protection of output I/O lines with transil?

[Otto Sykora]

I have now some new project and there are various I/O going stright
out of a complex hybrid chip to external wiring which is a house
installation.

The previous circuits had either NOTHING as protection or large PTC
resistors in the lines and couple of zener diodes to ground on each
lead.

I need to do something of 'present day' kind, but it should still do
the job well. I though abt some transil /transorb etc diodes, however
it looks like that those suitable for protection of 5V logic lines
have leakage of abt 1mA!

And do I have to still add some serial PTC resistors in this case?

How is this handeld to day in general?

 

[Rene]

I have now some new project and there are various I/O going stright
out of a complex hybrid chip to external wiring which is a house
installation.

The previous circuits had either NOTHING as protection or large PTC
resistors in the lines and couple of zener diodes to ground on each
lead.

I need to do something of 'present day' kind, but it should still do
the job well. I though abt some transil /transorb etc diodes, however
it looks like that those suitable for protection of 5V logic lines
have leakage of abt 1mA!

And do I have to still add some serial PTC resistors in this case?

How is this handeld to day in general?

In this case, couldn't You work with optocouplers? That way no dangerous
stuff can ever reach Your big chip (apart from really heavy things maybe
like lightning, don't know about that). You would have to build an extra psu
as well for complete protection off course (afa it can ever be "complete").

Sincerely,
Rene

P.S. My suggestion is from a hobbyist's point of view. When I build one
thing for my own use, an extra cost is often not of that much importance
(hey, it's a hobby and when I make something, I want it to be as good as
I can build). Might be that You are working on some commercial thing were
money is much more important and an other option would have a better
cost-benefit relationship. So it's just "my two cents" ;-).

 

[Homer J Simpson]

The previous circuits had either NOTHING as protection or large PTC
resistors in the lines and couple of zener diodes to ground on each
lead.

I would add buffers to the I/O lines. They are cheap to replace - use
sockets.

 

[[email protected]]

I would add buffers to the I/O lines. They are cheap to replace - use
sockets.

I don't know about the latest generation gear from Audio Precision, but
on their original gear, that was their solution. The bus drivers were
socketed.

 

[Otto Sykora]

no way for sockets here, the units are small and all smd stuff on it,
no way to place any sockets etc.

I just like to know if someone has somerecent experience with transil
etc protection and if still a series ptc resistor is used in such case
etc.

 

[Otto Sykora]

yes I work this way so far, looking for oc going into my cct. BUt
those do not solve everything. small oc have also abt 80V C-E, so it
must be more protected here. The regulations for building wiring are
somehow complex, but it seems that some transil etc have to be placed
in front of the oc still. also I wonder, if there is still the need of
an series ptc resistor nowadays when the transils are used.

 

[Homer J Simpson]

no way for sockets here, the units are small and all smd stuff on it,
no way to place any sockets etc.

Find a way. You'll curse the day you didn't.

I just like to know if someone has somerecent experience with transil
etc protection and if still a series ptc resistor is used in such case
etc.

I would have no faith in a PTC (or an NTC) used for this. A VDR maybe.

 

[[email protected]]

no way for sockets here, the units are small and all smd stuff on it,
no way to place any sockets etc.

I just like to know if someone has somerecent experience with transil
etc protection and if still a series ptc resistor is used in such case
etc.

It would really help to know from what exactly you are trying to
protect these drivers. Static or transient? ESD? Speed of signal? Load
capacitance?