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UL 62368 short circuit test of power supply

Posted by: JJJJ on 01/13/2022

We are having our power supply tested by UL. They are performing UL 62368 B.4 short circuit tests.

One thing they decided to short is our Power Integrations Tinyswitch III - TNY276GN. Our circuit is roughly similar to the one provided as an example in the datasheet.

In this, the EN/UV (pin 1) is connected directly to an opto.

They are shorting pin 4 (connected to the transformer) directly to pin 4. This damages the opto and the circuit will no longer pass hipot.

This test seems inappropriate to us, given that the short has to jump the empty space and then another pin.

Do you have experience with this sort of test being performed and passed?  Is there a rule that device's missing pin is supposed to keep this test from being performed?

Comments

Submitted by PI-Jedidiah on 01/19/2022

Hi JJJJ,

Can you share with us your schematic? If it's hipot failure due to optocoupler, we can't do anything with the optocoupler you are using. You may try to use other optocoupler that won't have high leakage current when tested for short circuit test. There are many optocoupler available and widely being used in many power supply applications. Certifying optocoupler for UL safety testing is supposed to be handled by their vendor/manufacturer.

Regards,

Jedidiah