Diode as Transient Suppressor

I am working on a circuit which failed the EMC Surge Transient Immunity Test (2kV level). The working voltage is 240Vac.

Someone suggested to add two back to back diodes across the Live and Neutral wire as a transient suppressor.


The suggested diode has a part number "M4", which is a classified as a general purpose diode. As I know we should use a T.V.S or an Avalanche type diode, I read the specification of that M4 diode. It does show the characteristics: "Non-Repetitive Peak Reverse Avalanche" which is 5mJ.

Then I found another avalanche type diode, the part number is "BYG10G". The "Non-Repetitive Peak Reverse Avalanche" is 20mJ

I have two questions:
1. Are these two diodes suitable for a transient suppressor(at 2kV level)?
2. Both diodes has "Non-Repetitive Peak Reverse Avalanche" characteristics, while the "BYG10G" is not much better than the "M4". Why "BYG10G" is classified as avalanche diode but "M4" is a general purpose diode?

Attached the datasheet for both diodes.

Thank you very much.

Hi,

Someone suggested to add two back to back diodes across the Live and Neutral wire as a transient suppressor.

Click to expand...

Is "someone" reliable? And will "someone" feel responsible if it doesnßt work.
(I´d not rely on that. In my eyes it´s nonsense)

Zeners instead of your recitifier diodes will limit voltage within their specified recommended operating area. But I doubt they are useful for mains applications.

Use filters, Cs and MOVs.

Klaus

KlausST said:

Hi,


Is "someone" reliable? And will "someone" feel responsible if it doesnßt work.
(I´d not rely on that. In my eyes it´s nonsense)

Zeners instead of your recitifier diodes will limit voltage within their specified recommended operating area. But I doubt they are useful for mains applications.

Use filters, Cs and MOVs.

Klaus

Click to expand...

I have tested the circuit with the Surge Test today. I found that both the M4 and the BYG10G work. However, having talked with the engineers, I have to clarify that there is a fuse and a MOV located before the back-to-back diode. The test is a safety test rather than a EMC test. It is required to remove the MOV to undergo this test. The purpose of the diode is short circuit the Live and Neutral when the Surge exist. Then the exccesive power will blow the fuse and so making the circuit safe.

I am sorry for any confusion.