Are we OK not using a proper high voltage rated Y capacitor with our SMPS?

[zenerbjt]

Dear Engineers,
We are using the THN 20-4811WI DCDC module with
Vin = 48VDC
Vout = 5VDC
Pout = 5.5W.

THN 20-4811WI
https://www.tracopower.com/int/model/thn-20-4811wi-a1

….In the application notes section (from above link) , there is a PDF called “EMI considerations”. This shows Y caps being used of voltage 2kV.

However, on our schematic, we don’t have such high voltage rated Y caps. In fact, we have a 500VDC rated capacitor across the isolation barrier, the VJ1206Y472KXEAC capacitor (4n7, 1206, 500VDC, X7R). This capacitor is not actually Y1 or Y2 rated, its just a general capacitor. Also across the isolation barrier, we have a 500V rated 1206, 1MEG resistor (ERJP08F1004V).
Incidentally, there are also three other DCDC modules across the same isolation barrier. (These are JTK3048S05 DCDC modules by XP power).

Do you think we will be OK not using such high voltage rated Y capacitors?

We are hoping that due to our 1MEG resistor across the isolation barrier....the voltage between primary and secondary will be pretty equal, so we wont need such high value rated Y capacitors?


VJ1206Y472KXEAC datasheet:
https://www.mouser.co.uk/datasheet/2/427/vjcommercialseries-1764145.pdf

ERJP08F1004V datasheet
https://docs.rs-online.com/ef78/0900766b812cb812.pdf

JTK3048S05 DCDC module
https://www.xppower.com/portals/0/pdfs/SF_JTK30.pdf

THN 20-4811WI datasheet

https://www.mouser.co.uk/datasheet/2/687/thn20wi-519375.pdf

 

[Easy peasy]

as it's low volts in and out 250Vac caps will be fine - they are high volts on mains equip due to lightning and other strikes ... conducted on mains lines ... which you don't have ...

 

[KlausST]

Hi,

It does not depend on the DC input or output voltages, it depends on which potential against earth they may/will be operated.

Example: the 5V output may be used to supply current_measurement_circuit riding on live mains level.
Then for sure you need high voltage rated Y capacitors.

Btw: On a quick view I can't find that the JC1206 are Y safety capacitors.

Klaus

 

[zenerbjt]

On a quick view I can't find that the JC1206 are Y safety capacitors.

Thanks, you mean the "VJ1206..."? (as in top post) .....no these are not safety rated capacitors. Is this a problem? As EasyPeasy was saying the voltage is low, we weont be connecting mains referenced circuits to the output or anything like that.......the output may get earth ground connected to it occasionally , eg due to a laptop USB connection etc.