dv/dt for high voltage X7R capacitor?

[carpenter]

How are SMD ceramic capacitors made of X7R material in terms of dV / dT?
Or otherwise , is a ceramic capacitor SMD 10nF 2000V suitable for use in triac subbler with R 39 Ohm? in 230V?

 

[KlausST]

Hi,

Worst case peak current of about 9A should be O.K.
But what about reading the datasheet?

Klaus

 

[carpenter]

I have 2225GC103KAT1A , unfortunately, the manufacturer in the datasheet is silent about the current load.
By the way, when I look at the price at the mouser, I find it absolutely crazy.
One understands why everything is made in China, there the price of the same C is more than 10 times lower

 

[FvM]

Here are current rating curves for a similar Kemet part

X7R has high dielectric losses, I doubt that's well suited as snubber

 

[mtwieg]

Most good manufacturers will suggest limits on rms current vs frequency, but not dv/dt or any sort of transient loading. As far as I know, there are no failure modes specifically related to dV/dt for MLCCs. Since class II dielectrics are piezoelectric, I've wondered if dv/dt might induce failure via mechanical shock, but have never seen evidence of this.

If your goal is to replace film capacitors with MLCCs for snubbers, be aware that class II dielectrics are nonlinear with voltage, unlike film caps or class I dielectric MLCCs.

--- Updated Mar 13, 2021 ---

X7R has high dielectric losses, I doubt that's well suited as snubber

Not sure why you'd say that. A snubber should be one application where a lossy capacitor isn't an issue. It just effectively absorbs some of the snubber resistance into itself. Just need to make sure Irms stays within its limits.

 

[FvM]

Not sure why you'd say that. A snubber should be one application where a lossy capacitor isn't an issue. It just effectively absorbs some of the snubber resistance into itself. Just need to make sure Irms stays within its limits.

O.k., I agree that the expectable losses in the snubber application stay within the rated limits.

Kemet has this comment in the KEM_CC105_HIVOLT datasheet

Application Note
X7R dielectric is not recommended for AC line filtering or pulse applications.

Kemet has a however a family of MLCC X and Y capacitors with specified pulse withstanding KEM_C1100_CAS_SMD.pdf (kemet.com)

 

[mtwieg]

Kemet has this comment in the KEM_CC105_HIVOLT datasheet

Kemet has a however a family of MLCC X and Y capacitors with specified pulse withstanding KEM_C1100_CAS_SMD.pdf (kemet.com)

These are interesting, thanks for sharing. But I'm about reading to deeply into their statements. Certainly normal MLCCs are not suited for line filtering because they often fail short. As for suitability for pulse applications, it's not clear what constitutes a "pulse application." These CAS caps are rated for impulses over 10x their rated working voltage, which is reasonable for a line filter. But for a snubber in a SMPS circuit, the peak voltages should never see such extreme outliers.

That also reminds me that when MLCCs are used in AC application, manufacturers recommend that the MLCC's voltage rating exceed the peak-to-peak voltage of the max AC voltage. But I've never really seen any reason provided. Any insight into why that might be the case?