Thanks guys. I of course meant to use the isolation transformer for the transformer-less power supply for isolation. But just using a transformer as you suggest would be more prudent.

Likes(0)Dislikes(1)

You are welcome Gerald.
I am looking forward for this article!

Best Regards

Likes(0)Dislikes(0)

Thanks Paris, you answered correctly, the key is the galvanic isolation which can only be achieved using transformers or opto-couplers (Or I missed something else?). I am still looking for a good project for a HV differential probe. When I find it I will share with this group.

Cheers,
Gerald

Likes(0)Dislikes(0)

Thanks for your support Beh. Hope to read from you soon.

Cheers,
Gerald

Likes(0)Dislikes(0)

No, Robert it’s not the same thing. The current transformer, when clamped on, uses the wire (of which we want to measure the current flow through it) as a single primary turn. In its secondary there are many more turns terminated with a resistor and the voltage developed there during measurements represents the magnitude of the current. It is evident that we can ground any side of the secondary (but normally we take care to ground the side which does not reverse the signal’s phase. This will happen if we clamp the transformer in the opposite way). The point is that we talk about a transformer, that is, about galvanic isolation.
In case of using a capacitor, there is no galvanic isolation. Anyway using a capacitor in order to see the current waveform on a resistor equals with selecting “AC coupling” at the oscilloscopes’ measuring input. But the key point, the lack of galvanic isolation ,that is, the question about where to connect the ground crocodile of the probe, still remains. Powering the scope by an isolation transformer is the only (temporary) solution. In any case, the chassis of the instrument should not be considered 100% safe for touching it…It should be perfectly floating, but…

Greetings!

Likes(2)Dislikes(0)

Thanks Parasuraman for your kind words and support

Likes(0)Dislikes(0)

Thanks Gerald! Indeed not reading anything about being able to safely measure on Differential High Voltages indeed worried me a bit in the above given Elektor DIY examples.

Likes(0)Dislikes(0)

Hi guys,
It seems to me that you could use the same principles of the capacitor in a transformer-less power supply to also safely scope mains power. Of course, it will cause the current to lead the AC voltage by 90o.

Likes(0)Dislikes(1)