Bipolar power supply from ready-made Chinese dc-dc step down LM2596 modules. Step-down voltage converter on LM2596 from the Stone Age Lm2596 power supply circuit

LM2596 - buck converter direct current, it is often produced in the form of ready-made modules, costing about $1 (search for LM2596S DC-DC 1.25-30 V 3A). By paying $1.5, you can buy a similar module on Ali with LED indication of input and output voltage, turning off the output voltage and fine-tuning buttons with displaying values ​​on digital indicators. Agree - the offer is more than tempting!

Below is circuit diagram of this converter board (key components are marked in the picture at the end). At the input there is protection against polarity reversal - diode D2. This will prevent the regulator from being damaged by incorrectly connected input voltage. Despite the fact that the lm2596 chip can process input voltages up to 45 V according to the datasheet, in practice the input voltage should not exceed 35 V for long-term use.

For lm2596, the output voltage is determined by the equation below. With resistor R2, the output voltage can be adjusted from 1.23 to 25 V.

Although the lm2596 chip is designed for a maximum current of 3 A of continuous operation, the small surface of the foil mass is not sufficient to dissipate the generated heat over the entire operating range of the circuit. Also note that the efficiency of this converter varies greatly depending on the input voltage, output voltage and load current. Efficiency can range from 60% to 90% depending on operating conditions. Therefore, heat removal is mandatory if continuous operation occurs at currents of more than 1 A.

According to the datasheet, the feedforward capacitor must be installed in parallel with resistor R2, especially when the output voltage exceeds 10 V - this is necessary to ensure stability. But this capacitor is often not present on Chinese inexpensive inverter boards. During the experiments, several copies of DC converters were tested under various operating conditions. As a result, we came to the conclusion that the LM2596 stabilizer is well suited for low and medium supply currents of digital circuits, but for higher output power values ​​a heat sink is required.

It turns out that on the LM2596 microassembly you can easily assemble a full-featured stabilized power supply that can be used in almost any laboratory power supply with protection against possible short circuits.

Maximum permissible characteristics and properties:

Foreign analogues: A complete analogue of this microcircuit is the MIC4576BU chip

Typical microcircuit connection circuit:

All components of the circuit used to assemble the structure in the first version correspond in nominal values ​​to those indicated in the datasheet (see the archive at the link above), only the tuning resistance of fifty kilo-ohms could not be found, so instead of it there is a resistance of 47 kilo-ohms. The advantage of this voltage stabilizer can be considered minimal heating at high currents, which is something that typical KRENOK and LM317 microassemblies cannot boast of.

Additionally, a signal can be sent to the fifth leg of the microassembly to turn off the device.

Option 2 - Adjustable stabilizer voltage based on LM2596T chip

LM2596T, operating in pulse mode, has a fairly high efficiency and allows currents with a nominal value of up to 2 A to flow through itself, without requiring a heat sink. For high load currents, it is necessary to use a radiator with a surface area of ​​at least 100 cm2. In addition, the radiator should be fixed to the microassembly using heat-conducting paste type KPT-8.

The circuit can be configured for any other fixed output voltage, that is, use the stabilizer as a DC-DC converter. To do this, you need to replace resistance R2 with a resistor calculated using the following mathematical formula:

R 2 = R 1 ×(V out / V ref-1)
or R 2 = 1210×(V out /1.23 - 1)

If you connect this design to a network step-down transformer with

Some time ago, while sitting in the car, I thought: why am I charging my phone through the car charger installed in the cigarette lighter. After all, there is often more than one “consumer”, and the cigarette lighter socket itself is sometimes needed. I formulated the specifications for myself: power supply from the on-board network through the ignition switch, output of 1-3 ports with a current of up to 2 A. I searched on the Internet and it turned out that I was far from the first who was puzzled by the problem and, even more, implemented it in various ways.

For my idea, I needed a voltage stabilizer that could withstand the on-board voltage and current up to 3 Amps. There are actually a huge number of implementation options, but they all boil down to one thing - a pulsed step-down converter. Why pulse? Because it has maximum efficiency. This means there will be almost nothing to heat up in the converter and the dimensions promise to be minimal.

A step-down converter is designed to reduce the voltage to the required value. Its power elements operate in key mode, simply on and off. At the moment of switching on, energy is accumulated by the inductor (coil on the core), at the moment when power element(transistor) is turned off, the inductor releases the stored energy to the load. As soon as the inductor releases the accumulated energy, the circuit that controls the output voltage will turn on the power transistor and the process will repeat.
IN currently All chargers for phones and tablets that are inserted into the cigarette lighter socket are made according to a circuit with a pulse step-down converter.

Delivery and appearance:
The board arrived in a sealed antistatic bag, which seems like a reason to rejoice, but in fact it should be taken for granted.
The soldering quality is quite good. Minor flux residue on the reverse side of the variable resistor terminals.
The variable multi-turn resistor allows you to accurately adjust the output voltage.


Mounting holes for screws are provided. There are no terminal blocks, the wires will have to be soldered. Under the chip there are holes with metallization for additional heat removal to reverse side fees.

The scheme couldn't be simpler:

The only thing is that the Chinese have different ratings for the inductor and capacitors. Apparently, whatever is available, they install it. It can't get any worse.

I quickly soldered the wires and the load in the form of a 2.2 Ohm 10 W wirewound resistor.
To limit the temperature during heating, the resistor was placed in water.


There are 2 voltages available at the stand: 12 Volts and 24 Volts. The first switch-on was carried out without a load, to adjust the output voltage so as not to burn the scarf. By rotating the screw of the resistor, I achieved an output voltage of 5 Volts.
A load of 2.2 Ohms implies a current of 2.27 Amps, which fits into the stated parameters of the board as well as my needs with a small margin, since I got hold of a dual connector from a dead motherboard:

1 Ampere per port.

10 minutes of work under load and the board heats up wildly. Photo from thermal imager:

back side

Achtung! Temperature is 115C on the diode and 110C on the microcircuit (side with parts) and 105C on the reverse side.
The throttle temperature is about 70C, a bit too much, but it does not reach saturation.
The maximum temperature for the diode is 150C, and for the microcircuit 125C.

It doesn't fit into any gates. I started to think that this was a defect or that I had once again bought cheap crap.
and discovered that this converter has lousy efficiency. And all due to the fact that the key element in the microcircuit is a bipolar transistor, which, although it operates in the key mode, when open, the voltage across it drops quite a bit.
Increasing the input voltage to 24 Volts did not help the situation.
Efficiency graph at a load current of 3 Amps:


Those. approximately 80% when powered from the vehicle's onboard network. The output on the microcircuit is released at a load of 3 A 3.7 W, and the diode and inductor also heat up. Replacing the diode (3A 40V) and inductor (47 μH), as well as installing a radiator, could solve the heating problem, but why such effort when you can get more advanced step-down converters for the same money.

An attempt to correct the situation:
I installed a small radiator on the reverse side through heat-conducting glue (I sawed the radiator from a faulty computer power supply).




I planned to take the diode there from the “duty room.” It’s a little more complicated with the inductor, but I think I could find one with a larger cross-section of the winding wire (taking into account the decent spread of inductance in the inductors used by the Chinese).
An attempt to turn on and take temperature readings led to a crash =) I mixed up the polarity and burned the microcircuit. I saved money; I had to immediately take 5 of them for experiments, but it would be better not to take them at all, because this ancient converter is so terrible that it doesn’t even work out 50% of the characteristics in the specific board used.

In the vastness of the network I discovered an atypical use of the LM2596 microcircuit - an amplifier audio frequency class D! The signal is supplied to input 4 " Feedback" The frequency of discrediting is really no more than 150 KHz. In no case is there a call to assemble an amplifier based on a converter; there are specialized microcircuits for this =)

The conclusions are disappointing:
The board as sold does not justify the stated characteristics. Moreover, the dependence on the load current is much higher than on the change in voltage. You can modify the board by replacing half of the parts, but what's the point?

Still, if you need a step-down converter, then the best alternative to the one under review would be converters assembled on microcircuits: LM2577, LM 2678 and similar. On this moment I have already ordered several boards to try

While I had been planning to install USB ports on the car for a very long time, my machine went to scrap :(


but still there was still a place where I would put the converter instead of the transformer power supply:
This time (where the creative inscription is):


These are two (front bar with USB ports plexiglass “case” walls torn from an old computer case):


Specially for the review I made a load plate for testing chargers(I even burned a couple, they couldn’t withstand the load). On Ali these are sold ready-made for about $1:

Step-down DC-DC converters are increasingly finding their use in everyday life, households, automotive applications, and also as regulated power supplies in a home laboratory.

For example, on a heavy-duty vehicle, the voltage of the on-board cable network may be +24V, but you need to connect a car radio or other device with an input voltage of +12V, then such a step-down converter will be very useful to you.

Many people order step-down DC-DC converters from various Chinese sites, but their power is quite limited, due to the Chinese saving on the cross-section of the winding wire, semiconductor devices and inductor cores, because the more powerful the converter, the more expensive it is. Therefore, I suggest you assemble a step-down DC-DC yourself, which will surpass the Chinese analogues in power and will also be more economical. According to my photo report and the presented diagram, it is clear that assembly will not take much time.

The LM2596 chip is nothing more than a switching step-down voltage regulator. It is available in both fixed voltage (3.3V, 5V, 12V) and adjustable voltage (ADJ). Our step-down DC-DC converter will be built on the basis of an adjustable microcircuit.

Converter circuit

Basic parameters of the LM2596 regulator

Input voltage………. up to +40V

Maximum input voltage………. +45V

Output voltage………. from 1.23V to 37V ±4%

Generator frequency………. 150kHz

Output current………. up to 3A

Current consumption in Standby mode………. 80uA

Operating temperature from -45°С to +150°С

Housing type TO-220 (5 pins) or TO-263 (5 pins)

Efficiency (at Vin= 12V, Vout= 3V Iout= 3A).......... 73%

Although the efficiency can reach 94%, it depends on the input and output voltage, as well as on the quality of the winding and the correct selection of the inductor inductance.

According to the graph taken from, with an input voltage of +30V, an output voltage of +20V and a load current of 3A, the efficiency should be 94%.

Also, the LM2596 chip has current and overheat protection. I note that on non-original microcircuits these functions may not work correctly or may be completely absent. A short circuit at the output of the converter leads to failure of the microcircuit (tested on two LMs), although there is nothing surprising here; the manufacturer does not write in the datasheet about the presence of short circuit protection.

Schematic elements

All element ratings are indicated on the electrical circuit diagram. The voltage of capacitors C1 and C2 is selected depending on the input and output voltage (input (output) voltage + margin of 25%), I installed the capacitors with a margin of 50V.

Capacitor C3 is ceramic. Its denomination is selected according to the table from the datasheet. According to this table, the capacitance C3 is selected for each individual output voltage, but since the converter in my case is adjustable, I used a capacitor of average capacity 1nF.

Diode VD1 must be a Schottky diode, or another ultra-fast diode (FR, UF, SF, etc.). It must be designed for a current of 5A and a voltage of at least 40V. I installed a pulse diode FR601 (6A 50V).

Choke L1 must be rated for a current of 5A and have an inductance of 68 μH. To do this, take a core made of powdered iron (yellow-white), outer diameter 27mm, inner 14mm, width 11mm, your dimensions may vary, but the larger they are, the better. Next, we wind two wires (the diameter of each wire is 1 mm) 28 turns. I wound a single core with a diameter of 1.4 mm, but with a high output power (40W), the inductor got very hot, also due to the insufficient cross-section of the core. If you wind two wires, then you won’t be able to put the winding in one layer, so you need to wind it in two layers, without insulation between the layers (if the enamel on the wire is not damaged).

A small current flows through resistor R1, so its power is 0.25W.

Resistor R2 is tuning, but can be replaced with a constant one; for this, its resistance is calculated for each output voltage according to the formula:

Where R1 = 1kOhm (according to the datasheet), Vref = 1.23V. Then, let's calculate the resistance of resistor R2 for the output voltage Vout = 30V.

R2 = 1 kOhm * (30V/1.23V - 1) = 23.39 kOhm (reducing to the standard value, we get resistance R2 = 22 kOhm).

Also, knowing the resistance of resistor R2, you can calculate the output voltage.

Testing a step-down DC-DC converter on LM2596

During testing, a radiator with an area of ​​≈ 90 cm² was installed on the chip.

I carried out tests on a load with a resistance of 6.8 Ohms (a constant resistor lowered into water). Initially, I applied a voltage of +27V to the converter input, the input current was 1.85A (input power 49.95W). I set the output voltage to 15.5V, the load current was 2.5A ( output power 38.75W). The efficiency was 78%, which is very good.

After 20 min. During operation of the step-down converter, diode VD1 heated up to a temperature of 50°C, inductor L1 heated up to a temperature of 70°C, and the microcircuit itself heated up to 80°C. That is, all elements have a temperature reserve, except for the throttle, 70 degrees is too much for it.

Therefore, to operate this converter at an output power of 30-40W or more, it is necessary to wind the inductor with two (three) wires and select a larger core. The diode and microcircuit can maintain a temperature of 100-120°C for a long time without any fears (except for heating everything nearby, including the case). If desired, you can install a larger radiator on the microcircuit, and you can leave long leads on the VD1 diode, then heat will be dissipated better, or attach (solder to one of the leads) a small plate (radiator). You also need to tin the tracks as best as possible. printed circuit board, or solder a copper core along them, this will ensure less heating of the tracks during long-term operation at a high output power.

Hello, dear visitors. I bought it on ebay a year ago DC-DC converters for a small laboratory power supply, and indeed for general development. And the price of 66 rubles turned out to be very attractive.

The general view of the converter is shown in the screenshot.

As you can see from the photo, the scarf is not big at all, and measures 41x20mm. The basis of this converter is the LM2596S chip

which is an adjustable, step-down pulse stabilizer voltage with a frequency of up to 150 kHz and a maximum output current of 3A. The stabilizer connection circuit is typical and is shown in Figure 1.

The maximum input voltage of the microcircuit is 40V; I didn’t have such a voltage at the moment, so I analyzed the stabilizer at a voltage at the device input of 27 volts. At the output, I set the voltage to 6.5 volts using a trimming resistor. The maximum current of 3A, with this installation and the absence of at least a small radiator, was considered too high. Therefore, a load current of 1.5 A was chosen. And so, having these parameter values, after half an hour of operation, the temperature of the microcircuit case was approximately 75 degrees Celsius. This state of affairs, I must say, pleased me. Those. when the microcircuit is supplied with a radiator or when blowing is used, the stabilizer output current of 3 amperes is quite realistic. The minimum voltage at the output of this particular stabilizer was 2.5 volts.

Based on this module, you can design a variety of homemade, adjustable, stabilized power supplies, both unipolar and bipolar. It can be used for nutrition LED lamps, is also suitable for powering DC electric motors used in micro drills, with the ability to adjust the speed. Such a stabilizer may well replace the linear stabilizer on the KR142EN5 microcircuit for powering circuits that include microcontrollers. Especially when the difference between the input voltage of the stabilizer and the output voltage is very large and it becomes necessary to use a heat sink for the microcircuit. It makes sense to use such a stabilizer to suppress excess voltage when the voltage of the secondary winding of the transformer you purchased is greater than necessary, but it is impossible or too lazy to wind up the turns. Then sixty-six rubles is nothing. Good luck. K.V.Yu.