Minimum Input Voltage of Buck Converter
buck converters work by storing energy in an inductor, then moving that energy into a grounded capacitor.

Identify the parameters that determine success or failure, including


switching frequency
duty cycle
load current, min and max
inductor overload current (saturation current, set by core cross section, and the type of material)
input voltage minimum and maximum
switching losses in the chopping transistors and the commutation diodes
ripple voltage in the input "DC"
input filtering resonances that interact with the switch_reg demand for energy
parasitic coupling, via fast voltage steps and fast current steps, that upset the regulating feedback circuit; this is a great way to implement some chaotic behavior, and require a bigger input voltage to remain above dropout levels
issues with very narrow pulse widths, needed as you attempt to operate near the minimum Load currents