Electronics > Projects, Designs, and Technical Stuff

1117 LDO and reverse polarity protection

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panoss:
I 've built a device which is powerεd by a 5V PSU.
The voltage firstly goes through an FQP27P06 (P-Channel MOSFET) for reverse polarity protection.
Then it goes to the 1117.
So my question is: do I need the MOSFET for reverse polarity protection?
Or the 1117 has it's own protection against reverse polarity?

balage:
Hi,

Here is the simplified internal schematic. I would say it is not reverse polarity protected. However I cannot see any path to the reverse current to flow as all of the transistors are blocking that way.

I use a schottky diode for revesre polarity protection. I don't know which one is the better... I always see the least in TI's reference designs. They must have a reason.

panoss:
If a reverse polarity PSU gets connected the current will stop at the transistors at the bottom of the schematic?

balage:
I think yes, they block the way. But the question is the voltage that those transistors can carry on their E-C without blowing.

When I get home I will try. :)

schmitt trigger:
My take on this is, unless the datasheet specifically indicates that it is reverse-polarity protected, and the reverse voltage withstanding level, I would assume that it is not protected.

For LDOs, I also prefer a PMOS rather than a schotky where extremely low dropouts are required.

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