Push Pull section short circuit protection

[gabo]

I would like to ask your opinion for the best solution for fusing the
following circuit in the case of short circuit of the following push
pull sections. This is an input/output section of the inverter/
charger. The use of N-Ch mosfets with body diodes is necessary because
in charger mode this circuit works as synchronous rectifier. The
problem is when the battery is connected in opposite polarity the bulk
capacitor is shorted , but most likely first the mosfets are burnt,
because of forward biased body diodes ( physically the D push and D
pull sections are created with a parralel connection of 10 Mosfets so
the resistance, and the resulting peak short circuit current is very
high. We failed to protect the mosfets by using 175 A fast automotive
fuse, because shorting of Mosfets is more rapid than fuse blowing and
I did not find very fast acting fuse for such a high currents.
The solution could be putting in paralel reverse biased diode with
fuse ( A ). Could you give me somebody a hint what kind of fuse should
be most suitable ? The reverse voltage it has to widthstand is now 12V
or 24 V , but in future designs it could be 48V ,72 V or even more
than 100V.
Of course any new ideas are welcomed and will be appriciated.
_________________
| | ------| |
O---------| |<-- /\ D push
| O A
| | _|__|
\ |

| /
|
----- ( - )
\ --------
/ /
\
A
\ / \
|-------
O------------------------------------ /
-------
| |
\ |
| -----
+ / -------
-------- ----- Cbulk
\ | | |
--- Ubat
| / |
| |
| ---- ( - )
\ | | |
---
----------------------------- /
-------

|
|
| |
------|
|
O---------| |<-- /\ D
pull ---
| | _|__|
|
---- ( - )

 

[Fred Bartoli]

gabo a écrit :

I would like to ask your opinion for the best solution for fusing the
following circuit in the case of short circuit of the following push
pull sections.

Your drawing is totally unreadable (line wrap).
You may use http://www.tech-chat.de/download.html and make it more compact.

 

[Stanislaw Flatto]

I would like to ask your opinion for the best solution for fusing the
following circuit in the case of short circuit of the following push
pull sections. This is an input/output section of the inverter/
charger. The use of N-Ch mosfets with body diodes is necessary because
in charger mode this circuit works as synchronous rectifier. The
problem is when the battery is connected in opposite polarity the bulk
capacitor is shorted , but most likely first the mosfets are burnt,
because of forward biased body diodes ( physically the D push and D
pull sections are created with a parralel connection of 10 Mosfets so
the resistance, and the resulting peak short circuit current is very
high. We failed to protect the mosfets by using 175 A fast automotive
fuse, because shorting of Mosfets is more rapid than fuse blowing and
I did not find very fast acting fuse for such a high currents.
The solution could be putting in paralel reverse biased diode with
fuse ( A ). Could you give me somebody a hint what kind of fuse should
be most suitable ? The reverse voltage it has to widthstand is now 12V
or 24 V , but in future designs it could be 48V ,72 V or even more
than 100V. *******************************************************************
Of course any new ideas are welcomed and will be appriciated.

*******************************************************************

Not new, old like the hills, a fuse (supposedly protective component)
and a semiconductor happily change functions with the semi protecting
the fuse.
Try to browse fuse manufacturers graphs and pay attention to current
that will blow the fuse at 1ms. Be sure that your semis can survive this
tsunami.
Been there, done it and discarded fuses as safety devices in such designs.

HTH

Stanislaw.

 

[Jasen]

I would like to ask your opinion for the best solution for fusing the
following circuit

use a fixed-pitch font, and no more than 70 columns.
it was unreadable.

 

[Marra]

I always fuse the power supply on my amplifier designs.

To get around blown output stages wiping out speakers with DC by using
a cheap microcontroller driving a relay on the output.

The relay is held off for 3 seconds at power up to stop massive clicks
through the speakers.
Also, if the micro sees DC for more than 500ms it shuts down the relay
and disconnects the amp output from the speakers.