... Use a 1N5822 from 5V to ground anode to ground and cathode to 5V . There is already an input protector in the DCin jack, A series diode pointing to the regulator.
Here is My $0.02 worth on Switchers @ $1.70 Ea...
http://www.electrodragon.com/?product=better-than-lm2596-dc-dc-step-down-adjustable-power-supply-module
Always better Prices.
Doc