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Testing isolation in SMPS transformers

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eem2am

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hello.

For 230VAC input , offline flyback transformers (fully isolated), how do you test to see if the transformer provides the necessary degree of isolation between primary and secondary?
 

Orson Cart

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Normally a "flash tester" is used - a small variac driving a stepup Tx with an output up to 4kV AC and a shut off ckt to disconnect the o/p if the current exceeds 5mA (for example) on the o/p, connect across the pri - sec windings
Regards, Orson Cart.
 
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eem2am

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Hi,

I am wondering why it needs to be AC?

Why not just connect the equipment to a DC voltage at the same value as the peak of the AC?
 

mtwieg

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It doesn't always have to be AC, but AC hipot testers are easier to make (just a big step up transformer and a variac) and are cheaper. Hipot testing with AC is usually sufficient, but sometimes testing with DC may be a good idea.
 
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