HI, I'm testing STEVAL-ISA178V1 evaluation board. When I connect the DC output to the oscilloscope, it gets short circuited.

[TAswi.1]

The fuse of the AC mains gets switched off. I tried to connect the oscilloscope through a 10k resistor and the same behavior was observed.

However, I could verify that the switching regulator works fine by measuring the voltage with a voltmeter. Both through the DC output terminal and across a 10k resistor. The reading was about (5.6V DC).

Any help or advice regarding this would be highly appreciated.

Thank you very much for your kind help!

[Peter BENSCH]

Of course the fuse gets blown - it would be a bad sign if it didn't! The STEVAL-ISA178V1 is a non-isolated buck regulator, i.e. the secondary side (DC) is not galvanically isolated from the mains!

The only way to make correct and, above all, protected measurements is to operate the STEVAL-ISA178V1 via an isolating transformer. Alternatively, only the oscilloscope can be operated with such a transformer, but then the STEVAL-ISA178V1 is fully connected to the mains voltage.

Please watch out for your life - working on mains voltage is life-threatening!

Regards

/Peter

[TAswi.1]

Hi Peter,

Thank you very much for your valuable and kind answer!

I'm evaluating the STEVAL-ISA178V1 to create a similar VIPER01 based AC-DC power regulator in a compact IoT device. And this device would have a touch screen and other surfaces that users would touch.

If such a Non-isolated buck regulator is used without "an isolating transformer" in the application circuit, would there be safety concerns? Particularly when obtaining safety certifications?

I'm a novice to the field and any input from you would be highly valuable.

Thanks and regards

Thisal

[Peter BENSCH]

Never, i.e. NEVER EVER, use a power supply unit that is not galvanically isolated to supply a device that is not fully insulated and completely protected against contact with electrically conductive parts!

There are safety regulations in every country in the world, so be sure to check them out! 

In order to develop a power supply unit, it is imperative that you know these guidelines before you start developing, and then the unit must also pass a safety test and be approved.

If you do not have these requirements, I strongly advise you to use a ready-made, approved and safe power supply unit.

Good luck and stay healthy

/Peter