Application of an electronic transformer for 12V halogen lamps. Electronic transformer circuit for halogen lamps. Improvement of Tasсhibra - capacitor in PIC instead of resistor

How to power a cordless screwdriver from an electrical outlet?

The cordless screwdriver is designed for screwing and unscrewing screws, self-tapping screws, screws and bolts. It all depends on the use of replaceable heads - bits. The scope of application of a screwdriver is also very wide: it is used by furniture assemblers, electricians, construction workers - finishers use it to secure plasterboard slabs and, in general, everything that can be assembled using a threaded connection.

This is the use of a screwdriver in a professional setting. In addition to professionals, this tool is also purchased exclusively for personal use when carrying out repair and construction work in an apartment or country house, or garage.

The cordless screwdriver is lightweight, small in size, and does not require a power connection, which allows you to work with it in any conditions. But the trouble is that the battery capacity is small, and after 30 - 40 minutes intensive work you have to charge the battery for at least 3 - 4 hours.

In addition, batteries tend to become unusable, especially when the screwdriver is not used regularly: they hung up a carpet, curtains, pictures and put it in a box. A year later, we decided to screw in a plastic baseboard, but the screwdriver didn’t work, and charging the battery didn’t help much.

A new battery is expensive, and it’s not always possible to immediately find exactly what you need on sale. In both cases, there is only one way out - to power the screwdriver from the mains through the power supply. Moreover, most often the work is carried out two steps away from a power outlet. The design of such a power supply will be described below.

In general, the design is simple, does not contain scarce parts, and can be repeated by anyone who is at least a little familiar with electrical circuits and knows how to hold a soldering iron in their hands. If we remember how many screwdrivers are in use, we can assume that the design will be popular and in demand.

The power supply must satisfy several requirements at once. Firstly, it is quite reliable, and secondly, it is small-sized and light and convenient to carry and transport. The third requirement, perhaps the most important, is a falling load characteristic, which allows you to avoid damage to the screwdriver during overloads. Simplicity of design and availability of parts are also important. All these requirements are fully met by the power supply, the design of which will be discussed below.

The basis of the device is an electronic transformer of the Feron or Toshibra brand with a power of 60 watts. Such transformers are sold in electrical goods stores and are designed to power halogen lamps with a voltage of 12 V. Typically, such lamps are used to illuminate shop windows.

In this design, the transformer itself does not require any modifications; it is used as is: two input network wires and two output wires with a voltage of 12 V. The circuit diagram of the power supply is quite simple and is shown in Figure 1.

Figure 1. Schematic diagram of the power supply

Transformer T1 creates a falling characteristic of the power supply due to increased leakage inductance, which is achieved by its design, which will be discussed above. In addition, transformer T1 provides additional galvanic isolation from the network, which increases the overall electrical safety of the device, although this isolation is already present in the electronic transformer U1 itself. By selecting the number of turns of the primary winding, it is possible to regulate the output voltage of the unit as a whole within certain limits, which allows it to be used with different types screwdrivers.

The secondary winding of transformer T1 is tapped from the midpoint, which makes it possible to use a full-wave rectifier with only two diodes instead of a diode bridge. Compared to a bridge circuit, the losses of such a rectifier, due to the voltage drop across the diodes, are two times lower. After all, there are two diodes, not four. In order to further reduce power losses on diodes, a diode assembly with Schottky diodes is used in the rectifier.

Low-frequency ripples of the rectified voltage are smoothed out by electrolytic capacitor C1. Electronic transformers operate at high frequencies, about 40 - 50 KHz, therefore, in addition to ripples at the mains frequency, these high-frequency ripples are also present in the output voltage. Considering that the full-wave rectifier increases the frequency by 2 times, these ripples reach 100 kilohertz or more.

Oxide capacitors have a large internal inductance, so they cannot smooth out high-frequency ripples. Moreover, they will simply uselessly heat up the electrolytic capacitor, and may even render it unusable. To suppress these ripples, a ceramic capacitor C2 is installed in parallel with the oxide capacitor, with a small capacitance and a small self-inductance.

Indication of the operation of the power supply can be checked by the lighting of the HL1 LED, the current through which is limited by resistor R1.

Separately, it should be said about the purpose of resistors R2 - R7. The fact is that the electronic transformer was originally designed to power halogen lamps. It is assumed that these lamps are connected to the output winding of the electronic transformer even before it is connected to the network: otherwise it simply does not start without a load.

If, in the design described, you plug in the electronic transformer into the network, then pressing the screwdriver button again will not make it rotate. To prevent this from happening, resistors R2 - R7 are provided in the design. Their resistance is chosen such that the electronic transformer starts up reliably.

Details and design

The power supply is housed in the housing of a standard battery that has expired, unless, of course, it has already been thrown away. The basis of the design is an aluminum plate with a thickness of at least 3 mm, placed in the middle of the battery case. The overall design is shown in Figure 2.

Figure 2. Power supply for cordless screwdriver

All other parts are attached to this plate: electronic transformer U1, transformer T1 (on one side), and the diode assembly VD1 and all other parts, including the power button SB1, on the other. The plate also serves as a common output voltage wire, so the diode assembly is installed on it without a gasket, although for better cooling the heat-removing surface of the VD1 assembly should be lubricated with heat-removing paste KPT-8.

Transformer T1 is made on a ferrite ring of standard size 28*16*9 made of HM2000 ferrite. Such a ring is not in short supply, it is quite common, and there should be no problems with its acquisition. Before winding the transformer, first, using a diamond file or just sandpaper, you should blunt the outer and inner edges of the ring, and then insulate it with varnished cloth tape or FUM tape, used for winding heating pipes.

As mentioned above, the transformer must have a large leakage inductance. This is achieved by the fact that the windings are located opposite each other, and not one under the other. Primary winding I contains 16 turns of two wires of PEL or PEV-2 grade. Wire diameter 0.8 mm.

Secondary winding II is wound with a bundle of four wires, the number of turns is 12, the wire diameter is the same as for the primary winding. To ensure symmetry of the secondary winding, it should be wound into two wires at once, or rather a bundle. After winding, as is usually done, the beginning of one winding is connected to the end of the other. To do this, the windings will have to be “ringed” with a tester.

The MP3-1 microswitch is used as the SB1 button, which has a normally closed contact. A pusher is installed in the bottom of the power supply housing, which is connected to a button through a spring. The power supply is connected to the screwdriver, exactly the same as a standard battery.

If you now place the screwdriver on a flat surface, the pusher presses the SB1 button through a spring and the power supply turns off. As soon as the screwdriver is picked up, the released button will turn on the power supply. All you have to do is pull the screwdriver trigger and everything will work.

A little about the details

There are few parts in the power supply. It is better to use imported capacitors; this is now even easier than finding domestically produced parts. The VD1 diode assembly of type SBL2040CT (rectified current 20 A, reverse voltage 40 V) can be replaced with SBL3040CT, or, in extreme cases, with two domestic KD2997 diodes. But the diodes indicated in the diagram are not in short supply, since they are used in computer power supplies, and buying them is not a problem.

The design of transformer T1 was discussed above. Any LED you have on hand will work as an HL1 LED.

Setting up the device is simple and comes down to simply unwinding the turns of the primary winding of transformer T1 to achieve the desired output voltage. The rated supply voltage of screwdrivers, depending on the model, is 9, 12 and 19 V. By unwinding the turns from transformer T1, 11, 14 and 20 V should be achieved, respectively.

Externally electronic transformer It is a small metal, usually aluminum, case, the halves of which are fastened together with only two rivets. However, some companies produce similar devices in plastic cases.

To see what's inside, these rivets can simply be drilled out. The same operation will have to be performed if alteration or repair of the device itself is planned. Although, given its low price, it is much easier to go and buy another one than to repair the old one. And yet, there were many enthusiasts who not only managed to understand the structure of the device, but also developed several switching power supplies based on it.

A schematic diagram is not included with the device, as with all current electronic devices. But the diagram is quite simple, contains a small number of parts and therefore schematic diagram an electronic transformer can be copied from a printed circuit board.

Figure 1 shows a diagram of a Taschibra transformer taken in a similar way. Converters manufactured by Feron have a very similar circuit. The only difference is in the design of the printed circuit boards and the types of parts used, mainly transformers: in Feron converters the output transformer is made on a ring, while in Taschibra converters it is on an W-shaped core.

In both cases, the cores are made of ferrite. It should be immediately noted that ring-shaped transformers, with various modifications of the device, are better rewindable than W-shaped ones. Therefore, if an electronic transformer is purchased for experiments and modifications, it is better to buy a device from Feron.

When using an electronic transformer only to power halogen lamps, the name of the manufacturer does not matter. The only thing you should pay attention to is the power: electronic transformers are available with a power of 60 - 250 W.

Figure 1. Diagram of an electronic transformer from Taschibra

Brief description of the electronic transformer circuit, its advantages and disadvantages

As can be seen from the figure, the device is a push-pull self-oscillator made according to a half-bridge circuit. The two arms of the bridge are made of transistors Q1 and Q2, and the other two arms contain capacitors C1 and C2, so this bridge is called a half bridge.

One of its diagonals is supplied with mains voltage, rectified by a diode bridge, and the other is connected to the load. In this case, this is the primary winding of the output transformer. Electronic ballasts for energy-saving lamps are made according to a very similar scheme, but instead of a transformer they include a choke, capacitors and filaments of fluorescent lamps.

To control the operation of transistors, windings I and II of the transformer are included in their basic circuits feedback T1. Winding III is the current feedback; the primary winding of the output transformer is connected through it.

The control transformer T1 is wound on a ferrite ring with an outer diameter of 8 mm. Basic windings I and II contain 3..4 turns each, and feedback winding III contains only one turn. All three windings are made of wires in multi-colored plastic insulation, which is important when experimenting with the device.

The elements R2, R3, C4, D5, D6 assemble the circuit for starting the autogenerator at the moment the entire device is connected to the network. The mains voltage rectified by the input diode bridge charges capacitor C4 through resistor R2. When the voltage across it exceeds the operating threshold of dinistor D6, the latter opens and a current pulse is formed at the base of transistor Q2, which starts the converter.

Further work is carried out without the participation of the starting circuit. It should be noted that the D6 dinistor is double-sided and can operate in alternating current circuits; in the case of direct current, the polarity of the connection does not matter. On the Internet it is also called “diak”.

The mains rectifier is made of four 1N4007 type diodes, resistor R1 with a resistance of 1 Ohm and a power of 0.125 W is used as a fuse.

The converter circuit as it is is quite simple and does not contain any “excesses”. After the rectifier bridge there is not even a simple capacitor provided to smooth out the ripples of the rectified mains voltage.

The output voltage directly from the output winding of the transformer is also supplied directly to the load without any filters. There are no circuits for stabilizing the output voltage and protection, so in the event of a short circuit in the load circuit, several elements burn out at once, as a rule, these are transistors Q1, Q2, resistors R4, R5, R1. Well, maybe not all at once, but at least one transistor for sure.

And despite this seemingly imperfection, the scheme fully justifies itself when used in normal mode, i.e. for powering halogen lamps. The simplicity of the circuit determines its low cost and widespread use of the device as a whole.

Study of the operation of electronic transformers

If you connect a load to an electronic transformer, for example, a 12V x 50W halogen lamp, and connect an oscilloscope to this load, then on its screen you will see the picture shown in Figure 2.

Figure 2. Oscillogram of the output voltage of the Taschibra 12Vx50W electronic transformer

The output voltage is a high-frequency oscillation with a frequency of 40KHz, modulated 100% by a frequency of 100Hz, obtained after rectifying the mains voltage with a frequency of 50Hz, which is quite suitable for powering halogen lamps. Exactly the same picture will be obtained for converters of a different power or from a different company, because the circuits are practically no different from each other.

If you connect an electrolytic capacitor C4 47uFx400V to the output of the rectifier bridge, as shown by the dotted line in Figure 4, then the voltage at the load will take the form shown in Figure 4.

Figure 3. Connecting a capacitor to the output of the rectifier bridge

However, we should not forget that the charging current of the additionally connected capacitor C4 will lead to the burnout, and quite noisy, of resistor R1, which is used as a fuse. Therefore, this resistor should be replaced with a more powerful resistor with a rating of 22Ohmx2W, the purpose of which is simply to limit the charging current of capacitor C4. As a fuse, you should use a regular 0.5A fuse.

It is easy to see that the modulation with a frequency of 100 Hz has ceased, leaving only high-frequency oscillations with a frequency of about 40 kHz. Even if during this study it is not possible to use an oscilloscope, this indisputable fact can be noticed by a slight increase in the brightness of the light bulb.

This suggests that the electronic transformer is quite suitable for creating simple switching power supplies. There are several options here: using the converter without disassembling, only by adding external elements and with minor changes to the circuit, very small, but giving the converter completely different properties. But we will talk about this in more detail in the next article.

How to make a power supply from an electronic transformer?

After everything that has been said in the previous article (see How does an electronic transformer work?), it seems that making a switching power supply from an electronic transformer is quite simple: put a rectifier bridge, a smoothing capacitor, and, if necessary, a voltage stabilizer at the output and connect the load. However, this is not quite true.

The fact is that the converter does not start without a load or the load is not sufficient: if you connect an LED to the output of the rectifier, of course, with a limiting resistor, you will be able to see only one LED flash when turned on.

To see another flash, you will need to turn off and turn on the converter to the network. In order for the flash to turn into a constant glow, you need to connect an additional load to the rectifier, which will simply take away the useful power, turning it into heat. Therefore, this scheme is used when the load is constant, for example, a motor direct current or an electromagnet, the control of which will be possible only through the primary circuit.

If the load requires a voltage of more than 12V, which is produced by electronic transformers, you will need to rewind the output transformer, although there is a less labor-intensive option.

Option for manufacturing a switching power supply without disassembling the electronic transformer

The diagram of such a power supply is shown in Figure 1.

Picture 1. Bipolar block power supply for amplifier

The power supply is made on the basis of an electronic transformer with a power of 105W. To manufacture such a power supply, you will need to make several additional elements: a mains filter, matching transformer T1, output choke L2, rectifier bridge VD1-VD4.

The power supply has been operating for several years with a ULF power of 2x20W without any complaints. With a nominal network voltage of 220V and a load current of 0.1A, the output voltage of the unit is 2x25V, and when the current increases to 2A, the voltage drops to 2x20V, which is quite enough for normal operation of the amplifier.

The matching transformer T1 is made on a K30x18x7 ring made of M2000NM ferrite. The primary winding contains 10 turns of PEV-2 wire with a diameter of 0.8 mm, folded in half and twisted into a bundle. The secondary winding contains 2x22 turns with a midpoint, the same wire, also folded in half. To make the winding symmetrical, you should wind it in two wires at once - a bundle. After winding, to obtain the midpoint, connect the beginning of one winding to the end of the other.

You will also have to make the inductor L2 yourself; for its manufacture you will need the same ferrite ring as for the transformer T1. Both windings are wound with PEV-2 wire with a diameter of 0.8 mm and contain 10 turns.

The rectifier bridge is assembled on KD213 diodes, you can also use KD2997 or imported ones, it is only important that the diodes are designed for an operating frequency of at least 100 KHz. If instead of them you put, for example, KD242, then they will only heat up, and you will not be able to get the required voltage from them. The diodes should be installed on a radiator with an area of ​​at least 60 - 70 cm2, using insulating mica spacers.

Electrolytic capacitors C4, C5 are made up of three parallel-connected capacitors with a capacity of 2200 microfarads each. This is usually done in all switching power supplies in order to reduce the overall inductance of the electrolytic capacitors. In addition, it is also useful to install ceramic capacitors with a capacity of 0.33 - 0.5 μF in parallel with them, which will smooth out high-frequency vibrations.

At the input of the power supply it is useful to install the input network filter, although it will work without it. As an input filter choke, a ready-made DF50GTs choke was used, which was used in 3USTST TVs.

All units of the block are mounted on a board made of insulating material in a hinged manner, using the pins of the parts for this purpose. The entire structure should be placed in a shielding case made of brass or tin, with holes provided for cooling.

A correctly assembled power supply does not require adjustment and starts working immediately. Although, before placing the block in the finished structure, you should check it. To do this, a load is connected to the output of the block - resistors with a resistance of 240 Ohms, with a power of at least 5 W. It is not recommended to turn on the unit without load.

Another way to modify an electronic transformer

There are situations when you want to use a similar switching power supply, but the load turns out to be very “harmful”. The current consumption is either very small or varies widely, and the power supply does not start.

A similar situation arose when they tried to install a lamp or chandelier with built-in electronic transformers instead of halogen lamps. LED. The chandelier simply refused to work with them. What to do in this case, how to make it all work?

To understand this issue, let's look at Figure 2, which shows a simplified circuit of an electronic transformer.

Figure 2. Simplified circuit of an electronic transformer

Let's pay attention to the winding of the control transformer T1, highlighted by a red stripe. This winding provides current feedback: if there is no current through the load, or it is simply small, then the transformer simply does not start. Some citizens who bought this device connect a 2.5W light bulb to it, and then take it back to the store, saying it doesn’t work.

And yet, in a fairly simple way, you can not only make the device work with virtually no load, but also provide short circuit protection in it. The method of such modification is shown in Figure 3.

Figure 3. Modification of the electronic transformer. Simplified diagram.

In order for the electronic transformer to operate without load or with minimal load, current feedback should be replaced with voltage feedback. To do this, remove the current feedback winding (highlighted in red in Figure 2), and instead solder a jumper wire into the board, naturally, in addition to the ferrite ring.

Next, a winding of 2 - 3 turns is wound onto the control transformer Tr1, this is the one on the small ring. And there is one turn per output transformer, and then the resulting additional windings are connected as indicated in the diagram. If the converter does not start, then you need to change the phasing of one of the windings.

The resistor in the feedback circuit is selected within the range of 3 - 10 Ohms, with a power of at least 1 W. It determines the depth of feedback, which determines the current at which generation will fail. Actually, this is the current of short-circuit protection. The greater the resistance of this resistor, the lower the load current the generation will fail, i.e. short circuit protection triggered.

Of all the improvements given, this is perhaps the best. But this will not prevent you from supplementing it with another transformer, as in the circuit in Figure 1.

Electronic transformers: purpose and typical use

Application of electronic transformer

In order to improve the electrical safety conditions of lighting systems, in some cases it is recommended to use lamps not with a voltage of 220V, but much lower. As a rule, such lighting is installed in damp rooms: basements, cellars, bathrooms.

For these purposes, they are currently mainly used halogen lamps with operating voltage 12V. These lamps are powered through electronic transformers, the internal structure of which will be discussed a little later. In the meantime, a few words about the normal use of these devices.

Externally, the electronic transformer is a small metal or plastic box from which 4 wires come out: two input wires labeled ~220V, and two output wires ~12V.

Everything is quite simple and clear. Electronic transformers allow brightness adjustment using dimmers(thyristor regulators) of course from the input voltage side. It is possible to connect several electronic transformers to one dimmer at once. Naturally, switching on without regulators is also possible. Typical circuit diagram for connecting an electronic transformer shown in Figure 1.

Figure 1. Typical circuit diagram for connecting an electronic transformer.

The advantages of electronic transformers, first of all, include their small dimensions and weight, which allows them to be installed almost anywhere. Some models of modern lighting devices designed to work with halogen lamps contain built-in electronic transformers, sometimes even several of them. This scheme is used, for example, in chandeliers. There are known options when electronic transformers are installed in furniture to provide internal lighting for shelves and hangers.

For indoor lighting, transformers can be installed behind a suspended ceiling or behind plasterboard wall coverings in close proximity to halogen lamps. At the same time, the length of the connecting wires between the transformer and the lamp is no more than 0.5 - 1 meter, which is due to high currents (at a voltage of 12V and a power of 60W, the current in the load is at least 5A), as well as the high-frequency component of the output voltage of the electronic transformer.

The inductive reactance of a wire increases with frequency and also with its length. Basically, the length determines the inductance of the wire. In this case, the total power of the connected lamps should not exceed that indicated on the label of the electronic transformer. To increase the reliability of the entire system as a whole, it is better if the power of the lamps is 10 - 15% lower than the power of the transformer.

Rice. 2. Electronic transformer for halogen lamps from OSRAM

That's probably all that can be said about the typical use of this device. There is one condition that should not be forgotten: electronic transformers do not start without load. Therefore, the light bulb must be permanently connected, and the lighting must be turned on with a switch installed in the primary network.

But the scope of application of electronic transformers is not limited to this: simple modifications, often without even requiring opening the case, make it possible to create switching power supplies (UPS) based on an electronic transformer. But before talking about this, you should take a closer look at the structure of the transformer itself.

In the next article we will take a closer look at one of the electronic transformers from Taschibra, and also conduct a small study of the operation of the transformer.

Transformers for halogen lamps

Spot recessed lamps Today they have become the same everyday normal thing in the interior of a house, apartment, or office as an ordinary chandelier or fluorescent lamp.

Many people have probably noticed that sometimes light bulbs, if there are several of them, glow differently in these same spotlights. Some lamps shine quite brightly, while others burn, at best, at half incandescence. In this article we will try to understand the essence of the problem.

So, first, a little theory. Halogen bulbs installed in recessed spotlights are designed for operating voltages of 220 V and 12 V. In order to connect light bulbs designed for a voltage of 12 V, a special transformer device is required.

Transformers for halogen lamps presented on our market are mostly electronic. There are also toroidal transformers, but in this article we will not dwell on them. We only note that they are more reliable than electronic ones, but provided that you have relatively stable voltage, and the transformer-lamp power is correctly balanced.

An electronic transformer for halogen lamps has a number of advantages compared to a conventional transformer. These advantages include: soft start (not all trans have it), short circuit protection (also not all), light weight, small size, constant output voltage (most), automatic adjustment of the output voltage. But all this will work correctly only with proper installation.

It just so happens that many self-taught electricians or people who lay wires read few books on electrical engineering, much less the instructions that come with almost all devices, in this case step-down transformers. In this very instruction it is written in black and white that:

1) the length of the wire from the transformer to the lamp should be no more than 1.5 meters, provided that the cross-section of the wire is at least 1 mm square.

2) if it is necessary to connect 2 or more lamps to one transformer, the connection is made according to the “star” circuit;

3) if you need to increase the length of the wire from the transformer to the lamp, then it is necessary to increase the cross-section of the wire in proportion to the length;

Following these simple rules will save you from many questions and problems that arise during the lighting installation process.

Without going too much into the laws of physics, let’s consider each of the points.

1) If you increase the length of the wires, the lamp will shine more dimly, and the wire may begin to heat up.

2) What is a star circuit? This means that a separate wire should be drawn to each lamp and, importantly, the length of all wires should be the same length, regardless of the distance transformer->lamp, otherwise the glow of all lamps will be different.

4) Each transformer for halogen lamps is designed for a certain power. There is no need to take a 300 W transformer and power a 20 W light bulb onto it.

Firstly, it’s pointless and secondly, there will be no coordination between the transformer and the lamp, and something from this chain will definitely burn out. It's just a matter of time.

For example, for a transformer with a power of 105 W, you can use 3 lamps of 35 W, 5 of 20 W, but this is subject to the use of high-quality transformers.

The reliability of a transformer largely depends on the manufacturer. Most of the electrical equipment presented on our market is manufactured, you know where, in China. The price, as a rule, corresponds to the quality. When choosing a transformer, carefully read the instructions (if any), or what is written on the box or the transformer itself.

As a rule, the manufacturer writes the maximum power that this device is capable of. In practice, it is necessary to subtract about 30% from this figure, then there is a chance that the transformer will last for some time.

If all the wiring has already been done and it is not possible to redo the wiring according to the “star” circuit, the best option would be to power each light bulb with its own separate transformer. At first, this will cost a little more than one trans for 3-4 lamps, but later, during operation, you will understand the advantages of this scheme.

What is the advantage? If one transformer fails, only one light bulb will not light, which, you see, is quite convenient, because the main lighting still remains in operation.

If you need to regulate the light intensity, that is, use a dimmer, you will have to abandon the electronic transformer, since most electronic transformers are not designed to work with a dimmer. In this case, you can use a toroidal step-down transformer.

If it seems a little expensive for you to “hang” a separate transformer on each light bulb, instead of light bulbs designed for 12 V, install 220 V lamps, equipping them with a soft start device, or, if the design of the lamps allows, change the lamps to others, to For example, MR-16 LED economy lamps. We described this in more detail in a previous article.

When choosing a transformer for halogen light bulbs, opt for high-quality, more expensive transformers. Such transformers are equipped with a variety of protections: against short circuits, against overheating, and are equipped with a soft start device for lamps, which significantly extends the life of the lamps by 2-3 times. And, in addition, high-quality transformers undergo many checks for operational safety, fire safety, and compliance with European standards, which cannot be said about cheaper models, which, for the most part, appear from nowhere.

In any case, it is better to entrust all rather complex technical issues, which include the choice of transformers for halogen lamps, to professionals.

Device smooth start incandescent lamps

Principle of operation of this device and the benefits of using it.

As is known, incandescent lamps and the so-called halogen lamps very often they fail. This is often due to unstable mains voltage and very frequent switching on of the lamps. Even if low-voltage lamps (12 volts) are used through a step-down transformer, frequent switching on of the lamps still leads to their rapid combustion. For more long term service of incandescent lamps, a device for smoothly switching on lamps was invented.

A device for soft starting of incandescent lamps ignites the lamp filament more slowly (2-3 seconds), thereby eliminating the possibility of lamp failure at the moment the filament is heated.

As is known in most cases incandescent lamps fail at the moment of switching on, by eliminating this moment, we will significantly extend the service life of incandescent lamps.

It is also necessary to take into account that when passing through the device for smooth switching of lamps, the network voltage stabilizes, and the lamp is not affected by sudden voltage surges.

Soft starters for lamps can be used with both 220-volt lamps and lamps operating through a step-down transformer. In both cases, the device for smoothly switching on lamps is installed in an open circuit (phase).

Please remember that when using the device in conjunction with step-down transformer, it must be installed before the transformer.

You can install the device for smooth switching of lamps in any accessible place, be it a junction box, a chandelier connector, a switch, or a recessed lamp.

It is not recommended to install in rooms with high humidity. Each individual device must be selected depending on the load that it will support; a soft-start device cannot be installed for lamps with an installed power lower than that of all the lamps it protects. You cannot use the device for smooth switching of lamps with fluorescent lamps.

By installing a device for smooth switching of lamps, you will forget for a long time about the problem of replacing halogen and incandescent lamps.

Many novice radio amateurs, and not only those, face problems in the manufacture of powerful power supplies. Nowadays a large number of electronic transformers have appeared on sale, used to power halogen lamps. The electronic transformer is a half-bridge self-oscillating pulse voltage converter. Pulse converters have high efficiency, small size and weight. These products are not expensive, about 1 ruble per watt. After modification they can be used experience in remaking the electronic transformer Taschibra 105W. Let's consider the circuit diagram of an electronic converter. The mains voltage is supplied through a fuse to the diode bridge D1-D4. The rectified voltage supplies half-bridge converter based on transistors Q1 and Q2. In the diagonal of the bridge formed by these transistors and capacitors C1, C2, winding I of the pulse transformer T2 is turned on. Starting the inverter is provided by a circuit consisting of resistors R1, R2, capacitor C3, diode D5 and diac D6. Transformer feedback T1 has three windings - the current feedback winding, which is connected in series with the primary winding of the power transformer, and two windings of 3 turns, feeding the base circuits of the transistors. The output voltage of the electronic transformer is rectangular pulses with a frequency 30 kHz modulated at 100 Hz. In order to use an electronic transformer as a power source, it must be finalize. We connect a capacitor at the output of the rectifier bridge to smooth out the ripples of the rectified voltage. The capacitance is selected at the rate of 1 µF per 1 W. The operating voltage of the capacitor should not be less than 400V. When a rectifier bridge with a capacitor is connected to the network, an inrush current occurs, so you need to break turn on one of the network wires an NTC thermistor or a 4.7 Ohm 5W resistor. This will limit the starting current. If a different output voltage is needed, we rewind the secondary winding of the power transformer. The diameter of the wire (harness of wires) is selected based on the load current. Electronic transformers are current feedback, so the output voltage will vary depending on from the load. If the load is not connected, the transformer will not start. In order for this not to happen, it is necessary change the current feedback circuit to the voltage feedback circuit. We remove the current feedback winding and replace it with a jumper on the board. Then we skip flexible stranded wire through a power transformer and make 2 turns, then pass the wire through feedback transformer and make one turn. The ends passed through a power transformer and the feedback transformer wires, we connect through two parallel connected resistors 6.8 Ohm 5 W. This current-limiting resistor sets the conversion frequency (approximately 30 kHz). As the load current increases, the frequency becomes higher. If the converter does not start, you need to change the winding direction. In Taschibra transformers, the transistors are pressed to the housing through cardboard, which is unsafe during operation. In addition, paper conducts heat very poorly. Therefore, it is better to install transistors through a heat-conducting gasket To rectify alternating voltage with a frequency of 30 kHz at the output of an electronic transformer install a diode bridge. The best results were shown, of all the tested diodes, by domestic ones KD213B (200V; 10A; 100 kHz; 0.17 µs). At high load currents they heat up, so they need to be install on the radiator through heat-conducting gaskets. Electronic transformers do not work well with capacitive loads or do not start at all. For normal operation, a smooth startup of the device is necessary. Ensuring a smooth start helps throttle L1. Together with a 100uF capacitor, it also performs the function of filtering rectified voltage. Inductor L1 50 μG is wound on a T106-26 core from Micrometals and contains 24 turns of 1.2 mm wire. Such cores (yellow, with one white edge) are used in computer power supplies. External diameter 27mm, internal 14mm, and height 12mm. By the way, in dead power supplies you can also find other parts, including a thermistor. If you have a screwdriver or other tool that accumulator battery developed its own resource, then a power supply from an electronic transformer can be placed in the housing of this battery. As a result, you will have a network-powered tool. For stable operation, it is advisable to install a resistor of approximately 500 Ohm 2W at the output of the power supply. During the process of setting up a transformer, you need to be extremely careful and careful. There is high voltage on the device elements. Do not touch the transistor flanges, to check if they are heating up or not. It is also necessary to remember that after switching off the capacitors remain charged for some time.

Experiments with electronic transformer "Tashibra"

0 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 this electronic transformer has many advantages. Light weight and dimensions (as with all similar circuits), ease of modification to suit your own needs, the presence of a shielding housing, low cost and relative reliability (at least, if extreme conditions and short circuits are avoided, a product made according to a similar circuit can work long years). The range of application of power supplies based on "Tashibra" can be very wide, comparable to the use of conventional transformers.
The use is justified in cases of shortage of time, funds, or lack of need for stabilization.
Well, shall we experiment? Let me make a reservation right away that the purpose of the experiments was to test the Tashibra starting circuit under various loads, frequencies and the use of various transformers. I also wanted to select the optimal ratings of the components of the PIC circuit and check the temperature conditions of the circuit components when operating under various loads, taking into account the use of the “Tashibra” case as a radiator.
Despite the large number of published electronic transformer circuits, I will not be too lazy to once again post it for review. Look at Fig.1, illustrating the "Tashibra" filling.

The diagram 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 circuits, the results of the experiments can be easily projected onto instances of both lower and higher power.
And let me remind you once again what Tashibra is missing for a full-fledged power supply.
1. Lack of an input smoothing filter (also an anti-interference filter, which prevents conversion products from entering the network),
2. Current PIC, which allows 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 correct all of the listed shortcomings of "Tashibra" and try to achieve its acceptable operation with the desired output characteristics. To begin with, we won’t even open the housing of the electronic transformer, but simply add the missing elements...

1. Input filter: capacitors C`1, C`2 with a symmetrical two-winding choke (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 µF per watt of power, and a discharge resistor with a resistance of 300-500 kOhm should be connected in parallel to 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 5-15Ohm/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 diode VD`1, capacitors C`4-C`5 and inductor L1 connected between them to obtain a filtered DC voltage at the “patient” output. In this case, the polystyrene capacitor placed directly behind the diode accounts for the main share of absorption of 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 voltage “dip” at the peak power of the device connected to the ET. But it is also recommended to install a non-electrolytic capacitor in parallel with it.

After adding the input circuit, changes occurred in the operation of the electronic transformer: the amplitude of the output pulses (up to the diode VD`1) increased slightly due to the 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 was practically absent. This is at the load calculated for the electric vehicle.
However, this is not enough. "Tashibra" does not want to start without significant load current.
Installing load resistors at the output of the converter to create any minimum current value capable of starting the converter only reduces the overall efficiency of the device. Starting at a load current of about 100 mA is carried out at a very low frequency, which will be quite difficult to filter if the power supply is intended for joint use with UMZCH and other audio equipment with low current consumption in the no-signal mode, for example. The amplitude of the pulses is also less than at full load. The change in frequency in different power modes is quite strong: from a couple to several tens of kilohertz. This circumstance imposes significant restrictions on the use of "Tashibra" in this (for now) form when working with many devices.
But let's continue.
There have been 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 the normal operation of the basic ET circuit. The offer, however, is tempting only because without disassembling the electric transformer, using 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 electric vehicle. Attempts to increase the current (like a 6.3VX0.3A light bulb connected to an additional winding) capable of providing NORMAL work ET, led only to starting the converter and lighting the light bulb. But perhaps someone will be interested in this result, because... connecting an additional transformer is also true in many other cases to solve many problems. So, for example, an additional transformer can be used in conjunction with an old (but working) computer power supply, capable of providing significant output power, but having a limited (but stabilized) set of voltages.

One could continue to search for the truth in the shamanism around "Tashibra", however, I considered this topic exhausted for myself, because to achieve the required result (stable start-up and return to operating mode in the absence of load, and, therefore, high efficiency; a slight change in frequency when the power supply is operating from minimum to maximum power and stable startup at maximum load) it is much more effective to get inside the “Tashibra” and make all the necessary changes in the circuit of the electric vehicle itself in the manner shown in Fig. 4. Moreover,
I collected about fifty similar circuits back in the era of Spectrum computers (specifically for these computers). Various UMZCHs, powered by similar power supplies, are still working somewhere. PSUs made according to this scheme showed their best performance, working while being assembled from a wide variety of components and in various options.

Are we redoing it? Certainly. Moreover, it is not at all difficult.

We solder the transformer. We warm 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 only in order to inquire about its winding data (by the way: W-shaped magnetic core with a round core, standard dimensions for computer power supplies 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 wire folded five times with a diameter of approximately 1.1 mm; all this without the slightest interlayer and interwinding insulation - just varnish) and make room for another transformer. For experiments, it was easier for me to use ring magnetic cores. They take up less space on the board, which makes it possible (if necessary) to use additional components in the volume of the case. In this case, a pair of ferrite rings with outer and inner diameters and heights of 32x20x6mm, respectively, folded in half (without gluing) - N2000-NM1 - was used. 90 turns of the primary (wire diameter - 0.65 mm) and 2X12 (1.2 mm) turns of the secondary with the necessary inter-winding insulation. The communication winding contains 1 turn of 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 in two layers of electrical tape, by the way, securely fixing the folded rings.

Before installing the transformer on the ET board, we unsolder the current winding of the commutating transformer and use it as a jumper, soldering it there, but without passing the transformer rings through the window. We install the wound transformer Tr2 on the board, soldering the leads in accordance with the diagram in Fig. 4

and pass the wire of winding III into the window of the commutating transformer ring. Using the rigidity of the wire, we form a semblance of a geometrically closed circle and the feedback loop is ready. In the gap in the mounting wire that forms windings III of both (switching and power) transformers, we solder a fairly powerful resistor (>1W) with a resistance of 3-10 Ohms.

In the diagram in Fig. 4, standard ET diodes are not used. They should be removed, as should resistor R1, in order to increase the efficiency of the unit as a whole. But you can neglect a few percent of the efficiency and leave the listed parts on the board. At least at the time of the experiments with ET, these parts 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 starting the converter, facilitating its operation on a capacitive load.
Transistors should definitely be installed on radiators through insulating heat-conducting gaskets (borrowed, for example, from a faulty computer power supply), thereby preventing them

accidental instant heating and providing some personal safety in case of touching the radiator while the device is operating. By the way, the electrical cardboard used in ET to insulate transistors and the board from the case is not thermally conductive. Therefore, when “packing” the finished power supply circuit into a standard case, exactly these gaskets should be installed between the transistors and the case. Only in this case will at least some heat removal be ensured. When using a converter with powers over 100W, an additional radiator must be installed on the device body. But this is for the future.
In the meantime, having finished installing the circuit, let’s perform one more safety point by connecting its input in series through an incandescent lamp with a power of 150-200W. The lamp, in the event of an emergency (short circuit, for example), will limit the current through the structure to a safe value and, in the worst case, create additional illumination of the work space. In the best case, with some observation, the lamp can be used as an indicator, for example, of through current. Thus, 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 confirmation - heating in through-current mode will be quite fast. When a working converter is operating, the glow of a 200-watt lamp filament, visible against the background of daylight, will appear only at the threshold of 20-35 W.
So, everything is ready for the first launch of the converted "Tashibra" circuit. To begin with, we turn it on - without load, but do not forget about the pre-connected voltmeter to the output of the converter and an oscilloscope. With correctly phased feedback windings, the converter should start without problems. If the start-up does not occur, then we pass the wire passed through the window of the commutating transformer (having previously unsoldered it from resistor R5) on the other side, giving it, again, the appearance of a completed turn. Solder the wire to R5. Apply power to the converter again. Did not help? Look for errors in installation: short circuit, “missing connections”, erroneously set values.
When a working converter is started with the specified winding data, the display of an oscilloscope connected to the secondary winding of transformer Tr2 (in my case, half of the winding) will display a time-invariant sequence of clear rectangular pulses. The conversion frequency is selected by resistor R5 and in my case, with R5 = 5.1Ohm, the frequency of the unloaded converter was 18 kHz. With a load of 20 Ohm - 20.5 kHz. With a load of 12 Ohm - 22.3 kHz. The load was connected directly to the instrument-controlled winding of the transformer with an effective voltage value of 17.5V. The calculated voltage value was slightly different (20V), but it turned out that instead of the nominal value of 5.1 Ohm, the resistance installed on the board R1 = 51 Ohm. Be attentive to such surprises from your 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 power supply, at a frequency of 20 kHz the installed transformer will be able to deliver no more than 60-65 W to the load.
Let's try to increase the frequency. When the resistor (R5) with a resistance of 8.2 Ohm is turned on, the frequency of the converter without load increases to 38.5 kHz, with a load of 12 Ohm - 41.8 kHz.

At this conversion frequency, with the existing power transformer, you can safely service a load of up to 120 W.
You can further experiment with the resistances in the PIC circuit, achieving the required frequency value, keeping in mind, however, that too high a resistance R5 can lead to generation failures and unstable startup of the converter. When changing the parameters of the PIC converter, you should 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 commutating transformer using the formulas posted on the page /stats/Blokpit02.htm, for example, or using one of Mr. Moskatov’s programs posted on the page of his website /Design_tools_pulse_transformers.html.
You can avoid heating resistor R5 by replacing it... with a capacitor.

In this case, the PIC circuit certainly acquires some resonant properties, but no deterioration in the operation of the power supply is manifested. Moreover, a capacitor installed instead of a resistor heats up significantly less than the 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 with a load. Startup and operation

the converter remained as stable as in the case of using a resistor in the PIC circuit. Note that the potential power of the power supply at such a frequency increases to 220 W (minimum).
Transformer power: values ​​are approximate, with certain assumptions, but not exaggerated.
Unfortunately, I did not have the opportunity to test a power supply with a large load current, but I believe that the description of the experiments performed is enough to draw the attention of many to such simple power converter circuits, worthy of use in a wide variety of designs .
I apologize in advance for possible inaccuracies, omissions and errors. I'll correct myself in answering your questions.

How to make a switching power supply from a burnt-out light bulb in an hour?

In this article you will find a detailed description of the process of manufacturing switching power supplies of different powers based on the electronic ballast of a compact fluorescent lamp.

You can make a switching power supply for 5...20 Watts in less than an hour. It will take several hours to make a 100-watt power supply./

Building a power supply won't be much more difficult than reading this article. And certainly, it will be easier than finding a low-frequency transformer of suitable power and rewinding its secondary windings to suit your needs.

Introduction.

The difference between a CFL circuit and a pulse power supply.

What power power supply can be made from CFLs?

Pulse transformer for power supply.

Input filter capacitance and voltage ripple.

20 Watt power supply.

100 watt power supply

Rectifier.

How to properly connect a switching power supply to the network?

How to set up a switching power supply?

What is the purpose of the switching power supply circuit elements?

Introduction.

Compact Fluorescent Lamps (CFLs) are now widely used. To reduce the size of the ballast choke, they use a high-frequency voltage converter circuit, which can significantly reduce the size of the choke.

If the electronic ballast fails, it can be easily repaired. But when the bulb itself fails, the light bulb is usually thrown away.

However, the electronic ballast of such a light bulb is an almost ready-made switching power supply unit (PSU). The only way the electronic ballast circuit differs from a real pulse power supply is the absence of an isolation transformer and a rectifier, if necessary./

At the same time, modern radio amateurs experience great difficulty in finding power transformers to power their homemade products. Even if a transformer is found, its rewinding requires the use of a large amount of copper wire, and the weight and dimensions of products assembled on the basis of power transformers are not encouraging. But in the vast majority of cases, the power transformer can be replaced with a switching power supply. If you use ballast from faulty CFLs for these purposes, the savings will amount to a significant amount, especially if we are talking about transformers of 100 watts or more.

It is a small metal, usually aluminum, case, the halves of which are fastened together with only two rivets. However, some companies produce similar devices in plastic cases.

To see what's inside, these rivets can simply be drilled out. The same operation will have to be performed if alteration or repair of the device itself is planned. Although, given its low price, it is much easier to go and buy another one than to repair the old one. And yet, there were many enthusiasts who not only managed to understand the structure of the device, but also developed several based on it.

A schematic diagram is not included with the device, as with all current electronic devices. But the circuit is quite simple, contains a small number of parts, and therefore the circuit diagram of an electronic transformer can be copied from a printed circuit board.

Figure 1 shows a diagram of a Taschibra transformer taken in a similar way. Converters manufactured by Feron have a very similar circuit. The only difference is in the design printed circuit boards and the types of parts used, mainly transformers: in Feron converters the output transformer is made on a ring, while in Taschibra converters it is on an W-shaped core.

In both cases, the cores are made of ferrite. It should be immediately noted that ring-shaped transformers, with various modifications of the device, are better rewindable than W-shaped ones. Therefore, if an electronic transformer is purchased for experiments and modifications, it is better to buy a device from Feron.

When using an electronic transformer only for power supply, the name of the manufacturer does not matter. The only thing you should pay attention to is the power: electronic transformers are available with a power of 60 - 250 W.

Figure 1. Diagram of an electronic transformer from Taschibra

Brief description of the electronic transformer circuit, its advantages and disadvantages

As can be seen from the figure, the device is a push-pull self-oscillator made according to a half-bridge circuit. The two arms of the bridge are Q1 and Q2, and the other two arms contain capacitors C1 and C2, so this bridge is called a half bridge.

One of its diagonals is supplied with mains voltage, rectified by a diode bridge, and the other is connected to the load. In this case, this is the primary winding of the output transformer. They are made according to a very similar scheme, but instead of a transformer they include a choke, capacitors and filaments of fluorescent lamps.

After rummaging around on the Internet and reading more than one article and discussion on the forum, I stopped and started disassembling the power supply. I must admit, the Chinese manufacturer Taschibra released an extremely high-quality product, the circuit diagram of which I borrowed from the site stoom.ru. The circuit is presented for a 105 W model, but believe me, differences in power do not change the structure of the circuit, but only its elements depending on the output power:

The circuit after the modification will look like this:

Now in more detail about the improvements:

• After the rectifier bridge, we turn on the capacitor to smooth out the ripples of the rectified voltage. The capacitance is selected at the rate of 1 µF per 1 W. Thus, for a power of 150 W, I must install a 150 uF capacitor for an operating voltage of at least 400V. Since the size of the capacitor does not allow it to be placed inside the metal case of the Taschibra, I take it out through the wires.
• When connected to the network, an inrush of current occurs due to the added capacitor, so you need to connect an NTC thermistor or a 4.7 Ohm 5W resistor to the break in one of the network wires. This will limit the starting current. My circuit already had such a resistor, but after that I additionally installed MF72-5D9, which I removed from an unnecessary computer power supply.

• Not shown in the diagram, but from a Computer power supply you can use a filter assembled on capacitors and coils; in some power supplies it is assembled on a separate small board soldered to the mains power socket.

If a different output voltage is required, the secondary winding of the power transformer will have to be rewinded. The diameter of the wire (harness of wires) is selected based on the load current: d=0.6*root(Inom). My unit used a transformer wound with wire with a cross-section of 0.7 mm²; I personally did not count the number of turns, since I did not rewind the winding. I unsoldered the transformer from the board, unwound the twisted wires of the secondary winding of the transformer, there were 10 ends in total on each side:

I connected the ends of the resulting three windings together in series into 3 parallel wires, since the cross-section of the wire is the same 0.7 mm2 as the wire in the transformer winding. Unfortunately, the resulting 2 jumpers are not visible in the photo.

Simple mathematics, a 150 W winding was wound with a 0.7 mm2 wire, which we managed to split into 10 separate ends, ringing the ends, divided into 3 windings each with 3+3+4 cores, turn them on in series, in theory you should get 12+12+12= 36 Volt.

• Let's calculate the current I=P/U=150/36=4.17A
• Minimum winding cross-section 3*0.7mm² =2.1mm²
• Let's check whether the winding can withstand this current d=0.6*root(Inom)=0.6*root(4.17A)=1.22mm²< 2.1мм²

It turns out that the winding in our transformer is suitable with a large margin. Let me run a little ahead of the voltage that the AC power supply supplied at 32 Volts.
Continuing the redesign of the Taschibra power supply:
Since the switching power supply has current feedback, the output voltage varies depending on the load. When there is no load, the transformer does not start, which is very convenient if used for its intended purpose, but our goal is a constant voltage power supply. To do this, we change the current feedback circuit to voltage feedback.

We remove the current feedback winding and replace it with a jumper on the board. This can be clearly seen in the photo above. Then we pass a flexible stranded wire (I used a wire from a computer power supply) through a power transformer in 2 turns, then we pass the wire through a feedback transformer and make one turn so that the ends do not unwind, additionally pull it through PVC as shown in the photo above. The ends of the wire passed through the power transformer and the feedback transformer are connected through a 3.4 Ohm 10 W resistor. Unfortunately, I did not find a resistor with the required value and set it to 4.7 Ohm 10 W. This resistor sets the conversion frequency (approximately 30 kHz). As the load current increases, the frequency becomes higher.

If the converter does not start, you need to change the winding direction, it is easier to change it on a small feedback transformer.

As I searched for my solution to the alteration, I accumulated a lot of information on pulse blocks Taschibra nutrition, I propose to discuss them here.
Differences between similar modifications from other sites:

• Current-limiting resistor 6.8 Ohm MLT-1 (it’s strange that the 1 W resistor did not heat up or the author missed this point)
• Current limiting resistor 5-10 W on the radiator, in my case 10 W without heating.
• Eliminate filter capacitor and high side inrush current limiter

Taschibra power supplies have been tested for:

• Laboratory Power Supplies
• Amplifier computer speakers(2*8 W)
• Tape recorders
• Lighting
• Electric tools

To power DC consumers, it is necessary to have a diode bridge and a filter capacitor at the output of the power transformer; the diodes used for this bridge must be high-frequency and correspond to the power ratings of the Taschibra power supply. I advise you to use diodes from a computer power supply or similar ones.

Many novice radio amateurs, and not only those, encounter problems in the manufacture of powerful power supplies. Nowadays, a large number of electronic transformers used to power halogen lamps have appeared on the market. The electronic transformer is a half-bridge self-oscillating pulse voltage converter.
Pulse converters have high efficiency, small size and weight.
These products are not expensive, about 1 ruble per watt. After modification, they can be used to power amateur radio designs. There are many articles on the Internet on this topic. I want to share my experience in remaking the Taschibra 105W electronic transformer.

Let's consider the circuit diagram of an electronic converter.
The mains voltage is supplied through a fuse to the diode bridge D1-D4. The rectified voltage powers the half-bridge converter on transistors Q1 and Q2. The diagonal of the bridge formed by these transistors and capacitors C1, C2 includes winding I of the pulse transformer T2. The converter is started by a circuit consisting of resistors R1, R2, capacitor C3, diode D5 and diac D6. Feedback transformer T1 has three windings - a current feedback winding, which is connected in series with the primary winding of the power transformer, and two 3-turn windings that supply the base circuits of the transistors.
The output voltage of the electronic transformer is a 30 kHz square wave modulated at 100 Hz.

In order to use the electronic transformer as a power source, it must be modified.

We connect a capacitor at the output of the rectifier bridge to smooth out the ripples of the rectified voltage. The capacitance is selected at the rate of 1 µF per 1 W. The operating voltage of the capacitor must be at least 400V.
When a rectifier bridge with a capacitor is connected to the network, a current surge occurs, so you need to connect an NTC thermistor or a 4.7 Ohm 5W resistor to the break in one of the network wires. This will limit the starting current.

If a different output voltage is needed, we rewind the secondary winding of the power transformer. The diameter of the wire (harness of wires) is selected based on the load current.

Electronic transformers are current-fed, so the output voltage will vary depending on the load. If the load is not connected, the transformer will not start. To prevent this from happening, you need to change the current feedback circuit to the voltage feedback circuit.
We remove the current feedback winding and replace it with a jumper on the board. Then we pass the flexible stranded wire through the power transformer and make 2 turns, then we pass the wire through the feedback transformer and make one turn. The ends of the wire passed through the power transformer and the feedback transformer are connected through two parallel-connected 6.8 Ohm 5 W resistors. This current-limiting resistor sets the conversion frequency (approximately 30 kHz). As the load current increases, the frequency becomes higher.
If the converter does not start, you need to change the winding direction.

In Taschibra transformers, the transistors are pressed to the housing through cardboard, which is unsafe during operation. In addition, paper conducts heat very poorly. Therefore, it is better to install transistors through a heat-conducting pad.
To rectify alternating voltage with a frequency of 30 kHz, we install a diode bridge at the output of the electronic transformer.
The best results were shown, of all the tested diodes, by domestic KD213B (200V; 10A; 100 kHz; 0.17 μs). At high load currents they heat up, so they must be installed on the radiator through heat-conducting gaskets.
Electronic transformers do not work well with capacitive loads or do not start at all. For normal operation, a smooth startup of the device is necessary. Throttle L1 helps ensure smooth starting. Together with a 100uF capacitor, it also performs the function of filtering rectified voltage.
The L1 50 µG inductor is wound on a T106-26 core from Micrometals and contains 24 turns of 1.2 mm wire. Such cores (yellow, with one white edge) are used in computer power supplies. External diameter 27mm, internal 14mm, and height 12mm. By the way, other parts can be found in dead power supplies, including a thermistor.

If you have a screwdriver or other tool whose battery has expired, then you can place a power supply from an electronic transformer in the battery housing. As a result, you will have a network-powered tool.
For stable operation, it is advisable to install a resistor of approximately 500 Ohm 2W at the output of the power supply.

During the process of setting up a transformer, you need to be extremely careful and careful. There is high voltage on the device elements. Do not touch the flanges of the transistors to check whether they are heating up or not. It is also necessary to remember that after switching off the capacitors remain charged for some time.

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 this electronic transformer has many advantages. Light weight and dimensions (as with all similar circuits), ease of modification to suit your own needs, the presence of a shielding housing, low cost and relative reliability (at least, if extreme conditions and short circuits are avoided, a product made according to a similar circuit can work long years).

The range of application of power supplies based on "Taskhibra" can be very wide, comparable to the use of conventional transformers.

The use is justified in cases of shortage of time, funds, or lack of need for stabilization.
Well, shall we experiment? Let me make a reservation right away that the purpose of the experiments was to test the Tasshibra triggering circuit under various loads, frequencies and the use of various transformers. I also wanted to select the optimal ratings of the components of the PIC circuit and check the temperature conditions of the circuit components when operating under various loads, taking into account the use of the Tasсhibra case as a radiator.

ET scheme Taschibra (Tashibra, Tashibra)

Despite the large number of published electronic transformer circuits, I will not be too lazy to once again post it for review. Look at Fig.1, illustrating the "Tashibra" filling.

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The diagram 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 circuits, the results of the experiments can be easily projected onto instances of both lower and higher power.

And let me remind you once again what Tashibra is missing for a full-fledged power supply.
1. Lack of an input smoothing filter (also an anti-interference filter, which prevents conversion products from entering the network),
2. Current PIC, which allows 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 correct all of the listed shortcomings of "Taskhibra" and try to achieve its acceptable operation with the desired output characteristics. To begin with, we won’t even open the housing of the electronic transformer, but simply add the missing elements...

1. Input filter: capacitors C`1, C`2 with a symmetrical two-winding choke (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.

The smoothing capacitor is usually selected at the rate of 1.0 - 1.5 μF per watt of power, and a discharge resistor with a resistance of 300-500 kOhm should be connected in parallel to the capacitor for safety (touching the terminals of a capacitor charged with a relatively high voltage is not very pleasant).
Resistor R`1 can be replaced with a 5-15Ohm/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 diode VD`1, capacitors C`4-C`5 and inductor L1 connected between them to obtain a filtered DC voltage at the “patient” output. In this case, the polystyrene capacitor placed directly behind the diode accounts for the main share of absorption of 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 voltage “dip” at the peak power of the device connected to the ET. But it is also recommended to install a non-electrolytic capacitor in parallel with it.

After adding the input circuit, changes occurred in the operation of the electronic transformer: the amplitude of the output pulses (up to the diode VD`1) increased slightly due to the 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 was practically absent. This is at the load calculated for the electric vehicle.
However, this is not enough. "Tashibra" does not want to start without significant load current.

Installing load resistors at the output of the converter to create any minimum current value capable of starting the converter only reduces the overall efficiency of the device. Starting at a load current of about 100 mA is carried out at a very low frequency, which will be quite difficult to filter if the power supply is intended for joint use with UMZCH and other audio equipment with low current consumption in the no-signal mode, for example. The amplitude of the pulses is also less than at full load.

The change in frequency in different power modes is quite strong: from a couple to several tens of kilohertz. This circumstance imposes significant restrictions on the use of "Tashibra" in this (for now) form when working with many devices.

But let's continue. There have been 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 the normal operation of the basic ET circuit. The offer, however, is tempting only because without disassembling the electric transformer, using 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 electric vehicle. Attempts to increase the current (such as a 6.3VX0.3A light bulb connected to an additional winding), capable of ensuring NORMAL operation of the ET, only resulted in the converter starting up and the light bulb lighting up.

But perhaps someone will be interested in this result, because... connecting an additional transformer is also true in many other cases to solve many problems. So, for example, an additional transformer can be used in conjunction with an old (but working) computer power supply, capable of providing significant output power, but having a limited (but stabilized) set of voltages.

One could continue to search for the truth in the shamanism around "Tashibra", however, I considered this topic exhausted for myself, because to achieve the desired result (stable start-up and return to operating mode in the absence of load, and, therefore, high efficiency; a slight change in frequency when the power supply is operating from minimum to maximum power and stable start-up 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 manner shown in Fig. 4.
Moreover, I collected about fifty similar circuits back in the era of Spectrum computers (specifically for these computers). Various UMZCHs, powered by similar power supplies, are still working somewhere. PSUs made according to this scheme showed their best performance, working while being assembled from a wide variety of components and in various options.

Are we redoing it? Certainly!

Moreover, it is not at all difficult.

We solder the transformer. We warm 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 technologies.

In this case, the transformer is soldered only in order to inquire about its winding data (by the way: W-shaped magnetic core with a round core, standard dimensions for computer power supplies 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 wire folded five times with a diameter of approximately 1.1 mm; all this without the slightest interlayer and interwinding insulation - just varnish) and make room for another transformer.

For experiments, it was easier for me to use ring magnetic cores. They take up less space on the board, which makes it possible (if necessary) to use additional components in the volume of the case. In this case, a pair of ferrite rings with outer and inner diameters and heights of 32x20x6mm, respectively, folded in half (without gluing) - N2000-NM1 - was used. 90 turns of the primary (wire diameter - 0.65 mm) and 2X12 (1.2 mm) turns of the secondary with the necessary inter-winding insulation.

The communication winding contains 1 turn of 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 in two layers of electrical tape, by the way, securely fixing the folded rings.

Before installing the transformer on the ET board, we unsolder the current winding of the commutating transformer and use it as a jumper, soldering it there, but without passing the transformer rings through the window.

We install the wound transformer Tr2 on the board, soldering the leads in accordance with the diagram in Fig. 4. and pass the winding wire III into the window of the commutating transformer ring. Using the rigidity of the wire, we form a semblance of a geometrically closed circle and the feedback loop is ready. We solder a fairly powerful resistor (>1W) with a resistance of 3-10 Ohms into the gap in the mounting wire that forms windings III of both (switching and power) transformers.

In the diagram in Fig. 4, standard ET diodes are not used. They should be removed, as should resistor R1, in order to increase the efficiency of the unit as a whole. But you can neglect a few percent of the efficiency and leave the listed parts on the board. At least at the time of the experiments with ET, these parts 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 starting the converter, facilitating its operation on a capacitive load.

Transistors should certainly be installed on radiators through insulating heat-conducting gaskets (borrowed, for example, from a faulty computer power supply), thereby preventing their accidental instant heating and ensuring some personal safety in case of touching the radiator while the device is operating.

By the way, the electrical cardboard used in ET to insulate transistors and the board from the case is not thermally conductive. Therefore, when “packing” the finished power supply circuit into a standard case, exactly these gaskets should be installed between the transistors and the case. Only in this case will at least some heat removal be ensured. When using a converter with powers over 100W, an additional radiator must be installed on the device body. But this is for the future.

In the meantime, having finished installing the circuit, let’s perform one more safety point by connecting its input in series through an incandescent lamp with a power of 150-200 W. The lamp, in the event of an emergency (short circuit, for example), will limit the current through the structure to a safe value and, in the worst case, create additional illumination of the work space.

In the best case, with some observation, the lamp can be used as an indicator, for example, of through current. Thus, 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 confirmation - heating in through-current mode will be quite fast.
When the converter is working properly, visible in the background daylight the glow of the filament of a 200-watt lamp will appear only at the threshold of 20-35 W.

First start

So, everything is ready for the first launch of the converted "Tashibra" circuit. To begin with, we turn it on - without load, but do not forget about the pre-connected voltmeter to the output of the converter and an oscilloscope. With correctly phased feedback windings, the converter should start without problems.

If the start-up does not occur, then we pass the wire passed through the window of the commutating transformer (having previously unsoldered it from resistor R5) on the other side, giving it, again, the appearance of a completed turn. Solder the wire to R5. Apply power to the converter again. Did not help? Look for errors in installation: short circuit, “missing connections”, erroneously set values.

When a working converter is started with the specified winding data, the display of an oscilloscope connected to the secondary winding of transformer Tr2 (in my case, half of the winding) will display a time-invariant sequence of clear rectangular pulses. The conversion frequency is selected by 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 transformer winding with an effective voltage value of 17.5 V. The calculated voltage value was slightly different (20 V), but it turned out that instead of the nominal 5.1 Ohm, the resistance installed on the board R1 = 51 Ohm. Be attentive to such surprises from your 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 power supply, at a frequency of 20 kHz the installed transformer will be able to deliver no more than 60-65 W to the load.

Let's try to increase the frequency. When a resistor (R5) with a resistance of 8.2 Ohms is turned on, the frequency of the converter without load increases to 38.5 kHz, with a load of 12 Ohms - 41.8 kHz.

At this conversion frequency, with the existing power transformer, you can safely service a load of up to 120 W.
You can further experiment with the resistances in the PIC circuit, achieving the required frequency value, keeping in mind, however, that too high a resistance R5 can lead to generation failures and unstable startup of the converter. When changing the parameters of the PIC converter, you should 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 commutating transformer using the formulas posted on the page //interlavka.narod.ru/stats/Blokpit02.htm, for example, or using one of Mr. Moskatov’s programs posted on the page of his website // www.moskatov.narod.ru/Design_tools_pulse_transformers.html.

Improvement of Tasсhibra - a capacitor in the PIC instead of a resistor!

You can avoid heating resistor R5 by replacing it... with a capacitor. In this case, the PIC circuit certainly acquires some resonant properties, but no deterioration in the operation of the power supply is manifested. Moreover, a capacitor installed instead of a resistor heats up significantly less than the 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 with a load.

The startup 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 power supply at such a frequency increases to 220 W (minimum).
Transformer power: values ​​are approximate, with certain assumptions, but not exaggerated.
Over 18 years of work at North-West Telecom, I have made many different stands for testing various equipment being repaired.
He designed several digital pulse duration meters, different in functionality and elemental base.

More than 30 improvement proposals for the modernization of units of various specialized equipment, incl. - power supply. For a long time now I have been increasingly involved in power automation and electronics.

Why am I here? Yes, because everyone here is the same as me. There is a lot of interest here for me, since I am not strong in audio technology, but I would like to have more experience in this area.

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