Why does output ripple exceed the limit on a batch?

Main answer · Wecent Editorial Team

Short answer: Ripple is the small fluctuation left on the DC output. A batch goes over the limit when the output capacitors are weaker than expected, other components shift, the layout or assembly differs or the test method changed. Compare good and bad units, check capacitor brand and lot and repeat the measurement with the same method before you decide.

What ripple is

A charger turns mains power into smooth DC, but a small variation remains on the output, at the switching frequency and at the mains frequency. Too much ripple can cause noise, heat or odd behaviour in connected devices.

Common causes in one batch

• Output capacitor differences. A different brand, lot or lower-quality part with higher equivalent resistance.
• Capacitor ageing or damage. Heat during soldering or storage.
• Tolerance stack. Several small shifts add up.
• Transformer or switch variation. Changes in the converter’s behaviour.
• Assembly issues. Poor solder joints or board contamination.
• Test conditions. Different load, cable, probe technique or bandwidth.
• Temperature. Cold or hot conditions change capacitor performance.

How to investigate

1. Re-measure good and bad units with the same set-up and settings.
2. Use short probe leads and the specified bandwidth limit.
3. Check the load level and the cable used.
4. Compare capacitor markings and batch codes.
5. Swap capacitors between a good and a bad unit.
6. Measure at different temperatures.

Fixes

• Specify the capacitor brand, series and rating, and ban substitutions.
• Add margin in the design, such as extra capacitance or lower-resistance parts.
• Improve layout near the output.
• Add incoming checks on capacitor lots.

Measurement matters

A method that is not standardised produces confusing results. Write down the probe type, bandwidth, load, cable and temperature in the test procedure.

Records

Record ripple data per batch. A slow drift upward is a warning before a failure.

Quick summary

Check capacitors and the method first, compare units and tighten both the spec and the design margin.

Example record

Batch number, sample size, measured ripple at stated load, capacitor lot, probe type, bandwidth limit, ambient temperature and result. One page per batch makes it easy to compare lots and to see whether the problem is a one-off or a trend. Share it with the factory when you raise a corrective action request.

Check for early warnings

If ripple creeps up over several batches, ask the factory what changed. Often a supplier change or a process shift is behind a slow drift, and catching it early costs far less than rejecting a whole batch.

Where this answer says to confirm with Wecent, the detail is not published on the product page and has to come from the datasheet or the factory. General facts come from the regulators, standards bodies or device makers named in the text.