From: James Cameron <quozl@laptop.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Mon, 20 Apr 2020 00:36:53 -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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Looking at your schematic, when Q2 or Q4 conduct, there may be a time
during which VCC will fall below VDD.

I've had this happen in exciting ways once before, with C1 catching
fire, and the fix that worked for me was a diode between VCC and
C1/U2.

On Mon, Apr 20, 2020 at 01:06:24AM -0600, James Burkart wrote:
> VDD is 5V, and it's provided by the LDO regulator. VCC is the battery
> voltage and is anywhere from 6.5 to 8.2V. I don't know what circumstances
> would lead to VCC dropping below VDD. Could you shed some light on this?
>=20
> On Mon, Apr 20, 2020, 12:25 AM David VanHorn <microbrix@gmail.com> wrote:
>=20
> > If vcc can rise above the input then most pnp regulators will fail
> >
> >
> > On Sun, Apr 19, 2020, 11:44 PM James Burkart <james@burkartstudios.com>
> > wrote:
> >
> > > Hey everyone! Here's a little motor driver board I made that works gr=
eat,
> > > until it doesn't. The voltage regulator keeps failing on me. I've use=
d a
> > > couple different LDO regulators and it always happens. It's always at
> > > random times. So I am pretty sure it's EMI from the brushed motors. I=
f
> > > someone here has a few minutes, could you look over my schematic and
> > > recommend changes?
> > >
> > > The board is powered from a 2S lipo, so 6.5 to 8.2V. For the flywheel
> > > output there are 2 motors in parallel that draw about 3A total when
> > > running, and a stall current of about 20A. The pusher output runs 1 m=
otor
> > > that draws about 100mA with a stall current of about 3A. I do use PWM=
 to
> > > control the speed of the pusher motor.
> > >
> > > If you're wondering, this driver board is for flywheel Nerf blasters.
> > >
> > > --
> > > Sincerely,
> > >
> > > James Burkart
> > > *925.667.7175*
> > >
> > > *Schematic:*
> > > https://drive.google.com/file/d/1dgLf3sFNzFxvEuzaqTuIHd4_VSUfNbg8
> > > --
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James Cameron
http://quozl.netrek.org/
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