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Qu1....Is HiPot Test for power supplies necessary to prevent data corruption?

Hi, We have an offline , isolated 25w Flyback SMPS in an earthed metal enclosure. This flyback

also acts as a "daisy chain" terminal for passing on a CAN bus wire pair.

(it has a CAN bus connecter with termination

resistor)

The CAN bus goes to other equipment along with the 24V output of this isolated SMPS.

The hipot test is done at 4kVrms/2 seconds/no breakover.

This seems a rather high voltage for a hipot test.

Though we are told that it is necessary to ensure that the data doesn't get corrupted.

I mean, ok, why not do the hipot test at 5kv then?..or 6kV?...and protect the data even more?

...and add in shielded cable for the data whilst we are about it?....etc etc

I mean, Even if the data does get corrupted during a typical mains transient (what do they last, some 50us max?),

the processors all have error routines to handle such things. The equipment we have here isn't

medical equipment.

So do you agree that 4kV hipot tests are not needed for safety, or for insulation withstand testing?...but to

ensure that data doesnt get corrupted?

Also,

Qu2   Y capacitor location for Conducted immunity?...for conducted EMC?

Hi, As you know , in an offline SMPS  supplied by L,N & E, the Y capacitors would go from

L and N to earth. They can be placed either upstream or downstream of the

common mode choke. Is the following right?..

(please assume that in all cases there is alreasy a Y capacitor across the isolation transformer, from quiet node(primary) to

quiet node(secondary)

1)..Placing the Y capacitors upstream of the common mode choke is best to give immunity of the SMPS (and whatever it supplies)

2)...Placing the Y capacitors downstream of the SMPS is best to get a conducted EMC pass of the SMPS?

3)...If you only have room for one Y capacitor, then where would you place it?...presumably after the diode bridge to either

HVDC+ or HVDC-, because in that case, it would  alternatively connect to L and N , every alternate 10ms?