Power unit. Power supply Diagram of a power supply with a fixed output voltage

Good day to all.

So, I once wrote a review of a set of car bluetooth headsets, the main unit of which (the part containing the speaker, microphone and all the buttons) is powered by a battery and mounted on the sun visor using a special metal bracket. Actually, you can watch this very review. So, after 7 months of operation, this set has proven itself only on the good side, except for one very important point for me - the power supply system. The battery used cannot be called capacious, and in actual use, its charge lasts for about a week and a half, after which it has to be recharged. As usual, the battery runs out at the most inopportune moment, and there are no notifications about the battery charge status. Of course, I could just connect the charger and leave everything in this state, but the wires stretching through the interior somehow confuse me. In general, it was necessary to do something and organize constant power supply to the unit without unnecessary wires and a weak battery. There is only one way out of this situation - connecting it to the car wiring, and in order to reduce the voltage from 12V to 5V you need this very converter.

After looking at offers on Aliexpress and eBay, my choice fell on a converter capable of delivering 3A. If you take it, then with a reserve - if necessary, you can connect something else to it :) The parcel was sent without a track and spent about 3 weeks on the way, after which it was successfully stuffed into the mailbox by a kind postman.

The converter is supplied in a sealed bag that does not have special slots to simplify the process of opening it. Without scissors or a knife, it is very difficult to open the bag.

The converter itself is very compact - 6.5 x 2.7 x 1.5 centimeters and is a small black plastic box with two “ears” for mounting and 4 wires coming from its depths. By the way, it claims to be “waterproof” - the entire filling is filled with something resembling bitumen :) There shouldn’t be any problems with connecting - the input and output are marked in the same way as the positive and negative contacts.


Since before making the purchase it was established that without a battery installed inside, but with the power connected, my bluetooth module does not work, I bought a converter without any connectors on the wires, since they would still have to be cut off.

I immediately checked how the converter copes with its main task - lowering the voltage. The battery output was 4.97V - excellent.


I thought for a long time about how best to connect it to the bluetooth module and did not find anything simpler than soldering wires to the contacts through which energy is supplied from the battery.

The voltage on a 100% charged battery is 4.2V, and on the converter - 4.97V. You can connect it like that - everything will work. Or you can lower the voltage to the battery charge level.


Personally, at first I soldered everything directly, but then I changed my mind and soldered a 1A fuse - it fit perfectly in the battery compartment, which is no longer needed. If you use thin wires, they can be passed under the battery compartment cover without making additional holes in the body of the bluetooth unit.

In general, the finished design looked like this:


I later insulated the places where the wires were soldered :)

Now all that's left to do is connect it all to the car's network. Everything here is strictly individual, but I was lucky, my car has wiring under the hatch, which has a constant 12V, and electricity is supplied even when the car is turned off, which ensures that the headset works 24 hours a day. The wires I need are hidden behind the interior lamp.


We connect, install the lamp back and check the functionality of the entire system. Everything started the first time. Hooray! The goal has been achieved. From the bluetooth module, I broke off the legs on which the metal plate was attached and attached it behind the rearview mirror using double-sided tape. Now it doesn’t dangle on the visor, doesn’t catch the eye, and still works great :)


To summarize everything that is written above, I can say that the reviewed converter was just perfect for my needs. Firstly, it actually lowers the voltage to the desired level. Secondly, it has a very compact size, which means it can be hidden behind the ceiling upholstery or in any other place without any problems. Thirdly, during operation it does not heat up, and if it does heat up, the heating is minimal - it was not possible to determine the temperature change by touch. Fourthly, it made it possible to get rid of unnecessary wires and forget about weekly battery charging. And fifthly, its price is very humane. In addition to my example, this converter is perfect for connecting recorders, radar detectors and other small automotive items powered by the on-board network. In general, I am 100% satisfied with the purchase.

That's probably all. Thank you for your attention and your time.

A 5-12 volt DC-DC boost converter is easiest to assemble using the LM2577, which provides 12V output using a 5V input signal and a maximum load current of 800 mA. M\C LM2577 is a boost forward pulse converter. It is available in three different output voltage versions: 12V, 15V and adjustable. Here is the detailed documentation.

The circuitry on it requires a minimum number of external components, and such regulators are cost-effective and easy to use. Other features include a built-in oscillator at a fixed frequency of 52 kHz that does not require any external components, a soft start mode to reduce inrush current, and a current control mode to improve input voltage tolerance and output variable load.

Characteristics of the converter on LM2577

• Input voltage 5V DC
• Output 12V DC
• Load current 800 mA
• Soft start function
• Overheat shutdown

An adjustable chip is used here LM2577-adj. To obtain other output voltages, you need to change the value of the feedback resistor R2 and R3. The output voltage is calculated using the formula:

V Out = 1.23V (1+R2/R3)

In general, LM2577 is inexpensive, the inductor in this circuit is unified - 100 μH and the maximum current is 1 A. Thanks to the pulsed operation, no large radiators are required for cooling - so this converter circuit can be safely recommended for repetition. It is especially useful in cases where you need to get 12 volts from the USB output.

To charge mobile devices, 5-volt power supplies operating from mains voltage are usually used. A voltage of 5 V can also be obtained from a 12-volt vehicle network or from a 12-volt power supply. This can be done using simple circuits with various voltage stabilizers.

In such circuits, the stabilizer will heat up noticeably, which will worsen its output current parameters. To prevent the stabilizer from overheating and failing, it must be placed on a heat sink. The voltage at the input to the stabilizer should not be higher than 15 V.

Most mobile devices detect connection to the charger by the presence of a jumper between the second and third pins. But USB switching schemes may be different. It’s better to read about this in the article.

The circuit uses only three components: the voltage regulator itself and two 16-volt capacitors with a nominal value of 100 and 330 nF.

You can use Soviet voltage stabilizers: 2-amp KR142EN5A or 1.5-amp KR142EN5B. Naturally, it is possible to replace them with foreign analogs shown in the picture, which shows the converter on the KR142EN5 stabilizer:

If your converter has an output current of no more than 0.1 A, then you can use stabilizers made in SO-8, SOT-89 or TO-92 housing. Circuits with such converters are presented in the figures below:

It is worth adding that the easiest way to make a converter is to remove the board from a ready-made car cigarette lighter adapter. The board of this adapter must be adapted to work outside the car. You can find a lot of information about this.

Additional Information:

Such voltage stabilizers can be found in TVs with picture tubes. Most often there are microcircuits of the 7805 and 7809 series.

In the absence of capacitors, the circuit is fully functional. The stabilizer has protection against overheating, however, the range is quite large - from 65 to 140. Then there is a sharp drop in voltage, and pulsations of the microcircuit appear.

In other words, if the circuit is powered by a battery, then there is no need for an input capacitor. It is recommended to set the output capacitor with a nominal value of 1 µF or less, otherwise its discharge may burn out the circuit if a short circuit occurs at the input (on the side where the battery is located).

Surges from inductive loads are not critical for this circuit.

DIY USB charger for Ni-Mh batteries

Currently, pulse converters are used almost everywhere and very often replace classic converters, which, as a rule, at high currents experience significant losses in the form of heat.

The diagram given here is a simple one pulse step-down converter from 12V to 5V. The circuit is based on a popular and inexpensive microcircuit.

The device is designed to work with a 12V vehicle on-board network and can be used to charge/power GPS navigators or mobile phones equipped with a USB connector.

In standby mode, the circuit is completely disconnected from the power source, and during normal operation it turns off immediately after the load is removed. The converter is started by briefly pressing the button and if a load, such as a telephone, was not previously connected to the output, the converter will automatically turn off.

Description of the operation of the voltage converter from 12 to 5 volts

As mentioned earlier, the circuit is built on the MC34063 chip, which is a controller containing the main components necessary for the manufacture of DC-DC converters.

The MC34063 contains temperature compensation, a voltage reference, a comparator, and a variable fill oscillator. In addition, this chip contains a current limiting circuit and an internal switch that can handle currents up to 1.5 A.

To make a converter, you need an op-amp, an inductor, a diode and several resistors and capacitors. The figure below shows the complete circuit diagram of the converter.

The heart of the device is the previously mentioned DD2 chip (MC34063), as well as inductor L1 and Schottky diode VD1. The diode plays a very important role - thanks to it, the circuit is closed for the flow of current from inductor L1, which occurs after the internal output switch MC34063 is turned off.

Capacitor C3 determines the operating frequency of the internal oscillator DD2 and with a capacitance of 470pf the frequency will be about 50 kHz. Resistor R5 is responsible for limiting the converter current and all the pulse current flows through it, which then flows to inductor L1. The current limit is set at about 1.1A.

Capacitor C1 filters the supply voltage. The output filter is a capacitor C4, and a 1.3 W zener diode VD3 protects the circuit from possible short-term voltage increases.

A very important element is R3, R7, since it is responsible for the output voltage. Their ratio is chosen in such a way that with an output voltage of 5V, the voltage at input 5 of the comparator of the DD2 microcircuit is 1.25V.

The big advantage of this scheme is the ability to automatically turn off the power after disconnecting the load. Transistor VT1 and resistors R1, R2 are responsible for this function. When turned off, resistor R1 ensures correct cutoff of transistor VT1. The system is started by briefly pressing the SW1 button.

The converter starts up, and transistor VT2 then maintains a low level based on VT1. Resistor R2 limits the base current of transistor VT1.

To control the current consumed by the load, an operational amplifier DD1 () is used. It operates as a non-inverting amplifier with a gain of 1000. The gain is determined by the values ​​of resistors R8 and R9.

Capacitor C2 filters the amplifier supply voltage. To control transistor VT2, a voltage divider is used across resistors R4 and R6, with a division coefficient of 2.

A slight voltage drop across the measuring resistor (shunt) R11 of the order of 5-6 mV will lead to the opening of transistor VT2 and maintaining the operation of the converter. Thus, to maintain the operation of the converter, it is enough that the current consumption is about 25-30mA. LED VD2 acts as a power indicator, and its current is limited by resistor R10.

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