UL testing support for transformer

Posted by: gapolekep on 11/30/2011

I inherited a design based on the TOP258. The design is now undergoing UL testing. The UL lab wants to run overload tests on the transformer. Their method of doing this is to short the output side of the transformer. The TOP258 protects itself when an output short is detected, so no overload occurs. Is there a way to bypass the short protection in the TOP258, or is there another way to test the transformer?

Thanks!

Comments

No the self protection feature (auto-restart) cannot be disabled. It is put in specifically so that the device is protected against output short circuits or feedback loop open circuits...

Thanks. So what can I tell my UL lab about how to perform a transformer overload test?

I am not sure that you need to advise them about anything actually. The feature is in there to protect the power supply from fault conditions. Besides UL typicaaly tests for single point failure (which in this case would be the short they p[lace at the transformer). Under these conditions there should be no problem of transformer saturation in the time frame that the fault is detected by the TOPSwitch and corrective action is taken. A good design that is done within PI guidelines will never experience such a problem.
Power supplies using TOPSwitch have been around for over a decade now and a great many of these have UL certification. I am sure they have their ways and procedures of testing the supplies with built in protection.