From: Harold Hallikainen <harold@mai.hallikainen.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 5 Feb 2020 12:11:13 -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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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 them=
..
>
> They (and actually most PNP based regulators) can be damaged by the input
> 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 th=
e
> same.   There are more modern parts that are immune.
>
> --
> David VanHorn
> Lead Hardware Engineer
>
> Backcountry Access, Inc.
> 2820 Wilderness Pl, Unit H
> Boulder, CO =A080301 USA
> phone:=A0303-417-1345 =A0x110
> email:=A0david.vanhorn@backcountryaccess.com=A0
>
> -----Original Message-----
> From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> On Behalf Of Jaso=
n
> 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 ratin=
g
> 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
> --
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