Halogen lamps are increasingly used every day in decorating various shopping malls and shop windows. The bright colors and richness of the image rendering make them increasingly popular. Their service life is much longer than that of conventional lamps. At the same time, they can work for a long time without switching off. Halogen lamps use filaments, but the glow process is different in comparison with incandescent lamps due to the filling of the cylinder with a special composition. Such light bulbs are used in various lamps, chandeliers, kitchen furniture and come in 220 and 12 volt. A power supply for halogen lamps with a voltage of 12 volts is necessary, because if they are connected directly to the electrical network, a short circuit will occur.
Specifications
The voltage of halogen lamps is not only 220 and 12 volts. On sale you can find 24 and even 6 volt light bulbs. The power can also be different - 5, 10, 20 watts. Halogen lamps from 220 V are connected directly to the network. Those that operate on 12 V require special devices that convert current from the network to 12 volts - so-called transformers or special power supplies.
Twelve volt halogens work very well. Previously, in the 90s, a large 50 Hz transformer was used, which ensured the operation of only one halogen lamp. Modern lighting uses pulsed high-frequency converters. They are very small in size, but can pull 2 - 3 lamps at the same time.
On the modern market there are both expensive and cheap power supplies. As a percentage of expensive ones, about 5% are sold, and much more cheap ones. Although, in principle, high cost is not a guarantee of reliability. Cool converters, unfortunately, do not use high-quality parts, but only use clever circuit “bells and whistles” that contribute to the normal operation of the power supply, at least during the warranty period. As soon as it runs out, the device burns out.
Classification
Transformers are electromagnetic and electronic (pulse). Electromagnetic ones are affordable, reliable, and can be made with your own hands if desired. They also have their disadvantages - decent weight, large overall dimensions, increased temperature during prolonged operation. And voltage drops significantly shorten the life of halogen lamps.
Electronic transformers weigh much less, they have a stable output voltage, they do not heat up much, they can have short-circuit protection and soft start, which increases the life of the lamp.
Transformers for halogen lamps
The analysis will be carried out using the example of a power supply from Feron German Technology. The output of this transformer is no less than 5 amperes. For such a small box the value is amazing. The case is made in a hermetically sealed manner, with the absence of any kind of ventilation. This is probably why some copies of such power supplies melt from high temperatures.
The converter circuit in the first version is very simple. The set of all the details is so minimal that it is unlikely that anything can be thrown out of it. When enumerating we see:
- diode bridge;
- RC circuit with a dinistor to start the generator;
- generator assembled on a half-bridge circuit;
- transformer that reduces the input voltage;
- low resistance resistor that serves as a fuse.
With a large voltage drop, such a converter will “die” 100%, taking the entire “blow” upon itself. Everything is made from a fairly cheap set of parts. Only there are no complaints about the transformers, because they are made to last.
The second option looks very weak and unfinished. Resistors R5 and R6 are inserted into the emitter circuits to limit the current. At the same time, the blocking of transistors in the event of a sharp increase in current is not thought out at all (it simply does not exist!). The electrical circuit (in the diagram it is red in the diagram) raises doubts.
The Feron German Technology company produces halogen lamps with a power of up to 60 watts. The output current of the power supply is 5 amperes. This is a bit much for such a light bulb.
When removing the cover, pay special attention to the dimensions of the radiator. For a 5 amp output they are very small.
Calculation of transformer power for lamps and connection diagram
Various transformers are sold today, so there are certain rules for selecting the required power. You should not take a transformer that is too powerful. It will work practically idle. Lack of power will lead to overheating and further failure of the device.
You can calculate the power of the transformer yourself. The problem is rather mathematical and is within the capabilities of every novice electrician. For example, it is necessary to install 8 halogen spot lights with a voltage of 12 V and a power of 20 watts. The total power will be 160 watts. We take approximately a 10% margin and purchase a power of 200 watts.
Scheme No. 1 looks something like this: there is a single-key switch on line 220, with the orange and blue wires connected to the transformer input (primary terminals).
On the 12 volt line, all lamps are connected to a transformer (to the secondary terminals). The connecting copper wires must have the same cross-section, otherwise the brightness of the light bulbs will be different.
Another condition: the wire connecting the transformer to the halogen lamps must be at least 1.5 meters long, preferably 3. If you make it too short, it will start to heat up and the brightness of the lamps will decrease.
Scheme No. 2 – for connecting halogen lamps. Here you can do things differently. Break, for example, six lamps into two parts. For each, install a step-down transformer. The correctness of this choice is due to the fact that if one of the power supplies breaks down, the second part of the lamps will still continue to work. The power of one group is 105 watts. With a small safety factor, we find that you need to purchase two 150-watt transformers.
Advice! Power each step-down transformer with its own wires and connect them in a junction box. Leave the connection points freely accessible.
Do-it-yourself power supply modification
To operate halogen lamps, pulsed current sources with high-frequency voltage conversion began to be used. During home production and setup, expensive transistors quite often burn out. Since the supply voltage in the primary circuits reaches 300 volts, very high requirements are placed on insulation. All these difficulties can be completely avoided by using a ready-made electronic transformer. It is used to power 12-volt halogen backlights (in stores), which are powered from a standard electrical outlet.
There is a certain opinion that getting a homemade switching power supply is a simple matter. You can only add a rectifier bridge, a smoothing capacitor and a voltage stabilizer. In reality, everything is much more complicated. If you connect an LED to the rectifier, then only one ignition can be detected when turned on. If you turn the converter off and on again, another flash will occur. In order for a constant glow to appear, it is necessary to connect an additional load to the rectifier, which, taking away useful power, would convert it into heat.
One of the options for self-manufacturing a switching power supply
The described power supply can be made from an electronic transformer with a power of 105 W. In practice, this transformer resembles a compact pulse voltage converter. For assembly, you will additionally need a matching transformer T1, a mains filter, a rectifier bridge VD1-VD4, and an output choke L2.
Bipolar power supply circuit Such a device operates stably for a long time with a low-frequency amplifier with a power of 2x20 watts. At 220 V and a current of 0.1 A, the output voltage will be 25 V; when the current increases to 2 amperes, the voltage drops to 20 volts, which is considered normal operation.
The current, bypassing the switch and fuses FU1 and FU2, goes to a filter that protects the circuit from interference from the pulse converter. The middle of capacitors C1 and C2 is connected to the shielding casing of the power supply. Then the current is supplied to input U1, from where a reduced voltage is supplied from the output terminals to the matching transformer T1. The alternating voltage from the other (secondary winding) rectifies the diode bridge and smoothes the L2C4C5 filter.
Self-assembly
Transformer T1 is manufactured independently. The number of turns on the secondary winding affects the output voltage. The transformer itself is made on a K30x18x7 ring magnetic core made of M2000NM ferrite. The primary winding consists of a PEV-2 wire with a diameter of 0.8 mm, folded in half. The secondary winding consists of 22 turns of PEV-2 wire, folded in half. By connecting the end of the first half-winding to the beginning of the second, we obtain the midpoint of the secondary winding. We also make the throttle ourselves. It is wound on the same ferrite ring, both windings contain 20 turns.
Rectifier diodes are located on a radiator with an area of at least 50 sq.cm. Please note that diodes whose anodes are connected to the negative output are insulated from the heat sink with mica spacers.
Smoothing capacitors C4 and C5 consist of three K50-46 connected in parallel with a capacity of 2200 μF each. This method is used to reduce the overall inductance of electrolytic capacitors.
It would be better to install a surge filter at the input of the power supply, but it is possible to work without it. For a line filter choke, you can use a DF of 50 Hz.
All parts of the power supply are mounted on a board made of insulating material. The resulting structure is placed in a shielding casing made of thin sheet brass or tinned sheet. Don't forget to drill holes in it for air ventilation.
A correctly assembled power supply does not require adjustment and starts working immediately. But just in case, you can check its performance by connecting a resistor with a resistance of 240 Ohms and a dissipation power of 3 W to the output.
Step-down transformers for halogen lamps generate a very large amount of heat during operation. Therefore, several requirements must be met:
- Do not connect the power supply without load.
- Place the unit on a non-flammable surface.
- The distance from the block to the light bulb is at least 20 centimeters.
- For better ventilation, install the transformer in a niche with a volume of at least 15 liters.
A power supply is required for halogen lamps operating on 12 volts. It is a kind of transformer that lowers the input 220 V to the required values.
The production and sale of household incandescent lamps is prohibited in EU countries, but halogen light bulbs (they also use a filament filament, but it is regenerated by filling the cylinder with a special composition) are still allowed. Here they are actively used, because everything is brought from China, and they do not care about all the prohibitions. Halogen lamps are used as recessed lamps in false ceilings, chandeliers, kitchen furniture, and not only in kitchen furniture. They come in two types - 12 volts and 220 volts. Well, power consumption also varies - 5, 10, 20 or more watts. With 220 volt lamps, everything is clear: they are simply plugged directly into the network, but for those that operate from 12, a special device is needed that converts 220 volts into 12. By the way! I strongly recommend not to buy or use 220-volt “spot” halogens at all. They have phenomenally low reliability, even those produced by “cool” companies. Well, unless you install a soft start device.
But 12-volt ones work relatively reliably; another thing is that this very converter comes into the “game”. Back in the 90s, it was a regular 50 Hz transformer, large and heavy. Moreover, each light bulb had to have its own separate transformer. In the early 90s, I did electrical work in a very cool (by then standards) auto parts store, where about 30 of these lamps were mounted in the ceiling, two wires went from each to a special box where we placed transformers. As of 2010, all transformers were working, although light bulbs, of course, had to be changed, albeit rarely. Now such transformers can also be bought, but they are expensive - about 20 dollars apiece. And few people buy them, and maybe no one at all. In use - pulsed high-frequency converters! Small, but such that they draw 50-60 watts (as written on the case), that is, you can connect 2-3 lamps to them.
Everything would be fine, but! There are two types of converters - cheap and expensive. At least 95% of the market is cheap converters. 5% is expensive, but high cost is not a guarantee against breakdowns. In general, I’ll tell you this: at present, the electronics industry could produce simply phenomenally reliable converters, but no one produces them, at least I haven’t come across them. Those that are expensive differ from cheap ones not in the quality of parts (they are the same everywhere), but in some circuit “bells and whistles” that really reduce the likelihood of the product being released, at least during the warranty period. And if cheap converters for 220-12 volts 50-60 watts cost 3-4 dollars, then expensive ones cost 12-15, and sometimes more.
Today we will talk about repairing cheap ones, fortunately I have about ten of them here. In general, almost everyone prefers to throw them away, but the funny thing is that when you buy a new cheap converter, you do not get any guarantee that it will not fail after a couple of hours of operation. And having a tester, a soldering iron and hands growing from the right place, you can quickly repair these things. And how come Chinese manufacturers haven’t thought of filling them with epoxy yet?
Here they are. Feron company. Herman Technology, for low-volts halogen lamps. Well, in general, you understand, right? 60 watts. That is 5 amperes at the output. Not bad for such a small thing. True, they all don’t work, and one, as you can see, even melted. Please note that the case is sealed, that is, there is no ventilation there. This is exactly the same way they now make power supply housings for laptops - they are hermetically glued together. That’s why these blocks fly out in batches. In half of the cases, the cause is overheating of the elements. The same goes for economy lamps. The white base where the circuit is located is completely sealed, although it should be like a grille. Ventilation - zero. It is clear that this was done so that nothing would work for a long time.
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We are performing an autopsy. We pay attention to the “radiators”. And this is for a thing that produces 5 amperes at the output:
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Let's draw the diagram:
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The converter circuit in option 1 is phenomenally simple. In fact, it’s the simplest thing imaginable; you can’t even throw away a single thing you did here. The bare minimum for it to work. A diode bridge, an RC circuit plus a dinistor for starting the generator, the generator itself assembled using a half-bridge circuit and a step-down transformer. At the input there is a low-resistance resistor that acts as a fuse. It must heroically burn down in the event of an emergency; no other protections are fundamentally provided. And this is all assembled from the cheapest parts. The only thing I have no complaints about is the transformers, they are made normally.
Option 2 is generally muddy. Yes, they inserted resistors R5-R6 into the emitter circuits, of the “current limiting” type, but this is stupid and pointless if there is no provision for blocking the transistors or another way to disrupt generation if this very current is exceeded. And the purpose of the circuit highlighted in red is completely unclear. Some local Chinese creativity.
We begin to check the parts with an ohmmeter without desoldering them from the board:
- In 8 out of 10 boards we find that the resistance of resistor R1 is infinity. That is, he burned down. In some cases, a cracked hull is even visible. This actually means with 100% probability that 2 power transistors have burned out (in this circuit, if one burns out, the second one automatically burns out). That is, we immediately change both the resistor and transistors. However, just in case, we checked the transistors (right on the board) and found out that in some blocks they flew out in a strange way: the collector junction has zero resistance, and the emitter junction has infinite resistance. This means that, most likely, resistors R3-R4 in the base circuit have also failed. We check with an ohmmeter. This is true. We look through the “glasses” and see cracks and peeling varnish. Yes, in the circuit according to option 2, of course, the transistors in the emitter circuit are broken. No other way. We change.
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- The symmetrical dinistor V1 cannot be checked with an ohmmeter. Normally it should give infinity in both directions. But even if it does, it doesn’t mean it works. However, in my version all 10 dinistors turned out to be working.
- Of course, there can be no talk about operating transistors with such, so to speak, “radiators”. We strengthen them and cut out a piece of the body in order to create natural cooling. The trannies will be placed in an inaccessible place, so there is no need to worry about safety. As a last resort, put on a heat-shrinkable casing.
- After all the replacements and improvements, we turn on the thing. Profit! On a 20-watt light bulb, after an hour of operation, the radiator barely warmed up to 35 degrees. This is fine. Although my advice: operate these transformers at a maximum of 2/3 of the declared power. Or better yet, half.
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4. In two other transformers assembled according to option 1, capacitor C1 turned out to be faulty. Moreover, it was not pierced, but dried out. That is, it has lost capacity. I am sure that this was due to overheating - this type of capacitor generally does not maintain temperature well.
I’ll talk about repairing expensive converters for halogen lamps another time. Currently, I am finishing making my own converter based on this Feron, which, in my opinion, should be free of all obvious shortcomings and work reliably.
You can, of course, ask yourself the question - why bother fixing them at all? Is the cost worth the result? Let's do the math. So I had 10 converters. Each is 4 dollars. Total – 40 dollars. 2 transistors cost 2×0.3 = $0.6. Resistor – $0.05. However, the resistors did not fail in all converters. In general, the entire repair cost $6. Profit - $34 and about two hours of work. With expensive ones it’s even more profitable.
In conclusion, I present 2 more schemes. I found them on the Internet, they are similar to mine, but still different.
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Let's take for example a standard electronic transformer labeled 12V 50W, which is used to power a table lamp. The schematic diagram will be like this:
The electronic transformer circuit works as follows. The mains voltage is rectified using a rectifier bridge to a half-sinusoidal voltage with double the frequency. Element D6 of type DB3 in the documentation is called “TRIGGER DIODE”, - this is a bidirectional dinistor in which the polarity of the inclusion does not matter and it is used here to start the transformer converter. The dinistor is triggered during each cycle, starting the generation of a half-bridge. The opening of the dinistor can be adjusted. This can be done use for example for the function of a connected lamp.The generation frequency depends on the size and magnetic conductivity of the feedback transformer core and the parameters of the transistors, usually in the range of 30-50 kHz.
Currently, the production of more advanced transformers with the IR2161 chip has begun, which provides both simplicity of design of the electronic transformer and a reduction in the number of components used, as well as high performance. The use of this microcircuit significantly increases the manufacturability and reliability of the electronic transformer for powering halogen lamps. The schematic diagram is shown in the figure.
Features of the electronic transformer on IR2161:
Intelligent half bridge driver;
Load short circuit protection with automatic restart;
Overcurrent protection with automatic restart;
Swing the operating frequency to reduce electromagnetic interference;
Micropower start-up 150 µA;
Possibility of use with phase dimmers with control by leading and trailing edges;
Compensation for output voltage offset increases lamp life;
Soft start, eliminating current overload of lamps.
Input resistor R1 (0.25 watt) is a kind of fuse. Transistors of type MJE13003 are pressed to the body through an insulating gasket with a metal plate. Even when operating at full load, the transistors heat up slightly. After the mains voltage rectifier, there is no capacitor to smooth out the ripples, so the output voltage of the electronic transformer when operating on a load is a 40 kHz rectangular oscillation, modulated by 50 Hz mains voltage ripples. Transformer T1 (feedback transformer) - on a ferrite ring, the windings connected to the bases of the transistors contain a couple of turns, the winding connected to the connection point of the emitter and collector of the power transistors - one turn of single-core insulated wire. Transistors MJE13003, MJE13005, MJE13007 are usually used in ET. Output transformer on a ferrite W-shaped core.
To use an electronic transformer in a pulse mode, you need to connect a rectifier bridge on high-frequency diodes to the output (regular KD202, D245 will not work) and a capacitor to smooth out ripples. At the output of the electronic transformer, a diode bridge is installed using KD213, KD212 or KD2999 diodes. In short, we need diodes with a low voltage drop in the forward direction, capable of operating well at frequencies of the order of tens of kilohertz.
The electronic transformer converter does not work normally without a load, so it must be used where the load is constant in current and consumes sufficient current to reliably start the ET converter. When operating the circuit, it must be taken into account that electronic transformers are sources of electromagnetic interference, therefore an LC filter must be installed to prevent interference from penetrating the network and the load.
Personally, I used an electronic transformer to make a switching power supply for a tube amplifier. It also seems possible to power them with powerful Class A ULFs or LED strips, which are specifically designed for sources with a voltage of 12V and a high output current. Naturally, such a tape is connected not directly, but through a current-limiting resistor or by correcting the output power of an electronic transformer.
Discuss the article ELECTRONIC TRANSFORMER DIAGRAM FOR HALOGEN LAMPS
The article describes the so-called electronic transformers, which are essentially pulsed step-down converters for powering halogen lamps rated at 12 V. Two versions of the transformers are proposed - on discrete elements and using a specialized microcircuit.
Halogen lamps are, in fact, a more advanced modification of a conventional incandescent lamp. The fundamental difference is the addition of vapors of halogen compounds to the lamp bulb, which block the active evaporation of metal from the surface of the filament during lamp operation. This allows the filament to be heated to higher temperatures, which gives higher light output and a more uniform emission spectrum. In addition, the lamp life is increased. These and other features make the halogen lamp very attractive for home lighting, and not only. A wide range of halogen lamps of various wattages for voltages of 230 and 12 V are commercially produced. Lamps with a supply voltage of 12 V have better technical characteristics and a longer service life compared to 230 V lamps, not to mention electrical safety. To power such lamps from a 230 V network, it is necessary to reduce the voltage. You can, of course, use a regular network step-down transformer, but this is expensive and impractical. The optimal solution is to use a 230 V/12 V step-down converter, often called an electronic transformer or halogen convertor in such cases. Two versions of such devices will be discussed in this article, both are designed for a load power of 20...105 W.
One of the simplest and most common circuit solutions for step-down electronic transformers is a half-bridge converter with positive current feedback, the circuit of which is shown in Fig. 1. When the device is connected to the network, capacitors C3 and C4 are quickly charged to the amplitude voltage of the network, forming half the voltage at the connection point. Circuit R5C2VS1 generates a trigger pulse. As soon as the voltage on capacitor C2 reaches the opening threshold of dinistor VS1 (24.32 V), it will open and a forward bias voltage will be applied to the base of transistor VT2. This transistor will open and current will flow through the circuit: the common point of capacitors C3 and C4, the primary winding of transformer T2, winding III of transformer T1, the collector-emitter section of transistor VT2, the negative terminal of the diode bridge VD1. A voltage will appear on winding II of transformer T1 that maintains transistor VT2 in the open state, while reverse voltage from winding I will be applied to the base of transistor VT1 (windings I and II are switched out of phase). The current flowing through winding III of transformer T1 will quickly introduce it into a saturation state. As a result, the voltage on windings I and II T1 will tend to zero. Transistor VT2 will begin to close. When it closes almost completely, the transformer will begin to come out of saturation.
Rice. 1. Circuit of a half-bridge converter with positive current feedback
Closing transistor VT2 and leaving transformer T1 from saturation will lead to a change in the direction of the EMF and an increase in voltage on windings I and II. Now a forward voltage will be applied to the base of transistor VT1, and a reverse voltage will be applied to the base of VT2. Transistor VT1 will begin to open. Current will flow through the circuit: positive terminal of the diode bridge VD1, collector-emitter section VT1, winding III T1, primary winding of transformer T2, common point of capacitors C3 and C4. Then the process is repeated, and a second half-wave of voltage is formed in the load. After startup, diode VD4 maintains capacitor C2 in a discharged state. Since the converter does not use a smoothing oxide capacitor (it is not necessary when working with an incandescent lamp; on the contrary, its presence worsens the power factor of the device), then at the end of the half-cycle of the rectified mains voltage, generation will stop. With the arrival of the next half cycle, the generator will start again. As a result of the operation of the electronic transformer, oscillations with a frequency of 30...35 kHz (Fig. 2), which are close in shape to sinusoidal, are formed at its output, followed by bursts with a frequency of 100 Hz (Fig. 3).
Rice. 2. Oscillations close in shape to sinusoidal with a frequency of 30...35 kHz
Rice. 3. Oscillations with a frequency of 100 Hz
An important feature of such a converter is that it will not start without load, since in this case the current through winding III T1 will be too small, and the transformer will not enter saturation, the self-generation process will fail. This feature makes idle protection unnecessary. A device with those shown in Fig. 1 nominal starts stably at a load power of 20 W.
In Fig. Figure 4 shows a diagram of an improved electronic transformer, to which a noise suppression filter and a load short circuit protection unit have been added. The protection unit is assembled on transistor VT3, diode VD6, zener diode VD7, capacitor C8 and resistors R7-R12. A sharp increase in load current will lead to an increase in the voltage on windings I and II of transformer T1 from 3...5 V in nominal mode to 9...10 V in short circuit mode. As a result, a bias voltage of 0.6 V will appear at the base of transistor VT3. The transistor will open and bypass the start circuit capacitor C6. As a result, the generator will not start with the next half-cycle of the rectified voltage. Capacitor C8 provides a protection shutdown delay of about 0.5 s.
Rice. 4. Scheme of an improved electronic transformer
The second version of the electronic step-down transformer is shown in Fig. 5. It is easier to repeat, since it does not have one transformer, but it is more functional. This is also a half-bridge converter, but controlled by a specialized IR2161S microcircuit. The microcircuit has all the necessary protective functions built in: against low and high mains voltage, against idle mode and short circuit in the load, and against overheating. The IR2161S also has a soft start function, which consists of a smooth increase in the output voltage when turned on from 0 to 11.8 V within 1 s. This eliminates a sudden surge of current through the cold filament of the lamp, which significantly, sometimes several times, increases its service life.
Rice. 5. Second version of the electronic step-down transformer
At the first moment, as well as with the arrival of each subsequent half-cycle of the rectified voltage, the microcircuit is powered through the diode VD3 from the parametric stabilizer on the zener diode VD2. If the power is supplied directly from a 230 V network without using a phase power regulator (dimmer), then the R1-R3C5 circuit is not needed. After entering the operating mode, the microcircuit is additionally powered from the output of the half-bridge through the d2VD4VD5 circuit. Immediately after startup, the frequency of the internal clock generator of the microcircuit is about 125 kHz, which is significantly higher than the frequency of the output circuit S13S14T1, as a result, the voltage on the secondary winding of transformer T1 will be low. The internal oscillator of the microcircuit is controlled by voltage, its frequency is inversely proportional to the voltage on capacitor C8. Immediately after switching on, this capacitor begins to charge from the internal current source of the microcircuit. In proportion to the increase in voltage across it, the frequency of the microcircuit generator will decrease. When the voltage on the capacitor reaches 5 V (approximately 1 s after switching on), the frequency will decrease to an operating value of about 35 kHz, and the voltage at the output of the transformer will reach the nominal value of 11.8 V. This is how a soft start is implemented, after its completion the DA1 chip goes into operating mode in which pin 3 of DA1 can be used to control output power. If you connect a variable resistor with a resistance of 100 kOhm in parallel with capacitor C8, you can, by changing the voltage at pin 3 of DA1, control the output voltage and adjust the brightness of the lamp. When the voltage at pin 3 of the DA1 chip changes from 0 to 5 V, the generation frequency will change from 60 to 30 kHz (60 kHz at 0 V is the minimum output voltage and 30 kHz at 5 V is the maximum).
The CS input (pin 4) of the DA1 chip is the input of the internal error signal amplifier and is used to control the load current and voltage at the half-bridge output. In the event of a sharp increase in load current, for example, during a short circuit, the voltage drop across the current sensor - resistors R12 and R13, and therefore at pin 4 of DA1 will exceed 0.56 V, the internal comparator will switch and stop the clock generator. In the event of a load break, the voltage at the output of the half-bridge may exceed the maximum permissible voltage of transistors VT1 and VT2. To avoid this, a resistive-capacitive divider C10R9 is connected to the CS input via diode VD7. When the voltage threshold across resistor R9 is exceeded, generation also stops. The operating modes of the IR2161S chip are discussed in more detail in.
You can calculate the number of turns of the output transformer windings for both options, for example, using a simple calculation method; you can select the appropriate magnetic core based on overall power using the catalog.
According to, the number of turns of the primary winding is equal to
N I = (U c max t 0 max) / (2 S B max),
where U c max is the maximum network voltage, V; t 0 max - maximum time of the open state of transistors, μs; S - cross-sectional area of the magnetic circuit, mm 2; B max - maximum induction, T.
Number of turns of the secondary winding
where k is the transformation coefficient, in our case we can take k = 10.
A drawing of the printed circuit board of the first version of the electronic transformer (see Fig. 4) is shown in Fig. 6, arrangement of elements - in Fig. 7. The appearance of the assembled board is shown in Fig. 8. covers. The electronic transformer is assembled on a board made of fiberglass foil on one side with a thickness of 1.5 mm. All surface-mount elements are installed on the side of the printed conductors, and lead-out elements are installed on the opposite side of the board. Most of the parts (transistors VT1, VT2, transformer T1, dinistor VS1, capacitors C1-C5, C9, C10) are suitable from mass-produced cheap electronic ballasts for T8 type fluorescent lamps, for example, Tridonic PC4x18 T8, Fintar 236/418, Cimex CSVT 418P, Komtex EFBL236/418, TDM Electric EB-T8-236/418, etc., since they have similar circuitry and element base. Capacitors C9 and C10 are metal film polypropylene, designed for high pulse current and alternating voltage of at least 400 V. Diode VD4 - any fast-acting diode with an acceptable reverse voltage in Fig. 11 of at least 150 V.
Rice. 6. Printed circuit board drawing of the first version of the electronic transformer
Rice. 7. Arrangement of elements on the board
Rice. 8. Appearance of the assembled board
Transformer T1 is wound on a ring magnetic core with a magnetic permeability of 2300 ± 15%, its outer diameter is 10.2 mm, its inner diameter is 5.6 mm, and its thickness is 5.3 mm. Winding III (5-6) contains one turn, windings I (1-2) and II (3-4) contain three turns of wire with a diameter of 0.3 mm. The inductance of windings 1-2 and 3-4 should be 10...15 μH. The output transformer T2 is wound on a magnetic core EV25/13/13 (Epcos) without a non-magnetic gap, material N27. Its primary winding contains 76 turns of 5x0.2 mm wire. The secondary winding contains eight turns of Litz wire 100x0.08 mm. The inductance of the primary winding is 12 ±10% mH. The noise suppression filter choke L1 is wound on a magnetic core E19/8/5, material N30, each winding contains 130 turns of wire with a diameter of 0.25 mm. You can use a standard two-winding inductor with an inductance of 30...40 mH that is suitable in size. It is advisable to use X-class capacitors C1, C2.
The printed circuit board drawing of the second version of the electronic transformer (see Fig. 5) is shown in Fig. 9, arrangement of elements - in Fig. 10. The board is also made of fiberglass foil on one side, surface-mount elements are located on the side of the printed conductors, and lead-out elements are on the opposite side. The appearance of the finished device is shown in Fig. 11 and fig. 12. Output transformer T1 is wound on a ring magnetic core R29.5 (Epcos), material N87. The primary winding contains 81 turns of wire with a diameter of 0.6 mm, the secondary winding contains 8 turns of wire 3x1 mm. The inductance of the primary winding is 18 ± 10% mH, the secondary winding is 200 ± 10% μH. Transformer T1 was designed for a maximum power of up to 150 W; to connect such a load, transistors VT1 and VT2 must be installed on a heat sink - an aluminum plate with an area of 16...18 mm 2, a thickness of 1.5...2 mm. In this case, however, a corresponding modification of the printed circuit board will be required. Also, the output transformer can be used from the first version of the device (you will need to add holes on the board for a different pin arrangement). Transistors STD10NM60N (VT1, VT2) can be replaced with IRF740AS or similar. Zener diode VD2 must have a power of at least 1 W, stabilization voltage - 15.6...18 V. Capacitor C12 - preferably a ceramic disk with a rated direct voltage of 1000 V. Capacitors C13, C14 - metal film polypropylene, designed for high pulsed current and alternating current voltage is at least 400 V. Each of the resistive circuits R4-R7, R14-R17, R18-R21 can be replaced with one output resistor of the appropriate resistance and power, but this will require changing the printed circuit board.
Rice. 9. Printed circuit board drawing of the second version of the electronic transformer
Rice. 10. Arrangement of elements on the board
Rice. 11. Appearance of the finished device
Rice. 12. Appearance of the assembled board
Literature
1. IR2161 (S) & (PbF). Halogen converter control IC. - URL: http://www.irf.com/product-info/datasheets/data/ir2161.pdf (04/24/15).
2. Peter Green. 100VA dimmable electronic converter for low voltage lighting. - URL: http:// www.irf.com/technical-info/refdesigns/irplhalo1e.pdf (04.24.15).
3. Ferrites and Accessories. - URL: http:// en.tdk.eu/tdk-en/1 80386/tech-library/epcos-publications/ferrites (04/24/15).
Publication date: 30.10.2015
Readers' opinions
- Veselin / 08.11.2017 - 22:18
Which electronic transformers on the market with it 2161 or similar - Edward / 12/26/2016 - 13:07
Hello, is it possible to install a 180W instead of a 160W transformer? Thank you. - Mikhail / 12/21/2016 - 22:44
I remade these ones http://ali.pub/7w6tj - Yuri / 08/05/2016 - 17:57
Hello! Is it possible to find out the frequency of the alternating voltage at the output of the transformer for halogen lamps? Thank you.
Electronic transformers are replacing bulky steel core transformers. The electronic transformer itself, unlike the classical one, is a whole device - a voltage converter.
Such converters are used in lighting to power 12-volt halogen lamps. If you have repaired chandeliers with a remote control, then you have probably encountered them.
Here is a diagram of an electronic transformer JINDEL(model GET-03) with short circuit protection.
The main power elements of the circuit are n-p-n transistors MJE13009, which are connected according to the half-bridge circuit. They operate in antiphase at a frequency of 30 - 35 kHz. All the power supplied to the load - halogen lamps EL1...EL5 - is pumped through them. Diodes VD7 and VD8 are necessary to protect transistors V1 and V2 from reverse voltage. A symmetrical dinistor (aka diac) is necessary to start the circuit.
On transistor V3 ( 2N5551) and elements VD6, C9, R9 - R11, a short circuit protection circuit is implemented at the output ( short circuit protection).
If a short circuit occurs in the output circuit, the increased current flowing through resistor R8 will cause transistor V3 to operate. The transistor will open and block the operation of the DB3 dinistor, which starts the circuit.
Resistor R11 and electrolytic capacitor C9 prevent false operation of the protection when the lamps are turned on. When the lamps are turned on, the filaments are cold, so the converter produces a significant current at the beginning of the start-up.
To rectify the 220V mains voltage, a classic bridge circuit of 1.5-amp diodes is used 1N5399.
Inductor L2 is used as a step-down transformer. It takes up almost half the space on the converter PCB.
Due to its internal structure, it is not recommended to turn on the electronic transformer without load. Therefore, the minimum power of the connected load is 35 - 40 watts. The operating power range is usually indicated on the product body. For example, on the body of the electronic transformer in the first photo the output power range is indicated: 35 - 120 watts. Its minimum load power is 35 watts.
It is better to connect halogen lamps EL1...EL5 (load) to an electronic transformer with wires no longer than 3 meters. Since significant current flows through the connecting conductors, long wires increase the total resistance in the circuit. Therefore, lamps located further away will shine dimmer than those located closer.
It is also worth considering that the resistance of long wires contributes to their heating due to the passage of significant current.
It is also worth noting that, due to their simplicity, electronic transformers are sources of high-frequency interference in the network. Typically, a filter is placed at the input of such devices to block interference. As we can see from the diagram, electronic transformers for halogen lamps do not have such filters. But in computer power supplies, which are also assembled using a half-bridge circuit and with a more complex master oscillator, such a filter is usually mounted.
