From: James Burkart <james@burkartstudios.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Mon, 20 Apr 2020 01:31:14 -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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Thanks James. I'll try a schottky diode between the LDO and filter cap.

On Mon, Apr 20, 2020, 1:37 AM James Cameron <quozl@laptop.org> wrote:

> 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 circumstanc=
es
> > would lead to VCC dropping below VDD. Could you shed some light on this=
?
> >
> > On Mon, Apr 20, 2020, 12:25 AM David VanHorn <microbrix@gmail.com>
> wrote:
> >
> > > 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.co=
m
> >
> > > wrote:
> > >
> > > > Hey everyone! Here's a little motor driver board I made that works
> great,
> > > > until it doesn't. The voltage regulator keeps failing on me. I've
> used 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.
> If
> > > > someone here has a few minutes, could you look over my schematic an=
d
> > > > recommend changes?
> > > >
> > > > The board is powered from a 2S lipo, so 6.5 to 8.2V. For the flywhe=
el
> > > > 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
> motor
> > > > 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 blaster=
s.
> > > >
> > > > --
> > > > 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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