1 minute vs 1 second isolation voltage test for isolated offline SMPS transformer

[Flyback]

Some offline transformers are spec'd for 3750vac for 1second (3mA).
Some are spec'd for 3750vac for 1 minute (3mA).

It is strange to me that power integrations, on their design software, only ever design the isolated flyback transformers to 3000vac for 1 second (thats for 200-265vac input).
(screenshot of design result attached)
Do you know why this is?

Why would anyone want to spec it for one minute?......no mains transient lasts for one minute?....they only last 50us

 

[ronsimpson]

Why would anyone want to spec it for one minute?......no mains transient lasts for one minute?....they only last 50us

It is hard to make a test machine that makes 3750 vac for 50uS. (I use vdc)
A test should be more sever than real world conditions.
A test should be easy to do.
A test should use normal test equipment.

 

[alec_t]

no mains transient lasts for one minute?....they only last 50us

One transient may last 50us, but what if there were a bunch of transients in quick succssion? It would be nice to know that your transformer could survive such a burst.

 

[Flyback]

Thanks, as you know, the MOV is going to take most of the transient........maybe allowing 1kv of let through at the most...but we have a TVS/clamp to eat that......so no high voltages on the transformer anywhewre near the 3kv level.

 

[alec_t]

...so no high voltages on the transformer anywhewre near the 3kv level.

Always assuming the MOV doesn't die open circuit when the first of a bunch of transients strikes .

 

[ronsimpson]

Primary to Secondary isolation testing is not about what voltage spike you might see on the power line. It is about isolating a person from the powerline. The leakage current is about not-shocking some one. The test is not about this one transformer but about proving that the 1,000,000th transformer does not have a wire misplaced and can not withstand high voltage.

This is a standard test that all power line products should pass. Smart engineers with experience on power supplies created this test to not kill people.

 

[Flyback]

Thankyou....


......We are wondering what kind of isolation test the following power supply is spec’d to?…..

It’s the Philips Xitanium Xtreme 75W LED driver…..AKA…
“Xitanium 75W 0.35-0.70A GL Prog sXt” (datasheet below)

The datasheet says it has “Basic” insulation.

That is, how would they have carried out the hi-pot test on it? (voltage setting?, time duration?, current limit setting?)

The following reveals that “basic insulation” means withstanding 1000V+2x(operating voltage)…however, I happen to know that Basic Insulation means 3750VAC for one minute for an isolated offline SMPS…..during that minute, the RMS current should not exceed 3.5mA.
https://electrical-engineering-portal.com/what-is-hipot-testing-dielectric-strength-test

Would you agree that at the Philips Approvals testing session for Dielectric withstand…they would have set the Hi-pot instrument to 3750VAC for one minute and set a current limit threshold of 3.5mA?

(the standards do not actually specify a current limit threshold)

Philips Xitanium Xtreme 75W LED driver datasheet:
https://www.docs.lighting.philips.c...m_75W_0.35-0.70A_GL_Prog_sXt_929000702302.pdf

Here is the product brochure
https://www.docs.lighting.philips.com/en_gb/oem/download/xitanium/Xitanium-XtremeLED-brochure.pdf