DER-95

30 W Adapter for Portable DVD

September 12, 2005

Page 17 of 22

Power Integrations

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11 Output Ripple Measurements

11.1.1 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 12 and Figure 13.

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).

Figure 12 – Oscilloscope Probe Prepared for Ripple Measurement. (End Cap and Ground Lead Removed)

Figure 13 – Oscilloscope Probe with Probe Master 5125BA BNC Adapter. (Modified with wires for probe

ground for ripple measurement, and two parallel decoupling capacitors added)

Probe Ground

Probe Tip