Laptop charging from the cigarette lighter in the car, schematic diagram

Laptop car charger with my own hands

Going somewhere in the trip or on nature, I necessarily take a laptop. The laptop is always at work: I either develop schemes or work with the site. As always the charge is running out at the most interesting place, unpleasant surprise, isn’t it? I thought about buying a charger from the cigarette lighter, but we have prices from 1500r. So and the desire to pay for a piece of metal, but there was a desire to collect myself, especially since the scheme is on the Internet, but as in the past time in search of an oscillator for argon arc welding, devices assembled mostly at UC3842. There was a way to build on the NE555, but as organized by the protection of the voltage, I did not like it, if the key will fly out, my laptop will fly out.

I understood the principle of such converters and assembled them myself from zeros. I drew a schematic of the car converter for a laptop, based on the TL494, which I have a lot of ordered from China.

Tl494 converter circuit

The Tl494 converter scheme

There is nothing special to tell, the generator for TL494 with voltage and current feedback. The generator is tuned to 134kHz, and the output frequency is 67kHz. I coordinated control of the oscillator via transistor repeater, to unload the chip. I built the repeater with 2SA733 and 2Sc945. The 60N03P armature transistor from my motherboard with 60A maximum current and 30V maximum voltage, the Schottky diode for 55A is the same. At the output for filtering and stabilizing the capacitance is ceramic and two 470µF electrolytes. On the minus busbar is a shunt for measuring current. Everything is calculated, ready to assemble. There is the main part of the converter which is not difficult to make.

To find out what inductance is needed, I will use the program BoosterRing 6.1 from the package All-in-One by Vladimir Denisenko

Calculate the Throttle for our converter

I choose the size of the ring and the material. Ring by the way from ATX power supply In the initial data I choose the type of reactor Inverting (buck-boost) voltage I choose based on the voltage in the vehicle onboard network minimum 11V, maximum 15V output voltage I choose 19.5V. Current consumption of 3A, and a frequency of 67kHz wire diameter 0.71mm, also check the box to use the desired wire diameter I press the button Calculate I know that I need to add four 1.2m long wire, wind 27 turns, and get the inductance of 70mcg. So I did that, got all parts ready and carefully unwound my choke. I stripped all the wires and checked them with a wiretap to see if they were shorted. Twisted the edges of all the wires into a braid and soldered. Then I used my new inductance meter, the readings were almost right, but there was nothing to measure, so I left it as is. The main part is done, the rest is just small stuff.

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The circuit board for the laptop charger

Converter PCB

I drew the board on a piece of 60x50mm thick textolite. Download PCB Read Get password from the archive

Laptop converter from below

Somehow I mixed up the drain and the sink, I had to cut the track and put a copper jumper. I corrected my mistake in the project

Starting up the converter for your notebook

The circuit did not start immediately, at first I had to solder a dozen resistors to exactly match the voltage and current protection. But in general, the circuit worked without any problems.

The scheme tried to load a light bulb 24V 100W, current limited to 2.9A, voltage sags.

Close-up of the converter board

I will post pictures of the converter from all sides

Close-up of the converter board

Close-up of the converter board

Close-up of the converter board

I can’t say it’s not bad, now I need to think about the case and the power cord. The power connector is rushing from China, soon I will publish pictures of the case. Also the circuit board will be working in a strong vibration, so you need to fill the circuit varnish. Edward

Laptop charging from the cigarette lighter in the car, schematic diagram

It is very good if you can do with their own hands a variety of crafts. So, if you do not have any desire to buy cheap, but with Chinese-quality voltage converter from 12 (car on-board voltage) in 18-20 volts (supply voltage of modern laptops of different models), it makes sense to collect it yourself. There are advantages and disadvantages. Of the disadvantages should be noted only that it will have to run and work. The main advantage is that it will cost less than the Chinese.

The cost of parts, even taking into account the fact that you will take new ones in the store, is not great. You can buy even cheaper at the market or flea markets. The ideal option is to find used parts. Much of the parts can be taken from a switching power supply. You can solder out electrolytic capacitors, diodes, transistors.

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You can even get them for free (or for a bargain), depending on your luck. Just pay special attention to their compatibility. The characteristics of analogs must by no means be worse than those shown in the schematic. It is better to choose with some reserve in characteristics. The second advantage is that the self-made device is more reliable. If you choose and assemble the radio components responsibly.

In this case you should not buy parts with the calculations to save money – all the characteristics must differ only in the larger side. This is a prerequisite for a quality product and its long-term and stable operation. Finally, it will be much more interesting to fiddle with yourself than to sit idly by the TV screen. Especially since there is nothing to watch.

And it is never superfluous to learn to do something with your own hands. In the future, this can turn into a hobby, and if the equipment malfunctions, you will not have to go to the workshop. In our country have always been valued and will be valued “capable hands”. In the days of the Union of Soviet Socialist Republics, forty years ago, the control circuit would have had to be made on an elemental basis.

But now everything is much simpler. One microcircuit can replace dozens of radio components and, accordingly, save a lot of time and money. When assembling this circuit it is necessary to take into account another nuance. Field effect transistors are afraid of static electricity. You need to take all measures to avoid the failure of a powerful (and quite expensive) element. But before you start working you should remember the main thing – take care of your safety. Do not forget about safety precautions.

Although you can do whatever you want at home, don’t forget to do the following things. You will also need a few other things to make your project a success. A soldering iron is better if it is not too powerful – 25, 40 or 65 watts is good. It will be just fine if it is low-voltage (designed for low voltage up to 36 volts) or powered by a divider transformer. It is highly desirable that it has a ground connection.

Tuning or retouching the seats with our own hands

First, it is much safer. Secondly, semiconductors are afraid of static electricity. This is especially true for field-effect transistors. In addition, a powerful soldering iron can burn parts. For a successful project you will need a tester. You can use a Chinese tester or a simple dial tester. It can be used to check the worthiness of radio components and check the voltage and other parameters.

Everything starts with the circuit.

Snapshot 6

But let’s leave all the talk and get straight to the subject of our conversation. Like any business begins with a plan, a radio device begins with a circuit diagram. In fact it is not complicated and can be put into practice even by a novice radio amateur.

It is based on a 555 series timer. It controls a powerful key switch, a field effect transistor. The conversion takes place due to the induction of the choke. Due to this it was possible to eliminate the use of a transformer. The output pulses are smoothed by electrolytic capacitors. The output voltage is stabilized with a stabilizing diode. It should be powerful enough – 1 or 1.2 watts. As we have already said the circuit diagram is not complicated, if you consider the modern elementary base:


For specialists, the circuit is simple.

The craft will cost quite inexpensive. As it is easy to understand from the circuit, the biggest load lies on the powerful key-field transistor and the output diodes. Keep in mind that these semiconductors must be designed for the maximum possible current. It is best to take Schottky diodes with a current of at least 10 Amps, but it is better to take more. In general, the rule in this case is simple – maximum parameters. This will allow you to get an output current of up to 5 amps without the risk of burning it. And it will greatly increase reliability in operation.


They will heat up during operation. For this reason it makes sense to equip them with an additional heatsink for better cooling. It is recommended to use a metal (aluminum) housing of the device as a radiator. The choke can also be wound independently – it consists of twenty to twenty-five turns of thick shielded wire (PEL, PEV and the like).

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It is easy to wind and this process will not take much time at all. The ring can be taken from the output filter of any power supply. They are usually labeled (yellow-white or white-green-painted). Finally, the conductors going to the cigarette lighter and directly to the laptop make a thick and flexible wire. Do not forget – the currents that will flow during operation, have significant values. In addition note, in the self-made it is quite possible to use standard connectors.

Still image10

The foundation of your inverter. One of the most critical tasks – making a printed circuit board. It is not difficult to make it yourself for your miracle of technology. You can use an ordinary dielectric plate, but it will be much better if you take a special dielectric plate coated with copper. In this case the parts will not have to be additionally fastened, reliability of installation will increase significantly. And the look will be just great.

So, to make a printed circuit board you need a plate of copper-coated gethinax or fiberglass (both single-sided and double-sided versions will do). It is best to etch the board with chemicals. You draw the conductive tracks with paint or varnish, then place it in the solution. The tracks remain, and the copper, where it has not been coated, will disappear.

Still image11

Conductive tracks can also be cut with a knife – a special knife cutter or a shoemaker is best. You can also use a regular knife, but it is more difficult. You can cut out the tracks however you want, but in full accordance with the schematic diagram. We made sure that you have a ready made version.


The circuit board is not big – it is about the size of a cigarette box. You can make a similar one for yourself by looking at the picture. This version is definitely workable, because we have already tested it. The layout of the circuit board for a DC-DC converter. You can take an off-the-shelf printed circuit board or make one yourself. If you choose to make it from aluminum, it can be used as a heat sink for the power elements of the unit – powerful transistors and diodes.

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But do not forget to make holes for ventilation, otherwise the device can overheat. And in case of significant overheating even fail. Note, the tracks, which are designed for high current, can be strengthened by well tinned (covered with an additional layer of tin) and soldered on the surface of additional conductors.

After you do the installation you should have a block like the one shown in the pictures below.

Still image13

An approximate result of your work. So, to summarize, you can say the following. The converter from the cigarette lighter to the laptop computer you can, even need to make yourself. It will not let you down at the most inopportune moment, will allow you to get the necessary voltage and current to work laptop (depends on the transistors, diodes and choke).

A distinctive feature of the converter is that the efficiency is quite high – in the range of 85 – 87%. Besides, if it suddenly breaks, you can always repair it yourself without going to predatory repair shops. Or even make another one.

Note that radio amateurism is a great and useful hobby and an opportunity to have a great time. We remind you that you can always buy all the components to assemble such a converter inexpensively. Or you can borrow the device for parts from your friends.

There is nothing scarce and expensive here. Note, there are also ready-made kits. But they will cost more than the components individually. But there is no need to bother. And do not forget to follow safety rules – life and health is much more expensive. Come to us. We have a lot of different useful schemes. Good luck in your endeavors.

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