From: Jason White <whitewaterssoftwareinfo@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 5 Feb 2020 12:36:57 -0800
Subject: Re: [EE] 78L05 (SO8) overshoot on removal of over-current event?
Thread-Topic: [EE] 78L05 (SO8) overshoot on removal of over-current event?
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While it is definitely possible, I don't recall it being damaged. We
went from a 28V transformer to 24V to 12V to 5V - big capacitors at
each linear regulator stage. Back then we fixed it just by putting a
higher current regulator for the 12V->5V on the PCB.

As soon as the larger regulator was wired in by a technician the
micro-controller (which was not touching any high voltage stuff)
stopped getting holes blown through it. We were able to reproduce the
issue on the two prototype boards we had.

On Wed, Feb 5, 2020 at 3:15 PM Harold Hallikainen
<harold@mai.hallikainen.org> wrote:
>
> I wonder if the overshoot could be due to the output capacitor. Is the
> input also dragged down in this condition? On input below output damaging
> the regulator, we used to put a diode between input and output to not let
> the input be more than 700 mV below the output.
>
> Harold
>
> > I've not seen this exactly, but I have seen a lot of problems with the =
L
> > version being defective in various ways.  I generally wouldn't trust th=
em.
> >
> > They (and actually most PNP based regulators) can be damaged by the inp=
ut
> > being shorted to ground, if the output capacitor is large.  This is not
> > well documented, you might have to go back to Motorola data sheets from
> > the 1980's to find it documented, but the output stages are still much =
the
> > same.   There are more modern parts that are immune.
> >
> > --
> > David VanHorn
> > Lead Hardware Engineer
> >
> > Backcountry Access, Inc.
> > 2820 Wilderness Pl, Unit H
> > Boulder, CO  80301 USA
> > phone: 303-417-1345  x110
> > email: david.vanhorn@backcountryaccess.com
> >
> > -----Original Message-----
> > From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> On Behalf Of Ja=
son
> > White
> > Sent: Wednesday, February 5, 2020 10:36 AM
> > To: Microcontroller discussion list - Public. <piclist@mit.edu>
> > Subject: [EE] 78L05 (SO8) overshoot on removal of over-current event?
> >
> > Hello everyone,
> >
> > At a previous job I observed a failure mode where the 100mA current rat=
ing
> > of a 78L05 type regulator (12->5V, SO8) was exceeded causing it to
> > saturate and then briefly overshoot to >7V when the load was removed
> > causing damage to 5V circuitry. (a micro-controller was driving a large
> > number of opto-isolators, all toggled on and off at the same time)
> >
> > Do anyone have any links to literature that documents this behavior?
> >
> > --
> > Jason White
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
>
>
> --
> FCC Rules Updated Daily at http://www.hallikainen.com
> Not sent from an iPhone.
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
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