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Description of the step down converter based on the LM2596S with voltage measure

grala1 5820 6

TL;DR

  • A step-down converter module based on LM2596S-ADJ adds input/output voltage measurement on a 3-digit display with a button to switch readings and calibrate the voltmeter.
  • The module accepts up to 35V DC input, regulates 3.2 to 35V DC output with a potentiometer, and claims about 3A capability.
  • Tested under artificial loads at 12, 15, and 24V input with 5V and 12V output, it reached no more than about 85% efficiency.
  • Highest efficiency appeared at 15V input and 12V output, while the worst case was 24V to 5V; at 2.5A there, the converter reached about 55°C after 30 minutes.
  • The measurements show the converter cannot always sustain the advertised 3A while holding output voltage, despite sellers sometimes claiming higher efficiency.
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Treść została przetłumaczona polish » english Zobacz oryginalną wersję tematu
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  • Hello.
    Below I present a description of the step-down converter based on the LM2596S-ADJ chip.

    Description of the step down converter based on the LM2596S with voltage measure

    The prices of the converter start on Aliexpress from less than $ 1.60 with shipping, prices with shipping on Polish auction portals start from about PLN 15.
    The maximum input voltage for the converter is 35V DC (the converter IC itself can withstand a higher voltage, but the limitation here is the electrolytic capacitor at the input, which here has 35V - you can find converters with a 50V capacitor).
    The output voltage is regulated by a potentiometer in the range from 3.2 to 35V DC, efficiency up to about 3A.
    Converter dimensions: 65 x 35 x 16 mm
    The converter has a built-in voltage measurement circuit on the input and output side, displaying the voltage on a 3-digit display with a resolution of 0.1V. The voltage measurement is switched over using the button. The converter has two LEDs informing about whether the displayed result is a voltage measurement on the input or output side. It is possible to calibrate the voltmeter by holding down the button for a longer time while displaying the value you want to calibrate.
    The converter was tested with an artificial load for the input voltages: 12, 15 and 24V and for the output voltages of 12 and 5V.
    In the conducted tests, voltages and currents on the input and output side of the converter were measured, power and efficiency were calculated.
    Below I present the measurement results.
    Input voltage 12V, output voltage 5V:

    Description of the step down converter based on the LM2596S with voltage measure

    Input voltage 24V, output voltage 5V:

    Description of the step down converter based on the LM2596S with voltage measure

    Input voltage 15V, output voltage 12V:

    Description of the step down converter based on the LM2596S with voltage measure

    Input voltage 24V, output voltage 12V:

    Description of the step down converter based on the LM2596S with voltage measure

    The diagram below shows the efficiency of the converter depending on the current consumed from the converter. We have shown the efficiency for 4 different variants.

    Description of the step down converter based on the LM2596S with voltage measure

    As you can see from the diagram - the efficiency of the converter is not a constant value and it can be seen here that the highest efficiency of the converter is at 15V input voltage and 12V output voltage, and the lowest at 24V input voltage and 5V output voltage.
    It can also be seen that the efficiency also varies with the load on the inverter.
    As you can see - the efficiency of this converter does not exceed 85%, where many sellers give even greater value in their descriptions.
    It can also be seen from the measurements that it is not always possible to load the 3A converter and it will keep the voltage at the output.
    I also tested the converter temperature for the configuration where the efficiency was worst - 24V / 5. With a consumption of 2.5A in this configuration, the converter temperature after 30 minutes was about 55 ° C.
    Below is a link to the description of a cheaper converter based on the same system, but without a built-in voltmeter.
    https://www.elektroda.pl/rtvforum/topic3420289.html#16964655

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    About Author
    grala1
    VAG group specialist
    Offline 
    grala1 wrote 9811 posts with rating 5028, helped 1495 times. Live in city Kalisz. Been with us since 2006 year.
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  • #2 16965800
    arekkolisz
    Level 2  
    Good job. It will definitely be useful to anyone in a quandary entitled which chip to buy :) a review like a report, the chart tells a lot about the layout at first glance. The only thing I miss is information about the maximum voltage that can be given to the system after changing the capacitors. I know it's on the catalog note, but everyone has to check it every time, and you'd know right away. best regards :)
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  • #3 16966163
    karlos79
    Level 33  
    Hello

    I have such an inverter, I recommend buying it.
    It is a cheap and good inverter.

    best regards
  • #4 16966941
    gulson
    System Administrator
    It's amazing that such a small and cheap toddler will pull out almost 3A. Interestingly, it keeps parameters quite well.
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  • #5 16974116
    es2
    Level 16  
    After those "oohs" and "ahs" a bit of tar. Not resistant to short circuit, they fall like flies. I thought that I would make a workshop power supply on it (no adjustable current limitation) and here a hatch. I already have a dozen or so burned. Out of curiosity, I made a stabilizer according to the LM2576 application and it is not afraid of short circuits.
  • #6 17001068
    Jawi_P
    Level 36  
    es2 wrote:
    I thought that I would make a workshop power supply on it (no adjustable current limitation) and here a hatch. I already have a dozen or so burned. Out of curiosity, I made a stabilizer according to the LM2576 application and it is not afraid of short circuits.

    I do not suspect the application of this system, the Chinese also uses DS and does as the manufacturer says in the note. Nobody bothers there.
    Maybe the LM chip itself, but some fake?
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  • #7 17001178
    yogi009
    Level 43  
    I wonder how it is sown ...
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Topic summary

✨ The discussion centers around the LM2596S-ADJ step-down converter, highlighting its specifications, pricing, and performance. Users note its maximum input voltage of 35V DC, adjustable output voltage from 3.2 to 35V DC, and efficiency up to 3A. The converter features a built-in voltage measurement circuit with a 3-digit display. While some users praise its affordability and performance, concerns are raised about its susceptibility to short circuits, with reports of failures under such conditions. Comparisons are made to the LM2576, which is noted for better short-circuit resistance.
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FAQ

TL;DR: Efficiency never exceeds 85 % under test [Elektroda, grala1, post #16964656] “It’s amazing that such a small and cheap toddler will pull out almost 3 A” [Elektroda, gulson, post #16966941] Budget LM2596S boards give 3–35 V out, but lack short-circuit protection. Why it matters: Knowing real limits prevents smoked boards and failed projects.

Quick Facts

• Input range: 4–35 V DC (limited by 35 V capacitor) [Elektroda, grala1, post #16964656] • Output range: 3.2–35 V DC, set by multiturn potentiometer [Elektroda, grala1, post #16964656] • Rated load current: up to 3 A; best results below 2 A [Elektroda, grala1, post #16964656] • Peak measured efficiency: approx. 83 % at 15 V→12 V [Elektroda, grala1, post #16964656] • Board size & cost: 65 × 35 × 16 mm, ≈ US$1.60 shipped [Elektroda, grala1, post #16964656]

What is the LM2596S step-down converter module?

It is a buck (step-down) regulator board built around the LM2596S-ADJ chip. The board adds an input/output voltmeter, LEDs, and a multiturn potentiometer so you can set 3.2–35 V DC output from a 4–35 V DC source [Elektroda, grala1, post #16964656]

How high can the input voltage go if I replace the capacitors?

LM2596S tolerates 45 V absolute-max (TI datasheet). Swapping the 35 V electrolytic for a 50 V unit lets the board safely run near 40 V. Leave a 5 V margin, so target 40 V max after the upgrade [Elektroda, arekkolisz, post #16965800]

How do I adjust the output voltage?

Turn the blue multiturn potentiometer clockwise to raise, counter-clockwise to lower. Measure on the onboard display or a multimeter. Each full turn changes about 1 V when near 5 V out — use small turns for fine control [Elektroda, grala1, post #16964656]

How efficient is the module at common settings?

Tests show 82–83 % at 15 V in, 12 V out; 75–78 % at 12 V in, 5 V out; and about 70 % when dropping 24 V to 5 V [Elektroda, grala1, post #16964656] Efficiency rises with load up to ≈1.5 A, then slowly falls.

Can it really supply 3 A continuously?

Only under the best ratio (15 V→12 V) with airflow. In worst-case 24 V→5 V, voltage sag starts near 2 A and the board heats above 55 °C after 30 min at 2.5 A [Elektroda, grala1, post #16964656]

Is the module short-circuit protected?

No. Users report instant failure during shorts: “not resistant to short circuit, they fall like flies” [Elektroda, es2, post #16974116] Add an external fuse or current-limit resistor.

How can I calibrate the onboard voltmeter?

Hold the pushbutton for ≥3 s while the desired side (IN/OUT) is displayed. Use the potentiometer that appears on screen to nudge the reading until it matches a reference meter, then release the button to store [Elektroda, grala1, post #16964656]

What temperatures should I expect under load?

At 24 V in, 5 V out, 2.5 A load, the board reached ~55 °C after 30 minutes in free air [Elektroda, grala1, post #16964656] Adding a 20 × 20 mm heatsink drops temperature by ~10 °C (author test).

How do I quickly test a new module’s efficiency?

  1. Feed a stable 12 V DC source.
  2. Set output to 5 V and load with a 2 Ω resistor.
  3. Measure input and output V × I; divide to get efficiency. Expect ~77 % [Elektroda, grala1, post #16964656]

Why choose LM2576 over LM2596S for a bench supply?

LM2576 boards include built-in current limiting that survives shorts, unlike many LM2596S clones that burn out when output is shorted [Elektroda, es2, post #16974116]

How do I raise current capability safely?

Parallel two identical boards, each set to the same voltage, and add 0.05 Ω ballast resistors to their outputs. This balances current and halves individual heating, keeping each under 2 A [DC–DC Design Note].

Where can I buy genuine modules and avoid fakes?

Buy from vendors that list brand chips (TI, ON). Check photos for laser-etched date codes. Realistic prices run US$1.50–2.50; extreme bargains may use remarked dies [Elektroda, Jawi_P, post #17001068]
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