Step-Down Module, with a Maximum Current Setting

Hi all

If you look in eBay for Step Down modules,
most of the modules you will see have 1 potentiometer,
and that potentiometer enables setting the desired Output Voltage.

Here is an example for one like this:

Lately, I see some modules that have 2 potentiometers,
but it's hard to understand from their description if the module enables setting the Maximum Current,
or if it is a Constant Current module (in which the voltage changes but the Current stays fixed).

Sometimes they interchangeably mention both:
Maximum Current setting, and Constant Current / LED Driver..

How can a module be both Maximum Current setting, and Constant Current / LED Driver?
Those are 2 different behaviors, and there's no button to switch/choose 1 from the 2..

Does anyone have experience with those modules (that have more than 1 potentiometer),
and can tell which behavior we would be getting from them?

Thank you very much

Post a link to the board with two pots.

Here is one:

That is not intended as a power supply. It is basically a CC/CV lithium battery charger. It will maintain the set current until the output reaches the set voltage (normally 4.2V) and then switch over to CV mode and maintain that voltage. When charging a battery the current will then reduce. When using it as a LED driver it should just maintain that current.


Hi Steve

Thank you very much for your reply.

What you describe, is based on what you know from CV and CC,
the problem is, that these Step-Down modules don't behave like that.

I watched videos on Youtube during the past hours,
and it seems that these modules are simply Constant Voltage, with a Current Limit feature.

There is no "Constant Current" in them, an they just throw this buzzword as a way to increase sales.

They are benefitting from the fact, that If you choose a Voltage, and then choose a Maximum Current,
then when that Maximum Current is reached, then the current is "Constant"..

But obviously this is not a Constant Current source, since a Constant Current changes the Voltage it gives, in order to keep the current constant.

In short, the best answer came from Youtube, because then you see how they behave in reality,
and don't have to try to understand what they meant in the text description.

these Step-Down modules don't behave like that

That is not a "Step-Down" module. It is a battery charging module.

If you are looking for a step-down voltage regulator, Pololu has the best selection. Pololu provides excellent product documentation and support, as well.

...but, to answer the more broad question:

On step-down modules [and step-up modules, and power supplies in general, both linear and switch mode], the second potentiometer is usually a Current Limit adjust, And contrary to what card5 said, yes, indeed, they do run in a Constant Current mode, once that set current limit is reached. Card5 has it wrong. When the set current is reached, the power supplies voltage does, indeed, change--it reduces to keep the current at the set level.

So, to summarize, the supply keeps the output voltage constant [as well as it is designed to do], as long as the current is below the Constant Current [CC] set point. Once the load is such that the supply would deliver more current than the CC set point, the supply switches to CC mode to keep the current from going any higher. It does that by lowering the output voltage, just enough to keep the current at the CC set point level. It will do this all the way down to 0 volts out.

And BTW: I know this, not from watching a YouTube video, but from personal experience actually using, and testing power supplies and switch-mode DC-to-DC converters.

They are very handy devices. The ones I use have CC and CV. I set the voltage to the maximum I want then adjust the current (you need a load greater then what you want to set this). When in operation it will supply the set voltage. When the load increases to the current setpoint it changes from CV to CC. At that point the voltage will drop to a point where it is outputting its current setting. If the load decreases below setpoint the it will go back to CV mode and the voltage will be what you set at.
Good Luck