It happens that when assembling a particular device, you need to decide on the choice of power source. This is extremely important when devices need a powerful power supply. It is not difficult to buy iron transformers with the necessary characteristics today. But they are quite expensive, and large size and weight are their main disadvantages. And the assembly and adjustment of good switching power supplies is a very complicated procedure. And a lot of people don't take it.
Next, you will learn how to assemble a powerful and at the same time simple power supply, taking an electronic transformer as the basis for the design. By and large, the conversation will be about increasing the power of such transformers.
For alteration, a 50-watt transformer was taken.
It was planned to increase its power to 300 watts. This transformer was purchased at a nearby store and cost about 100 rubles.
The standard transformer circuit looks like this:
The transformer is a conventional push-pull half-bridge autogenerator inverter. The symmetrical dinistor is the main triggering component of the circuit as it supplies the initial pulse.
The circuit uses 2 high-voltage reverse-conducting transistors.
The transformer circuit before rework contains the following components:
- Transistors MJE13003.
- Capacitors 0.1uF, 400V.
- A transformer having 3 windings, two of which are master and have 3 turns of wire with a cross section of 0.5 sq. mm. Another one as feedback by current.
- The input resistor (1 ohm) is used as a fuse.
- Diode bridge.
Despite the lack of protection against short circuit in this option, the electronic transformer works without failures. The purpose of the device is to work with a passive load (for example, office "halogens"), so there is no stabilization of the output voltage.
As for the main power transformer, its secondary winding produces about 12 V.
Now take a look at the transformer circuit with increased power:
It has even fewer components. From the original circuit, a feedback transformer, a resistor, a dinistor and a capacitor were taken.
The remaining parts were removed from old computer PSUs, and these are 2 transistors, a diode bridge and a power transformer. Capacitors were purchased separately.
It does not hurt to replace the transistors with more powerful ones (MJE13009 in the 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 microfarads, but 1.5 microfarads is also possible.
The power transformer was removed from the 450W ATX PSU. All standard windings were removed from it and new ones were wound. The primary winding was wound with a triple wire of 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 empirically, and the 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.
Be sure to use a 40-60 W incandescent safety lamp when you turn it on for the first time.
It is worth noting that at the time of starting the lamp will not flash, since there are no smoothing electrolytes after the rectifier. The output is high frequency, 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 up to 30 A if a heatsink is attached to it.
The secondary winding was supposed to be 15 V, although in reality it turned out a little more.
Everything that was at hand was taken as a load. This is a powerful lamp from a 400 W movie projector at a voltage of 30 V and 5 20-watt lamps at 12 V. All loads were connected in parallel.
Biometric lock - LCD layout and assembly
At present, pulse electronic transformers, due to their small size and weight, low price and wide range, are widely used in mass equipment. Due to mass production, electronic transformers are several times cheaper than conventional inductive iron transformers of the same power. Although electronic transformers from different companies may have different designs, the circuit is almost the same.
Take for example a standard electronic transformer marked 12V 50W, which is used to power table lamp. circuit diagram will be like this:
The electronic transformer circuit works as follows. The mains voltage is rectified by means of a rectifier bridge to a half-sine wave with twice the frequency. The D6 element of the DB3 type is called "TRIGGER DIODE" in the documentation, it 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 fires during each cycle, starting the half-bridge generation. The opening of the dinistor can be adjusted. This can use for example for the connected lamp function.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.
At present, the production of more advanced transformers with the IR2161 chip has begun, which provides both the simplicity of the electronic transformer design and the reduction in the number of components used, as well as high performance. The use of this chip 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;
Operating frequency sweep to reduce electromagnetic interference;
Micro power trigger 150uA;
Can be used with phase dimmers with leading and trailing edge control;
Output voltage offset compensation increases lamp life;
Soft start, excluding lamp current overloads.
The input resistor R1 (0.25 watts) is a kind of fuse. Transistors type MJE13003 are pressed to the case through an insulating gasket with a metal plate. Even when operating at full load, the transistors heat up weakly. After rectifier mains voltage there is no capacitor to smooth out the ripple, so output voltage electronic transformer when working on a load is a rectangular oscillation of 40 kHz, modulated by ripples of the mains voltage of 50 Hz. Transformer T1 (feedback transformer) - on a ferrite ring, the windings connected to the bases of the transistors contain a pair of turns, the winding connected to the junction point of the emitter and the collector of power transistors - one turn of a single-core insulated wire. In ET, transistors MJE13003, MJE13005, MJE13007 are usually used. Output transformer on a ferrite W-shaped core.
To use an electronic transformer in a pulse one, you need to connect a rectifier bridge on high-frequency high-power 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 placed on diodes KD213, KD212 or KD2999. 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.
An electronic transformer converter does not work normally without a load, so it must be used where the load is constant in current and consumes enough current to start the ET converter with confidence. 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 into the network and into the load.
Personally, I used an electronic transformer to make a switching power supply for a tube amplifier. It also seems possible to feed them with powerful ULF class A or led strip, which are just designed for sources with a voltage of 12V and a large output current. Naturally, such a tape is not connected directly, but through a current-limiting resistor or by correcting the output power of an electronic transformer.
Discuss the article SCHEME OF ELECTRONIC TRANSFORMER FOR HALOGEN LAMPS
Electronic transformers are replacing bulky steel core transformers. By itself, an electronic transformer, unlike the classical one, is a whole device - a voltage converter.
Such converters are used in lighting to power halogen lamps at 12 volts. If you repaired chandeliers with a remote control, then you probably met them.
Here is the schematic of the electronic transformer JINDEL(model GET-03) with short circuit protection.
The main power elements of the circuit are npn transistors MJE13009, which are connected according to the half-bridge scheme. They operate in antiphase at a frequency of 30 - 35 kHz. All the power supplied to the load is pumped through them - halogen lamps EL1 ... EL5. Diodes VD7 and VD8 are needed to protect transistors V1 and V2 from reverse voltage. A symmetrical dinistor (aka diac) is needed to start the circuit.
On transistor V3 ( 2N5551) and elements VD6, C9, R9 - R11, an output short-circuit protection circuit is implemented ( short circuit protection).
If a short circuit occurs in the output circuit, then the increased current flowing through the resistor R8 will cause the transistor V3 to fire. The transistor will open and block the operation of the DB3 dynistor, which starts the circuit.
Resistor R11 and electrolytic capacitor C9 prevent false protection when the lamps are turned on. At the moment 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 mains voltage 220V, a classic bridge circuit of 1.5-ampere diodes is used. 1N5399.
The inductor L2 is used as a step-down transformer. It occupies almost half of the space printed circuit board converter.
By virtue of its internal device, the electronic transformer is not recommended to be turned on without load. Therefore, the minimum power of the connected load is 35 - 40 watts. On the body of the product, the operating power range is usually indicated. For example, on the body of an electronic transformer, which is shown in the first photo, the output power range is 35 - 120 watts. Its minimum load power is 35 watts.
Halogen lamps EL1 ... EL5 (load) are best connected to an electronic transformer with wires no longer than 3 meters. Since a significant current flows through the connecting conductors, long wires increase the total resistance in the circuit. Therefore, lamps located farther 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 a significant current.
It is also worth noting that, due to their simplicity, electronic transformers are sources of high-frequency interference in the network. Usually, a filter is placed at the input of such devices, which blocks interference. As you can see from the diagram, there are no such filters in electronic transformers for halogen lamps. But in computer blocks power supplies, which are also assembled according to the half-bridge scheme and with a more complex master oscillator, such a filter is usually mounted.
When assembling a particular design, sometimes the question of a power source arises, especially if the device requires powerful block power, and without reworking it is indispensable. Nowadays, it is not difficult to find iron transformers with the required parameters, they are quite expensive, and besides, their large size and weight are their main drawback. Good switching power supplies are difficult to assemble and set up, so they are not available to many. In his release, the video blogger Aka Kasyan will show the process of building a powerful and especially simple block power supply based on an electronic transformer. Although to a greater extent this video is devoted to reworking and increasing its power. The author of the video does not have a goal to finalize or improve the circuit, he just wanted to show how you can in a simple way increase output power. In the following, if you wish, all ways to refine such circuits with protection against short circuits and other functions can be shown.
You can buy an electronic transformer from this Chinese store.
An electronic transformer with a power of 60 watts was used as an experimental one, from which the master intends to draw as many as 300 watts. In theory, everything should work.
The transformer for alterations was bought for only 100 rubles at a construction store.
Here is a classic taschibra type electronic transformer circuit. This is a simple push-pull half-bridge self-oscillating inverter with a start circuit based on a symmetrical dinistor. It is he who gives the initial impulse, as a result of which the circuit starts. There are two high voltage reverse conduction transistors. In the native circuit, there were mje13003, two half-bridge capacitors for 400 volts, o.1 uF, a feedback transformer with three windings, two of which are master or base windings. Each of them consists of 3 turns of wire 0.5 millimeters. The third winding is the current feedback.
At the input there is a small 1 ohm resistor as a fuse and a diode rectifier. Electronic transformer in spite of a simple circuit works flawlessly. This option does not have protection against short circuits, therefore, if you close the output wires, there will be an explosion - this is at least.
There is no stabilization of the output voltage, since the circuit is designed to work with a passive load in the face of office halogen lamps. The main power transformer has two - primary and secondary. The latter is designed for an output voltage of 12 volts plus or minus a couple of volts.
The first tests showed that the transformer has quite a lot of potential. Then the author found on the Internet a patented scheme for a welding inverter built almost according to such a scheme and immediately created a board for a more powerful version. I made two boards, because at the beginning I wanted to build a resistance welding machine. Everything worked without any problems, but then I decided to rewind the secondary winding to shoot this video, since the initial winding gave out only 2 volts and a huge current. And to measure such currents on this moment there is no possibility due to the lack of the necessary measuring equipment.
You have more than powerful circuit. There are even fewer details. A couple of little things were taken from the first scheme. This is a feedback transformer, a capacitor and a resistor in the start circuit, a dinistor.
Let's start with transistors. On the native board were mje13003 in the to-220 package. Were replaced by more powerful mje13009 from the same line. the diodes on the board were of the n4007 type at one ampere. I replaced the assembly with a current of 4 amperes and with a reverse voltage of 600 volts. Any diode bridges of similar parameters will do. The reverse voltage must be at least 400 volts and the current must be at least 3 amperes. Half-bridge film capacitors with a voltage of 400 volts.
I think that the advantages of this transformer have already been appreciated by many of those who have ever dealt with the problems of powering various electronic structures. And the advantages of this electronic transformer are not few. Light weight and dimensions (as with all similar circuits), ease of alteration for one's own needs, the presence of a shielded case, low cost and relative reliability (at least if extreme modes and short circuits are not allowed, a product made according to a similar circuit is able to work long years).
The range of application of power supplies based on "Tasсhibra" can be very wide, comparable to the use of conventional transformers.
Application is justified in cases of lack of time, funds, lack of need for stabilization.
Well, let's experiment, shall we? I will make a reservation right away that the purpose of the experiments was to test the Taschibra start-up circuit at various loads, frequencies and the use of various transformers. I also wanted to choose the optimal ratings of the POS circuit components and check the temperature regimes of the circuit components when working for various loads, taking into account the use of the Tasсhibra case as a radiator.
Scheme ET Taschibra (Tashibra, Tashibra)
Despite the large number of published electronic transformer circuits, I will not be too lazy to put it on display again. See fig1 illustrating the filling of "Tashibra".Excluded fragment. Our magazine exists on donations from readers. The full version of this article is only available
The scheme is valid for ET "Tashibra" 60-150W. The mockery was carried out on ET 150W. It is assumed, however, that due to the identity of the schemes, the results of experiments can be easily projected onto specimens with both lower and higher power.
And once again I remind you what is missing "Tashibra" for a full-fledged power supply.
1. The absence of an input smoothing filter (it is also an anti-interference filter that prevents conversion products from entering the network),
2. Current POS, which allows the excitation of the converter and its normal operation only in the presence of a certain load current,
3. No output rectifier,
4. Lack of output filter elements.
Let's try to fix all the listed shortcomings of "Tasсhibra" and try to achieve its acceptable operation with the desired output characteristics. To begin with, we will not even open the case of the electronic transformer, but simply add the missing elements...
1. Input filter: capacitors C`1, C`2 with a symmetrical two-winding inductor (transformer) T`1
2. diode bridge VDS`1 with smoothing capacitor C`3 and resistor R`1 to protect the bridge from the charging current of the capacitor.
A smoothing capacitor is usually selected at the rate of 1.0 - 1.5 microfarads per watt of power, and a discharge resistor with a resistance of 300-500 kOhm should be connected in parallel with the capacitor for safety (touching the terminals of a charged relatively high voltage capacitor - not very nice).
Resistor R`1 can be replaced with a 5-15Ω/1-5A thermistor. Such a replacement will reduce the efficiency of the transformer to a lesser extent.
At the output of the ET, as shown in the diagram in Fig. 3, we connect a circuit of the diode VD`1, capacitors C`4-C`5 and the inductor L1 connected between them - to obtain a filtered constant voltage at the output of the "patient". In this case, the polystyrene capacitor, placed directly behind the diode, accounts for the main share of the absorption of the conversion products after rectification. It is assumed that the electrolytic capacitor, "hidden" behind the inductance of the inductor, will perform only its direct functions, preventing the voltage "failure" at the peak power of the device connected to the ET. But in parallel with it, it is recommended to install a non-electrolytic capacitor.
After the addition of the input circuit, changes occurred in the operation of the electronic transformer: the amplitude of the output pulses (up to the VD`1 diode) increased slightly due to an increase in the voltage at the input of the device due to the addition of C`3, and modulation with a frequency of 50 Hz is practically absent. This is at the design load for ET.
However, this is not enough. "Tashibra" does not want to start without a significant load current.
Installation of load resistors at the output of the converter for the occurrence of any minimum value current, capable of starting the converter, only reduces the overall efficiency of the device. Starting at a load current of about 100mA is performed at a very low frequency, which will be quite difficult to filter if the power supply is supposed to be used with UMZCH and other audio equipment with low current consumption in no signal mode, for example. The amplitude of the pulses is also less than at full load.
The change in frequency in modes of different power is quite strong: from a couple to several tens of kilohertz. This circumstance imposes significant restrictions on the use of "Tashibra" in this (still) form when working with many devices.
But let's continue. There were proposals to connect an additional transformer to the ET output, as shown, for example, in Fig.2.
It was assumed that the primary winding of the additional transformer is capable of creating a current sufficient for normal operation. basic scheme THIS. The proposal, however, is tempting only because without disassembling the ET, with the help of an additional transformer, you can create a set of necessary (to your liking) voltages. In fact, the no-load current of the additional transformer is not enough to start the ET. Attempts to increase the current (like a 6.3VX0.3A light bulb connected to an additional winding), capable of ensuring the NORMAL operation of the ET, only led to starting the converter and lighting the light bulb.
But, perhaps, someone will be interested in this result as well. connecting an additional transformer is also true in many other cases for solving many problems. So, for example, an additional transformer can be used in conjunction with an old (but working) computer PSU, capable of providing significant output power, but having a limited (but stabilized) set of voltages.
One could continue to search for the truth in shamanism around "Tashibra", however, I considered this topic exhausted for myself, because to achieve the desired result (stable start and exit to the operating mode in the absence of load, and, therefore, high efficiency; a slight change in frequency when the PSU is operating from minimum to maximum power and stable start at maximum load) it is much more effective to get inside the Tashibra "and make all the necessary changes in the circuit of the ET itself in the way as shown in Figure 4.
Moreover, I collected about fifty similar circuits back in the days of the era of Spectrum computers (just for these computers). Various UMZCH, powered by similar PSUs, are still working somewhere. PSUs made according to this scheme proved to be the best, working, being assembled from a wide variety of components and in various versions.
Are we redoing? Of course!
Moreover, it is not difficult at all.We solder the transformer. We heat it up for ease of disassembly in order to rewind the secondary winding to obtain the desired output parameters as shown in this photo or using any other technology.
In this case, the transformer is soldered out only in order to take an interest in its winding data (by the way: W-shaped magnetic circuit with a round core, standard dimensions for computer PSUs with 90 turns of the primary winding, wound in 3 layers with a wire with a diameter of 0.65 mm and 7 turns secondary winding with a fivefold folded wire with a diameter of approximately 1.1 mm; all this without the slightest interlayer and interwinding insulation - only varnish) and make room for another transformer.
For experiments, it was easier for me to use ring magnetic circuits. They take up less space on the board, which makes it possible (if necessary) to use additional components in the body volume. In this case, we used a pair ferrite rings with external, internal diameters and height, respectively, 32X20X6mm, folded in half (without gluing) - H2000-HM1. 90 turns of the primary (wire diameter - 0.65 mm) and 2x12 (1.2 mm) turns of the secondary with the necessary winding insulation.
The communication winding contains 1 turn of the mounting wire with a diameter of 0.35 mm. All windings are wound in the order corresponding to the numbering of the windings. Insulation of the magnetic circuit itself is mandatory. In this case, the magnetic circuit is wrapped with two layers of electrical tape, reliably, by the way, fixing the folded rings.
Before installing the transformer on the ET board, we solder the current winding of the switching transformer and use it as a jumper, soldering it there, but not passing the transformer ring through the window.
We install the wound transformer Tr2 on the board, soldering the leads in accordance with the diagram in Fig. 4. and passing the winding wire III through the ring window of the switching transformer. Using the rigidity of the wire, we form a kind of geometrically closed circle and the feedback loop is ready. In the gap of the mounting wire, which forms the windings III of both (switching and power) transformers, we solder a sufficiently powerful resistor (> 1W) with a resistance of 3-10 Ohms.
In the diagram in Figure 4, standard ET diodes are not used. They should be removed, as, indeed, the resistor R1 in order to increase the efficiency of the unit as a whole. But you can also neglect a few percent efficiency and leave the listed details on the board. At least at the time of the experiments with ET, these details remained on the board. The resistors installed in the base circuits of the transistors should be left - they perform the functions of limiting the base current when the converter is started, facilitating its work on a capacitive load.
Transistors should certainly be installed on radiators through insulating heat-conducting pads (borrowed, for example, from a faulty computer PSU), thereby preventing them from accidental instantaneous heating and providing some of their own safety in case the radiator is touched during operation of the device.
By the way, the electrical cardboard used in ET to isolate transistors and the board from the case is not heat-conductive. Therefore, when "packing" the finished power supply circuit into a standard case, such gaskets should be installed between the transistors and the case. Only in this case will at least some kind of heat sink be provided. When using a converter with powers over 100W, it is necessary to install an additional heatsink on the device case. But this is so - for the future.
In the meantime, having completed the installation of the circuit, we will perform another safety point by turning on its input in series through a 150-200 W incandescent lamp. The lamp, in case of an emergency (short circuit, for example), will limit the current through the structure to a safe value and, in the worst case, will create additional illumination of the workspace.
At best, with some observation, the lamp can be used as an indicator, for example, of a through current. So, a weak (or somewhat more intense) glow of the lamp filament with an unloaded or lightly loaded converter will indicate the presence of a through current. The temperature of the key elements can serve as a confirmation - heating in the through current mode will be quite fast.
When a working converter is working, the glow of a filament of a 200-watt lamp visible against the background of daylight will appear only at the threshold of 20-35 watts.
First start
So, everything is ready for the first launch of the converted "Tashibra" scheme. We turn it on for a start - without load, but do not forget about the pre-connected voltmeter to the output of the converter and the oscilloscope. With correctly phased feedback windings, the converter should start without problems.If the start did not occur, then the wire passed into the window of the switching transformer (having previously soldered it from the resistor R5), we pass it on the other side, giving it, again, the appearance of a finished coil. Solder the wire to R5. Reapply power to the converter. Did not help? Look for errors in installation: short circuit, "non-solder", erroneously set ratings.
When starting a working converter with the specified winding data, the display of the oscilloscope connected to the secondary winding of the transformer Tr2 (in my case, to half of the winding) will display a sequence of clear rectangular pulses. The conversion frequency is selected by the resistor R5 and in my case, with R5 = 5.1 Ohm, the frequency of the unloaded converter was 18 kHz.
With a load of 20 ohms - 20.5 kHz. With a load of 12 ohms - 22.3 kHz. The load was connected directly to the instrument-controlled winding of the transformer with effective value voltage 17.5 V. The calculated voltage value was somewhat different (20 V), but it turned out that instead of the nominal value of 5.1 ohms, the resistance installed on the board R1 = 51 ohms. Be attentive to such surprises from Chinese comrades.
However, I considered it possible to continue the experiments without replacing this resistor, despite its significant but tolerable heating. When the power delivered by the converter to the load was about 25 W, the power dissipated by this resistor did not exceed 0.4 W.
As for the potential power of the PSU, at a frequency of 20 kHz, the installed transformer will be able to deliver no more than 60-65W to the load.
Let's try to increase the frequency. When the resistor (R5) with a resistance of 8.2 ohms is turned on, the frequency of the converter without load increased to 38.5 kHz, with a load of 12 ohms - 41.8 kHz.
With such a conversion frequency, with the existing power transformer, you can safely serve a load with a power of up to 120W.
You can experiment further with the resistances in the POS circuit, achieving the required frequency value, bearing in mind, however, that too much resistance R5 can lead to generation failures and unstable start-up of the converter. When changing the PIC parameters of the converter, it is necessary to control the current passing through the converter keys.
You can also experiment with the PIC windings of both transformers at your own peril and risk. In this case, you should first calculate the number of turns of the switching transformer according to the formulas posted on the page //interlavka.narod.ru/stats/Blokpit02.htm, for example, or using one of the programs of Mr. Moskatov posted on the page of his website // www.moskatov.narod.ru/Design_tools_pulse_transformers.html.
Tashibra improvement - a capacitor in the PIC instead of a resistor!
You can avoid heating the resistor R5 by replacing it with ... a capacitor. In this case, the POS circuit certainly acquires some resonant properties, but no deterioration in the operation of the PSU is manifested. Moreover, a capacitor installed instead of a resistor heats up much less than a replaced resistor. Thus, the frequency with a 220nF capacitor installed increased to 86.5 kHz (without load) and amounted to 88.1 kHz when operating on a load.
The start-up and operation of the converter remained as stable as in the case of using a resistor in the PIC circuit. Note that the potential power of the PSU at this frequency increases to 220 W (minimum).
Transformer power: values are approximate, with certain assumptions, but not overestimated.
For 18 years of work in North-West Telecom, he has manufactured many different stands for testing various equipment being repaired.
Designed several, different in functionality and element base, digital meters pulse duration.
More than 30 rationalization proposals for the modernization of units of various specialized equipment, incl. - power supply. For a long time I have been more and more engaged in power automation and electronics.
Why am I here? Yes, because everyone here is the same as me. There are a lot of interesting things for me here, since I am not strong in audio technology, but I would like to have more experience in this particular direction.
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