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mandag den 3. oktober 2022 kl. 00.40.26 UTC+2 skrev Clifford Heath:
On 2/10/22 23:35, Mike Monett VE3BTI wrote:
Lasse Langwadt Christensen <lang...@fonz.dk> wrote:
look closer at the schematic, the reverse protection does work
the first FET is reverse so initially the body diode will work as a
series diode and when the FET turns on so there is no voltage drop
Very nice catch. It works. Thanks.
I got tripped up on this recently. What\'d weird is that without the body
diode, the source and drain must be connected in the expected direction
(and it sorta works) but with the body diode, it *must* be in the
reverse direction. Very confusing at first sight.
fets without a body diode are very rare
We make a gadget that\'s powered by a 12 volt wart, and sometimes a
user applies 24 and blows one up.
We have a polyfuse and a 12 volt TVS and they sometimes fry the TVS.
It\'s posssible that most any useful polyfuse+TVS combo can be teased
to destruction.
I think Phil H mentioned some gadget, a polyzorb or something, that
would be better. I can\'t find it.
=============
I like crowbars. No finesse required.
It can be done wrong.
** A 16amp triac with a 12v zener provides full protection.
Soft gate drive can be a hazard.
Zener+triac could allow a couple of volts of negative swing.
Will trip at 13V with normal polarity and about 1.5V reverse.
Anyone stupid enough to use the wrong voltage/ polarity wall wart deserves to see it die.
Except that said stupid person will ship it back for us to fix.
On Sun, 2 Oct 2022 15:47:33 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
mandag den 3. oktober 2022 kl. 00.40.26 UTC+2 skrev Clifford Heath:
On 2/10/22 23:35, Mike Monett VE3BTI wrote:
Lasse Langwadt Christensen <lang...@fonz.dk> wrote:
look closer at the schematic, the reverse protection does work
the first FET is reverse so initially the body diode will work as a
series diode and when the FET turns on so there is no voltage drop
Very nice catch. It works. Thanks.
I got tripped up on this recently. What\'d weird is that without the body
diode, the source and drain must be connected in the expected direction
(and it sorta works) but with the body diode, it *must* be in the
reverse direction. Very confusing at first sight.
fets without a body diode are very rare
The EPC gan parts don\'t exactly have a body diode, but turn on soft at
around -2 volts. Somehow.
mandag den 3. oktober 2022 kl. 00.40.26 UTC+2 skrev Clifford Heath:
On 2/10/22 23:35, Mike Monett VE3BTI wrote:
Lasse Langwadt Christensen <lang...@fonz.dk> wrote:
look closer at the schematic, the reverse protection does work
the first FET is reverse so initially the body diode will work as a
series diode and when the FET turns on so there is no voltage drop
Very nice catch. It works. Thanks.
I got tripped up on this recently. What\'d weird is that without the body
diode, the source and drain must be connected in the expected direction
(and it sorta works) but with the body diode, it *must* be in the
reverse direction. Very confusing at first sight.
fets without a body diode are very rare
John Larkin wrote more smartarse BS
------------------------------------------------------------
Phil Allison
Sylvia Else wrote:
=============
I like crowbars. No finesse required.
It can be done wrong.
** Yawwwwwnnnnn...........
** A 16amp triac with a 12v zener provides full protection.
Soft gate drive can be a hazard.
** Drivel.
John Larkin wrote:
On Sun, 2 Oct 2022 13:13:39 +0100, Clive Arthur
clive@nowaytoday.co.uk> wrote:
On 30/09/2022 21:14, John Larkin wrote:
We make a gadget that\'s powered by a 12 volt wart, and sometimes a
user applies 24 and blows one up.
We have a polyfuse and a 12 volt TVS and they sometimes fry the TVS.
It\'s posssible that most any useful polyfuse+TVS combo can be teased
to destruction.
I think Phil H mentioned some gadget, a polyzorb or something, that
would be better. I can\'t find it.
We might fine-tune the polyfuse+TVS, or maybe go polyfuse and SCR
crowbar, or something.
This is all entangled with parts availabity. Ideally the box would
just work from 12 or 24, but that has separate complications.
We once used a TI electronic fuse IC, but it liked to blow up.
12V LDO regulator with thermal shutdown.
That would work if the LDO can stand +24v input. It still needs
reverse protection.
May as well just let it work from +10 to +40. The customer can use the
wrong wart and never notice the difference.
I suspect that negative-center warts are rare these days.
My next problem is a bulletproof UVLO and switcher sequencing.
Reverse protection is also important to protect against an input short,
which can blow up stuff by forcing currents from output to input.
That\'s one of the three ways to blow up a 317, and one of the two to
blow up an 78xx regulator. (Input overvoltage is the other main one,
and for a 317, discharging a big ADJ pin bypass backwards.
Cheers
Phil Hobbs
I like crowbars. No finesse required.
It can be done wrong.
** Yawwwwwnnnnn...........
** A 16amp triac with a 12v zener provides full protection.
Soft gate drive can be a hazard.
** Drivel.
A soft gate drive, like just a zener,
John Larkin wrote WORSE smartarse BS
------------------------------------------------------------
I like crowbars. No finesse required.
It can be done wrong.
** Yawwwwwnnnnn...........
** A 16amp triac with a 12v zener provides full protection.
Soft gate drive can be a hazard.
** Drivel.
A soft gate drive, like just a zener,
** Drivel.
FOAD you wanker.
......... Phil
On Sun, 2 Oct 2022 17:52:38 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
On Sun, 2 Oct 2022 13:13:39 +0100, Clive Arthur
clive@nowaytoday.co.uk> wrote:
On 30/09/2022 21:14, John Larkin wrote:
We make a gadget that\'s powered by a 12 volt wart, and sometimes a
user applies 24 and blows one up.
We have a polyfuse and a 12 volt TVS and they sometimes fry the TVS.
It\'s posssible that most any useful polyfuse+TVS combo can be teased
to destruction.
I think Phil H mentioned some gadget, a polyzorb or something, that
would be better. I can\'t find it.
We might fine-tune the polyfuse+TVS, or maybe go polyfuse and SCR
crowbar, or something.
This is all entangled with parts availabity. Ideally the box would
just work from 12 or 24, but that has separate complications.
We once used a TI electronic fuse IC, but it liked to blow up.
12V LDO regulator with thermal shutdown.
That would work if the LDO can stand +24v input. It still needs
reverse protection.
May as well just let it work from +10 to +40. The customer can use the
wrong wart and never notice the difference.
I suspect that negative-center warts are rare these days.
My next problem is a bulletproof UVLO and switcher sequencing.
Reverse protection is also important to protect against an input short,
which can blow up stuff by forcing currents from output to input.
That\'s one of the three ways to blow up a 317, and one of the two to
blow up an 78xx regulator. (Input overvoltage is the other main one,
and for a 317, discharging a big ADJ pin bypass backwards.
Cheers
Phil Hobbs
I once mightily abused an LM317 adjust pin to see if I could break it.
No feasible abuse did.