Lightning Surge Protection of a Differential Amplifier

[mocuZ]

Hi

I am currently stuck on the following problem: I am using a differential amplifier as a line driver in a single-ended configuration. I want to protect both the input and outputs from eventual lightning surges. I started to look for a solution and I came out with this SLVU2.8 (which is great in terms of board space and pin configuration). My first question is: if I use this TVS will the outputs still be phase reversal protected (as they would be if a current limiting
resistor is used with schottky diodes tied to power supply)? What happens when a lightning strikes? Where do the surge go? Will there be any damage to the PCB if I just apply the application ciruit as it is shown in the datasheet (Protection of a unidirectional line on page 3)? Should I take some other precautions?

My second struggle is with the outputs: do I use the same configuration for each of the outputs as for the input? What happens when something comes back from the transmission line?


I will appreciate any advice or help.

Thank, you.

 

[KeepItSimpleStupid]

The telephone system is really the place to start: See https://www.electro-tech-online.com...ds_bellcore_tr-nwt-001089_and_fcc_part_68.pdf to give you an idea.

Your going to need more help if your protecting from lightning and it won't happen in your device.

You should really take a look at a typical telephone NID device: e.g. https://catalog.corning.com/CableSy....aspx?cid=copper_nids_web&pid=21746&vid=22472 or similar.

Also take a look here: https://www.l-com.com/item.aspx?id=42422#.UICRRNeB11E

Protecting against lightning REQUIRES a low Z path to ground to the reference of the building, so the strike doesn't impact the rest of the structure. You can't do that in the building. You have to look at how CATV is protected, the telephone line and the install of a whole house surge suppressor is installed. The closest relative to what you want to do is the telephone NID.

 

[mocuZ]

Hi, KeepItSimpleStupid,

Thanks a lot for the information. This is a start.

 

[KeepItSimpleStupid]

Can I ask for info like:
1) Is this building to building?
2) Distance
3) Data rate/frequency
4) Planned cable

Are you considering optical isolation?

PS: KISS is OK instead of KeepItSimpleStupid

 

[mocuZ]

Well ... various scenarios are possible: building to building, inside building. The distance also varies from lets say 30m to over 600m. The planned cable is simple twisted pair. Frequency does not exceed 10MHz.

 

[KeepItSimpleStupid]

Inside of a building, you can also have issues. In a data center where I worked, a major Ethernet switch was taken out going from one side of the room to another. The fix was to use fiber inside.

This kind of potential difference doesn't usually happen. There is something called an Uffer ground for buildings.

The ground potential can be raised during a storm, so over an area there can be a gradient. That's why the cement around pools are electrically bonded with a wire grid.

 

[westom]

Well ... various scenarios are possible: building to building, inside building. The distance also varies from lets say 30m to over 600m.

Protection is always about how current gets to earth. Anything that would stop that current only suffers even higher voltages. Surge is a current source. Voltage increases as necessary so that a current (typically 20, 000 amps) will still flow.

Devices mounted on towers to measure lightning currents use the single point connection technique. Every wire that enters the box first connects to the same point. Either directly via a wire. Or via a protector device. Most important - all wires make that short connection to the same point. Only then will current have no reason to be incoming and outgoing via that box.

Same solution applies to every building. Each wire inside every incoming cable first makes a low impedance (ie 'less than 3 meter') connection to single point earth ground. Only then will a destructive current need not enter the building. Protection again is never about a protector. That current connects low impedance (ie no sharp wire bends, no metallic conduit) to earth by a wire. Or makes the same low impedance connection via a protector. Protection means you provide the best (low impedance) connection to earth. And know why that current need not enter your building or box.

In all cases, no protector does protection. Protection is only provided by a ground point. For every building, that is single point earth ground. Protectors or hardwire connection do same. Make a low impedance (ie no splices) connection to earth. If any incoming wire doesn't, then all protection is compromised.

Protection is never about stopping or blocking a surge. Protection is always about giving that current (ie 20,000 amps) a low impedance connection to the single point ground. So that no current need pass through a box or be inside a building.

 

[picbits]

I'd strongly conside going fibre optic between the two sites.