How to measure % of ripples at output of a D.C charger

May help:
http://www.eet-china.com/ARTICLES/2003AUG/PDF/2003AUG06_BT_ST_HBM_DA_AN05.PDF

Chargers may be pulsating DC. An osciliscope is mandatory. Ripple may change with load.

Chargers may be pulsating DC. An osciliscope is mandatory. Ripple may change with load.

Sir,

Please suggest how to connect CRO and the procedure. We have CRO at our lab.

You might want to do the calibration of the 10X probe, but you don't strictly have to unless the ripple frequency is high.

If you haven't done it before, there should be a calibration tab on the face of the scope. Adjust scope for a stable signal and adjust the small screw on the scope end of the cable until the waveform is flat.

With the DC adapter, AC couple the adapter and find the p-p voltage and measure the DC voltage with a meter under known loads. Unfortunately, this gives peek to peek ripple and you can convert that to % ripple.

There are meters which measure TRMS AC voltages and have selections for AC and AC+DC. That's a very easy way to measure RMS ripple.