Flyback Transformer: sleeving question

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Hi,

I'm designing a Flyback Transformer of a 25 W power supply.

The power supply will be UL tested in Europe. The norm that will be
followed is the UL 60950.

The UL safety engineer told that the Hi-Pot test will be carried out
after leaving the power supply in the humid room for 12 hours at 93%
of humidity.

He suggested me to add sleeving to the transformer.

My question is:
On which leads am I supposed to add sleeving?
Primary? Secondary? Auxiliary? All?


Thanks,
Enrico Migliore
 

HI,
Yes the best precaution is to use on all (Primary, Secondary and Auxiliary) leads to avoid any flash over.
By the way you did not tell what voltage will be on Primary, Secondary or Auxiliary?.
 

Hi,

thank you for your answer.

>Yes the best precaution is to use on all (Primary, Secondary and Auxiliary) leads to avoid any flash over.
Is that based on your direct experience or it's just a guess?

The voltage of the Hi-Pot test is 3000 Vrms.

Enrico Migliore
 

yuo add it where the parts of very most different voltages are near each other.

Maybe you check it first b4 give to UL

...you hold the trafo over a steaming kettle for a few minutes, then do a flash test and see if/where it flashes.

..put tube where it flashed........just put tube anyway, to make it look like you care.

Search under "conductor spacing distances", conductor creepage distance" , conductor clearance distances, "PCB layout rules for track spacing" etc etc
 

Hi,

thank you for your answer

> flash test and see if/where it flashes.

what's a flash test?

Enrico Migliore
 

You should only use a sleeve across the barrier being hipot tested. I assume that your aux winding is common to the primary winding, so you shouldn't need a sleeve between those two. Just one between the secondary and everything else.
 

Hi,
Can you give a brief drawing of your expected windings enabling to say some thing more accurately.
What I said is based on my experience on SMPS transformers. I am producing normally up to 24 Watts.
 

Hi,

my Taiwanese supplier requires 0.05 USD for sleeving, with UL class A qualified tubes, all 8 leads.

That's a reasonable price, so I decided to add sleeves.

Thank you for your answers.

Enrico Migliore
 

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