Output (based on the original schematic)
Updated Schematic (with the optional ripple filter)
Output (based on the updated schematic)
Note, For the circuit that I use, the values for the optional output ripple filter are L2 = 33uH, C1 = 100uF, 35V.
Below is the waveform of a cheap LM2596 module that supports adjustable output.
The above waveform is taken from the module below.
Review of DC to DC buck converter based on LM2596http://www.hobbyelectronics.net/review_dctodcmodule.html