Overvoltage to X2 capacitor in 60W offline flyback

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treez

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Hello
We have a Panasonic ECQU2A224 220nF X2 capacitor in the AC filter of our offline
60W Flyback SMPS. When the product is connected to the mains at mains peak, the voltage
on this capacitor peaks up to 580Vpk.

The datasheet says it can withstand up to 1768VDC for up to 60 seconds, so it sounds liek it can handle it.
However, over time, do you think in say 5 years the capacitor may give up and die if it is switched on every day?

ECQU2A224 DATASHEET
https://www.farnell.com/datasheets/...MIlLadrJ_B4AIVy7_tCh1Jfw2uEAAYAiAAEgKcIPD_BwE
 

I think the more important question is where does the 580V come from?
But yes, it should be suitable otherwise. With the exception of thermal stress which accumulates damage over time, very few components have limited operational cycles.

Brian.
 
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Thanks, the voltage is due to the ringing between the filter L's and C's when there is a step input of the mains at mains peak.
We are actually told that mains peak in UK can go up to 404Vpk, and the peak of LC ringing can be up to twice that, so this capacitor could in theory experience 808Vpk (though the damping resistances would take that down a bit)
(Damping like resistance of the filter inductors, the 2R7 inrush resistor)
 

The ringing on the X2 capacitor's voltage when turned on at mains peak is as follows...VAC input is 265VAC.
Is this a "long term reliability" problem for the X2 capacitor?
 

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  • X2 capacitor voltage.jpg
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Is this real life or a simulation. If a simulation, are you taking into account the load on the rectified output (which will draw power from the peak) and the source impedance?

To be honest, it is what X2 capacitors are made for so I don't see any problems but if ringing is a real concern, try reducing the 'Q' of the inductors by adding a resistor across them.

Brian.
 
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Apparently a real measurement. And absolutely no problem you need to worry about.
 
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