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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Power from another source fed to 1117 regulator output pin
Date: Mon, 30 Sep 2024 05:21:28 -0700
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On 9/30/2024 4:37 AM, Pimpom wrote:
> I've been looking at the schematic of a popular product that has two options as 
> the power source. One source is a Vin point (pin or DC jack) that goes to a 
> 1117-5V regulator, the other is a USB port. The USB +5V line joins the 1117 
> output via a Schottky diode.
> 
> Does this mean that the 1117 has no problem with this arrangement - that is, 
> with power coming from another source to its output pin?

Short the LDO's input to GND and consider how it will (mis)behave.