Energy-saving lamps are widely used in everyday life and in production; over time they become unusable, but many of them can be restored after simple repairs. If the lamp itself fails, then from the electronic “stuffing” you can make a fairly powerful power supply for any desired voltage.
What does the power supply look like? energy saving lamp
In everyday life, you often need a compact, but at the same time powerful low-voltage power supply; you can make one using a failed energy-saving lamp. In lamps, lamps most often fail, but the power supply remains in working order.
In order to make a power supply, you need to understand the operating principle of the electronics contained in an energy-saving lamp.
Advantages of switching power supplies
In recent years, there has been a clear tendency to move away from classic transformer power supplies to switching ones. This is due, first of all, to the major disadvantages of transformer power supplies, such as large mass, low overload capacity, and low efficiency.
The elimination of these shortcomings in switching power supplies, as well as the development of the element base, has made it possible to widely use these power units for devices with power from a few watts to many kilowatts.
Power supply diagram
The principle of operation of a switching power supply in an energy-saving lamp is exactly the same as in any other device, for example, in a computer or TV.
In general terms, the operation of a switching power supply can be described as follows:
- The alternating mains current is converted into direct current without changing its voltage, i.e. 220 V.
- A pulse-width converter using transistors converts DC voltage into rectangular pulses with a frequency of 20 to 40 kHz (depending on the lamp model).
- This voltage is supplied to the lamp through the inductor.
Let's look at the circuit and operating procedure of a switching lamp power supply (figure below) in more detail.
Electronic ballast circuit for an energy-saving lamp
The mains voltage is supplied to the bridge rectifier (VD1-VD4) through a limiting resistor R 0 of small resistance, then the rectified voltage is smoothed on a high-voltage filter capacitor (C 0), and through a smoothing filter (L0) is supplied to the transistor converter.
The transistor converter starts at the moment when the voltage on capacitor C1 exceeds the opening threshold of dinistor VD2. This will start the generator on transistors VT1 and VT2, resulting in self-generation at a frequency of about 20 kHz.
Other circuit elements such as R2, C8 and C11 play a supporting role, making it easier to start the generator. Resistors R7 and R8 increase the closing speed of the transistors.
And resistors R5 and R6 serve as limiting ones in the base circuits of transistors, R3 and R4 protect them from saturation, and in the event of a breakdown they play the role of fuses.
Diodes VD7, VD6 are protective, although many transistors designed to work in such devices have such diodes built-in.
TV1 – transformer, with its windings TV1-1 and TV1-2, voltage feedback from the output of the generator is supplied to the base circuits of transistors, thereby creating conditions for the operation of the generator.
In the figure above, the parts that must be removed when remaking the block are highlighted in red; points A–A` must be connected with a jumper.
Modification of the block
Before you begin remaking the power supply, you should decide what current power you need to have at the output; the depth of the upgrade will depend on this. So, if a power of 20-30 W is required, then the alteration will be minimal and will not require much intervention in the existing circuit. If you need to get a power of 50 watts or more, then a more thorough upgrade will be required.
It should be kept in mind that the output of the power supply will be DC voltage, not AC. It is impossible to obtain an alternating voltage with a frequency of 50 Hz from such a power supply.
Determining power
Power can be calculated using the formula:
P – power, W;
I – current strength, A;
U – voltage, V.
For example, let’s take a power supply with the following parameters: voltage – 12 V, current – 2 A, then the power will be:
Taking into account the overload, 24-26 W can be accepted, so the manufacture of such a unit will require minimal intervention in the circuit of a 25 W energy-saving lamp.
New parts
Adding new parts to the diagram
The added details are highlighted in red, these are:
- diode bridge VD14-VD17;
- two capacitors C 9, C 10;
- additional winding placed on ballast choke L5, the number of turns is selected experimentally.
The added winding to the inductor plays another important role as an isolation transformer, protecting against mains voltage reaching the output of the power supply.
To determine the required number of turns in the added winding, do the following:
- a temporary winding is wound onto the inductor, approximately 10 turns of any wire;
- connected to a load resistor with a power of at least 30 W and a resistance of approximately 5-6 Ohms;
- connect to the network, measure the voltage at the load resistance;
- divide the resulting value by the number of turns to find out how many volts there are per 1 turn;
- calculate the required number of turns for a permanent winding.
A more detailed calculation is given below.
Test activation of the converted power supply
After this, it is easy to calculate the required number of turns. To do this, the voltage that is planned to be obtained from this block is divided by the voltage of one turn, the number of turns is obtained, and approximately 5-10% is added to the result obtained in reserve.
W=U out /U vit, where
W – number of turns;
U out – required output voltage of the power supply;
U vit – voltage per turn.
Winding an additional winding on a standard inductor
The original inductor winding is under mains voltage! When winding an additional winding on top of it, it is necessary to provide inter-winding insulation, especially if a PEL type wire is wound, in enamel insulation. For interwinding insulation, you can use polytetrafluoroethylene tape to seal threaded connections, which is used by plumbers; its thickness is only 0.2 mm.
The power in such a unit is limited by the overall power of the transformer used and permissible current transistors.
High Power Power Supply
This will require a more complex upgrade:
- additional transformer on a ferrite ring;
- replacing transistors;
- installing transistors on radiators;
- increasing the capacity of some capacitors.
As a result of this modernization, a power supply with a power of up to 100 W is obtained, with an output voltage of 12 V. It is capable of providing a current of 8-9 amperes. This is enough to power, for example, a medium-power screwdriver.
The diagram of the upgraded power supply is shown in the figure below.
100W power supply
As can be seen in the diagram, resistor R0 has been replaced with a more powerful one (3-watt), its resistance has been reduced to 5 Ohms. It can be replaced with two 2-watt 10 ohm ones, connecting them in parallel. Further, C 0 - its capacity is increased to 100 μF, with an operating voltage of 350 V. If it is undesirable to increase the dimensions of the power supply, then you can find a miniature capacitor of such a capacity, in particular, you can take it from a point-and-shoot camera.
To ensure reliable operation of the unit, it is useful to slightly reduce the values of resistors R 5 and R 6, to 18–15 Ohms, and also increase the power of resistors R 7, R 8 and R 3, R 4. If the generation frequency turns out to be low, then the values of capacitors C 3 and C 4 – 68n should be increased.
The most difficult part may be making the transformer. For this purpose, ferrite rings of appropriate sizes and magnetic permeability are most often used in pulse blocks.
The calculation of such transformers is quite complicated, but there are many programs on the Internet with which this is very easy to do, for example, “Pulse transformer calculation program Lite-CalcIT”.
What does a pulse transformer look like?
The calculation carried out using this program gave the following results:
A ferrite ring is used for the core, its outer diameter is 40, its inner diameter is 22, and its thickness is 20 mm. The primary winding with PEL wire - 0.85 mm 2 has 63 turns, and the two secondary windings with the same wire have 12.
The secondary winding must be wound into two wires at once, and it is advisable to first slightly twist them together along the entire length, since these transformers are very sensitive to the asymmetry of the windings. If this condition is not met, then the diodes VD14 and VD15 will heat up unevenly, and this will further increase the asymmetry, which will ultimately damage them.
But such transformers easily forgive significant errors when calculating the number of turns, up to 30%.
Since this circuit was originally designed to work with a 20 W lamp, transistors 13003 were installed. In the figure below, position (1) is medium power transistors; they should be replaced with more powerful ones, for example, 13007, as in position (2). They may have to be installed on a metal plate (radiator) with an area of about 30 cm2.
Trial
A test run should be carried out with certain precautions taken so as not to damage the power supply:
- The first test run should be carried out using a 100 W incandescent lamp to limit the current to the power supply.
- Be sure to connect a 3-4 Ohm load resistor with a power of 50-60 W to the output.
- If everything went as expected, let it run for 5-10 minutes, turn it off and check the degree of heating of the transformer, transistors and rectifier diodes.
If no errors were made during the process of replacing parts, the power supply should work without problems.
If a trial run shows that the unit is working, all that remains is to test it in the full load. To do this, reduce the resistance of the load resistor to 1.2-2 Ohms and connect it directly to the network without a light bulb for 1-2 minutes. Then turn off and check the temperature of the transistors: if it exceeds 60 0 C, then they will have to be installed on radiators.
As a radiator, you can use either a factory radiator, which will be the most correct solution, or an aluminum plate with a thickness of at least 4 mm and an area of 30 sq.cm. It is necessary to place a mica gasket under the transistors; they must be secured to the radiator using screws with insulating bushings and washers.
Lamp block. Video
About how to do pulse block power supply from an economy lamp, video below.
You can make a switching power supply from the ballast of an energy-saving lamp yourself, with minimal skills in working with a soldering iron.
Many thanks to the manufacturers of modern energy-saving lamps. The quality of their products constantly makes us think and pushes us to new technical solutions.
This time we will consider the topic of converting a failed energy-saving lamp into an LED one. Today we'll go the more traditional route using an LED driver, but... The most interesting part of the conversion is the LED itself.
The other day I came across several samples of the Chinese electronics industry. These LEDs themselves are interesting, although they do not have outstanding characteristics. But the fact that this LED provides a circular radiation pattern raises it to absolutely new level and gives us an excellent tool for modernizing lighting systems.
As a radiator, I used the aluminum universal profile AP888, already known from the previous article, produced by Yug-Service LLC. Unfortunately, I only had a piece of it a little over 10mm thick. There was a fear that the power of 9 W might not be enough for an LED. But the desire to conduct an experiment won out.
A small drawback of this profile in relation to the new LED is that the central hole is 8 mm in diameter, and the thread of the “tail” of the LED is M6.
The easiest way out:
- drill the hole to 10 mm;
- screw the bolt into the M6 nut;
- carefully, hitting the head of the bolt with a hammer, press the nut into the profile. The bolt is needed so as not to accidentally jam the threads in the nut.
LED 7V, power 7-9 W, 12 V, 600-800 mA. As a driver, I used a widely used 700 mA driver for three LEDs from the same Chinese manufacturer.
Then, as always, everything is simple. We know how to disassemble an energy-saving light bulb, the main thing is not to break the bulb. And we prepare the entire kit for assembly.
1. Drill holes in the cover of the base housing to attach the radiator and wires.
2. Solder the positive wire of the driver to central contact LED. Don't forget to first thread it through the radiator and the base cover.
3. Apply heat-conducting paste (KTP-8) to the thread of the LED and screw it into place. We attach the cover of the base housing to the radiator.
4. The negative wire of the driver must be connected to the radiator.
5. Solder the driver network wires into the base.
6. Collect everything into one.
7. The upgraded lamp is ready for use.
As for my concerns about the LED overheating due to the insufficient heatsink size, we can say that they turned out to be groundless. The temperature at the “LED-radiator” point after several hours of operation stopped at around 59-62 ºС (temperature environment 23 ºС). In principle, this is acceptable, but if the radiator is increased by 5-10 mm, then you don’t have to worry about anything at all.
Everything is simple, beautiful and most importantly – accessible and not expensive.
I bought 10 W 900 lm warm LEDs for testing white light on AliExpress. The price in November 2015 was 23 rubles per piece. The order arrived in a standard bag, I checked everything was in good order. 
To power LEDs in lighting devices, special units are used - electronic drivers, which are converters that stabilize the current rather than the voltage at their output. But since the drivers for them (I also ordered on AliExpreess) were still on the way, I decided to power them from ballast from energy-saving lamps. I've had several of these faulty lamps. whose filament in the bulb burned out. As a rule, the voltage converter for such lamps is working properly, and it can be used as a switching power supply or LED driver.
We disassemble the fluorescent lamp. 
For the conversion, I took a 20 W lamp, the choke of which can easily deliver 20 W to the load. For a 10W LED, no further modifications are required. If you plan to supply more powerful LED, you need to take a converter from a more powerful lamp, or install a choke with a larger core.
Installed jumpers in the lamp ignition circuit. 
I wound 18 turns of enamel wire around the inductor, solder the terminals of the wound winding to the diode bridge, apply mains voltage to the lamp and measure the output voltage. In my case, the unit produced 9.7V. I connected the LED through an ammeter, which showed a current passing through the LED of 0.83A. My LED has an operating current of 900mA, but I reduced the current to increase the resource. I assembled the diode bridge on the board using a hinged method.
Remodeling scheme. 
I installed the LED using thermal paste on a metal lampshade of an old table lamp. 
I installed the power board and diode bridge into the body of a table lamp. 
When working for about an hour, the LED temperature is 40 degrees. 
To the eye, the illumination is like that of a 100-watt incandescent lamp. 
Energy-saving light bulbs are widely used for both domestic and industrial purposes. Over time, any lamp becomes faulty. However, if desired, the lamp can be revived by assembling a power supply from an energy-saving lamp. In this case, the filling of a failed light bulb is used as components of the block.
Pulse block and its purpose
At both ends of the fluorescent lamp tube there are electrodes, an anode and a cathode. Applying power causes the lamp components to heat up. After heating, electrons are released, which collide with mercury molecules. The consequence of this is ultraviolet radiation.
Due to the presence of phosphor in the tube, the phosphor is converted into the visible glow of the light bulb. The light does not appear immediately, but after a certain period of time after connecting to the power supply. The more worn out the lamp is, the longer the interval.
The operation of a switching power supply is based on the following principles:
- Conversion alternating current from the mains to the permanent one. In this case, the voltage does not change (that is, it remains 220 V).
- Transformation of DC voltage into rectangular pulses due to the operation of a width pulse converter. The pulse frequency ranges from 20 to 40 kHz.
- Supplying voltage to the lamp using a choke.
Source uninterruptible power supply(UPS) consists of a number of components, each of which has its own marking in the circuit:
- R0 - plays a limiting and protective role in the power supply. The device prevents and stabilizes excessive current flowing through the diodes at the time of connection.
- VD1, VD2, VD3, VD4 - act as bridge rectifiers.
- L0, C0 - are transmission filters electric current and protect against voltage surges.
- R1, C1, VD8 and VD2 - represent a chain of converters used during startup. The first resistor (R1) is used to charge capacitor C1. As soon as the capacitor breaks through the dinistor (VD2), it and the transistor open, resulting in self-oscillation in the circuit. Next, a rectangular pulse is sent to the diode cathode (VD8). A negative indicator appears, covering the second dinistor.
- R2, C11, C8 - facilitate the start of operation of the converters.
- R7, R8 - optimize the closing of transistors.
- R6, R5 - form boundaries for electric current on transistors.
- R4, R3 - are used as fuses during voltage surges in transistors.
- VD7 VD6 - protect power supply transistors from return current.
- TV1 is a reverse communication transformer.
- L5 - ballast choke.
- C4, C6 - act as isolation capacitors. Divide all the tension into two parts.
- TV2 is a pulse type transformer.
- VD14, VD15 - pulse diodes.
- C9, C10 - filter capacitors.
Note! In the diagram below, the components that need to be removed when remaking the block are marked in red. Points A-A connected by a jumper.
Only a thoughtful selection of individual elements and their correct installation will allow you to create an efficiently and reliably operating power supply.
Differences between a lamp and a pulse unit
The circuit of the energy-saving lamp is in many ways similar to the structure of a switching power supply. That is why it is not difficult to make a switching power supply. To remake the device, you will need a jumper and an additional transformer that will issue pulses. The transformer must have a rectifier.
To make the power supply lighter, the glass fluorescent bulb is removed. The power parameter is limited to the highest throughput transistors and sizes of cooling elements. To increase power, it is necessary to wind additional winding on the inductor.
Modification of the block
Before you start remaking the power supply, you need to choose output power current The degree of modernization of the system depends on this indicator. If the power is in the range of 20-30 W, there will be no need for deep changes in the circuit. If the planned power is more than 50 W, a more systematic upgrade is needed.
Note! There will be a constant voltage at the output of the power supply. It is not possible to obtain an alternating voltage at a frequency of 50 Hz.
Power determination
Power is calculated according to the formula:
As an example, consider the situation with a power supply having the following characteristics:
- voltage - 12 V;
- current strength - 2 A.
We calculate the power:
P = 2 × 12 = 24 W.
The final power parameter will be higher - approximately 26 W, which allows for possible overloads to be taken into account. Thus, to create a power supply, a fairly minor intervention in the circuit of a standard 25 W economy lamp will be required.
New components
New electronic components include:
- diode bridge VD14-VD17;
- 2 capacitors C9 and C10;
- winding on the ballast choke (L5), the number of turns of which is determined empirically.
The additional winding performs another important function - it is a separating transformer and protects against voltage penetration into the UPS outputs.
To calculate the required number of turns in the additional winding, perform the following steps:
- Temporarily apply a winding to the inductor (approximately 10 turns of wire).
- We connect the winding to the load resistance (power from 30 W and resistance 5-6 Ohms).
- We connect to the network and measure the voltage at the load resistance.
- We divide the result obtained by the number of turns and find out how many volts there are for each turn.
- We find out the required number of turns for a permanent winding.
The calculation procedure is shown in more detail below.
To calculate the required number of turns, divide the planned voltage for the block by the voltage of one turn. The result is the number of turns. It is recommended to add 5-10% to the final result, which will allow you to have a certain margin.
Do not forget that the original inductor winding is under mains voltage. If you need to wind a new layer of winding on it, take care of the inter-winding insulating layer. It is especially important to observe this rule when a PEL type wire in enamel insulation is applied. Polytetrafluoroethylene tape (0.2 mm thick) is suitable as an interwinding insulating layer, which will increase the density of threaded connections. This type of tape is used by plumbers.
Note! The power in the block is limited by the overall power of the transformer involved, as well as the maximum possible current of the transistors.
Making your own power supply
You can make a UPS yourself. For this you will need minor changes in the electronic throttle jumper. Next, the connection is made to the pulse transformer and rectifier. Individual elements schemes are deleted due to their uselessness.
If the power supply is not too high-power (up to 20 W), it is not necessary to install a transformer. A few turns of conductor wound around a magnetic circuit located on the ballast of the light bulb is enough. However, this operation can only be carried out if there is sufficient space for the winding. For example, a conductor of the MGTF type with a fluoroplastic insulating layer is suitable for it.
Usually not much wire is needed, since almost the entire lumen of the magnetic circuit is given over to the insulation. It is this factor that limits the power of such blocks. To increase power you will need a pulse type transformer.
A distinctive characteristic of this type of SMPS (switching power supply) is the ability to adapt it to the characteristics of the transformer. In addition, the system does not have a feedback loop. The connection diagram is such that there is no need for particularly accurate calculations of the transformer parameters. Even if a gross error is made in the calculations, the uninterruptible power supply will most likely function.
A pulse transformer is created on the basis of a choke, on which a secondary winding is superimposed. As such, varnished copper wire is used.
The interwinding insulating layer is most often made of paper. In some cases, a synthetic film is applied to the winding. However, even in this case, you should additionally protect yourself and wrap 3-4 layers of special electrical protective cardboard. As a last resort, paper with a thickness of 0.1 millimeter or more is used. Copper wire is applied only after this safety measure has been provided.
As for the diameter of the conductor, it should be as large as possible. The number of turns in the secondary winding is small, so the appropriate diameter is usually selected by trial and error.
Rectifier
To prevent saturation of the magnetic circuit in the uninterruptible power supply, only full-wave output rectifiers are used. For a pulse transformer operating to reduce voltage, a circuit with a zero mark is considered optimal. However, for it it is necessary to make two absolutely symmetrical secondary windings.
For a switching uninterruptible power supply, a conventional rectifier operating according to the diagram is not suitable diode bridge(on silicon diodes). The fact is that for every 100 W of transported power, the losses will be at least 32 W. If you make a rectifier from powerful pulsed diodes, the costs will be high.
Setting up an uninterruptible power supply
When the power supply is assembled, all that remains is to connect it to the largest load to check whether the transistors and transformer are overheating. The maximum temperature for the transformer is 65 degrees, and for transistors - 40 degrees. If the transformer gets too hot, you need to take a conductor with a larger cross-section or increase the overall power of the magnetic circuit.
The above actions can be performed simultaneously. For transformers made from choke balances, it will most likely not be possible to increase the cross-section of the conductor. In this case, the only option is to reduce the load.
High Power UPS
In some cases, the standard ballast power is not enough. As an example, let's take the following situation: you have a 24 W lamp and you need a UPS for charging with characteristics of 12 V/8 A.
To implement the scheme, you will need an unused computer power supply. From the block we take out the power transformer along with the R4C8 circuit. This chain protects power transistors from excessive stress. We connect the power transformer to the electronic ballast. In this situation, the transformer replaces the inductor. Below is a diagram for assembling an uninterruptible power supply based on an energy-saving light bulb.
It is known from practice that this type of block makes it possible to receive up to 45 W of power. The heating of the transistors is within the normal range, not exceeding 50 degrees. To completely eliminate overheating, it is recommended to install a transformer with a large core cross-section into the transistor bases. Transistors are placed directly on the radiator.
Potential Bugs
There is no point in simplifying the circuit by applying the base windings directly to the power transformer. If there is no load, considerable losses will occur, since a large current will flow into the transistor bases.
If a transformer is used with an increase in load current, the current in the transistor bases will also increase. It has been empirically established that after the load reaches 75 W, saturation occurs in the magnetic circuit. The result of this is a decrease in the quality of the transistors and their excessive heating. To prevent such developments, it is recommended to wind the transformer yourself using a larger core cross-section. It is also possible to fold two rings together. Another option is to use a larger conductor diameter.
The base transformer, which acts as an intermediate link, can be removed from the circuit. For this purpose, the current transformer is connected to a dedicated winding power transformer. This is done using a high-power resistor based on a feedback circuit. The disadvantage of this approach is the constant operation of the current transformer under saturation conditions.
It is unacceptable to connect the transformer together with the choke (located in the ballast converter). Otherwise, due to the decrease in overall inductance, the frequency of the UPS will increase. The consequence of this will be losses in the transformer and excessive heating of the rectifier transistor at the output.
We must not forget about the high responsiveness of diodes to increased reverse voltage and current. For example, if you put a 6-volt diode in a 12-volt circuit, this element will quickly become unusable.
Transistors and diodes should not be replaced with low-quality electronic components. The performance characteristics of the Russian-made element base leave much to be desired, and the replacement will result in a decrease in the functionality of the uninterruptible power supply.
Hello friends. In the era of LED technology, many still prefer to use fluorescent lamps(they are also housekeepers). This is a type of gas-discharge lamps, which many consider, to put it mildly, not a very safe type of lighting.
But, despite all doubts, they have successfully hung in our homes for decades, which is why many still have non-working economy lamps.
As we know, the operation of many gas-discharge lamps requires high voltage, sometimes several times higher than the mains voltage, and an ordinary housekeeper is no exception.
Such lamps have built-in pulse converters, or ballasts. As a rule, in budget options a half-bridge self-oscillating converter is used according to a very popular circuitry. The circuitry of such a power supply works quite reliably, despite the complete absence of any protection other than a fuse. There is not even a normal master oscillator here. The triggering circuit is built on the basis of a symmetrical diac.
The circuit is the same as that of, only instead of a step-down transformer, a storage choke is used from there. I intend to quickly and clearly show you how such power supplies can be turned into a full-fledged step-down switching power supply, plus provide galvanic isolation from the network for safe operation.
To begin with, I want to say that the converted unit can be used as a basis for chargers and power supplies for amplifiers. In general, it can be implemented where there is a need for a power source.
You just need to modify the output with a diode rectifier and a smoothing capacitor.
Any housekeeper of any power is suitable for conversion. In my case, this is a fully working 125 Watt lamp. First you need to open the lamp, take out the power supply, and we no longer need the bulb. Don’t even think about breaking it, because it contains very toxic mercury vapors that are deadly to living organisms.
First of all, we look at the ballast circuit.
They are all the same, but may differ in the number of additional components. A rather massive inductor is immediately noticeable on the board. We heat up the soldering iron and solder it.
We also have a small ring on the board.
This is a flux feedback transformer and it consists of three windings, two of which are master windings,
and the third is the flux feedback winding and contains only one turn.
And now we need to connect the transformer from computer unit power supply as shown in the diagram.
That is, one of the terminals of the network winding is connected to the feedback winding.
The second pin is connected to the junction point of the two half-bridge capacitors.
Yes, friends, this process is complete. See how simple it is.
Now I will load the output winding of the transformer to make sure there is voltage.
Don't forget, the initial launch of the ballast is done with a safety light. If the power supply is needed for low power, you can do without any transformer at all, and wind the secondary winding directly onto the inductor itself.
It wouldn't hurt to install power transistors on the radiators. During operation under load, their heating is a natural phenomenon.
The secondary winding of the transformer can be made for any voltage.
To do this, you need to rewind it, but if the block is needed, for example, for charger car battery, then you can do without any rewinding. For the rectifier it is worth using pulse diodes, again, optimal solution– this is our KD213 with any letter.
In the end, I want to say that this is only one of the options for remaking such blocks. Naturally, there are many other ways. That's all, friends. Well, as always, KASYAN AKA was with you. Until next time. Bye!
Etching printed circuit boards
Homemade miniature low-voltage soldering iron Clock on gas-discharge indicators - etching of circuit boards
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