I would like to have a clean output from a linear regulator (variable 1-5V) but also a small heatsink on it, so I thought about placing a ready-to-use step-down module before it, and to wire it so that the voltage drop on the linear regulator is almost constant.
Since the step-down (buck) are non-isolated, in practice they also have three pins only.
My idea is to have a circuit like this:
In other words, the potentiometer defines the final voltage at the output. The DC-DC regulator is set to have a constant 4V voltage on its output, that corresponds to the drop between input and output of the linear regulator.
Provided I use capacitors (ceramic and electrolytic) and ferrites between step-down and linear regulator, plus a ferrite also after the linear regulator, would it work? I have no other idea about how to set the same thing without using a double potentiometer.
I wrongly used the ADJ pin of the step-down as if it were the ADJ pin of the linear regulator. It was wrong, because the step-down is a complete module, where I use the GND line. I updated the schematics.