Docedison:
... 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...
DC Step-Down ADJ Module, 2.5-4A, MP2307 - ElectroDragonAlways better Prices.
Doc
Yes, great price. But they do need to work on their usage of engineering units:
Output Current: 2V continuously, and peak value at 4V
Lefty