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I tested 3-level PFC voltage initialization event in practice using 1 x single ended probe to measure the output voltage as well as 3 x differential probes to measure the precharge voltage levels of all flying capacitors. All of the voltage waveforms match (very close) the simulation model results apart from the C1. I measured the capacitor voltage with DMM and found it to be very close to the simulated voltage level of around 19V.


This leads me on to the question, why is the differential probe giving me false reading on the oscilloscope (around 85V same as the voltage of C2)? Is this a loading effect or something else? NOTE: C2 is a film capacitor of 4.7uF while the remaining C1 and C2 are tiny 47nF ceramic caps. Also in both cases transistors are not switching and the output load is set to around 10W. Input voltage to the system is a rectified 230Vac signal.


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