Phantom power protective diodes

[KA-Electonics.com]

Ok, so are you only talking about circuits that do not have protection diodes like those used in most ICs?

Not really. ESD diodes are for ESD events and can't handle phantom fault currents with their orders-of-magnitude higher stored charge than the human body model.

In both JS-001-2012 and MIL-STD-883H the charged human body is modeled by a 100 pF capacitor and a 1500 ohm discharging resistance. During testing, the capacitor is fully charged to several kilovolts (2 kV, 4 kV, 6 kV and 8 kV are typical standard levels) and then discharged through the resistor connected in series to the device under test.

A 100 pF charged to 2KV is 200 nano-coulombs vs the 2.25 milli-coulomb charge of a 47µF charged to 48V.
A "big" external diode is needed to steer that charge directly to the rail capacitors.
There are obviously other fault mechanisms that can pack a similar punch as phantom.

If the TVS do not introduce distortion with low-to-mid source impedances and add a lot of capacitance there's no reason why they can't be used in addition to diodes.

 

[JohnRoberts]

Wayne (AKA KA-Electronics) was involved in the classic THAT white paper about phantom caps energy content.

the phantom menace

JR

 

[Admiral-dk]

Thank you for the Article JR - Very informative and from the Real World testing.

Per

 

[Mr. Moscode]

I assume this is what this is about. 1n4004 on up to 4007 should do. I would think any reverse leakage noise would be absorbed by the low Z output stages.

https://www.thatcorp.com/datashts/THAT_1606-1646_Datasheet.pdf
P. 9:

 

[Mr. Moscode]

I would also think a few ohms in series with out - and + before the diodes would help push a charge to the diodes, assuming you don't need to drive 250 ft of line.