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View Full Version : Measuring ripple current



ashiekh
02-28-2018, 10:36 AM
One can measure the voltage using the DC setting on a DMM; in principle the AC setting would measure the ripple, but is limited by the frequency it can handle. Anyone compared the AC reading for a PC power supply to the oscilloscope to see how closely they match?

Never mind... found some specs for the Fluke 101, it is only good to 500 Hz for AC volts, even if it can measure frequency to 100 kHz

Apologies for wasting time.

Found a circuit good to 500 kHz, which should be enough for most switched mode power supplies
http://www.ti.com/lit/an/snoa690/snoa690.pdf

Per Hansson
03-28-2018, 11:58 AM
Many meters (https://www.eevblog.com/forum/testgear/multimeter-spreadsheet/) can do 20khz at AC, it used to be the "design factor" in past days so you could also measure sound systems (human hearing goes to ca 20Khz).
That said it does not automatically mean that the meter will show a sensible reading.
At least that has been my experience, even when measuring a complex AC signal (and not just ripple).

https://www.eevblog.com/forum/testgear/the-uni-t-ut139c-and-my-power-supply-ripple/

ashiekh
03-28-2018, 01:00 PM
I am guessing we need to cover switching frequencies which (fortunately) are above the audible.