When we need to power an electronic circuit with a voltage lower than the one available from the power source, a practical solution is to use a regulator module based on the LM2596.
This small module can reduce a DC input voltage and provide a regulated output. The adjustment is usually made using a small trimpot installed on the board itself.
In this project, I show how to modify the module and use an external potentiometer, making the adjustment more accessible and allowing it to be installed on the panel of a variable power supply.
What Is the LM2596?
The LM2596 is a switching regulator integrated circuit used in step-down converters, also known as buck converters.
Its function is to convert one DC voltage into another lower DC voltage.
This means that, for example, we can use a 12 V power source and adjust the output to a value below that, as long as the module’s limits are respected.
The basic process is:
DC input voltage → LM2596 converter → regulated DC output voltage
It is important to note that the LM2596 is not a step-up converter.
It reduces the voltage, but it cannot provide an output voltage higher than the input voltage.
What Does Step-Down Mean?
Step-down means reducing the voltage.
If the module receives 12 V at the input, it can produce lower voltages, such as 9 V, 5 V, or 3.3 V, depending on the conditions and the range allowed by the circuit.
It cannot convert those 12 V into 15 V.
To increase a voltage, a step-up or boost converter would be required. There are also modules capable of increasing or decreasing voltage, known as buck-boost converters.
This distinction prevents a common misconception: believing that a power supply described as variable can produce any voltage regardless of the power source being used.
Why Is the LM2596 Different from a Linear Regulator?
A linear regulator controls voltage by dissipating part of the difference between the input and output as heat.
The approximate power dissipated by it can be calculated as:
P = (Vin − Vout) × I
If a linear regulator receives 12 V, provides 5 V, and carries 1 A, the approximate dissipation will be:
P = (12 − 5) × 1 = 7 W
This energy is converted mainly into heat.
The LM2596 operates as a switching regulator. It switches internally on and off at high frequency and uses components such as an inductor, diode, and capacitors to transfer energy more efficiently.
This reduces losses in many applications, although it does not completely eliminate heating.
What Is the Inductor on the Module Used For?
The inductor is one of the most visible components on the board.
It temporarily stores energy in its magnetic field and participates in the switching conversion process. Together with the diode, capacitors, and LM2596, it helps produce a regulated DC voltage at the output.
The input capacitor helps stabilize the incoming power supply.
The output capacitor reduces the variations produced by switching and helps deliver a more stable voltage to the load.
The selection and quality of these components affect the module’s performance.
How Is the Output Voltage Adjusted?
In the adjustable version, the LM2596 uses a feedback network.
Part of the output voltage is fed back to the control terminal of the integrated circuit. The regulator compares this information with an internal reference and adjusts the switching to maintain the output at the defined value.
On the module, the trimpot is part of this resistor network.
When we turn the adjustment, we change the proportion of the voltage sent to the feedback circuit. The circuit responds by increasing or decreasing the output voltage.
Therefore, the trimpot does not act directly as a resistor in series with the load. It is part of the regulator’s control system.
Why Install an External Potentiometer?
The trimpot found on LM2596 modules is small and is designed primarily for occasional adjustments using a screwdriver.
If the module is installed inside an enclosure, this component may be difficult to reach.
An external potentiometer offers several advantages:
- Adjustment available on the front panel.
- Greater ease of use.
- Possibility of installing a larger knob.
- Better organization of the power supply.
- Adjustment without opening the enclosure.
- Use of an external scale or markings.
This modification can turn the module into a simple variable power supply for workbench experiments.
Can I Use Any Potentiometer?
No.
The external potentiometer must have a value and connection compatible with the original trimpot and the module’s feedback network.
Replacing the component with a randomly selected value can change the adjustment range, make regulation difficult, or cause the voltage to rise to a level that is dangerous for the load.
Before making the modification, you need to:
- Identify the value of the original trimpot.
- Record how its terminals are connected.
- Check which terminals actually participate in the adjustment.
- Choose a compatible potentiometer.
- Reproduce the connection correctly.
- Measure the output before connecting any circuit.
Modules that look similar may use different components or layouts. The modification must be performed based on the specific unit that will be used.
How Do You Identify the Potentiometer Terminals?
A standard potentiometer has three terminals:
- One end of the resistive track.
- The other end of the track.
- The moving wiper.
Between the two ends, we find approximately its nominal resistance.
Between the wiper and each end, the resistance varies as the shaft is turned.
A multimeter, with the component disconnected from power, helps identify these terminals.
When replacing the trimpot with an external control, it is essential to understand whether the circuit uses all three terminals or whether the potentiometer is used as a two-terminal variable resistor.
Do a Standard Potentiometer and a Multi-Turn Trimpot Adjust in the Same Way?
Not necessarily.
Many LM2596 modules use a multi-turn trimpot. This allows small changes to be made to the output voltage.
When it is replaced with a conventional single-turn potentiometer, the entire adjustment range is concentrated into a much smaller movement.
The result can be a very sensitive control: a small turn may cause a significant change in voltage.
For more gradual adjustment, it may be useful to use:
- A multi-turn potentiometer.
- A knob potentiometer with a counter.
- Two controls, one for coarse adjustment and another for fine adjustment.
- A voltage range deliberately limited by resistors.
These alternatives require proper design. It is not enough to simply add components without analyzing the feedback network.
Precautions When Using Wires for the External Potentiometer
The potentiometer installed on the panel needs to be connected to the board with wires.
Because these wires are part of the feedback network, long connections can pick up noise and interference. A poor connection can also cause the regulator to lose its proper reference.
Therefore:
- Use short wires.
- Make secure solder joints.
- Avoid routing the wires close to the inductor.
- Keep them away from high-current cables.
- Mechanically secure the potentiometer.
- Insulate all exposed terminals.
It is also wise to evaluate how the circuit behaves if the wiper loses contact. Depending on the connection, a failure could cause the output voltage to increase.
Always Adjust the Output Before Connecting the Load
After assembly, turn on the module without connecting the Arduino or another sensitive circuit.
Use a multimeter to check the output.
The recommended procedure is:
- Check the input polarity.
- Connect the power source to the module.
- Measure the voltage at the output terminals.
- Turn the potentiometer slowly.
- Confirm the direction of adjustment.
- Set the desired voltage.
- Turn off the power.
- Connect the load.
- Turn the power back on and check the voltage under load.
Never use only the visual position of the knob as a reference. The voltage must be measured.
Can I Power an Arduino with an LM2596?
Yes, as long as the output is correctly adjusted and the connection is appropriate for the board being used.
The official name of the platform is Arduino, without an accent, although the form “Arduíno” also appears in Portuguese searches.
On boards that operate with 5 V logic, there are different power supply options.
Powering Through the 5 V Pin
If the LM2596 is adjusted to provide 5 V, the output can be connected directly to the 5 V rail only when this method of powering the board is appropriate.
In this case, the onboard regulator is normally bypassed. An overvoltage on this pin can reach the microcontroller and other components directly.
The voltage must be carefully checked before making the connection.
Powering Through VIN
The VIN pin normally supplies the regulator on the board. Therefore, it needs to receive a voltage higher than the logic voltage, within the range specified for the Arduino model being used.
Applying only 5 V to VIN may not result in 5 V in the circuit because there is a voltage drop across the onboard regulator.
The choice between VIN and the 5 V pin depends on the board and the available voltage.
Be Careful When Connecting USB and an External Power Supply at the Same Time
When powering the Arduino from an external power supply, we also need to consider the USB connection.
Depending on the board, the selected connection point, and the way it is powered, two power sources may interact or cause reverse current flow.
You should not assume that every simultaneous connection is safe.
Before connecting the USB cable, check the specific power supply circuit of the board. If the LM2596 is connected directly to the 5 V rail, even greater care is required.
How Much Current Can the Module Provide?
Many LM2596 modules are advertised with high current ratings, often close to 3 A. This value should not be understood as a guarantee of continuous operation under all conditions.
The practical current capability depends on:
- Input voltage.
- Output voltage.
- Efficiency.
- Switching frequency.
- Inductor used.
- Diode installed.
- PCB traces.
- Ventilation.
- Thermal dissipation.
- Quality of the module itself.
Under certain conditions, the circuit may require additional cooling. In others, the inductor or diode may limit performance before the integrated circuit does.
The correct approach is to test the power supply with the intended load and monitor temperature and stability.
Is Current “Pushed” into the Arduino?
The power supply does not automatically force its maximum current into the load.
If a module can provide up to a certain current, it means the load can draw current within that limit.
The Arduino and connected components consume current according to their characteristics.
The main dangers are applying the wrong voltage, reversing polarity, creating a short circuit, or demanding more current than the module can provide.
The Input Voltage Must Be Higher Than the Output Voltage
Because the LM2596 is a step-down converter, it needs to receive a voltage higher than the desired output, with sufficient margin to operate correctly.
If the input falls too close to or below the adjusted output voltage, the module will stop regulating.
For example, a module configured for 5 V may not maintain that output when powered by a battery whose voltage has fallen to a value very close to 5 V.
In this situation, turning the potentiometer in an attempt to compensate will not help. The circuit topology does not allow the voltage to be increased.
Input Power and Output Power
The module does not create energy.
The approximate power delivered to the load can be calculated as:
Pout = Vout × Iout
The input power will be higher because the converter has losses:
Pin = Pout / efficiency
If the output provides 5 V and 1 A, we have:
Pout = 5 × 1 = 5 W
With a hypothetical efficiency of 85%:
Pin = 5 / 0.85 ≈ 5.88 W
This difference appears mainly as heat.
Does the LM2596 Produce a Perfectly Clean Voltage?
No.
Because it operates by switching, the module can produce small ripples and high-frequency noise at the output.
In many digital applications, this may be acceptable. In analog circuits, sensitive sensors, radio, and audio applications, the noise may affect operation.
The quality depends on the module, the load, wire organization, and filtering.
To evaluate the output in greater detail, an oscilloscope is more appropriate than a multimeter alone, since a multimeter may indicate the average value without revealing the full ripple.
Uses for a Variable Power Supply with an LM2596
After being installed in an enclosure with terminals and an external control, the power supply can be used for experiments such as:
- Powering Arduino boards.
- Testing LEDs and resistors.
- Compatible small motors.
- Electronic modules.
- Fans.
- Relays.
- Sensors.
- Low-voltage circuits.
- Charging only when an appropriate circuit for the battery is present.
The LM2596 should not automatically be considered a battery charger. A battery requires control compatible with its chemistry, voltage, current, and charging process.
The Module Does Not Replace a Laboratory Power Supply
A variable power supply built with an LM2596 is useful, but it does not necessarily offer all the features of a bench power supply.
A laboratory power supply may include:
- Adjustable current limiting.
- Short-circuit protection.
- Accurate indicators.
- Fine and coarse adjustments.
- Isolated outputs.
- Output enable control.
- Additional thermal protection.
The LM2596 module primarily provides step-down voltage regulation. Additional features need to be analyzed and added to the project.
See the LM2596 Module Modification
In the video, I show how to modify the LM2596 step-down board to work with an external potentiometer and create a simple variable power supply:
The assembly is a good opportunity to understand switching regulation, feedback, voltage conversion, and precautions when powering circuits.
The most important point is to always measure the output before connecting the load. A small movement of the adjustment can result in a voltage that is unsuitable for the Arduino or the component being tested.
To further explore voltage regulators, adjustable power supplies, rectification, filtering, and converters, also visit the Power Supplies section.