Boomstick diode question

[morbidalex666]

Hi,
What does the 1n5817 diode on the +9v input serve for?
I am only asking because some people over at FSB don't use it at all or put it to ground.
Is it omittable?
Thanks

[sgmezei]

It looks to be a reverse polarity protection diode. Just in case you plug in the wrong power supply, you won't blow anything up.

[morbidalex666]

Well yeah but usually this polarity protection diode goes to ground, right?
Maybe I am a little too new to all this diying but I also like to learn things, hence the newbie question.

[oldhousescott]

It is a polarity protection diode, it just happens to be in series with the power supply instead of in parallel. It will drop a bit of voltage, but being a Schottky only about half a volt or less. What it does do is not pass any current if the polarity is reversed. With the conventional parallel protection diode to ground, the power supply is essentially shorted in the case of a reverse polarity connection. Several things could happen in this scenario, many of them undesirable.