EP-86 – 6.6 W, 3.3 V, 2 A PoE Powered Device

13-Apr-2006

Page 22 of 28

Power Integrations, Inc.

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10.4 Output Ripple Measurements

10.4.1 Ripple Measurement Technique

For DC output ripple measurements, a modified oscilloscope test probe must be utilized

in order to reduce spurious signal pickup. Details of the probe modification are provided

in Figures 22 and 23.

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. Since the aluminum electrolytic type capacitor is polarized,

proper polarity must be observed when connecting it to the output (see below).

Figure 22

– Oscilloscope Probe Prepared for Ripple Measurement (End cap and ground lead removed).

Figure 23

– 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