On the schematics for this DC/DC converter, there is a diode D2 which is placed between V+ and V-

enter image description here On the actual board, the value for D2 is a M4 400V rectifier.

What's the purpose of this rectifier? It doesn't seem to be doing anything?

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    \$\begingroup\$ I can't see V+ and V-. I'm blind. \$\endgroup\$ – Harry Svensson Jul 25 '17 at 6:37

This diode is used for reverse polarity protection (with a fuse placed before IN+). When reverse voltage is applied the diode conducts and blows the fuse.

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  • \$\begingroup\$ Yep, and here's a guy "with a suspicious accent" who blew it by trying to charge a reversed polarity battery. The diode sacrificed itself to save the power supply. youtube.com/watch?v=xSXvqrEwssk \$\endgroup\$ – Sredni Vashtar Jul 25 '17 at 9:23

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