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Diff probe leakage current giving "fake" scope shots

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cupoftea

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Hi,
The blue trace in the attached two scopes is the post rectifier DC bus capacitor (5u6 Film) of a 240VAC 150W One transistor forward with HV transformer reset. (with 150W load). Its taken with a TA041 Diff probe.

In one, taken up to 5 seconds after switch ON , the blue trace is always running down to a “valley” of some 165V.
In the other, the blue trace is sometimes going down to some 40V.
The reason for the 160V valley (or any “valley” voltage above 40V) is the leakage current in the TA041 Diff probe.

Do you agree, we must float the scope to avoid this and get a proper waveform?

We cannot afford a better probe, and an isolation transformer and 100:1 probe gives the same problem.

TA041 diff probe
 

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  • BLUEV5U6 YELLV33UF 265VAC 150W__after first few secs.jpg
    BLUEV5U6 YELLV33UF 265VAC 150W__after first few secs.jpg
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  • BLUEV5U6 YELLV33UF 265VAC 150W__first few secs.jpg
    BLUEV5U6 YELLV33UF 265VAC 150W__first few secs.jpg
    173.5 KB · Views: 67

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