Capacitor selection for EFT (Burst)

Thread Starter

Kaustubhj996

Joined Oct 10, 2023
3
Hello All,
How I can choose right Capacitor for EFT burst on Supply line or I/O Port, it is related to clamping voltage, Peak current, time of Burst.
it will helpful me and others also, Thank You
 
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MisterBill2

Joined Jan 23, 2018
17,814
Please start by explaining what a "EFT burst" is. I have never heard of such in my long career and so it has no meaning to me. And my mind reading skills are also very poor, meaning that I can not sense what the TS is thinking.
 

Papabravo

Joined Feb 24, 2006
21,003
The closest thing might be an EMP (Electro Magnetic Pulse) burst, but you won't get one of those from a capacitor. It basically takes the detonation of a nuclear weapon. I think detonation one of those might attract a good deal of unwanted attention in your direction.
 
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MisterBill2

Joined Jan 23, 2018
17,814
OK, it seems that I am not the only one who has no idea as to what a "EFT burst" is.
And I am really wanting to know. So how about an explanation from the Original Poster?
 

MisterBill2

Joined Jan 23, 2018
17,814
OK, thanks to Burtus we have a definition that I copied from the link to Wickipedia:

"The cause of electrical fast transients (EFT) come from an arc when mechanical contact is open due to a switching process.[5] Given the fast rise time and voltage of these pulses having a solid ground connection is important during the testing process.[6] Testing for EFT often requires a capacitive coupling clamp (CCL), which is employed to add disturbances to nominal signals.[7]"

I did not follow all of the links to all of the descriptions. But now we have a bunch of unknowns, such as what current is interrupted at what voltage for the specific test in question?And just what sort of "capacitive coupling clamp" to add what sort of added disturbance?
( Note also the additional of (CCL), which is not even a correct acronym for the expression it is to stand for.
 

Thread Starter

Kaustubhj996

Joined Oct 10, 2023
3
Please start by explaining what a "EFT burst" is. I have never heard of such in my long career and so it has no meaning to me. And my mind reading skills are also very poor, meaning that I can not sense what the TS is thinking.
I am talking about Electrical fast Transient (IEC61000-4-4)
 

seanstevens

Joined Sep 22, 2009
236
I am talking about Electrical fast Transient (IEC61000-4-4)
This is part of EMC surge and burst immunity test carried out on DC & AC products. Have you ever been to an EMC test house to see the very large and heavy machines that carry out these tests? Ours cost $17k 15 years ago! They are incredibly complex due to the precise timing and voltages they generate and are very dangerous if not used correctly. Good luck making one!
 

MisterBill2

Joined Jan 23, 2018
17,814
Thanks for the explanation. My employer did purchase some sort of bench tester for leakage tests and ground lead integrity, but it was not big nor heavy. It was a typical bench top package size and able to spot ground leakage and poor green-wire connections. EMC testing has not been required for products that I have designed or been involved with. And the leakage testing was for use by the repair team, used on items that they repaired.
 

Thread Starter

Kaustubhj996

Joined Oct 10, 2023
3
This is part of EMC surge and burst immunity test carried out on DC & AC products. Have you ever been to an EMC test house to see the very large and heavy machines that carry out these tests? Ours cost $17k 15 years ago! They are incredibly complex due to the precise timing and voltages they generate and are very dangerous if not used correctly. Good luck making one!
i am just asking how to select capacitor to prevent my circuit from EFT Or what is selection criteria of capacitor for EFT?
 

Papabravo

Joined Feb 24, 2006
21,003
i am just asking how to select capacitor to prevent my circuit from EFT Or what is selection criteria of capacitor for EFT?
IIRC it is more complicated that "slapping a cap" on your circuit. It involves cable shielding and the enclosure as well. Since we made network components the cabling was a primary source of vulnerability. I'm curious to know why you think a capacitor might be the solution.
 

AnalogKid

Joined Aug 1, 2013
10,944
You want a capacitor with very low ESR (Equivalent Series Resistance) and ESL (Equivalent Series Inductance). Examples are ceramic, multi-layer ceramic, and stacked metal foil; basically, capacitors that do not have a wound construction.

Another way to suppress a transient is to clamp it with a very fast diode. This approach does not add capacitance to a device input or output circuit that might affect how the device operates.

ak
 

AnalogKid

Joined Aug 1, 2013
10,944
My employer did purchase some sort of bench tester for leakage tests and ground lead integrity, but it was not big nor heavy.
Yeah, we had one of those for testing for UL/CSA compliance. It could test the current level through power line filter capacitors, insulation resistance of power transformers, ground current faults, etc. It could ramp up at variable speeds to a few kV of AC or DC, and dwell there for the test period. Perfect for what it was designed for, but not the right tool for this thread.

ak
 

MisterBill2

Joined Jan 23, 2018
17,814
Now it is a bit interesting. AN "ELECTRICAL FAST TRANSIENT"would evidently carry some power to be more than just noise that gets filtered out. And now that I went back and followed the links to the test descriptions, those do constitute rather brutal tests.
Our solution used in auto plants was a suitable constant voltage transformer. Usually 1 KVA or 500VA rated, depending on the load.That must have been adequate, we never had problems.
And it is entirely possible that even a regular controls transformer would lack the frequency response to pass a high-speed burst. At least, those with ratings of at least 250 VA.
 
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AnalogKid

Joined Aug 1, 2013
10,944

seanstevens

Joined Sep 22, 2009
236
i am just asking how to select capacitor to prevent my circuit from EFT Or what is selection criteria of capacitor for EFT?
Sorry, my misunderstanding. As suggested by AK, TVS is the usual device to protect your I/O, caps can be used sometimes but only on slow control lines. I presume the burst/surge is capacitively induced into your I/Os not directly.
 
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