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I've made a quick test where I put 12V from a dc power supply to a 15V regulator - so the "input" was lower than the voltage regulator output.
When I measured it, I had a 5V output, and it was what I'm looking for intially, and the regulator wasn't hot.
So I would like to refer to your expertise and ask you if it is a good way to get 5V without any issue like a current drop for example, which is crucial for the working of my components?
Absolutely no. Closed loop regulators use an internal voltage reference (e.g. 1.25V) and compare it to a fraction of the output to provide load and input voltage regulation.
That is not a good way to get 5V.
The behaviour of such a regulator is unspecified when the input is below the rated output voltage.
The regulator cannot operate in those conditions. The output you get is a result of the internal resistances and the state of various transistors.
Since the regulator can't actually regulate its output, you cannot expect it to stay at 5V when you put a load on it.
So, don't do it.
Get a 7805, or better a switching regulator than can reduce the voltage more efficiently.
