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Date: Mon, 20 Apr 2020 18:33:00 -0700
Subject: Re: [EE] LDO reg keeps failing. Looking for suggestions.
Thread-Topic: [EE] LDO reg keeps failing. Looking for suggestions.
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I disagree.
The failure mechanism is well documented, where Vout > Vin.
The point of D8 is to prevent the input pin from being more than a diode dr=
op below Vout in that situation.
But the problem mechanism here isn't Vin falling, it's Vout rising.
________________________________
From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Isaac =
Marino Bavaresco <isaacbavaresco@gmail.com>
Sent: Monday, April 20, 2020 7:12 PM
To: piclist@mit.edu <piclist@mit.edu>
Subject: Re: [EE] LDO reg keeps failing. Looking for suggestions.

I think D8 is not necessary and may be detrimental in case of reverse
polarity connection.

If added, D8's cathode should be connected to where D9's  cathode is. As
you added D9, D8 is not necessary.

That configuration used to be suggested in older regulators datasheets
for application where Vin could fall too quickly as result of a sudden
current sink from other circuits, then current would backflow from the
output capacitor to the input pin. With D9 present, that not possible,
the only path to discharge C1 is through the regulator itself.

Cheers,

Isaac




Em 20/04/2020 21:56, James Burkart escreveu:
> Thanks for the info, everyone!
>
> So I added a 4.7uF cap to the output of the reg, added a shunt schottky
> diode across the regulator, and another schottky diode feeding the input
> filter cap.
>
> How does that look?
>
> --
> Sincerely,
>
> James Burkart
> *925.667.7175*
>
> [image: image.png]
>


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