Driver for 12V halogen lamps. What is the difference between a power supply for LED lamps and an electronic transformer for halogen lamps? Transformers for halogen lamps
Electronic transformers are replacing bulky steel core transformers. The electronic transformer itself, unlike the classical one, is a whole device - a voltage converter.
Such converters are used in lighting to power 12-volt halogen lamps. If you have repaired chandeliers with a remote control, then you have probably encountered them.
Here is a diagram of an electronic transformer JINDEL(model GET-03) with short circuit protection.
The main power elements of the circuit are n-p-n transistors MJE13009, which are connected according to the half-bridge circuit. They operate in antiphase at a frequency of 30 - 35 kHz. All the power supplied to the load - halogen lamps EL1...EL5 - is pumped through them. Diodes VD7 and VD8 are necessary to protect transistors V1 and V2 from reverse voltage. A symmetrical dinistor (aka diac) is necessary to start the circuit.
On transistor V3 ( 2N5551) and elements VD6, C9, R9 - R11, a short circuit protection circuit is implemented at the output ( short circuit protection).
If a short circuit occurs in the output circuit, the increased current flowing through resistor R8 will cause transistor V3 to operate. The transistor will open and block the operation of the DB3 dinistor, which starts the circuit.
Resistor R11 and electrolytic capacitor C9 prevent false operation of the protection when the lamps are turned on. When the lamps are turned on, the filaments are cold, so the converter produces a significant current at the beginning of the start-up.
To rectify the 220V mains voltage, a classic bridge circuit of 1.5-amp diodes is used 1N5399.
Inductor L2 is used as a step-down transformer. It takes up almost half the space on the converter PCB.
Due to its internal structure, it is not recommended to turn on the electronic transformer without load. Therefore, the minimum power of the connected load is 35 - 40 watts. The operating power range is usually indicated on the product body. For example, on the body of the electronic transformer in the first photo the output power range is indicated: 35 - 120 watts. Its minimum load power is 35 watts.
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. Typically, a filter is placed at the input of such devices to block interference. As you can see from the diagram, there are no such filters in electronic transformers for halogen lamps. But in computer 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.
The device has a fairly simple circuit. A simple push-pull oscillator, which is made according to a half-bridge circuit, the operating frequency is about 30 kHz, but this figure is highly dependent on the output load.
The circuit of such a power supply is not very stable, it does not have any protection against short circuit at the output of the transformer, perhaps precisely because of this, the circuit has not yet found wide application in amateur radio circles. Although recently there has been a promotion of this topic on various forums. People offer various options for modifying such transformers. Today I will try to combine all these improvements in one article and offer options not only for improvement, but also for strengthening ET.
We won’t go into the basics of how the circuit works, but let’s get down to business right away.
We will try to refine and increase the power of the Chinese Taschibra electric vehicle by 105 watts.
To begin with, I want to explain why I decided to take on the powering and alteration of such transformers. The fact is that recently a neighbor asked me to make him a custom-made charger for a car battery that would be compact and lightweight. I didn’t want to assemble it, but later I came across interesting articles that discussed remaking an electronic transformer. This gave me the idea - why not try it?
Thus, several ETs from 50 to 150 Watts were purchased, but experiments with conversion were not always completed successfully; of all, only the 105 Watt ET survived. The disadvantage of such a block is that its transformer is not ring-shaped, and therefore it is inconvenient to unwind or rewind the turns. But there was no other choice and this particular block had to be remade.
As we know, these units do not turn on without load; this is not always an advantage. I plan to get a reliable device that can be freely used for any purpose without fear that the power supply may burn out or fail during a short circuit.
Refinement No. 1
The essence of the idea is to add short-circuit protection and also eliminate the above-mentioned drawback (activation of a circuit without an output load or with a low-power load).
Looking at the unit itself, we can see the simplest UPS circuit; I would say that the circuit has not been fully developed by the manufacturer. As we know, if you short-circuit the secondary winding of a transformer, the circuit will fail in less than a second. The current in the circuit increases sharply, the switches instantly fail, and sometimes even the basic limiters. Thus, repairing the circuit will cost more than the cost (the price of such an ET is about $2.5).
The feedback transformer consists of three separate windings. Two of these windings power the base switch circuits.
First, remove the communication winding on the OS transformer and install a jumper. This winding is connected in series with the primary winding of the pulse transformer.
Then we wind only 2 turns on the power transformer and one turn on the ring (OS transformer). For winding, you can use a wire with a diameter of 0.4-0.8 mm.
Next, you need to select a resistor for the OS, in my case it is 6.2 ohms, but a resistor can be selected with a resistance of 3-12 ohms, the higher the resistance of this resistor, the lower the short-circuit protection current. In my case, the resistor is a wirewound one, which I do not recommend doing. We select the power of this resistor to be 3-5 watts (you can use from 1 to 10 watts).
During a short circuit on the output winding of a pulse transformer, the current in the secondary winding drops (in standard ET circuits, during a short circuit, the current increases, disabling the switches). This leads to a decrease in the current on the OS winding. Thus, generation stops and the keys themselves are locked.
The only drawback of this solution is that in the event of a long-term short circuit at the output, the circuit fails because the switches heat up quite strongly. Do not expose the output winding to a short circuit lasting more than 5-8 seconds.
The circuit will now start without load; in a word, we have a full-fledged UPS with short-circuit protection.
Improvement No. 2
Now we will try to smooth out the mains voltage from the rectifier to some extent. For this we will use chokes and a smoothing capacitor. In my case, a ready-made inductor with two independent windings was used. This inductor was removed from the UPS of the DVD player, although homemade inductors can also be used.
After the bridge, an electrolyte with a capacity of 200 μF should be connected with a voltage of at least 400 Volts. The capacitor capacity is selected based on the power of the power supply 1 μF per 1 watt of power. But as you remember, our power supply is designed for 105 Watts, why is the capacitor used at 200 μF? You will understand this very soon.
Refinement No. 3
Now about the main thing - increasing the power of the electronic transformer and is it real? In fact, there is only one reliable way to power it up without much modification.
For powering up, it is convenient to use an ET with a ring transformer, since it will be necessary to rewind the secondary winding; it is for this reason that we will replace our transformer.
The network winding is stretched across the entire ring and contains 90 turns of wire 0.5-0.65 mm. The winding is wound on two folded ferrite rings, which were removed from an ET with a power of 150 watts. The secondary winding is wound based on needs, in our case it is designed for 12 Volts.
It is planned to increase the power to 200 watts. That is why an electrolyte with a reserve, which was mentioned above, was needed.
We replace the half-bridge capacitors with 0.5 μF; in the standard circuit they have a capacity of 0.22 μF. Bipolar keys MJE13007 are replaced with MJE13009.
The power winding of the transformer contains 8 turns, the winding was done with 5 strands of 0.7 mm wire, so we have a wire in the primary with a total cross-section of 3.5 mm.
Go ahead. Before and after the chokes we place film capacitors with a capacity of 0.22-0.47 μF with a voltage of at least 400 Volts (I used exactly those capacitors that were on the ET board and which had to be replaced to increase the power).
Next, replace the diode rectifier. In standard circuits, conventional rectifier diodes of the 1N4007 series are used. The current of the diodes is 1 Ampere, our circuit consumes a lot of current, so the diodes should be replaced with more powerful ones in order to avoid unpleasant results after the first turn on of the circuit. You can use literally any rectifier diodes with a current of 1.5-2 Amps, a reverse voltage of at least 400 Volts.
All components except the generator board are mounted on a breadboard. The keys were secured to the heat sink through insulating gaskets.
We continue our modification of the electronic transformer, adding a rectifier and filter to the circuit.
The chokes are wound on rings made of powdered iron (removed from a computer power supply unit) and consist of 5-8 turns. It is convenient to wind it using 5 strands of wire with a diameter of 0.4-0.6 mm each.
We select a smoothing capacitor with a voltage of 25-35 Volts; one powerful Schottky diode (diode assemblies from a computer power supply) is used as a rectifier. You can use any fast diodes with a current of 15-20 Amps.
Today, electromechanics rarely repair electronic transformers. In most cases, I myself don’t really bother with working on resuscitating such devices, simply because, usually, buying a new electronic transformer is much cheaper than repairing an old one. However, in the opposite situation, why not work hard to save money. In addition, not everyone has the opportunity to get to a specialized store to find a replacement there, or go to a workshop. For this reason, any radio amateur needs to be able to and know how to check and repair pulse (electronic) transformers at home, what ambiguous issues may arise and how to resolve them.
Due to the fact that not everyone has an extensive amount of knowledge on the topic, I will try to present all available information as accessible as possible.
A little about transformers
Fig.1: Transformer.
Before proceeding to the main part, I will give a short reminder about what an electronic transformer is and what it is intended for. A transformer is used to convert one variable voltage to another (for example, 220 volts to 12 volts). This property of an electronic transformer is very widely used in radio electronics. There are single-phase (current flows through two wires - phase and “0”) and three-phase (current flows through four wires - three phases and “0”) transformers. The main significant point when using an electronic transformer is that as the voltage decreases, the current in the transformer increases.
A transformer has at least one primary and one secondary winding. The supply voltage is connected to the primary winding, a load is connected to the secondary winding, or the output voltage is removed. In step-down transformers, the primary winding wire always has a smaller cross-section than the secondary wire. This allows you to increase the number of turns of the primary winding and, as a result, its resistance. That is, when checked with a multimeter, the primary winding shows a resistance many times greater than the secondary. If for some reason the diameter of the secondary winding wire is small, then, according to the Joule-Lance law, the secondary winding will overheat and burn the entire transformer. A transformer malfunction may consist of a break or short circuit (short circuit) of the windings. If there is a break, the multimeter shows one on the resistance.
How to test electronic transformers?
In fact, to figure out the cause of the breakdown, you don’t need to have a huge amount of knowledge; it’s enough to have a multimeter on hand (standard Chinese, as in Figure 2) and know what numbers each component (capacitor, diode, etc.) should produce at the output. d.).
Figure 2: Multimeter.
The multimeter can measure DC, AC voltage and resistance. It can also work in dialing mode. It is advisable that the multimeter probe be wrapped with tape (as in Figure No. 2), this will protect it from breaks.
In order to correctly test the various elements of the transformer, I recommend desoldering them (many try to do without this) and examining them separately, since otherwise the readings may be inaccurate.
Diodes
We must not forget that diodes only ring in one direction. To do this, set the multimeter to continuity mode, the red probe is applied to the plus, the black probe to the minus. If everything is normal, the device makes a characteristic sound. When the probes are applied to opposite poles, nothing should happen at all, and if this is not the case, then a breakdown of the diode can be diagnosed.
Transistors
When checking transistors, they also need to be unsoldered and the base-emitter, base-collector junctions must be wired, identifying their permeability in one direction and the other. Typically, the role of a collector in a transistor is performed by the rear iron part.
Winding
We must not forget to check the winding, both primary and secondary. If you have problems determining where the primary winding is and where the secondary winding is, then remember that the primary winding gives more resistance.
Capacitors (radiators)
The capacitance of a capacitor is measured in farads (picofarads, microfarads). To study it, a multimeter is also used, on which the resistance is set to 2000 kOhm. The positive probe is applied to the minus of the capacitor, the negative to the plus. Increasing numbers should appear on the screen up to almost two thousand, which are replaced by one, which stands for infinite resistance. This may indicate the health of the capacitor, but only in relation to its ability to accumulate charge.
One more point: if during the dialing process there is confusion about where the “input” is located and where the “output” of the transformer is located, then you just need to turn the board over and on the back side at one end of the board you will see a small marking “SEC” (second), which indicates the output, and on the other “PRI” (first) the input.
And also, do not forget that electronic transformers cannot be started without loading! It is very important.
Electronic transformer repair
Example 1
The opportunity to practice repairing a transformer presented itself not so long ago, when they brought me an electronic transformer from a ceiling chandelier (voltage - 12 volts). The chandelier is designed for 9 bulbs, each 20 watts (180 watts in total). On the packaging of the transformer it also said: 180 watts. But the mark on the board said: 160 watts. The country of origin is, of course, China. A similar electronic transformer costs no more than $3, and this is actually quite a bit when compared with the cost of the other components of the device in which it was used.
In the electronic transformer I received, a pair of switches on bipolar transistors burned out (model: 13009).
The operating circuit is a standard push-pull, in place of the output transistor is a TOP inverter, whose secondary winding consists of 6 turns, and the alternating current is immediately redirected to the output, that is, to the lamps.
Such power supplies have a very significant drawback: there is no protection against short circuit at the output. Even with a short-circuit of the output winding, you can expect a very impressive explosion of the circuit. Therefore, it is highly not recommended to take risks in this way and short-circuit the secondary winding. In general, it is for this reason that radio amateurs do not really like to mess with electronic transformers of this type. However, some people, on the contrary, try to modify them on their own, which, in my opinion, is quite good.
But let's get back to the point: since there was a darkening of the board right under the keys, there was no doubt that they failed precisely because of overheating. Moreover, the radiators do not actively cool the case box filled with many parts, and they are also covered with cardboard. Although, judging by the initial data, there was also an overload of 20 watts.
Due to the fact that the load exceeds the capabilities of the power supply, reaching the rated power is almost equivalent to failure. Moreover, ideally, with a view to long-term operation, the power of the power supply should be not less, but twice as much as necessary. This is what Chinese electronics is like. It was not possible to reduce the load level by removing several light bulbs. Therefore, the only suitable option, in my opinion, to correct the situation was to increase the heat sinks.
To confirm (or refute) my version, I launched the board directly on the table and applied the load using two halogen pair lamps. When everything was connected, I dripped a little paraffin onto the radiators. The calculation was as follows: if the paraffin melts and evaporates, then we can guarantee that the electronic transformer (fortunately, if only it is itself) will burn out in less than half an hour of operation due to overheating. After 5 minutes of operation, the wax still did not melt, it turned out that the main problem is related precisely to poor ventilation, and not to a malfunction of the radiator. The most elegant solution to the problem is to simply fit another larger housing under the electronic transformer, which will provide sufficient ventilation. But I preferred to connect a heat sink in the form of an aluminum strip. Actually, this turned out to be quite enough to correct the situation.
Example 2
As another example of repairing an electronic transformer, I would like to talk about repairing a device that reduces the voltage from 220 to 12 Volts. It was used for 12 Volt halogen lamps (power - 50 Watt).
The copy in question stopped working without any special effects. Before I got it into my hands, several craftsmen refused to work with it: some could not find a solution to the problem, others, as mentioned above, decided that it was not economically feasible.
To clear my conscience, I checked all the elements and traces on the board and found no breaks anywhere.
Then I decided to check the capacitors. The diagnostics with a multimeter seemed to be successful, however, taking into account the fact that the charge accumulated for as long as 10 seconds (this is a lot for capacitors of this type), a suspicion arose that the problem was in it. I replaced the capacitor with a new one.
A small digression is needed here: on the body of the electronic transformer in question there was a designation: 35-105 VA. These readings indicate at what load the device can be turned on. It is impossible to turn it on without a load at all (or, in human terms, without a lamp), as mentioned earlier. Therefore, I connected a 50-watt lamp to the electronic transformer (that is, a value that fits between the lower and upper limits of the permissible load).
Rice. 4: 50W halogen lamp (package).
After connection, no changes occurred in the performance of the transformer. Then I completely examined the design again and realized that during the first check I did not pay attention to the thermal fuse (in this case, model L33, limited to 130C). If in the continuity mode this element gives one, then we can talk about its malfunction and an open circuit. Initially, the thermal fuse was not tested for the reason that it is attached tightly to the transistor using heat shrink. That is, to fully check the element, you will have to get rid of the heat shrinkage, and this is very labor-intensive.
Fig. 5: Thermal fuse attached by heat shrink to the transistor (the white element pointed to by the handle).
However, to analyze the operation of the circuit without this element, it is enough to short-circuit its “legs” on the reverse side. Which is what I did. The electronic transformer immediately started working, and the earlier replacement of the capacitor turned out to be not superfluous, since the capacity of the previously installed element did not meet the declared one. The reason was probably that it was simply worn out.
As a result, I replaced the thermal fuse, and at this point the repair of the electronic transformer could be considered complete.
Write comments, additions to the article, maybe I missed something. Take a look at, I will be glad if you find something else useful on mine.
Currently, pulsed electronic transformers, due to their small size and weight, low price and wide range, are widely used in mass equipment. Thanks to mass production, electronic transformers are several times cheaper than conventional inductive transformers on iron of similar power. Although electronic transformers from different companies may have different designs, the circuit is practically the same.
Let's take for example a standard electronic transformer labeled 12V 50W, which is used to power a table lamp. The schematic diagram will be like this:
The electronic transformer circuit works as follows. The mains voltage is rectified using a rectifier bridge to a half-sinusoidal voltage with double the frequency. Element D6 of type DB3 in the documentation is called “TRIGGER DIODE”, - this is a bidirectional dinistor in which the polarity of the inclusion does not matter and it is used here to start the transformer converter. The dinistor is triggered during each cycle, starting the generation of a half-bridge. The opening of the dinistor can be adjusted. This can be done use for example for the function of a connected lamp.The generation frequency depends on the size and magnetic conductivity of the feedback transformer core and the parameters of the transistors, usually in the range of 30-50 kHz.
Currently, the production of more advanced transformers with the IR2161 chip has begun, which provides both simplicity of design of the electronic transformer and a reduction in the number of components used, as well as high performance. The use of this microcircuit significantly increases the manufacturability and reliability of the electronic transformer for powering halogen lamps. The schematic diagram is shown in the figure.
Features of the electronic transformer on IR2161:
Intelligent half bridge driver;
Load short circuit protection with automatic restart;
Overcurrent protection with automatic restart;
Swing the operating frequency to reduce electromagnetic interference;
Micropower start-up 150 µA;
Possibility of use with phase dimmers with control by leading and trailing edges;
Compensation for output voltage offset increases lamp life;
Soft start, eliminating current overload of lamps.
Input resistor R1 (0.25 watt) is a kind of fuse. Transistors of type MJE13003 are pressed to the body through an insulating gasket with a metal plate. Even when operating at full load, the transistors heat up slightly. After the mains voltage rectifier, there is no capacitor to smooth out the ripples, so the output voltage of the electronic transformer when operating on a load is a 40 kHz rectangular oscillation, modulated by 50 Hz mains voltage ripples. Transformer T1 (feedback transformer) - on a ferrite ring, the windings connected to the bases of the transistors contain a couple of turns, the winding connected to the connection point of the emitter and collector of the power transistors - one turn of single-core insulated wire. Transistors MJE13003, MJE13005, MJE13007 are usually used in ET. Output transformer on a ferrite W-shaped core.
To use an electronic transformer in a pulse mode, you need to connect a rectifier bridge on high-frequency diodes to the output (regular KD202, D245 will not work) and a capacitor to smooth out ripples. At the output of the electronic transformer, a diode bridge is installed using KD213, KD212 or KD2999 diodes. In short, we need diodes with a low voltage drop in the forward direction, capable of operating well at frequencies of the order of tens of kilohertz.
The electronic transformer converter does not work normally without a load, so it must be used where the load is constant in current and consumes sufficient current to reliably start the ET converter. When operating the circuit, it must be taken into account that electronic transformers are sources of electromagnetic interference, therefore an LC filter must be installed to prevent interference from penetrating the network and the load.
Personally, I used an electronic transformer to make a switching power supply for a tube amplifier. It also seems possible to power them with powerful Class A ULFs or LED strips, which are specifically designed for sources with a voltage of 12V and a high output current. Naturally, such a tape is connected not directly, but through a current-limiting resistor or by correcting the output power of an electronic transformer.
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