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For a power supply circuit, I need to add an X2 capacitor. I have space constrains - so, considering choosing a very small SMD component.

The product will be connected to 230V 50Hz mains voltage. The capacitor I am thinking about is 250VAC rated and according to data sheet can cope with 2.5kV surge impulses (data sheet link: https://datasheet.lcsc.com/lcsc/2305040944_PSA-Prosperity-Dielectrics-FH20X153K302EGG_C5557973.pdf)

Are my considerations making sense? Is it ok to use 250VAC X2 in 230VAC environment? Normally, when derating capacitors, I put at least 50%. But, in this particular case, all capacitors from 275VAC are too bulky for my application.

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  • \$\begingroup\$ That's quite a small value for an X2 capacitor; I'm more curious what you're doing, and if it's the correct choice / will work in general? \$\endgroup\$ Commented Sep 22, 2023 at 4:03
  • \$\begingroup\$ It's for a power supply module that will provide 5V / 1A to a household device in Europe (230V / 50Hz). The power supply module will have two caps (one before common mode and another one after the common mode choke). The first cap will be 220nF and the second one (a small one - couple of nF). The values for the caps were determined experimentally in the EMC lab. When you say small value - do you mean the capacitance value or the rated voltage value of the cap? \$\endgroup\$ Commented Sep 22, 2023 at 4:31
  • \$\begingroup\$ The product line only goes up to 56nF. Are you going to use four (or more) in parallel, then? Am also curious how stable they are with respect to applied voltage; X7R are voltage-dependent, and it's possible they lose value significantly at mains peak voltage (where it's also most needed!). I would want to test that, personally. \$\endgroup\$ Commented Sep 22, 2023 at 5:43

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Is it ok to use 250VAC X2 in 230VAC environment?

No (Or barely).

250V-rated capacitors are designed for 220V ±10%. Today's nominal mains voltage range for Europe is 230V ±10% i.e. 253V maximum which is 1% above the the voltage rating of your capacitor. Equipment for Europe is usually advertised as "Can operate within 180 ~ 264V range" which covers the UK's used-to-be-nominal voltage, 240V (with 10% tolerance of course), and these equipment generally have 275V-rated capacitors.

So, I'd strongly suggest to use a 275V-rated capacitor instead. But you have a physical limitation:

in this particular case, all capacitors from 275VAC are too bulky for my application.

According to test data given in the datasheet, the capacitors are tested with 312V for 1000 hrs (and with 1000Vac for 0.1s every hour). This doesn't mean that the capacitor can be used with voltages slightly higher than the rated – if it did then the manufacturer would give a voltage rating of higher than 250V.

The final thing to note: In addition to size and availability, environmental conditions need to be considered because some capacitors' voltage rating is temperature-dependent i.e. at higher temperatures the rated voltage may need to be de-rated. I don't know if yours is one of those.

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