Fluorescent and halogen lamps are gradually becoming a thing of the past, giving way to LED lamps. In the lamps where they were used, unnecessary electronic transformers were left, which were responsible for lighting these lamps. It seems that unnecessary - a place in the trash heap. But this is not the case. These transformers can be used to assemble powerful power supplies that can power power tools, LED strips, and more.
Content
- Electronic transformer device
- DIY assembly
- Conversion into a power supply
Electronic transformer device
The massive transformers we are accustomed to have recently begun to be replaced by electronic ones, which are distinguished by their low cost and compactness. The dimensions of the electronic transformer are so small that they are built into the housings of compact fluorescent lamps (CFLs).
All such transformers are made according to the same scheme, the differences between them are minimal. The circuit is based on a symmetrical oscillator, otherwise called a multivibrator.
They consist from a diode bridge, transistors and two transformers: matching and power. These are the main parts of the circuit, but not all. In addition to them, the circuit includes various resistors, capacitors and diodes.
Schematic diagram of an electronic transformer.
In this circuit, direct current from the diode bridge is fed to the transistors of the oscillator, which pump energy into the power transformer. The ratings and type of all radio components are selected so that a strictly defined voltage is obtained at the output.
If you turn on such a transformer without load, then the autogenerator will not start and there will be no voltage at the output.
DIY assembly
Electronic ballast can be bought in a store or found in your bins, but the most interesting option would be to assemble an electronic transformer with your own hands. It is assembled quite simply, and most of the necessary parts can be dig into broken power supplies and in energy-saving lamps.
- Required components: A diode bridge with a reverse voltage of at least 400 V and a current of at least 3 A or four diodes with the same characteristics.
- 5 amp fuse.
- Symmetrical dynistor DB3.
- 500 kOhm resistor.
- 2 resistors 2.2 Ohm, 0.5 W.
- 2 bipolar transistors MJE13009.
- 3 film capacitors 600 V, 100 nF.
- 2 toroidal cores.
- Lacquered wire 0.5 mm².
- Conventional insulated wire 2.5 mm².
- Radiator for transistors.
- Bread board.
It all starts with a breadboard, on which you will install all the radio components. On the market, you can buy two types of boards - with one-sided metallization on brown fiberglass.
And with double-sided end-to-end, on green.
The choice of the board depends on how much time and effort you will spend on assembling the project.
Brown boards are of disgusting quality. They are metallized in such a thin layer that tears are visible in some places. It is poorly wetted with solder, even if you use a good flux. And everything that was soldered - comes off along with the metallization at the slightest effort.
Green ones cost one and a half to two times more, but everything is in order with the quality. Metallization on them with thickness has no problems. All holes in the board are tinned at the factory, due to which copper does not oxidize and there are no problems with soldering.
You can find and buy these layouts both in the nearest radio store and on aliexpress. In China, they cost half the price, but delivery will have to wait.
Choose radio components with long leads, they will come in handy when installing the circuit. If you are going to use used parts, be sure to check their functionality and the absence of external damage.
The only detail you have to make yourself is the transformer.
The matching wire must be wound with a thin wire. Number of turns in each winding:
- I - 7 turns.
- II - 7.
- III - 3.
Do not forget to fix the windings with tape, otherwise they will creep.
The power transformer consists of only two windings. Wrap the primary with a 0.5mm² wire, and the secondary - 2.5mm². The primary and secondary housing consist of 90 and 12 turns, respectively.
For soldering, it is better not to use "old-fashioned" soldering irons - they can easily burn temperature-sensitive radioelements. Take a better soldering iron with power adjustment, they do not overheat, unlike the first ones.
install the transistors on the radiators in advance. Doing this on an already assembled board is extremely inconvenient. You need to assemble the diagram from small details to large ones. If you install the large ones first, they will get in the way when soldering the small ones. Consider this.
When assembling, look at the schematic diagram, all connections of radioelements must correspond to it. Slide the leads of the parts into the holes on the board and bend them in the desired direction. If the length is not enough, extend them with a wire. After soldering, glue the transformers to the board with epoxy resin.
After assembly, connect a load to the terminals of the device and make sure that it works.
Conversion into a power supply
It happens that the batteries of the power tool fail, but there is no opportunity to buy a new one. In this case, an adapter in the form of a power supply will help. After a little modification, such an adapter can be assembled from an electronic transformer.
Details that will be needed for the rework:
- NTC thermistor 4 ohm.
- Capacitor 100 μF, 400 V.
- Capacitor 100 uF, 63V.
- Film capacitor 100 nF.
- 2 resistors 6.8 Ohm, 5 W.
- 500 ohm resistor, 2 W.
- 4 diodes KD213B.
- Radiator for diodes.
- Toroidal core.
- Wire with a cross section of 1.2 mm².
- A piece of a circuit board.
Before starting, check if you have forgotten any part. If all parts are in place, start converting the electronic transformer into a power supply.
Solder a 400 V, 100 μF capacitor to the diode bridge output. To reduce the charging current of the capacitor, solder the thermistor into the break in the power wire. If you forget to do this, the diode bridge will burn out the first time you plug it into the network.
Disconnect the second winding of the matching transformer and replace it with a jumper. Add one winding to both transformers. Make one turn on the matching one, and two on the power one. Connect the windings to each other by soldering two parallel-connected 6.8 Ohm resistors into the wire break.
To make a choke, wind 24 turns of 1.2 mm² wire around the core and secure it with tape. Then, on the breadboard, assemble the remaining radio components according to the diagram and connect the assembly to the main circuit. Remember to install diodes on the heatsink, when working under load, they get very hot.
Secure the entire structure in any suitable enclosure and the power supply can be considered assembled.
After final assembly, plug in the device and test its operation. It should give out a voltage of 12 volts. If the power supply gives them out, you did your job perfectly well. If it doesn't work, check if you took a non-working transformer.
