[Moved]Resilience of ceramic capacitors to overvoltage?

[treez]

How resilient are X7R ceramic capacitors to short term overvoltages.

In other words, say i have a 16V, X7R, 22uF sepic capacitor, and every time i switch on the sepic, i get a 20V spike across the 16V ceramic for about 30us......is that going to be ok?

How long will such a capacitor last.?

 

[treez]

Overvoltage transients on ceramic capacitors?

Can 50V ceramic capacitors withstand overvoltage transients up to 60V , such as 1ms overvoltage transients at 60V?

 

[albbg]

Re: Overvoltage transients on ceramic capacitors?

I think it will survive, however it's good practice the capacitor is operated at 50-60% of its voltage rating.
You can be interested in this article:

**broken link removed**

 

[treez]

Re: Overvoltage transients on ceramic capacitors?

Thanks, albbg, page 5, figure 4 of your article shows that the instant breakdown voltage for a 50v, 10uF, X7R capacitor is 1000V.
This surely cannot be right?

 

[andre_luis]

Re: Overvoltage transients on ceramic capacitors?

As far I understood, at page 6 it is stated that 50v rating should be avoided as much as possible for applications prone to face such overvoltages:

"for both AC and DC loads, the use of higher rated voltage MLCCs (200 and 500 V) is generally recommended instead of the standard 50 V products."

 

[D.A.(Tony)Stewart]

Re: Overvoltage transients on ceramic capacitors?

age 5, figure 4 of your article shows that the instant breakdown voltage for a 50v, 10uF, X7R capacitor is 1000V.
This surely cannot be right?

Figure 4 show the max value 1uF ( 1000nF) at 500V surge withstanding, the much higher density 10uF part is not shown.

Capacitors of this density are not made with high density dielectric with large gap electrodes they are high K but also very small gaps of many very thin layers.

Like a spark plug will fire at 1V/um in air from exceeding the dielectric strength, but in this case it is not the energy of the surge but the energy of the follow-on power after "crowbar" SCR effect. When it arcs, it melts to a short circuit from the storage capacitance and low ESR. THey are not self-healing like some plastic films. Also it does not occur on smaller values of ceramics which can tolerate a higher voltage transients, because they have a higher ESR by design.

Although some ceramics are designed for "flexible mitigation" meaning they fuse open after arcing into a failed short circuit so that the Automotive 12Vdc wiring does not melt tracks or blow an inline fuse.

50V caps are suitable for a 12V automotive system.

50V 10uF caps are NOT suitable for a 48V LED system, that has overvoltage transients.

Always derate by minimum 25% unless you can guarantee to have transient sub-microsecond OVP protection have other over voltage protection. ( not TVS on a high current drive)

The only valid way to measure nano or sub-microsecond transients is with a proper calibrated probe using 50 Ohm termination and R divider network or FET buffered probe.
If a reasonably low ESR MLCC Ceramic capacitor fails from overvoltage on a DC bus, it crowbars like an SCR and melts down in a low impedance short, unless specifically designed and rated to mitigate this.

 

[treez]

[Moved]Re: Resilience of ceramic capacitors to overvoltage?

is it true that the higher the capacitance of a ceramic capacitor, the less able it is to withstand overvoltage transients above its rating?
eg a 50V, 10uF ceramic capacitor, would be quickly destroyed if it received a few millisecond transients per day to 55V?