or PVC film. In high-quality and many good ETs, it is made on a volumetric radiator, which usually fits tightly to the body from the inside, also using it to dissipate heat.
The presence of overload protection (SC) can be determined by the presence of at least one additional low-power transistor and low-voltage electrolytic capacitor on the board.
If you plan to purchase an ET, then note that there are many flagship models that are cheaper in price than their “more powerful” copies. Electronic transformers.
Success in life and creative work to all.
It happens that when assembling a particular device, you need to decide on the choice of power source. This is extremely important when devices require a powerful power supply. Today it is not difficult to purchase iron transformers with the necessary characteristics. But they are quite expensive, and their large size and weight are their main disadvantages. And assembling and setting up good switching power supplies is a very complicated procedure. And many people don’t take it up.
Next, you will learn how to assemble a powerful and yet simple power supply, using an electronic transformer as the basis for the design. By and large, the conversation will be about increasing the power of such transformers.
A 50-watt transformer was taken for the conversion.
It was planned to increase its power to 300 W. This transformer was purchased at a nearby store and cost about 100 rubles.
A standard transformer circuit looks like this:
The transformer is a conventional push-pull half-bridge self-generating inverter. The symmetrical dinistor is the main component that triggers the circuit, since it supplies the initial impulse.
The circuit uses 2 high-voltage transistors with reverse conductivity.
The transformer circuit before modification contains the following components:
Despite the lack of short-circuit protection in this option, the electronic transformer operates without failure. The purpose of the device is to work with a passive load (for example, office halogen lights), so there is no output voltage stabilization.
As for the main power transformer, its secondary winding produces about 12 V.
Now take a look at the transformer circuit with increased power:
There are even fewer components in it. A feedback transformer, resistor, dynistor and capacitor were taken from the original circuit.
The remaining parts were taken from old computer power supplies, and these are 2 transistors, a diode bridge and a power transformer. Capacitors were purchased separately.
It wouldn’t hurt to replace the transistors with more powerful ones (MJE13009 in a TO220 package).
The diodes were replaced with a ready-made assembly (4 A, 600 V).
Diode bridges from 3 A, 400 V are also suitable. The capacitance should be 2.2 μF, but 1.5 μF is also possible.
The power transformer was removed from the 450 W ATX format power supply. All standard windings were removed from it and new ones were wound. The primary winding was wound with triple wire 0.5 sq. mm in 3 layers. The total number of turns is 55. It is necessary to monitor the accuracy of the winding, as well as its density. Each layer was insulated with blue electrical tape. The calculation of the transformer was carried out experimentally, and a golden mean was found.
The secondary winding is wound at the rate of 1 turn - 2 V, but this is only if the core is the same as in the example.
When you first turn it on, be sure to use a 40-60 W incandescent safety lamp.
It is worth noting that at the moment of startup the lamp will not flash, since there are no smoothing electrolytes after the rectifier. The output frequency is high, so in order to make specific measurements, you must first rectify the voltage. For these purposes, a powerful dual diode bridge assembled from KD2997 diodes was used. The bridge can withstand currents of up to 30 A if a radiator is attached to it.
The secondary winding was supposed to be 15 V, although in reality it turned out to be a little more.
Everything that was at hand was taken as a load. This is a powerful lamp from a film projector rated at 400 W at a voltage of 30 V and 5 20-watt lamps at 12 V. All loads were connected in parallel.
Biometric lock - LCD display diagram and assembly
