I am a little confused regarding TVS diodes power ratings.
If I put an SMA TVS diode directly Between DC+ and DC- (my Earth and GND are connected) then it will be enough to pass the surge test but in which category?
If I put the SMA package which is rated for 400W then can I pass 4KV surge or it is underestimated?
these power ratings in TVS diodes are not clear for me.
How can I use TVS parameters to understand which IEC 61000-4-5 (surge) category can be passed by each TVS package? (SMA, SMB, SMC, SML packages)
ST Micro’s AN4275 is a useful resource on this topic.
TVS diode power ratings describe the peak instantaneous power dissipation in a device when a waveform of standard shape and the maximum amplitude tolerable by the device in question is applied. It is probably not the best parameter to use for this application.
There is not a direct relationship between a TVS diode package size and a resulting ability to meet IEC6100-4-5 requirements at any particular class. One reason is that the standard applies at the equipment level; the device in which the diode is used is tested, not the diode itself. The specification of the rest of the system and how the diode is used in it are necessary pieces of information in order to address the question properly.
Another reason is that the standoff voltage of a device influences the amount of stress placed upon it during surge testing; a device that breaks down at 6.3V for example will dissipate less power when an amp of surge current is passed through it than one with a 63V reverse breakdown.
Based on the reference above, the worst-case scenario under IEC61000-4-5 involves application of the class test voltage through a 2 ohm resistance. For class 4 (4kV) this implies that a protection device capable of withstanding at least 4000V/2Ω=2000A of peak reverse current (based on an 8x20us waveform) is required in order to say that the protection device is sufficient to provide protection to class 4 levels, given no further information. Note that this is well beyond the capacity of any of the common SM(x) diode package styles.
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