Electronics > Beginners
Filtering 19kHz switching noise from UPS AC output
ogden:
--- Quote from: Novgorod on July 03, 2019, 07:26:41 am ---The scope doesn't have the greatest dynamic range and I only measured at 500kS/s, but anything beyond 100kHz seems insignificant compared to the 19kHz ripple.
--- End quote ---
That UPS can easily output nasty high-frequency spikes that are outside of your "scope" bandwidth. Any chances to look at waveform using at least 20MHz scope? BTW I would test that "primadonna supply" using regular (pseudo-sine) UPS, also double-check that there is no grounding/earthing fault in the UPS/suply or just discontinuity.
firas:
A simple electric load filter from this company meets the needs. Previously I read on the site about this problem
https://www.schaffner.com/
Novgorod:
--- Quote from: firas on July 04, 2019, 02:04:17 pm ---A simple electric load filter from this company meets the needs. Previously I read on the site about this problem
https://www.schaffner.com/
--- End quote ---
I looked at the EMC/EMI filters from that company before but according to the rejection curves, they perform worse at 20kHz than the one I've already posted.
capt bullshot:
Back to original post: I wouldn't bet on the 19kHz ripple to cause the problem, might also be something else. Totally different impedance characteristics of the UPS output vs. normal mains could cause trouble also with strange loads that I can't imagine of right at the moment, but there's always something new that one hasn't seen before.
So an oscilloscope plot of voltage and current (if possible) of the load running at the UPS could be at least interesting, maybe this can give some hints (voltage + current would help more than voltage alone). Also insightful might be a peek into the guts of the load.
Anyway, one thing to test would be a simple series inductor placed (rated for the required amperes at some ten milihenries - a low (1V ... 5V) voltage secondary of an ordinary transformer might do, maybe with the primary shorted if the secondary is above 5V rated) in series to the UPS output. Or just a simple series resistor in the single Ohm range, with appropriate power dissipation rating.
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