Probing an offline Boost PFC

[Flyback]

Hi,
We are doing an offline Boost PFC. We have a diff probe, but due to its long leads, the scope traces from it are swamped in common mode noise.
We know of the potential severe danger to health of cutting off the earth lead from the scope supply.
Though we can't afford an isol txfmr...and so if we cut off the earth, and probe using a home brew coax probe, will the traces be very noisy due to the cutting of the earth wire from the mains cable to the scope?

 

[Nigel Goodwin]

Should make no difference at all, and there's little (or none at all?) danger in doing so if you know EXACTLY what you're doing, and why. It's probably more dangerous having an earthed scope in such circumstances, as it's very easy to get a full mains shock hand to hand straight across the chest with an earthed scope.

 

[danadak]

Isolation safety :

https://download.tek.com/document/3AW_19134_2_MR_Letter.pdf

https://www.eeweb.com/wp-content/uploads/articles-app-notes-files-power-supply-noise-measurement-1290016135.pdf

https://assets.testequity.com/te1/Documents/pdf/handheld-floating-measurement.pdf

You can isolate a scope with an isolation transformer, or use a car battery, a cheap auto car inverter
to provide the scope power. Those inverters can be noisy, sometimes a line filter appropriate.

DIY diff probes :

High Voltage Differential Probe for Oscilloscopes - PCBWay Collaboration

High Voltage Differential Probe for Oscilloscopes - PCBWay Collaboration: In the last ten years, the power electronics industry has been growing at an incredibly fast pace. However, despite this trend, articles and projects in the maker community regarding this topic are very scarce. This could...

www.instructables.com

DIY Cheap HV differential oscilloscope probe - Page 1

DIY Cheap HV differential oscilloscope probe - Page 1

www.eevblog.com

Regards, Dana.