DER-75
2.4W Power Supply using LNK520P
September 12, 2005
9.3 Output Ripple Measurements
9.3.1 Ripple Measurement Technique
For DC output ripple measurements, a modified oscilloscope test probe must be utilized
in order to reduce spurious signals due to pickup. Details of the probe modification are
provided in Figure 13 and Figure 14.
The 5125BA probe adapter is affixed with two capacitors tied in parallel across the probe
tip. The capacitors include one (1) 0.1 µF/50 V ceramic type and one (1) 1.0 µF/50 V
aluminum electrolytic. The aluminum electrolytic type capacitor is polarized, so
proper polarity across DC outputs must be maintained (see below).
Probe Ground
Probe Tip
Figure 13 – Oscilloscope Probe Prepared for Ripple Measurement. (End Cap and Ground Lead Removed)
Figure 14 – Oscilloscope Probe with Probe Master 5125BA BNC Adapter. (Modified with wires for probe
ground for ripple measurement, and two parallel decoupling capacitors added)
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