Summary of LM2596 DC-DC Converter Module Testing
Summary: Cheap LM2596 step-down modules work but have limitations: output adjustable ~1.23–25V, efficiency 60–90% depending on conditions, and practical input should stay below ~30V due to 35V caps. Tiny PCB ground area limits heat dissipation, so a heatsink is required for continuous >1A and 3A continuous is not recommended. Some boards include a polarity protection diode; many omit the feedforward capacitor required above 10V, risking instability for sensitive loads.
Parts used in the LM2596 DC-DC Converter Module:
- LM2596 switching regulator IC
- Inductor (coil)
- Input electrolytic capacitor (35V rating)
- Output electrolytic capacitor (35V rating)
- Polarity protection diode (D2) — present on some variants
- Adjustable feedback resistors R1 and R2
- Optional feedforward capacitor (not present on this board)
- Soldered PCB with ground plane
- Output and input screw terminals or pads
LM2596 based step-down DC-DC converter modules can be bought on eBay quite cheaply for around a dollar each. But how do they perform? Is it safe to use it to power your design? Let’s find out.
According to TI’s website, these LM2596 step-down (buck) regulators are sold for $1.8 each for a quantity of a thousand. So how a finished converter could be sold for just above a dollar each is quite a mystery to me. Anyway, the picture below is the board I received. It appears that there are a few variations to this design (slightly different inductor size or capacitor size/voltage rating, etc.) but they all are largely based on the reference design.
Below is the reverse engineered circuit diagram of this particular converter board I have (key components are also marked in the picture above for reference). The inclusion of a polarity protection diode (D2) is certainly a nice feature. It will prevent you from damaging the regulator should the input voltage be reversed. Of course, if the input power supply has very low output impedance and high current capability this tiny diode might not be able to save the board in an input voltage reversal situation. Also, not all variants of this step-down DC-DC converter have this diode. Although LM2596 can handle input voltages up to 45V, the input and output capacitors used are both rated for 35V only so in practice input voltage should stay below 30V for long term uses.
For LM2596, the output voltage is determined by the equation below. Given the component values used in this module the output voltage can be adjusted between 1.23V to 25V.
23
R1R2+1
Although LM2596 is rated for a maximum current of 3A in continuous operation, the tiny surface area of the ground plane on this board is not sufficient to dissipate the amount of heat generated over the entire operation range of the converter. And the efficiency of this converter varies quite a bit depending on the input voltage, output voltage and the load current. The efficiency can range from 60% to 90% depending on the operating conditions. As you can see in the video later, a heatsink is a must if continuous operation at over 1A is required.
According to the datasheet, a feedforward capacitor is needed in parallel of R2 when the output voltage is greater than 10V to ensure stability. But this capacitor is not present on this converter board. Even though in my limited testing the module was able to work across its output range, I would not recommend using this module to supply power to sensitive devices if higher than 10V supply voltage is needed. Instabilities could cause the output to deviate from the set voltage.
Simple switching regulators are typically designed to work optimally within a small range of output voltages once the key components (e.g. the inductor) had been chosen. This can be clearly seen from the datasheet in choosing inductors and output capacitors.
In the video below, I tested this DC-DC converter board under various operating conditions and measured its efficiencies. To conclude, these switching regulator boards are well suited for low to medium current draw digital circuitry but for higher current applications a heat sink is needed and even so I would not recommend running it at the maximum 3A load especially if the input voltage is high.
For more detail: LM2596 DC-DC Converter Module Testing
- What output voltage range can this module provide?
Based on the component values used the output can be adjusted from about 1.23V to 25V. - Can I use the module with input voltages up to 45V as the LM2596 supports?
No; although LM2596 supports up to 45V, the input and output capacitors on this board are rated 35V, so practical input should stay below about 30V for long term use. - Is it safe to run the module at its 3A rated output continuously?
No; the small PCB ground area cannot dissipate heat sufficiently, and continuous 3A operation is not recommended. - Do these modules need a heatsink for high current?
Yes; a heatsink is a must for continuous operation over about 1A. - Does the module include polarity protection?
Some variants include a polarity protection diode (D2), but not all modules have it. - Is the feedforward capacitor present for outputs above 10V?
No; the feedforward capacitor required by the datasheet for stability above 10V is not present on this converter board. - Are these modules stable for powering sensitive devices above 10V?
No; because the feedforward capacitor is missing, instability could cause the output to deviate when set above 10V, so they are not recommended for sensitive devices at those voltages. - What efficiency can be expected from these modules?
Efficiency varies with input, output, and load, and can range from about 60% to 90%. - Are these inexpensive modules suitable for low to medium current digital circuits?
Yes; they are well suited for low to medium current digital circuitry.
