LM5116 Buck Converter

Input 6-100V, Output 1.215-80V, Often Limited to 32V to Protect Condensators, Current 20A, CV, CC

The LM5116 from Texas Instruments is a popular step-down converter capable of outputting significant currents of up to 20A.

The board above costs around EUR 4 including heat sinks and is a heavy-duty workhorse for hobbyist projects. It supports both constant voltage and constant current, settable via two clearly marked potentiometers. Turn them rightwards to increase their setting, and leftwards to decrease.

:warning: The board comes with a tiny switch at the input terminal. Make sure this switch is in ON position or else there will be no output voltage.

To adjust the voltage, connect a voltmeter to the output terminal, then turn the potentiometer marked CV (turn right to raise and left to lower).

To adjust the constant current requires a load to be connected to the output terminal (preferrably a dedicated electronic load device where you can vary the load, but any load will do).

You can now measure the current that flows at the output terminal with a DC clamp ampere meter (do not use a simple multimeter. It typically support high currents only for a few seconds before it starts to smoke).

A red LED close to the input terminal tells you if your output is above the constant current: if the LED is dim or off, then the Buck converter has actively lowered or shutdown the current (by lowering the voltage, and if that still did not suffice, by turning the output off).

You can then turn the *CC potentiometer rightwards to increase the constant voltage until the red LED starts to fully glow again (if you wanted to allow higher currents at the output).

If you find that the breakout board provides much less current than 20A before it starts to drop the voltage and shutdown, regardless of what you do, make sure your input power supply is capable of providing enough energy in the first place. The Buck can’t generate current out of nothing.

For example, if you supply 24V and want to draw 10A at 12V, your power supply must be capable of supplying at least 24V at 5A. If it does not, or if you have accidentally set it to some constant current cap, the LM5116 tries to maintain the set constant current by gradually decreasing the voltage.

Property Value
Input Voltage 6-100V
Output Voltage 1.215-80V (may be lower in breakout boards
Max Output Current 20A
Efficiency up to 96%
Switching Frequency 50kHz-1MHz (programmable)

The maximum output current of 20A requires heat sinks. Fortunately, many breakout boards come with them premounted. That said, you should test and experiment for yourself to see at which parameters the LM5116 gets too hot.

This depends on how much “work” it needs to do, so it is related to the actual input and output voltages you have set, and the voltage difference between them. So you might get away with a fairly cool LM5116 at high currents for hours, while other setups may experience excess heat even after a few minutes.

One cause of excessive heat is when you do not supply enough input power: if the power source cannot provide enough current to drive the output terminal, the LM5116 works very hard to try and provide the set constant current nevertheless (i.e. by lowering the voltage). This is inefficient and makes no sense. You should always use the constant current setting to limit the output current to a safe level that does not cause excessive input currents that your input power supply cannot handle.

Feature Supported
Constant Current yes
Output Shortcut Protection yes
Over Voltage Protection yes
Thermal Protection yes
Softstart yes, programmable

Data Sheet


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(content created Feb 27, 2024)