TVS Diodes power ratings for IEC 61000-4-5

[MEHRANPOUR]

Hi,
I want to put a TVS diode between positive and GND lines (Earth and GND are the same in my board) on my board to pass the surge test (IEC 61000-4-5).
When you check datasheets of TVS diodes they are mostly mentioned the IEC standards that they support, but my problem is I don't know which package(SMA, SMB, SMC) is suitable for my case.
If I want to pass the category 4 in surge test which is 4kV Do I need SMC (500W)package ? or SMA package (400W) is enough?
How can I do the calculation from a TVS diode datasheet to comply with the standard?
My board is a 48V DC Drive

 

[KlausST]

Hi,

You may calculate the pulse energy that has to be dissipated by the diode.
Or you run a simulation doing the math for you.

Klaus

 

[FvM]

You should clarify which of the 61000-4-5 test pulses has to be handled by the protection circuit, also what's the intended TVS voltage. TVS ratings are referring to 10/1000 us pulses which have relative low current. Level 4 1.2/50 us test pulse has 2 kA peak current and exceeds the ratings of the mentioned diodes.

Another point is that sufficient TVS diode rating doesn't guarantee that your circuit survives the TVS clamp voltage.

 

[FvM]

According to my reading of the standard, power lines have to be tested with 1.2/50 µs (8/20 µs short circuit) pulses. You should choose TVS diodes that are specified for 8/20 µs, e.g. Littelfuse LTKAK3 series.