Step down voltage regulators or buck converters take an unstable high DC voltage and convert it to a lower stable DC voltage. Specifications list the regulated output voltage and current but check the input voltage maximum to ensure suitability. Some of the regulators allow for the output to be changed, although the adjusting potentiometer is designed for low frequency use and not for continual voltage adjustment.
The regulator will have a cut off voltage where the input voltage gets down near the output voltage and it can no longer regulate, instead turning off.
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