DER-19

TOP245P Multiple Output Set Top Box

March 30, 2004

Page 21 of 25

Power Integrations, Inc.

Tel: +1 408 414 9200 Fax: +1 408 414 9201

www.powerint.com

11.5 Output Ripple Measurements

11.5.1 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 20 and Figure 21.

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 20 - Oscilloscope Probe Prepared for Ripple Measurement.

(End Cap and Ground Lead Removed)

Figure 21 - 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